PLANCK2026 and 6th EuCAPT Symposium

18 May 2026, 09:00 → 22 May 2026, 19:30 Europe/Zurich

500/1-001 - Main Auditorium (CERN)

Clara Murgui Galvez (CERN), Guilherme Guedes, Itay Bloch, Maksym Ovchynnikov (CERN), Mario Reig Lopez (Instituto de Física Corpuscular (IFIC)), Matthew Philip Mccullough (CERN), Miguel Escudero Abenza (CERN), Sokratis Trifinopoulos (SISSA), Sung Mook Lee (CERN), Valerie Domcke (CERN)

PLANCK2026 and the 6^th EuCAPT Symposium will be held jointly at CERN from May 18 to 22, 2026.

 

PLANCK2026 is the 28th in the series of Conferences "From the Planck scale to the electroweak scale". The Conference is intended to bring together researchers working in high energy physics, covering a wide variety of formal, phenomenological and cosmological theoretical topics related to the present experimental programmes. 

The European Consortium for Astroparticle Theory (EuCAPT, https://www.eucapt.org), with central hub at CERN, aims to bring together the European community of theoretical astroparticle physicists and cosmologists. The annual symposium is the flagship event of our consortium, aiming to provide an interdisciplinary Europe-wide forum to discuss opportunities and challenges in Theoretical Astroparticle Physics and Cosmology.

The event will take place at CERN, with online participation possible. We invite all scientists active in these fields of research to join us remotely or in person from May 18 to 22, 2026. The conference will feature invited presentations, and young scientists will have the opportunity to present their work with plenary lightning talks, dedicated parallel sessions and in a poster session.

Registrations and abstracts received by March 22 will have priority. There is no conference fee for this event.

Confirmed invited speakers include:

EuCAPT (May 19-20):

• James Alvey
• Anton Chudaykin
• Melissa Diamond
• Willem Elbers
• Keisuke Inomata
• Daniel Naredo
• Brodie Popovic
• Wenzer Qin
• Jorinde van de Vis
• Weishuang Linda Xu

PLANCK (May 18, 19, 21, 22):

• Prateek Agrawal
• Mikael Chala
• Louie Dartmoor Corpe
• Hooman Davoudiasl
• Jorge de Blas
• Jordy de Vries
• Sebastian Ellis
• Admir Greljo
• Johan Henriksson
• Gudrun Hiller
• Giulia Isabella
• Felix Kahlhoefer
• Denys Malyshev
• Georges Obied
• Keith Olive
• Ryan Plestid
• Maria Ramos
• Sophie Renner
• Juan Rojo
• Kai Schmitz
• David Shih
• David Sutherland
• Anders Thomsen
• Lian-Tao Wang

                        

   

Monday 18 May

09:00 → 09:30 Welcome

Conveners: Gautier Hamel de Monchenault (CERN), Miguel Escudero Abenza (CERN)

GHM_2026-05-18_Planck.pdf

Welcome_local.pdf

09:30 → 10:00 FERMIACC: Agents for Particle Theory

Speaker: Prateek Agrawal (University of Oxford)

Agrawal_planck2026-fermiacc-cern.pdf

10:00 → 10:30 Physics opportunities at future colliders

Speaker: Dr Jorge de Blas (Universidad de Granada (ES))

Physics_Future_Colliders_deBlas.pdf

10:30 → 11:15 Coffee break

11:15 → 11:45 Probing Black Holes with Scattering Amplitudes

Speaker: Giulia Isabella

Giulia.pdf

11:45 → 12:15 Effective field theory meets Conformal field theory

Speaker: Johan Henriksson (CERN)

Henriksson-EFT-meets-CFT-planck.pdf

12:15 → 12:45 The phenomenology of non-decoupling physics

Speaker: David Sutherland

nonDecouplingPhenoDSutherland.pdf

12:45 → 14:00 Lunch break

14:00 → 14:30 Directions and challenges in BSM flavor

Speaker: Gudrun Hiller (CERN)

BSMflavor-PlanckCERN2026-ghiller.pdf

14:30 → 15:00 Exploring the flavour of EFTs at colliders

Speaker: Sophie Alice Renner (University of Glasgow (GB))

PLANCK2026Renner.pdf

15:00 → 15:30 Rethinking the Flavor Puzzles: New Perspectives and Opportunities

Speaker: Admir Greljo (Universitaet Basel (CH))

Greljo-Planck-2026.pdf

15:30 → 16:20 Coffee break

16:20 → 18:20 Parallel Session: Council Chamber

16:20 How far can the QCD axion hide?

The axion is one of the most compelling candidates for physics beyond the Standard Model, as it simultaneously provides a solution to the strong CP problem and a viable dark matter candidate. In post-inflationary scenarios, the minimal QCD axion model leads to strong constraints on the axion mass from the dark matter relic abundance. Specific quantization relations hold for the axion-gauge couplings which constrain further the parameter space. In this work, we test how robust these phenomenological features are in multiple-axion scenarios. Considering a two-axion framework, we explore whether new regions of parameter space remain theoretically and phenomenologically motivated.

Speaker: FUENSANTA VILCHES BRAVO (Universidad de Granada)

VilchesBravo_Planck2026.pdf

16:40 Supercooled audible axions

Axion-like particles (ALPs) are among the most promising dark matter candidates. However, a large part of parameter space, in particular the regime of large decay constants where the ALP becomes effectively invisible, remains hard to probe experimentally. In the audible axion mechanism, invisible ALPs generate a sizable primordial gravitational wave (GW) background via a tachyonic resonance induced by their coupling to a dark Abelian gauge field. I will discuss the impact of trapped misalignment, which delays the onset of ALP oscillations, on the dynamics of the audible axion mechanism. This includes the enhancement of the resulting GW signal, tachyonic production of Standard Model photons, and the possibility to generate intergalactic magnetic fields.

Speaker: Daniel Schmitt (KIT)

Schmitt_Planck.pdf

17:00 Axion cosmology with parametric resonance

In this work, we study the cosmological implications of an initial displacement of the Peccei-Quinn breaking field generated during inflation and the subsequent oscillations of the field around its minimum. These
oscillations induce a parametric resonance effect, leading to the exponential growth of perturbations. In our
analysis, we employ lattice simulations to investigate the abundance of axions produced by this resonance, as
well as the formation and dynamics of the resulting topological defects.

Speaker: Riccardo Natale (DESY)

Axion_cosmology_with_parametric_resonance.pptx

17:20 Cosmological Aspects of Axion-Monopole Interactions

We propose a minimal and natural dark-sector framework in which dark matter is composed of magnetic monopoles coupled to a light axion field. Through the Witten effect, the axion background induces electric charge on the monopoles, turning them into dyons that in turn modify the axion potential. This monopole-dependent axion mass provides a simple, radiatively stable mechanism for dark-sector interactions and allows the axion to act as a dynamical dark-energy component. The resulting slow evolution of the axion field at late times can naturally produce the polarization rotation associated with the reported CMB cosmic birefringence signal and may also accommodate the evolving dark-energy behavior suggested by recent DESI data. This framework offers a unified and economical explanation for multiple late-time cosmological hints.

Speaker: Hengameh Bagherian (University of Chicago)

PLANCK2026.pdf

17:40 Higher Axions

A large fraction of the experimental efforts searching for the (QCD) axion focus on smaller-scale, time-intensive, resonant searches. These searches would greatly benefit from a precise estimate of the axion mass. In theory, the axion mass can be inferred from the observed dark matter abundance and numerical simulations point towards an axion mass (slightly) higher than currently searched for. These numerical predictions require axion models to have both high quality and a predictive cosmological history - that is - a post-inflationary scenario.

In this talk, I want to introduce the minimal requirements to obtain axions with exponentially good quality and a predictive cosmological scenario. These ingredients appear in theories where an axion coming from a higher-form gauge field mixes with the phase of a complex scalar field. We present a simple toy model on a 5-dimensional manifold with boundary. If time permits, we show how these scenarios may arise in string theory compactifications and discuss how to overcome additional complications these specific UV completions introduce.

Speaker: Arthur Platschorre (Cornell University)

Higher_Axions_Slides_Planck.pdf

18:00 Towards a Post-Inflationary Composite Axion Model

Composite axions offer a scenario where the axion emerges as a pion-like state, avoiding fine-tuning of elementary scalars and ameliorating the axion quality problem. Despite these advantages, their post-inflationary cosmology remains largely unexplored, with challenges including the domain wall problem and the presence of exotic relics. We propose two composite axion models with an effective domain wall number and study the dilution of relics via a short period of inflation. One model is based on an chiral gauge theory, while the other employs a ``gauged'' Peccei-Quinn symmetry in vector-like gauge theories. We identify the viable parameter space in which axion strings re-enter the horizon before or even after the QCD transition and axion dark matter is dominantly produced from the decay of the string-wall network.

Speaker: Mohamed Mahdi (SISSA)

planck26_Mahdi (1).pdf

16:20 → 18:20 Parallel Session: Main Auditorium

16:20 Electroweak high-order effects at high energies: from theory to phenomenology

Precision electroweak calculations are becoming increasingly important for probing the Higgs sector and searching for new physics. In this talk, I will present recent progress in analytic two-loop electroweak calculations at high energies [2603.08789]. As a key example, I will discuss Higgs boson pair production, where NLO EW corrections reach the level of −10% at high energies. By exploiting the mathematical structure in this limit, we obtain more than one hundred expansion terms, enabling precise predictions in the phenomenologically relevant phase space region at the LHC.

I will further discuss how precise control of higher-order electroweak effects enables realistic probes of new physics. In particular, at future e+e- colliders such as FCC-ee, electroweak loop effects can significantly enhance observable deviations predicted in models with extended Higgs sectors [2509.05421].

These results demonstrate how advances in multi-loop electroweak calculations translate into powerful tools for precision Higgs and BSM studies at current and future colliders.

Speaker: Hantian Zhang (CERN)

EW_PLANCK_Zhang_2026.pdf

16:40 Testing unitarity violation at future colliders

In this talk I will discuss two recent proposals relying on the anomalous growth of the cross section of WW production from fermion antifermion pairs, to probe the unitarity violation of the quark (CKM) and lepton (PMNS) mixing matrices. The unitarity violation can be seen within the context of effective field theories, wherein contrary to the other Low energy tests, the strength of the bound grows with the collider center of mass energy provided that one stays below the threshold of the heavy particles responsible for restoring the unitarity of the mixing matrices. Applying the idea in practice I will then discuss practical usages of the test for present and future colliders and compare the preliminary forecasts with complementary flavour bounds.

Speaker: Kristjan Müürsepp (INFN-LNF, Frascati and NICPB, Tallinn, Estonia)

Planck_Muursepp.pdf

17:00 Isolating chirality-breaking SMEFT operators with Drell-Yan angular analysis

In recent years it was argued that it is possible to leverage the growing-with-energy effects induced by (some of) the SMEFT higher dimensional operators to efficiently probe new physics indirectly at hadron colliders. In the context of this high-energy precision program the DY process plays a central role, being the most precise channel at the LHC. In this work we further develop this program, presenting realistic projections for the sensitivity of the LHC with $\mathcal{L}=300$ fb$^{-1}$ and the HL-LHC with $\mathcal{L}=3$ ab$^{-1}$ to chirality-breaking dimension-six SMEFT interactions. In more detail, we provide the $95\%$ CL one-dimensional bounds on such operators at $\sqrt{s}=13$ TeV, using both the di-lepton transverse momentum $(p_\text{T}^{\ell \ell})$ and the di-lepton invariant mass $(m_{\ell \ell})$ distributions of two observables: the inclusive DY process cross-section and the $A_0-A_2$ observable, which is a specific combination of moments of the angular distribution of such process. The latter, according to the so-called Lam-Tung relation, vanishes in the SM up to corrections of order $\mathcal{O}(\alpha_s)$, and the only dimension-six operators that contribute to such observable at this order are the chirality-breaking ones, making the $A_0-A_2$ observable the perfect candidate to bound such operators. Comparing the bounds we obtained, it emerges that the $m_{\ell\ell}$ distribution of the cross-section is the one that provides the tightest bounds. Remarkably, however, we find that for the $A_0-A_2$ observable, the $m_{\ell \ell}$ distribution provides bounds that are significantly stronger than those provided by the $p_\text{T}^{\ell \ell}$ one. As a consequence of this fact and of its capability of selecting chirality-breaking operators among all other dimension-six interactions, the $m_{\ell \ell}$ distribution of the $A_0-A_2$ observable proves to be a key observable in the context of global SMEFT fits.

Speaker: Lorenzo Rolla

Rolla_L_Planck2026Def.pdf

17:20 Dispersion relations in dimension-six SMEFT at one loop

Dispersion relations impose theoretical constraints on SMEFT Wilson coefficients by linking low-energy EFT amplitudes to cross sections in the underlying UV theory. Unlike the case at dimension eight, the indefinite sign of these relations at dimension six makes it difficult, a priori, to extract useful information.
In this work, we show, using dispersion relations applied to different classes of dimension-six SMEFT operators, that broad classes of UV models exhibit a definite sign at one loop. This enables the extraction of nontrivial information about the UV theory directly from the sign of an observed deviation.
We further analyze sign correlations across different flavor entries and among different Wilson coefficients, helping to assemble a consistent picture from several observables.

Speaker: Pablo Olgoso Ruiz (University of Padova)

presentation_olgoso.pdf

17:40 Global Analysis of Linear Standard Model Extensions at HL-LHC and FCC-ee

Linear Standard Model Extensions (LSMEs) are a motivated set of simplified models for exploring the phenomenology of physics beyond the Standard Model (BSM) and assessing the reach of future colliders. They capture a wide range of BSM physics: any particle coupling linearly to the Standard Model (SM) with relevant or marginal interactions is an LSME. Examples include vector-like fermions, new gauge bosons, strongly coupled composite resonances, $R$-parity-violating supersymmetry, or, more generally, any field whose quantum numbers permit such linear couplings to the SM. The finite possibilities have all been classified. We study the indirect sensitivity of the HL-LHC and FCC-ee future colliders to all LSMEs in a global analysis using the power of the Standard Model Effective Field Theory (SMEFT) framework, incorporating one-loop renormalisation group running and matching effects, to perform a
more systematic survey than would otherwise have been feasible without recent SMEFT developments.

Speaker: Victor Maura Breick (King's College London)

Global_LSMEs_PLANCK.pdf

18:00 New Insights into Two-Loop Running in Effective Field Theories

We present a novel approach to extract two-loop anomalous dimensions in bosonic Effective Field Theories (EFTs) by viewing the 4D theory as the infrared limit of its 5D counterpart upon compactification. In this framework, 4D ultraviolet (UV) divergences are read directly from the infrared (IR) poles arising during the matching from 5D to 4D. This method offers significant technical advantages: it eliminates the need for IR regulators and avoids gauge-breaking counter-terms.

The utility of this approach is demonstrated through several high-impact applications, including a cross-check of recent dimension-six SMEFT results and the first two-loop renormalization of dimension-eight Higgs operators. Additionally, we determine the dimension-six singlet spectrum for the large-flavor Abelian Higgs model at its charged fixed point.

Speaker: JAVIER LÓPEZ MIRAS

New_insights_into_2loop_rges.pdf

16:20 → 18:20 Parallel Session: TH Conference Room

16:20 Goofy transformations and RG fixed points

I will pedagogically introduce the recently discovered goofy transformations. Originally, goofy transformations were identified in explicit discussions of the two-Higgs-doublet model (2HDM), but their understanding is mandatory to describe the renormalization group (RG) fixed point structure of quantum field theories in general. Even though goofy transformations are, by definition, explicitly broken by the kinetic terms, the parameter relations they impose on the potential can be stable under RG running to all orders. In the SM, goofy transformations of the Higgs generally prohibit its bare mass parameter and are intertwined with the Yukawa couplings, for what reason they may have important applications for the electroweak hierarchy problem and the Standard Model flavor puzzle.

Speaker: Andreas Trautner

Trautner_Goofy_PLANCK_CERN_26_v2.pdf

16:40 GOOFy "symmetries" - a systematic approach

We have investigated in detail a new class (GOOFy) of transformations for bosonic and fermionic fields that leave the Lagrangian density unchanged.
The transformations act upon complex scalar fields $\Phi$ and $\Phi^\dagger$ employing generalized charge conjugation transformation ($C$) in a {\it non-consistent manner}, i.e. allowing for $\Phi^\dagger \to (\Phi^\dagger)^\prime \neq (\Phi^\prime)^\dagger$. Requiring invariance of the kinetic terms under such transformations specifies the form of $(\Phi^\dagger)^\prime$. An analogous strategy is also adopted for fermionic fields. This offers a systematic way to construct new GOOFy-invariant field-theoretical models. It turns out that theories which are invariant with respect these GOOFy transformations satisfy relations among parameters that are found to be RGE-stable up to two and three loop orders, thus constituting fixed-points under running of the RGE. This has been verified for various theories containing different numbers of bosonic and fermionic fields. In particular it has been shown that the Standard Model~(SM) can not be a viable electroweak theory if demanding invariance under GOOFy transformations. However, the two-Higgs-Doublet Model (2HDM) may be invariant under GOOFy transformations (Yukawa couplings included), providing an interesting phenomenological example of physics beyond the SM. The most striking aspect of this study is the RGE stability of new relations between model parameters in a wide class of field theories. I am also going to present a set of new relations between 2HDM potential parameters that constitute a fixed point under the running of the RGE up to at least three loop order.\

Literature:

1. B. Grzadkowski and O. M. Ogreid, ``GOOFy - a systematic approach,'' arXiv:2602.20849,

2. P. M. Ferreira, B. Grzadkowski and O. M. Ogreid, ``Imaginary scaling,'' arXiv:2506.21145,

3. P. M. Ferreira, B. Grzadkowski, O. M. Ogreid and P. Osland, ``New symmetries of the two-Higgs-doublet model,'' Eur. Phys. J. C 84 (2024) no.3, 234, arXiv:2306.02410.

Speaker: Bohdan Grzadkowski

Planck26_B_Grzadkowski_5.pdf

17:00 Negative running of gravitational positivity

The interplay between positivity bounds and gravity beyond tree level has attracted significant attention recently. In this talk, we focus on the one-loop RG flow of the leading operator in the four-dimensional EFT of shift-symmetric scalars. We show that in the presence of non-minimally coupled matter, minimal gravitational couplings can induce a negative running of the corresponding Wilson coefficient. Revisiting dispersive bounds, positive contributions from infrared-divergent graviton loops are found to overcome this effect and restore positivity, provided the number of non-minimally coupled particles is bounded according to the species bound. We extend this framework to four-photon and four-graviton amplitudes, for which we also find new results.

Speaker: JAIME FERNANDEZ TEJEDOR (Instituto de Física Teórica - CSIC/UAM)

Jaime_Fernandez.pdf

17:20 Charge Quantisation and Monopoles in the Standard Model

We present a systematic study of these group choices using a unifying charge operator, $Q_6$, which characterizes both electric representations and magnetic 't Hooft lines through an index $n_6$. We introduce the concept of the degree of compositeness and demonstrate its direct connection to the emergence of electric 1-form symmetries in the infrared. A key result of this work is the construction of a new renormalizable, anomaly-free model that fills the previously unoccupied $p = 1$ case. We provide a complete analysis of the monopole spectrum across all embeddings and establish their UV–IR correspondence.

Speaker: Yunji Ha (Institute of Particle Physics Phenomenology)

PLANCK_2026_quantization.pdf

17:40 Dynamical Love numbers from shell effective field theory

I will discuss the construction of a novel effective field theory for a compact body coupled to gravity, whose key feature is that the dynamics of gravitational perturbations is explicitly determined by known solutions in black hole perturbation theory in four dimensions. In this way the physics of gravitational perturbations in curved space is already encoded in the effective field theory. I will explain how to model a compact body (in particular a black hole) as a spherical shell, whose finite size regulates short-distance divergences in four dimensions and whose tidal responses are described by higher-dimensional operators.

Speaker: Davide Perrone (Universite de Geneve (CH))

Perrone_Planck_eucapt.pdf

18:00 EFT and anomalies at finite temperature

In this talk, I will apply an Effective Field Theory framework to study quantum field theories at finite temperature in the presence of external fields. This setting is relevant to both early-universe physics and condensed matter systems. I will present a direct approach based on the imaginary-time (path-integral) formalism.

Particular emphasis will be placed on the chiral anomaly and its connection to transport phenomena such as the Chiral Magnetic Effect and the Chiral Vortical Effect, with careful attention to the role of different regularization schemes. The case of massive fermions will also be discussed.

Speaker: Diego Saviot

SAVIOT - PLANCK2026.pdf

Tuesday 19 May

09:00 → 09:30 New ideas for sub-GeV direct detection

Speaker: Ryan Plestid (CERN)

Plestid_New_Ideas_DD.pdf

09:30 → 10:00 Dark sectors, strong and feeble

Speaker: Felix Kahlhoefer

Planck2026.pdf

10:00 → 10:30 Nuclear, atomic, and molecular probes of the QCD theta term

Speaker: Jordy de Vries

Planck2026_EDMs.pdf

10:30 → 11:15 Coffee break

11:15 → 12:55 Parallel Session: CP/Scalars/Baryons -- Council Chamber

11:15 Baryogenesis from primordial CP violation

I will present a novel baryogenesis mechanism during the reheating phase after inflation. This mechanism uses exotic CP-violating sources which have no contribution to electric dipole moments, and are sourced through complex inflaton couplings to Higgs and gravity.

Speaker: Dr Venus Keus (Dublin Institute for Advanced Studies (DIAS))

Venus_Keus-Planck2026.pdf

11:35 Zero-temperature baryon number violation from the dynamics of Standard Model electroweak textures

It was recently shown that baryon number in the Standard Model can be efficiently violated at zero temperature, from Higgs bubble collisions in a strongly first-order electroweak phase transition [2508.21825], thus opening up new possibilities of realizing electroweak baryogenesis in models with a low reheat temperature and large bubble wall velocity.
In this study, the production of baryon number can be attributed to the dynamics of electroweak textures which are non-trivial Higgs field configurations formed upon spontaneous electroweak symmetry breaking. Textures can decay leading to transitions in the Chern-Simons number, which is converted into baryon number via the Standard Model chiral anomaly. This work has been carried out by relying on large-scale (3+1)D real-time lattice simulations of the Higgs and SU(2)-gauge bosons, where true vacuum critical bubbles are nucleated at initial time.
There are many ways in which this first analysis could be improved and extended: by adding the hypercharge gauge boson, adding plasma effects, studying the non-runaway regime, and most importantly, adding CP-violation in the simulations, which I will discuss in this presentation.

Speaker: Martina Cataldi (University of Hamburg)

Cataldi_Planck2026.pptx

11:55 D/H vs. inhomogeneities: Constraints on Baryogenesis Scenarios

Recent constraints coming from deuterium-to-hydrogen (D/H) measurements provide a way to probe baryogenesis scenarios where the production of baryons is inhomogeneous. In this work, we study the compatibility of various baryogenesis models with the bound from D/H measurements. We start by applying the bound to EW baryogenesis and show that these models are well within the allowed region of the parameter space, even by increasing the precision of D/H measurements. Following, we apply the bound to baryogenesis via domain walls, where the length scale of inhomogeneities is determined by the Hubble length at the time of domain-wall annihilation. We obtain the bound on the annihilation temperature of domain walls in some specific cases. Finally, we discuss some more exotic models of baryogenesis which involve relativistic bubbles.

Speaker: Bruno Missoni (SISSA)

Missoni, Planck 2026.pdf

12:15 baryons from evaporating primordial black holes

We propose a new pathway to the baryon asymmetry in which small primordial black holes (PBHs) act as localized, short-lived baryogenesis engines after the electroweak phase transition (EWPT). Hawking emission from evaporating PBHs deposits energy into the surrounding plasma, creating over-pressured hot spots that drive near-acoustic shock fronts. Inside these fronts the Higgs expectation value is driven to the symmetric phase while remaining broken outside, yielding moving interfaces that source chiral charge; active sphalerons in the restored regions then convert this into baryon number. We compute the time-dependent Hawking power across Standard Model species, estimate the microscopic Landau–Pomeranchuk–Migdal thermalization length that sets the initial hot-spot size, and solve the hydrodynamics of the expanding front. Adapting electroweak baryogenesis methods to moving walls, we derive the resulting baryon yield for PBH populations with realistic time-dependent mass functions resulting from critical collapse theory. Crucially, the mechanism supplies the needed out-of-equilibrium dynamics without requiring new physics to render the EWPT first order.

Speaker: Miguel Etienne A Vanvlasselaer (ICCUB)

Presentation_Planck_Vanvlasselaer.pdf

12:35 Light states in multi-Higgs potentials with multiple candidate vacua

It was recently shown that in multi-Higgs models with a CP invariant potential and spontaneous CP violation, despite having free quadratic parameters that could induce a decoupling regime for the new scalars, that possibility cannot be fully realized. Contrary to expectations, there are states with masses that cannot be much larger than the electroweak scale once perturbativity constraints are imposed on the quartic couplings. This phenomenon is related to the existence of a second candidate vacuum; in that case, both candidate vacua are simply related via a CP transformation.
The analysis of this "multiple possible vacua" - "existence of light states" connection is now extended to (i) 2 Higgs doublets models with both a CP violating potential and CP violating candidate vacua ('mixed CP violation'), and (ii) some 3 Higgs doublets where further insights can be obtained.

Speaker: Dr Miguel Ruben Nebot Gómez (U. of Valencia - IFIC)

Nebot_LightStates_Planck2026.pdf

11:15 → 12:55 Parallel Session: INFLATION -- TH Conference Room

11:15 Quintessence from string theory

I will present various realisations of quintessence from string theory, tackling the comparison to data, including the question of the phantom regime and the coupling to matter. If time allows, I will also comment on the conjectured absence of a cosmological event horizon.

Speaker: Dr David Andriot (Unite Reseaux du CNRS (FR))

Talk Planck 05 2026.pdf

11:35 Gravitational Particle Production in Multifield Inflation

Gravitational particle production offers a minimal mechanism for generating relic particles in the early universe, relying only on the nonadiabatic evolution of quantum fields in an expanding spacetime. In this talk, I investigate this mechanism in the context of multifield inflation, where curved field-space trajectories and additional scalar degrees of freedom can substantially alter the production history relative to the standard single field picture. I develop a general framework for computing the abundance of gravitationally produced particles and show how it depends on the inflationary path, effective masses, and post-inflationary evolution. Multifield effects can induce transient nonadiabaticity, modify the scaling of particle yields, and open new regions of parameter space for the gravitational production of dark sector relics. These results demonstrate that multifield dynamics can substantially modify gravitational particle production and the resulting relic abundance.

Speaker: Sarunas Verner (University of Chicago)

planck_2026_sarunas_verner.pdf

11:55 On the stability of gauge-field backreaction in axion inflation

An axion-like field coupled to an Abelian gauge field provides one of the simplest inflationary models that is free from the eta problem and possesses an efficient reheating mechanism. For sufficiently large coupling, this system enters a regime of strong gauge-field backreaction, exhibiting rich and intricate dynamics. In this work, we employ a semi-analytical method, the gradient-expansion formalism, to perform a comprehensive parameter scan and determine the precise conditions under which backreaction sets in. Previous studies have shown that the Anber-Sorbo solution, in which the potential-gradient force acting on the axion is balanced by Hubble friction and gauge-field backreaction, is unstable. Here, we broaden the parameter space and identify a new region in which the Anber-Sorbo solution remains stable despite strong backreaction. Although our analysis is restricted to a homogeneous axion field and to perturbations that depend only on time, we expect that this stability property can be extrapolated to generic time- and space-dependent perturbations. This newly identified region therefore represents a distinct type of backreaction - stable backreaction - which may not be accompanied by the rapid growth of perturbations. Finally, we present a more stringent criterion for the onset of (unstable) backreaction, based on crossing the instability threshold, and apply this criterion to two benchmark inflationary models.

Speaker: Oleksandr Sobol (University of Münster)

Slides-Planck2026-Sobol.pdf

12:15 Warm Inflation with the Standard Model

We show for the first time that warm inflation is feasible with Standard Model (SM) gauge interactions alone. Our model consists of a minimal extension of the SM by a single scalar inflaton field with an axion-like coupling to gluons and a monomial potential. The effects of light fermions, which were previously argued to render warm inflation with the SM impossible, are alleviated by Hubble dilution of their chiral chemical potentials. Our model only features one adjustable combination of parameters and accommodates all inflationary observables. We briefly discuss implications for axion experiments, dark matter, and the strong CP-problem.

Speaker: Marco Drewes (Universite Catholique de Louvain (UCL) (BE))

Drewes Planck 2026.pdf

12:35 Removing the Cosmological Bound on the Axion Scale via Confinement During Inflation

We implement a scenario of early relaxation of the axion via a high scale confinement within $SU(5)$ grand unified theory and study an epoch of strong QCD in inflationary cosmology. We consider scenarios in which, during inflation, the $SU(5)$ is either entirely or partially in the confining phase. This generates an early potential for the axion and dilutes its energy density removing any cosmological upper bound on the decay constant.
We show that a phase of strong QCD can be realized by at least two mechanisms:
1) a direct coupling between the inflaton and the gauge fields and/or
2) by restoration of the $SU(5)$ symmetry during the inflationary epoch.
In the latter case, strong coupling is already achieved via the RG running of the $SU(5)$ gauge coupling. We show that the mechanism works for all known realizations of the invisible axion idea:
Peccei-Quinn (PQ) type formulations in which the anomalous global symmetry is realized via additional scalars (DFSZ) or heavy fermions (KSVZ) as well as the two-form gauge axion formulation based entirely on the QCD gauge redundancy without any anomalous global symmetry. Even if the expectation value of the PQ scalar vanishes during inflation, the axion is a well defined degree of freedom represented by the phase of the fermion 't Hooft determinant. For the DFSZ case, this phase is composed out of a condensate of the ordinary quarks, amounting to an early universe version of the $\eta'$-meson. In all considered scenarios, the present day axion can be a viable dark matter candidate for an arbitrarily large value of the decay constant.

Speaker: Lucy Elisabeth Komisel (Max Planck Institute for Physics, LMU Munich)

PLANCK26_Komisel.pdf

11:15 → 12:55 Parallel Session: PHASE TRANSITIONS -- Main Auditorium

11:15 Quantum Imprints on Confinement: SU(N) Yang Mills Confinement PT at finite theta

We analyze the impact of a finite theta angle on the first-order confinement PT in SU(N) Yang-Mills theory, where CP violation arises at
$\theta = \pi$ due to the multibranched structure of the Yang-Mills vacuum. Using holography and lattice QCD inputs, we show that at finite
$\theta, N$, the supercooling regime of the metastable deconfined phase is reduced. We also study the interplay between the confinement PT and the production of domain walls, elaborating on their stability and potential for gravitational wave (GW) emission. Finally, we showcase the possibility of two distinct GW sources: one from the confinement PT and another from domain wall annihilation.

Speaker: Nicklas Ramberg (SISSA Trieste)

SU(N) with Finite Theta Planck.pdf

11:35 Does the Electron EDM Preclude Electroweak Baryogenesis?

Electroweak baryogenesis (EWBG) constitutes a theoretically compelling and experimentally testable mechanism for explaining the origin of the baryon asymmetry of the universe (BAU). New results for the electric dipole moment (EDM) of the electron place significant constraints on the beyond Standard Model CP-violation needed for successful EWBG. Using a specific model illustration, we show how new developments in EWBG quantum transport theory that include CP-violating sources first order in gradients imply more relaxed EDM constraints -- and thereby greater EWBG viability -- than implied by previous approximation formulations. We also illustrate how these developments enable a more realistic treatment of CP-conserving interactions that can also have a decisive impact on the predicted BAU.

Speaker: Yuanzhen Li

EWBG_YuanzhenLi_CERN.pdf

11:55 Uncertainty budgets for bubble wall velocities in cosmological phase transitions

First-order cosmological phase transitions could have been central to early-universe phenomena such as baryogenesis and gravitational waves (GW). Predicting such GW signatures requires not only reliable equilibrium thermodynamics but also an accurate determination of the terminal velocity of the nucleated bubbles during the transition.

In this talk, I present progress towards quantifying the theoretical uncertainties of bubble wall velocities. Using the WallGo package [1] applied to extensions of the Standard Model, I will identify several order-one sources of uncertainty, including missing out-of-equilibrium species in the collision terms, treatments of thermal masses, inputs from thermal equilibrium such as the nucleation temperature, and ansatz choices for bubble profiles. By mapping out this uncertainty budget, I will highlight the most critical directions for improving the reliability of wall velocity, and thus GW predictions [2].

[1] A. Ekstedt, O. Gould, J. Hirvonen, B. Laurent, L. Niemi, P. Schicho, and J. van de Vis, How fast does the WallGo? A package for computing wall velocities in first-order phase transitions, JHEP 04, 101 (2025),[2411.04970].
[2] J. van de Vis, P. Schicho, L. Niemi, B. Laurent, J. Hirvonen, O. Gould, WallGo investigates: Theoretical uncertainties in the bubble wall velocity, [2510.27691].

Speaker: Philipp Schicho (University of Geneva)

planck26.pdf

12:15 Tunneling decay at fixed charge: nucleation theory

The standard semiclassical description of vacuum decay at zero temperature assumes a neutral metastable state and a real $O(4)$-symmetric Coleman bounce. At finite density this framework is incomplete whenever a conserved $\mathrm{U}(1)$ charge is fixed, since tunneling must occur in a definite charge sector. In that case the Euclidean path integral is charge-projected, the boundary conditions become twisted in Euclidean time, and the relevant saddle is intrinsically complex in the original field variables.

We develop and solve the corresponding fixed-charge bounce problem for bubble nucleation out of a homogeneous charged medium. The decay exponent is reformulated as a real variational problem for two independent Euclidean fields, $\phi$ and $\bar\phi$, and is expressed as the action difference between the fixed-$Q$ bounce and the metastable homogeneous reference state in the same charge sector, plus the conjugate twist contribution. The construction smoothly reproduces ordinary Coleman tunneling as $Q\to0$, while at finite $Q$ it yields genuinely charged saddles that generically break exact $O(4)$ symmetry. Our results provide, to our knowledge, the first explicit computation-ready framework for false-vacuum decay at fixed charge, with direct relevance for phase transitions in dense relativistic systems.

Speaker: Dr GIULIO BARNI (IFT-UAM/CSIC Madrid)

Fixed_Q_tunneling_PLANCK26_Barni_Giulio.pdf

12:35 Dark Sector Karaoke: A 3D EFT for a Pitch-Perfect Phase Transition.

We explore the dynamics of cosmological phase transitions in a dark sector model featuring a dark photon associated with a U(1)D gauge symmetry and radiative symmetry breaking. Our analysis focuses on different approaches to construct the effective potential: the high-temperature approximation, a full numerical evaluation of the thermal integrals, and a dimensionally reduced 3D effective theory built with DRalgo, at both leading and next-to-leading order. We as well explore the effect of including the running of the parameters in order to respect the hiercarchy scales.
We investigate how these methods impact the characterization of the phase transition, particularly in the supercooled regime.

Speaker: Cristina Puchades Ibanez (JGU Mainz)

Dark_Karaoke_PLANCK.pdf

12:55 → 14:00 Lunch break

14:00 → 14:10 EuCAPT welcome

Convener: Silvia Pascoli (Universita e INFN, Bologna (IT))

Pascoli_EuCAPT_Symposium.pdf

14:10 → 14:40 Cosmological Implications of a New Determination of Primordial 4He

Speaker: Keith A. Olive (University of Minnesota (US))

Plank26.pdf

14:40 → 15:10 Overview of neutrino masses in cosmology

Speaker: Willem Elbers

elbers_eucapt_slides.pdf

15:10 → 15:30 Charting the Future: The APPEC Roadmap

Speaker: Joachim Kopp (Johannes Gutenberg Universitaet Mainz (DE))

2026-05-appec-at-eucapt.pdf

15:30 → 16:20 Coffee break

16:20 → 16:50 Tensions in Lambda CDM and The Stability of Dark Energy

Speaker: Brodie Popovic

EuCAPT (1).pdf

16:50 → 17:20 Reanalysis of the DESI DR1 full-shape data

Speaker: Anton Chudaykin

CERN_Chudaykin.pdf

17:20 → 17:50 EuCAPT 5min flash talks

17:20 A cosmologist's take on Little Red Dots

The James Webb Space Telescope (JWST) has uncovered a population of compact, high-redshift sources, the Little Red Dots (LRDs), which may host supermassive black holes (BHs) significantly heavier than their stellar content compared with local scaling relations. These objects challenge standard models of early galaxy formation and may represent an extreme class of early BH hosts. In this walk, we investigate whether these BHs could have a primordial origin. We first show that the direct formation of these BH masses in the early Universe is excluded by stringent CMB μ-distortion limits. We then investigate the assembly of massive BHs from lighter, observationally allowed primordial black holes (PBHs) via hierarchical mergers, finding that, although this channel can operate depending on the merger history, it faces challenges in explaining the observations due to the rarity of the required high-redshift dark matter halos. Finally, we estimate gas accretion onto intermediate-mass PBHs, while jointly tracking metallicity evolution, and identify regions of parameter space in which such growth could reproduce the observed properties of LRDs. As a special case, we focus on the strongly lensed source QSO1, whose extremely low metallicity and large mass provide a stringent test of these formation channels.

Speaker: Loris Del Grosso

slides_5min.pdf

17:25 Non-linear evolution of primordial parity violation

Parity violation is a new probe of the primordial universe. However, we need to connect the primordial universe to the observables. Recent hints of parity violation in the large scale structure of the universe motivate us to investigate how the observables are affected by late-time physical processes. In this work, we present an analytical expression for the parity violating 4-point correlation function of matter density fields at 1-loop order, that can be used to probe primordial parity violation. Based on arXiv:2510.06164

Speaker: Sha Azyzy (MPA)

Sha_CERN_EuCAPT.pdf

17:30 Hints for an AdS Universe from DESI

In this talk, I will present recent BAO results from DESI suggesting that dark energy may be evolving. I will briefly discuss equation of state parametrizations and focus on a simple quintessence model with a Higgs like potential. This approach suggests that the Universe may already be in, or could evolve into, an AdS phase, potentially leading to a future cosmological collapse.

Speaker: Ioannis Gialamas (National Institute of Chemical Physics and Biophysics)

talk_CERN_Gialamas_v2.pdf

17:35 Properties of the neutrino clustering

We investigate the clustering of neutrinos on both galactic and extragalactic scales, with the aim of probing their standard and non-standard properties. In the standard scenario, we explore whether neutrino clustering measurements can be used to constrain the dark matter halo mass of the Milky Way. In the non-standard scenario, we examine how neutrino–dark matter interactions could imprint detectable features on the local distribution of cosmological neutrinos. Our phenomenological approach aims to produce testable predictions for future direct detection experiments such as PTOLEMY.

Speaker: Pietro Ghedini (IFIC, CSIC - UV)

talk_EuCAPT_Ghedini.pdf

17:40 On EFT constraints from quasi-normal modes

Recently, a conjecture on the behavior of quasi-normal modes in theories beyond General Relativity has been proposed and applied to put bounds on EFT coefficients. I will show, using simple dimensional analysis considerations, that the bound is irrelevant for any practical purpose.

Speaker: Leonardo JULIANO (Scuola Normale Superiore, INFN)

EuCAPT_2026.pdf

17:50 → 18:00 SCOAP3: Sponsoring Consortium for Open Access Publishing in Particle Physics

Speaker: Anne Gentil-Beccot (CERN)

202605 SCOAP3.pdf

202605 SCOAP3.pptx

18:00 → 20:00 Reception and Poster Session

Wednesday 20 May

09:00 → 09:30 Stellar Remnants as Dark Matter Factories and Detectors

Speaker: Melissa D. Diamond

Stars_DM_pdf.pdf

09:30 → 10:00 Indirect detection of thermal electroweak dark matter

Speaker: Weishuang Linda Xu

WIMPS_wlxu.pdf

10:00 → 10:30 EuCAPT 5min flash talks

10:00 $\phi$-Dwarfs: White Dwarfs probe Quadratically Coupled Scalars

Ultralight scalar fields quadratically coupled to electrons can be sourced in dense stars, triggering phase transitions or leading to a new ground state of matter. I will show that white dwarfs provide a robust laboratory for testing this physics through distinctive features in the mass-radius relation, including forbidden gaps corresponding to ranges of radii with no stable configurations. Confronting these predictions with precise measurements of Sirius B and Procyon B, together with the broader white dwarf population, yields new constraints on scalar theories and probes previously unexplored regions of parameter space. These constraints are independent of whether the scalar field constitutes dark matter.

Speaker: Kai Bartnick (Technical University of Munich)

KB_PhiDwarfs.pdf

10:05 Constraints on Dark Matter Models from Supermassive Black Hole Evolution

In this talk I will introduce, (https://inspirehep.net/literature/2967464), which is accepted as a PRL letter, in which we show that a semi-analytical model for the evolution of galaxies and supermassive black holes within the ΛCDM paradigm can yield the stellar mass-BH mass relations that reproduce both the JWST and pre-JWST observations. Either fuzzy or warm dark matter would suppress the formation of the smaller galactic halos that play important roles in the CDM fit to the high-redshift SMBH data. We show how current data can be used to impose very stringent constraints on deviations from CDM, in an even more powerful way than the light from stars. This opens a new very powerful avenue to test deviations from CDM using gravitational wawes.

Speaker: Juan Urrutia (KBFI)

Constraints on Dark Matter from SMBH Evolution — EUCAPT 2026.pdf

10:10 Resonant Dark Matter Production in Astrophysical Environments

Astrophysical plasmas provide a powerful laboratory for feebly interacting dark sectors. In this talk, we present a systematic study of resonant axion-plasmon and dark-plasmon dark matter production in compact astrophysical environments, focusing on core-collapse supernovae, white dwarfs, and neutron stars. Our analysis builds on recent work on resonant in-medium production and extends it to a unified treatment across environments with very different densities, temperatures, and plasma properties. We consider both the standard resonant production mechanism and the modifications induced by strong magnetic fields, which can alter the photon dispersion relations, shift the resonance conditions, and open additional regions of efficient production. By comparing these effects across stellar environments, we assess where resonant production is most important and identify the regimes in which magnetic fields significantly enhance the signal. The goal is to provide a complete picture of resonance-driven production of axion-like and dark-photon-like dark matter in astrophysical media, and to clarify the complementarity of supernovae, white dwarfs, and neutron stars as probes of light dark sectors.

Speaker: María José Fernández Lozano

10:15 Dark matter spikes in galactic X-ray binaries

Dark matter (DM) may form very steep density enhancements—spikes—around black holes. Recent studies have suggested that unusually rapid orbital‑period decay in two nearby black‑hole X‑ray binaries could be explained by the presence of DM spikes.
If spikes are indeed present in these systems—where current formation models do not predict them—the implications would be profound, pointing to dense dark‑matter structures far more widespread than expected.

We reassess these claims using N‑body simulations, and extend the analysis to a similar third system not previously explored in this context. Our results show that feedback effects significantly reshape the spikes, ruling out the shallow density profiles proposed earlier. Longer‑term evolution may further modify the spike, highlighting the need for improved modelling of binaries embedded in dense dark‑matter environments.

Based on 2510.11635 - Phys. Rev. D 113, 043043 (2026)

Speaker: Francesca Scarcella

Eucapt26_Scarcella.pdf

10:20 Light dark matter searches with space- and Moon-based radio telescopes

Ground-based radio telescopes are routinely used to search for light dark matter candidates such as axion-like particles or dark photons. However, these instruments face inherent limitations in probing masses below $10^{-7}$ eV, due to the effect of the Earth's ionosphere. Current and planned space- or Moon-based radio telescopes can overcome this limitation and open a largely unexplored discovery space. In this talk, I will present a systematic sensitivity study of resonant dark-matter conversion into radio signals in three nearby astrophysical environments: the Sun, the Earth, and Jupiter. I will first discuss the intrinsic limitations set by environmental noise for space-based observations, and then derive sensitivity projections for the parameter space of the two candidates using existing and planned instruments. I will show that particularly strong prospects arise for dark-photon searches using the Sun as a target, and for axion-like particle conversion in Jupiter’s magnetosphere.

Speaker: Ruben Zatini (IAC -Instituto de Astrofísica de Canarias)

EuCAPT_2026.pdf

10:25 Modeling electronic final states in liquid xenon for light dark matter detection

Liquid xenon is an important target material for the direct detection of light dark matter (DM) via electron recoils. Consequently, accurate modeling of the DM-electron interaction in this medium is crucial. In particular, a proper description of the electron final states plays a key role in modeling the electronic response of the detector. We follow a novel approach in which the final states are described as linear combinations of positive-energy eigenstates of the Schrödinger equation, combined with a DFT modeling of the liquid xenon phase. These states replace the single positive-energy eigenstate approximation commonly adopted when liquid xenon targets are treated as collections of non-interacting atoms. Our approach therefore represents a step towards a more realistic description of liquid xenon as an interacting many-body system. This talk presents preliminary results comparing the existing literature with DM-electron scattering rates obtained with our description of the final states.

Speaker: Theresa Magdalena Backes

Liquid_Xenon_Electronic_States.pdf

10:30 → 11:15 Coffee breaks

11:15 → 11:45 The poltergeist mechanism - Enhancement of scalar-induced gravitational waves with early matter-dominated era -

Speaker: Keisuke Inomata

inomata_planck_eucapt_may_20_2026.pdf

11:45 → 12:15 Electroweak baryogenesis

Speaker: Jorinde van de Vis (CERN)

EWBGJvdVis.pdf

12:15 → 12:45 EuCAPT 5min flash talks

12:15 Cosmological gravitational particle production: Scalars and fermions

In this talk, I will discuss the gravitational production of scalars and fermions during inflation. For scalars, I will compare Bogolyubov coefficient and Starobinsky stochastic approaches, showing that they only agree in the limit of infinitely long inflation. High-scale inflation is very efficient in particle production, leading to constraints on the existence of free, light, and stable scalars: such particles are viable only if their masses are below the eV scale or if the reheating temperature is in the GeV range. For fermions, I will show how the production efficiency depends on the particle mass, which is generated via the Yukawa coupling and sensitive to the corresponding scalar field value. Scalar fields can experience large quantum fluctuations during inflation, driving the average field to the Hubble scale and above. Thus, fermions can be very heavy during inflation, enhancing particle production.
Based on 2503.14652 and 2509.01673.

Speaker: Duarte Da Silva Feiteira

presentation_eucapt_slides_pdf.pdf

12:20 Quantum production of gravitational waves after inflation

A variety of mechanisms in the early Universe lead to the generation of gravitational waves (GWs). In this talk, I will present a novel source of GWs generated by vacuum fluctuations after inflation. Since gravitons are minimally coupled, their quantum creation takes place during inflation but is absent in an unperturbed Universe during the radiation-dominated epoch, as they behave as conformally invariant particles. However, the presence of inhomogeneities breaks the conformal flatness of the metric, allowing scalar metric perturbations to induce the quantum production of gravitons. The resulting GW spectrum from this mechanism peaks around the GHz frequency range, distinguishing it from other astrophysical and cosmological backgrounds and underscoring the need for detectors sensitive to these high frequencies.

Speaker: Alina Mierna

Slides_Alina_Mierna.pdf

12:25 The phenomenology of axion relic pockets

Axion relic pockets are phase-transition remnants consisting of regions of false vacuum stabilised from collapse by a hot axion gas. Axion relic pockets can comprise dark matter, but little is known about their phenomenology. We consider trapped axions coupled to electromagnetism and show that axion-photon conversion occurs in atomic electric fields, leading to high-energy electromagnetic cascades that may be detectable by neutrino, cosmic-ray, and dark-matter experiments. Calculating the interaction rate requires accounting for the pocket's compactness and spherical geometry. The distribution of electromagnetic showers is inherently isotropic, and upward-going showers provide a smoking-gun signal for the model. Using recent data from "Medium Energy Starting Events" of the IceCube neutrino telescope, we derive the first limits on axion relic pockets. We also comment on the prospects for detecting axion relic pockets with atmospheric detectors, including fluorescence detection by the Pierre Auger Observatory and radio Cherenkov detection by balloon-borne payloads, such as ANITA and PUEGO. These results open a new observational window on dark matter and motivate dedicated searches for the associated electromagnetic showers across existing and forthcoming high-energy facilities.

Speaker: Charalampos Nikolis

eucapt-nikolis.pdf

12:30 Reviving PBHs: primordial black holes from supercooled phase transitions revisited

Black holes in the asteroid-mass range, $10^{15}$ - $10^{20}$ kg, provide a compelling candidate for dark matter. This window remains largely unconstrained observationally, while the low masses provide an interesting challenge in explaining their possible origin. In this talk, I will discuss a particular formation scenario of such objects, where curvature perturbations responsible for gravitational collapse into black holes are generated by a cosmological first-order phase transition. If the transition is strongly supercooled and slow compared to the Hubble expansion, fluctuations in the bubble nucleation history in different patches of the Universe can produce a large spectrum of curvature perturbations. I will present a covariant formalism that can be adopted to compute the evolution of energy-density fluctuations within a fixed comoving volume. Within this formalism, I will highlight the crucial role of energy flux carried by expanding bubble walls in amplifying curvature perturbations to the level required for black hole formation. Finally, I will identify the transitions for which the population of produced black holes can fully explain the abundance of Dark matter observed today.

Speaker: Piotr Toczek (University of Warsaw)

EuCAPT26_Toczek.pdf

12:35 Metastable strings at PTA: classical stability analysis

Metastable strings can arise because of a two-step symmetry breaking chain of the type $SU(2) \to U(1) \to 1$. These strings can decay via quantum tunnelling through the nucleation of monopole anti-monopole pairs, and have recently been considered as candidates for explaining the gravitational-wave background observed by pulsar timing arrays. In our work, we study the classical stability of such metastable strings in a concrete model realizing this symmetry breaking pattern. We identify regions of parameter space in which the string solutions are classically stable or unstable. Our results show that classical instabilities can impact the parameter space relevant for explaining the PTA signal.

Speaker: Maxime Grandjean (VUB & FWO)

Slides EUCAPT - Maxime Grandjean.pdf

12:40 Supercooled tachyonic phase transitions

Classically scale-invariant (CSI) Standard Model extensions can induce strongly supercooled phase transitions in the early Universe. In a large portion of the CSI model parameter space, bubble nucleation is inefficient, preventing the Universe from transitioning to the true vacuum. Instead, symmetry breaking proceeds via classical rolling through a tachyonic regime of the scalar potential after an extended period of thermal inflation, leading to exponential amplification of large-scale field fluctuations. I will discuss the generation of curvature perturbations during this supercooling phase, with a focus on the resulting scalar-induced gravitational wave background. This novel symmetry-breaking mechanism renders nearly the entire CSI model parameter space testable by upcoming gravitational-wave observatories.

Speaker: Daniel Schmitt (KIT)

Schmitt_EuCAPT.pdf

12:45 → 14:00 Lunch break

14:00 → 14:30 Not-quite-primordial black holes

Speaker: Dr Wenzer Qin (New York University)

2026-05-20 Planck+EuCAPT_pdf.pdf

14:30 → 15:00 Neutrinos from the most energetic cosmic rays

Speaker: Daniel Naredo

Naredo_EuCAPT.pdf

15:00 → 15:30 EuCAPT 5min flash talks

15:00 Injecting particles in the Early Universe: a BBN perspective.

We present updated constraints on unstable massive relics decaying into Standard Model particles during and prior to Big Bang Nucleosynthesis (BBN), focusing on channels that do not primarily produce neutrinos. We analyse the impact of electromagnetic and hadronic energy injection on light-element abundances, incorporating an improved treatment of neutron–proton interconversion, hadrodisintegration, and photodisintegration processes. We find that meson-induced interconversions dominate constraints at early times, while hadro- and photodisintegration become relevant at later epochs. Compared to previous studies, our results show improved constraints, especially at earlier times when interconversions dominate the limits.

Speaker: Sara Bianco (DESY-T Hamburg)

Eucapt26-1.pdf

15:05 Colour-Flavour Locked Self-Interacting Dark Matter

We present a self-interacting dark matter (SIDM) model based on a dark SU(N) gauge theory spontaneously
broken to a non-abelian global symmetry. The non-abelian structure naturally separates self-scattering and
annihilation channels, allowing resonant enhancement of self-interactions to address the core–cusp problem
while remaining consistent with experimental bounds. The relic abundance is set by freeze-out into light dark
sector states, which couple to the Standard Model via effective kinetic mixing. The model’s parameters are
fixed by relic density, small-scale structure, and resonance conditions, making it testable in upcoming direct
detection experiments.

Speaker: Lorenzo De Ros (JGU Mainz)

Planck_EuCAPT_2026.pdf

15:10 Archival radio data, leading axion constraints

Pulsars' magnetospheres are excellent laboratories for axion indirect detection. Recent developments in the field have shown that 1) neV-0.1meV axions can be efficiently produced in the polar cap region of pulsars, even if they do not contribute to the Dark Matter density of the Universe, and even for very feebly coupled axions; and that 2) these axions gravitationally accumulate to extremely high densities around the pulsar, leading into powerful radio emission when axions cross the resonant surface. In this talk I will present the first search for this signal using archival VLA observations of the Crab pulsar, which result into leading constraints in the $\mu$eV mass range, and illustrate the way forward to approach the QCD band from radio observations.

Speaker: Toni Bertólez-Martínez (University of Wisconsin-Madison)

15:15 Sub-GeV Scalar Dark Matter in a Higgs-Mixed Dark Sector: From Neutrino Masses to Astrophysical Signals

We investigate sub-GeV scalar dark matter embedded in a rich dark sector linking cosmology, neutrino physics, and astrophysical observables. The framework features a complex scalar dark matter candidate interacting via a Higgs-mixed mediator associated with the spontaneous breaking of a dark $U'(1)$ symmetry.

We first perform a numerical exploration of the scalar and dark matter sector and identify regions of parameter space where thermal production can reproduce the observed relic abundance while remaining consistent with existing constraints. We then extend the model by introducing a sterile neutrino and a pair of dark neutrinos charged under the broken symmetry. A large-scale numerical scan reveals viable regions where the mediator can decay before Big Bang Nucleosynthesis while simultaneously generating sub-eV active neutrino masses.

Finally, we discuss the phenomenological implications of this framework, including potential connections to the Galactic $511~\mathrm{keV}$ line, and to gravitational-wave signals from the dark-sector phase transition.

Speaker: Elina Merkel (University of Bologna & INFN Bologna)

EuCAPT_Elina_Merkel.pdf

15:20 Spectra of primordial magnetic fields at the electroweak phase transition

There is evidence today that galactic voids are permeated by a largely homogeneous and extremely weak magnetic field. While magnetic fields are not uncommon in the Universe, their presence in the low-density voids is somewhat perplexing. There are competing theories for the origin of these fields: they may be of galactic origins or entirely primordial. In this talk, we will begin by looking at how the combined magnetic field of galaxies is unlikely to explain the observed spectra. Then we turn to the alternative, primordial explanation and we show how a primordial magnetic field spectrum may be generated using a lattice model. In particular, we show that the spectrum can be obtained in an entirely analytic way, which agrees with the numerical results.

Speaker: Károly Seller (ELTE Eötvös Loránd University)

Seller_EuCAPT26.pdf

15:30 → 16:20 Coffee break

16:20 → 16:50 Machine Learning and AI in Gravitational Wave Science

Speaker: James Alvey (University of Cambridge)

2026-05-20 EuCAPT.pdf

16:50 → 17:20 First-Principles Formalism for Simulating Self-Interacting Dark Matter

Speaker: Maria Ramos

Planck-SIDM.pdf

17:20 → 17:50 EuCAPT Symposium: Closing Remarks and Future Directions

Speaker: David Marsh

EuCAPT_Symposium_closing_2026.pdf

19:00 → 21:00 Meet up at Bains des Paquis

Paquis.pdf

Thursday 21 May

09:00 → 09:30 The Future of BSM Searches at ATLAS and CMS

Speaker: Louie Dartmoor Corpe (Université Clermont Auvergne (FR))

LCorpe_PLANCK_FutureOfSearchesAtLHC_May2026.pdf

09:30 → 10:00 Physics with TeV Neutrinos and Muons from the LHC

Speaker: Juan Rojo Chacon (Nikhef National institute for subatomic physics (NL))

rojo-PLANCK26-LHCneutrinos.pdf

10:00 → 10:30 Searching for the Unknown at the Electron-Ion Collider

Speaker: Hooman Davoudiasl

HDavoudiasl-Planck-EuCAPT-2026.pdf

10:30 → 11:15 Coffee break

11:15 → 12:55 Parallel Session: AXIONS -- Council Chamber

11:15 Counting axions with IAXO

The existence of multiple axion species is a generic prediction of a number of extensions of the Standard Model. If more than one axion couples to photons, their combined signal in helioscope experiments may mimic that of a single axion with different parameters. This raises a fundamental question: if a next-generation helioscope such as IAXO detected a signal, would we be able to disentangle whether it originated from one or multiple axions? To answer this question, we first recast current CAST bounds and derive IAXO/IAXO+ projections in the two-axion parameter space, identifying the regions where a signal could be observed. Then, we analyze the spectral signatures of a two-axion system in both the quasi-degenerate and hierarchical mass regimes and point out where IAXO can discriminate a two-axion signal from the single-axion hypothesis given the expected energy resolutions of the detector.

Speaker: Carlos Miro Arenas

PLANCK2026_Carlos-Miro.pdf

11:35 The structure of multi-axion solutions to the strong CP problem

Multi-axion solutions to the strong CP problem predict new axion states beyond the traditional QCD axion. These new axions may modify the relation between the QCD axion mass and its photon coupling, hence moving the QCD band, or be discovered in new regions of parameter. I will explore the general structure of multi-axion solutions to the strong CP problem and identify the conditions under which axions can populate different regions of the mass vs photon coupling parameter space: the region to the right of the QCD line, the experimentally interesting region to its left, and scenarios in which the QCD line itself is displaced to the right. I will highlight classes of well-motivated UV complete theories where these different scenarios arise naturally. I will discuss that, beyond a potential solution to the strong CP and dark matter problems, discovering such new axions could have strong implications for our understanding of fundamental physics and the ultraviolet completion of the Standard Model.

Speaker: Mario Fernandez Navarro (University of Zurich)

Planck2026_MFN.pdf

11:55 Axions from the flavour deconstruction of QCD

We study the implications of an axion solution to the strong CP problem in a model where QCD is deconstructed in flavour. The first layer of deconstruction $SU(3)_{12}\times SU(3)_3$ predicts two physical axions: one always behaves as the the usual QCD axion while the other one can be greatly displaced from the traditional QCD line. A light axion with suppressed photon coupling appears when the deconstruction occurs near the TeV scale and the associated heavy gauge boson (coloron) is mostly coupled to light quarks, making this scenario testable at current and future high energy colliders. Otherwise, the exotic axion is heavy and with a standard photon coupling, which is better tested by astrophysical signatures. If QCD is completely deconstructed $SU(3)_{1}\times SU(3)_2\times SU(3)_3$, then a third, further heavier physical axion is predicted. We study axion dark matter in this framework and provide simple but ultraviolet complete models that connect the Peccei-Quinn scale with the scale of vector-like quarks participating in the origin of CKM quark mixing.

Speaker: Marta Fuentes Zamoro

flavour_axion.pdf

12:15 Intrinsically Quantum Effects of Axion Dark Matter are Undetectable

In this talk, I will present a unified quantum framework for axion dark matter detection. Drawing on a quantum-optics-inspired formalism, we describe realistic axion dark matter detection schemes through a density matrix and a corresponding quasi-probability distribution. We show that the intrinsically quantum nature of the dark matter field will remain unobservable with current or foreseeable technology due to mode averaging and extremely low conversion efficiency. Our results exemplify why the classical-field treatment of wave dark matter remains both accurate and sufficient for present searches, and also provides a general method to compute effects arising from dark matter states.

Speaker: Dhong Yeon Cheong

Planck_Cheong_15min.pdf

12:35 Axion Detection With Coiled Optical Fibers

We propose a novel interferometric approach to axion searches based on long, coiled optical fibers in an external magnetic field. Considering fiber boundary conditions and bending, I will show that in silica fibers the leading signal is a phase shift of the photon. A key observation is that the axion field will effectively get confined along the fiber, despite no direct interaction between axions and the fiber material. In contrast, there exist parameter regions where axion leakage occurs. Due to this, I will show that hollow-core fibers with a refractive index close to unity can yield significantly enhanced signals. These setups have the potential to set new constraints, especially in the regime of large axion mass.

Speaker: Tongxuan Zhang (Ludwig Maximilian University of Munich)

PLANCK2026_TZ.pdf

11:15 → 12:55 Parallel Session: FLAVOR -- Main Auditorium

11:15 Artificial intelligence techniques for the flavor problem.

In this talk I will provide an overview on recent applications of Reinforcement Learning (RL) techniques to the flavor problem in particle physics. Traditional approaches to fermion masses and mixing often rely on extensions of the Standard Model based on horizontal symmetries, but the vast landscape of possible models makes systematic exploration infeasible. Recent works have shown that RL can efficiently navigate this landscape by constructing models that reproduce observed quark and lepton observables.

Speaker: Prof. Davide Meloni (Universita degli Studi Roma Tre (IT))

meloni_planck.pdf

11:35 Recent $B$ physics results from Belle II

The Belle and Belle II experiments have collected a $1.2~\mathrm{ab}^{-1}$ sample of $e^+ e^-\to B\bar{B}$ collisions at a center-of-mass energy corresponding to the $\Upsilon(4S)$ resonance. We present recent $B$ physics results from the Belle and Belle II collaboration. These include measurements of the ratios for exclusive $B\to D^{(*)}\ell \nu$ decays $R(D^{(*)})$ in decays where the other $B$ in the event is reconstructed in hadronic or semileptonic final states. We also present recent results on $B\to K^{(*)}\nu\bar{\nu}$ using an inclusive tagging technique, including the first results from Belle. We will also present a search for inclusive decays $B\to X_s\nu\bar{\nu}$, where $X_s$ is a hadronic system with strangeness. We will also present searches for the decays $B^+\to K^+\tau^+\tau^-$ and $B^0\to K^0_S\tau^+\tau^-$. The asymmetric-energy SuperKEKB collider provides a boost to the $B$ mesons in the laboratory frame, allowing measurements of time-dependent $C\!P$ violation. We present measurements of time-dependent $C\!P$ violation in both hadronic and radiative penguin $B$ decays, including measurements of the $C\!P$ asymmetries in $B\to \eta' K^0$, and the radiative decays $B\to \rho^0\gamma$ and $B\to K^0 \pi^0 \gamma$.

Speaker: Giovanni Gaudino (University Federico II and INFN, Naples (IT))

2026-05-21-Belle2-Gaudino.pdf

11:55 Data-driven and model-independent analyses of current b→sℓℓ measurements

We present a critical assessment of the present B-physics anomalies in exclusive $b\to s \ell \ell$ transitions. We analyse the complementary role of the $B\to K^* \mu \mu$ observables and other $b\to s \ell \ell$ measurements in probing new physics contributions within a model-independent framework. We investigate the impact of different local form factor calculations on the interpretation of present tensions with QCD factorisation predictions. Using updated CMS and LHCb results, we compare new physics fits and data-driven hadronic fits, highlighting how current uncertainties limit decisive conclusions.

Speaker: Siavash Neshatpour (IP2I Lyon/Université Claude Bernard Lyon 1)

Neshatpour_Planck2026.pdf

12:15 What can we learn from charged lepton flavor (non-)conservation?

Upcoming experiments are set to dramatically improve the search for charged lepton flavor violation, with the sensitivity to the rates of $\mu \to eee$ decay and $\mu N\to e N$ conversion expected to improve by four orders of magnitude in the near future. I discuss the impact of these measurements in reshaping our picture of the flavor structure of fundamental interactions and in connection with the Higgs hierarchy puzzle. I evaluate this in the broad scenario of Strongly Interacting Light Higgs and considering the mechanism of partial compositeness. In generic models of partial compositeness, the existing constraints from $\mu \to e \gamma$ and electric dipole moment (EDM) of electron, require the scale of Higgs compositeness to be above $\sim \mathcal{O}(100)$ TeV, pushing these models outside the reach of the LHC and future colliders. Moreover in this case the upcoming $\mu \to eee$ and $\mu N \to e N$ measurements will provide barely comparable bounds despite their remarkable improvement. I will show, however, that models where the strongly coupled sector have an accidental $SU(3)\times \rm{CP}$ symmetry, broken by the elementary-composite mixings: (1) lead to an accidental alignment of Yukawa and dipole couplings, substantially suppressing the bound from the $\mu \to e \gamma$ and electron EDM on the compositeness scale to below a TeV. (2) are probed by the upcoming $\mu \to eee$ and $\mu N\to e N$ experiments for compositeness scale at a few TeV. (3) provide a direct target for current and future collider experiments. I will discuss how the accidental symmetry can arise in the infrared compatible with the dynamical generation of flavor hierarchies in the ultraviolet. I will also survey the bounds and projections for models with other flavor symmetry groups.

Speaker: Majid Ekhterachian (Scoula Normale Superiore, Pisa)

Lepton Flavor- Planck26.pdf

12:35 Trimaximal Mixing Patterns Meet the First JUNO Result

The JUNO experiment has recently released its first measurement results based on 59.1 days of data, achieving unprecedented precision in measuring the lepton mixing angle $\theta_{12}$. This significant improvement places stringent constraints on certain neutrino mass models and flavor mixing patterns. In this work, we examine the impact of the latest JUNO results on the two trimaximal (i.e., TM1 and TM2) mixing patterns. They are two well-motivated variants of the tri-bimaximal mixing pattern and predict specific correlations between $\theta_{12}$ and $\theta_{13}$. After taking into account the first JUNO results, the TM1 mixing pattern sits on the edge of the experimentally allowed $1\sigma$ region, while the TM2 mixing pattern lies outside the $3\sigma$ region. To reconcile these TM mixing patterns with the latest experimental data, we further investigate the renormalization group (RG) running effects on them in the both Majorana and Dirac neutrino cases. Our analytical and numerical results show that RG corrections can bring the two TM mixing patterns into excellent agreement with the latest JUNO data if neutrino masses are quasi-degenerate. However, the Majorana case faces severe constraints from neutrinoless double beta decay limits, and particularly, the TM2 mixing pattern with Majorana neutrinos has been essentially ruled out. In the Dirac case, the TM1 mixing pattern is fully consistent with current data including beta decay results, whereas the TM2 pattern is strongly constrained by the KATRIN limit and even could be largely ruled out if the KATRIN experiment reaches its final sensitivity without any discovery. Future high-precision measurements of lepton mixing parameters and absolute neutrino masses in both oscillation and non-oscillation experiments will provide decisive tests of these mixing patterns.

Speaker: Dr Di Zhang (Technical University of Munich)

Planck_Di.pdf

11:15 → 12:55 Parallel Session: TH Conference Room

11:15 Searching for Ultraheavy Dark Matter with Magnetic Levitation

Magnetic levitation is emerging as a promising platform to probe a variety of Beyond Standard Model scenarios, with the first search for ultralight, wavelike dark matter recently performed. However, with force and displacement sensitivities approaching the quantum frontier, magnetic levitation offers a largely untapped opportunity to search for the feeble impulses expected from the scattering of ultraheavy dark matter particles. In this talk, I will present the first search for ultraheavy dark matter using a magnetically levitated sensor. I will show that the state-of-the-art in magnetic levitation can achieve impulse sensitivities as low as $\Delta p \sim 10^{-16}\,\mathrm{N\,s}$. Using this figure of merit, I will present leading sensitivities to ultraheavy dark matter with masses around $m_\mathrm{DM} \sim 10^{7} \,\mathrm{GeV}$, surpassing those recently achieved by optical levitation strategies. This work opens a new experimental window into the search for dark matter, simultaneously showcasing the potential of magnetic levitation as a precision probe of fundamental physics.

Speaker: Dorian Amaral (IFAE)

PLANCK 2026.pdf

11:35 Gravitational waves from phase transitions in dark sectors

First order phase transitions in a dark sector may produce an observable stochastic gravitational-wave background, and several models featuring such signal were proposed in the last years in view of the existing and near-future gravitational-wave data. For moderately strong phase transitions, hydrodynamical simulations suggest that the sound waves produced by the collisions of true-vacuum bubbles are the main source of gravitational-waves. It is often assumed that these sound waves propagate in the dark sector fluid only, however, the validity and implications of this assumption are not discussed in detail. In this talk, we present a method to take into account the coupling between the dark and visible fluids. With this framework at hand, we show that even though bubble expansion may influence the dark fluid only, sound waves in the visible fluid can be later induced. Using the sound-shell model, we find that such sound wave “leaking” leads to a suppression of the gravitational-wave amplitude compared to the case of a decoupled dark sector.

Speaker: Helena Kolešová (University of Stavanger)

GW_hidden_sector_Kolesova_EuCAPT.pdf

11:55 Probing Freeze-In Dark Matter with Direct Detection

Freeze-in offers a well-motivated production mechanism for dark matter that interacts very weakly with the Standard Model. We study MeV-scale fermionic dark matter coupled through vector portal mediators, including kinetically mixed dark photons and anomaly-free gauge extensions such as $U(1)_{L_i-L_j}$ and $U(1)_{B-L}$. We explore the impact of low reheating temperatures on the relic abundance and identify viable regions of parameter space consistent with current experimental constraints.

We construct benchmark scenarios that illustrate how upcoming direct detection experiments can probe these models through both electron and nuclear recoil signals. In particular, for dark matter masses in the range of 50–500 MeV, large regions of parameter space become accessible if freeze-in occurs at low reheating temperatures. Furthermore, enhanced coherent elastic nuclear scattering of solar neutrinos can provide an additional signature of the new interactions involved. These results demonstrate that next-generation direct detection experiments can test freeze-in dark matter scenarios and provide a complementary probe of light vector mediators connected to dark matter and the neutrino sector.

Speaker: Patrick Foldenauer (Consejo Superior de Investigaciones Cientificas (CSIC) (ES))

Planck_PF.pdf

12:15 Superhorizon Isocurvature as Window into Dark Matter Production

In the presence of primordial isocurvature perturbations, the superhorizon evolution of curvature perturbations becomes nontrivial. This evolution is able to uncover the nature of dark matter. If there is a radiation-like dark sector, its isocurvature can leave an imprint on the inflaton sector, even without non-gravitational interactions. If non-adiabatic interactions happen in the dark sector, the fluctuations from the inflaton sector can leave their mark in turn.
In this talk, we draw a simple picture of how to understand the dynamics of these fluctuations from first principles and without brute-force cosmic perturbation theory. We show how this setup can source isocurvature in simple models such as dark matter freeze-in and freeze-out from the Standard Model radiation bath, as well as in simple secluded dark sector models. We demonstrate that future measurements can potentially discriminate the mechanisms responsible for the origin of dark matter.

Speaker: Christopher Gerlach (Johannes Gutenberg-Universität Mainz)

Gerlach_PLANCK_2026_Isocurvature_Export.pdf

12:35 Direct Detection of Nuclear Atomic Dark Matter

We present a comprehensive study of the cosmology and experimental signatures of a Standard Model-like dark sector in which the neutron is the lightest stable baryon. This framework naturally provides a self-interacting dark matter (DM) candidate, the dark neutron, as well as an interacting atomic sub component from relic dark protons. By computing the dark neutron-proton freezeout process for a range of masses and couplings, we identify regions of parameter space which can already be ruled out by limits on DM self-interactions and study the laboratory signatures of those models which produce a viable atomic subcomponent. This framework encompasses models such as Twin Higgs scenarios which can resolve the little hierarchy problem, as well as provide a simple path to explaining the coincidence problem.

Speaker: Micah Mellors

PLANCK 2026 Mellors.pdf

12:55 → 14:00 Lunch break

14:00 → 15:40 Parallel Session: DARK MATTER -- Council Chamber

14:00 Sterile neutrino Dark Matter in the minimal Dirac Seesaw

I will discuss our recent paper where we study sterile neutrino dark matter in a minimal Type-I Dirac seesaw framework where the states responsible for generating Dirac neutrino masses at tree level can be viable dark matter candidates. A $\mathcal{Z}_6$ symmetry, spontaneously broken to a residual $\mathcal{Z}_3$ by the vacuum expectation value of a singlet scalar, forbids Majorana mass operators and ensures neutrino Diracness. The lightest sterile neutrino is produced non-thermally via freeze-in from decays of Standard Model particles and an additional scalar state. We show that the presence of an additional right-handed mixing angle, $\theta_R$, opens up viable regions of parameter space where the observed dark matter relic abundance can be reproduced while maintaining cosmological stability. This mainly stems from the absence of X-ray astrophysical constraints in our scenario. We further find that the freeze-in production of right-handed neutrinos yields a negligible contribution to $\Delta N_{\rm eff}$, consistent with current cosmological bounds.

Speaker: Aditya Batra (CFTP-IST, U. Lisboa)

Batra.pdf

14:20 Cosmological Probes of The Neutrino-DM Portal

Neutrinos offer a promising window into new physics, and recent data prompt a re-evaluation of their role in the early universe. Neutrino (ν) portals facilitate thermal dark matter (DM) production, representing one of the few remaining benchmarks in the freeze-out paradigm, yet they remain exceptionally difficult to probe. In this talk, we review the current status of the νDM portal, focusing on how interactions between these sectors could influence the evolution of cosmological perturbations. We specifically highlight the role of resonantly enhanced scattering, demonstrating how these precision effects, localized to specific redshift ranges, significantly alter the matter power spectrum and the interpretation of high-multipole CMB and weak lensing data. We conclude by discussing the prospects for future surveys to test these dark-sector interactions rigorously and to unveil the fundamental properties of the neutrino-DM connection.

Speaker: Sebastian Trojanowski

STrojanowski_nuDMinteractions.pdf

14:40 Successful SIDM in QCD-like theories: the role of the topological angle

Self-Interacting Dark Matter (SIDM) has been proposed to address tensions between simulations of collisionless cold dark matter and some astrophysical observations. QCD-like theories naturally provide dark matter candidates—dark pions or dark baryons—that reproduce the observed relic abundance, while potentially providing significant self-interactions. It is often believed that such models are no longer viable SIDM candidates as they typically fail to provide velocity-dependent self-interactions, which are favoured by current data. We show that the inclusion of a topological theta angle, and the induced CP-violating interactions, drastically modify this picture: on the one hand, it generates resonant self-interactions for pion dark matter. On the other hand, it induces velocity-dependent self-interactions for baryon dark matter, with dark pions acting as light mediators.

Speaker: Giacomo Landini

Planck26_v2.pdf

15:00 Wallions: Dark Matter from the Boundaries of Field Space

We present a new framework for (ultra)light dark matter based on a scalar field that experiences boundaries in field space. These boundaries give rise to wallions, scalar field excitations whose masses are exponentially suppressed yet radiatively stable. After introducing the basic setup, we discuss the behavior of wallions in the early universe and sketch a mechanisms through which such field-space boundaries can arise dynamically. We then outline probes that could be sensitive to this scenario.

Speaker: Mathias Becker (University of Padova)

Planck26.pdf

15:20 Beyond 3→2: Towards Realistic SIMP Dark Matter

Strongly interacting dark sectors with pseudo–Nambu–Goldstone bosons provide a versatile framework for sub-GeV dark matter. While the original SIMP paradigm emphasises number-changing processes as the origin of the relic abundance, the phenomenology of pionic dark matter is considerably richer. Depending on the spectrum and couplings, the relic density can WIMP-annihilations, semi-annihilations involving vector mesons and further processes like $\pi\pi\pi\to\pi\rho$. A consistent treatment therefore requires a framework that simultaneously captures pion dynamics, vector mesons, anomalous interactions, and portal effects.
We consider QCD-like dark sectors in which the dark matter candidates are pions. The effective theory is formulated using the Hidden Local Symmetry (HLS) approach, and is applicable to complex, real, and pseudo-real fermion theories.
As a minimal benchmark, we focus on the pseudo-real symmetry-breaking pattern $SU(4)/Sp(4)$.

Speaker: Halvor Melkild (University of Oslo)

Melkild_planck26.pdf

14:00 → 15:40 Parallel Session: FLAVOR/MODEL BUILDING -- Main Auditorium

14:00 Constraints from Monopole Production on Flavour Deconstruction Models

Extensions of the Standard Model featuring flavour non-universal gauge symmetries provide a well-motivated framework to address the hierarchical structure of Yukawa couplings (a.k.a. the flavour puzzle) with TeV-scale new physics, while remaining compatible with current phenomenological bounds. Such constructions often involve multiple layers of new physics, with gauge symmetries broken sequentially at different energy scales. These symmetry-breaking chains typically include the spontaneous breaking of semi-simple gauge groups at scales well below the grand unification scale, generically leading to the production of relatively light magnetic monopoles.

In this work, we highlight the connection between flavour-motivated gauge extensions and monopole production in the early Universe. The cosmological and astrophysical constraints on these light monopoles strongly motivate a low scale of inflation, with suggestive connections between early universe dynamics (e.g. primordial GW) and flavour physics.

Speaker: Marko Pesut (Paul Scherrer Institute)

PLANCK_PESUT.pdf

14:20 One-parameter models and fermion mass relations

Modular flavour symmetries offer a particularly economical approach to the flavour puzzle, replacing large flavon sectors with a single modulus field that controls all fermion sectors. In this talk, I will present recent progress on one-parameter constructions, in which fermion mass hierarchies are fully determined by this common modulus. I will discuss a classification of viable hierarchy patterns, explicit examples based on finite modular groups, and the resulting fermion mass relations. In a representative toy model, the down-quark sector is reproduced with remarkable accuracy, while the charged-lepton sector can be brought into agreement through realistic, albeit constrained, supersymmetric threshold effects. Altogether, this framework provides a simple and promising setting for addressing the flavour puzzle.

Speaker: Salvador Centelles Chulia (IFIC (CSIC - U. Valencia))

Slides_one_parameter_models_PLANCK.pdf

14:40 Can Randomness lead to non-anarchical mixing angles ?

We revisit the proposal of Craig and Sutherland that Anderson localization in a disordered fermion theory space can generate small neutrino masses from TeV scale physics \citecraig2018exponential. Building on this idea, we ask a broader question: can randomness in fermion mass parameters also give rise to nonanarchical neutrino mixing angles, and how does the answer depend on the geometry of the mass graph? To explore this, we analyse three representative geometries a nearest neighbour chain, a fully connected non local model, and the Petersen graph in both Dirac and Majorana neutrino realisations. In the regime of strong diagonal disorder, all geometries display robust localization and naturally generate the observed neutrino mass scale, with the corresponding flavour mixing angles reflecting the random localization centres and thus taking an anarchical form. In the regime of weak disorder, where localization is milder, and eigenmodes can exhibit quasidegeneracies, light neutrino masses can emerge through GIM-mechanismlike cancellations among the heavy states. The weak disorder with geometry dependent weak localization constitutes a distinct pathway to structured mixings within disordered theory spaces. Overall, our results delineate the regimes in which disorder driven mechanisms produce hierarchical masses and identify the conditions under which structured flavour mixing can arise.

Speaker: Aadarsh Singh

CERN-pdf.pdf

15:00 Flavor hierarchies with nonminimal irreducible representations

We consider a novel class of flavor models where the spurion breaking the flavor symmetries of the Standard Model transforms in a non-minimal irrep. Starting from initial $\mathcal{O}(1)$ untuned entries in the UV, we find that flavor hierarchies can be generated accidentally via multiple insertions of the spurion. By considering non-Abelian symmetries, we show that the pattern of flavor-violating operators at dim-6 SMEFT can be distinct from analogous Abelian mechanisms such as MFV and Froggatt-Nielsen. As an example of the phenomenological difference, we highlight the potential for unsuppressed flavour violation in kaon mixing, motivating a broad experimental programme in the future. This is based on our recent work, arxiv:2510.03403.

Speaker: Graeme Crawford

Planck2026_GC.pdf

15:20 Flavour hierarchies from higher flavour spin

We propose a framework for $U(2)$ flavour models in which the effective flavour spurions arise from a small set of fields in higher $U(2)$ representations with generic vacuum expectation values, in the spirit of recent $U(3)^5$ constructions. Flavour hierarchies are generated by selection rules associated with $SU(2)$ tensor product decompositions. As a concrete example, we apply this idea to a $U(2)_{q+\ell}$ setup and show that a single field with flavour spin $j\geq3/2$ can account for the observed SM flavour pattern. We then present simple UV completions of this construction and discuss the scalar potential for the higher flavour spin field.

Speaker: Alessandro Valenti (University of Basel)

slides_AV.pdf

14:00 → 15:40 Parallel Session: PHASE TRANSITIONS -- TH Conference Room

14:00 Matchotter:Automatic Dimensional Reduction with Functional Methods

Dimensional reduction is a key tool for computing the electroweak phase transition in scenarios beyond the Standard Model. Achieving high precision in this framework requires the systematic inclusion of higher-dimensional operators, a task that rapidly becomes technically challenging.

In this work, we show that functional methods provide a highly efficient and scalable framework to extend dimensional reduction to higher orders in the operator expansion. Building on this approach, we develop "Matchotter": a fully automated tool that performs the matching procedure with minimal human intervention, effectively reducing a highly non-trivial calculation to the click of a button.

Speaker: Mr ADRIÁN Moreno Sánchez (Universidad de Granada)

Matchotter.pdf

14:20 Hot news on the phase-structure of the SMEFT

We perform dimensional reduction of the electroweak sector of the dimension-six SMEFT up to $\mathcal{O}(g^4)$ in coupling constants $g$. This analysis includes one-loop contributions to kinetic terms and quartic couplings; as well as two-loop contributions, where operators such as four-fermion interactions first appear, to squared mass terms. Using lattice data, we also provide evidence that, in contrast with previous statements in the literature, the SMEFT may undergo a
first-order phase transition even for null $|\phi|^6$ at zero temperature, where $\phi$ is the Higgs doublet. This opens the door to entirely unexplored directions in model building.

Speaker: Maria Cristina Fiore (Universidad de Granada)

PLANCK2026_Fiore.pdf

14:40 Limits of EFTs at finite temperature for strong phase transitions

Phase transitions are violent and interesting phenomena that could have occurred in the early universe. Possible techniques to study these phenomena can be used in the presence of a hierarchy of scales, leading to the construction of finite temperature Effective Field Theories by integrating out heavier scales. These EFTs are reliable when the dynamics are mainly encoded in the most relevant operators. I will discuss the limits of such EFTs, showing how higher-dimensional operators affect the prediction of stronger transitions, including those detectable by LISA.
These considerations impact the applicability of effective theory techniques, including their use in lattice studies.
I will then discuss how subtleties associated with these operators, such as gauge and renormalization group dependence, can emerge and how they are addressed only when higher loop computations are taken into account. Finally, I will compare the impact of these higher order corrections with that of higher dimensional operators on the predicted strength of the transition.

Speaker: Fabio Bernardo

Presentation_FABIO_BERNARDO_Planck_new.pdf

15:00 Hybrid Partial Dressing: Renormalization Group Improved Thermal Resummation at All Temperatures

We present a novel resummation scheme for quantum field theory at finite temperature, with particular applicability to the study of phase transitions in beyond-Standard-Model (BSM) scenarios. In the high-temperature limit, our approach reproduces results consistent with those obtained from dimensional reduction to three-dimensional effective field theories (3D EFTs), while exhibiting reduced theoretical uncertainties. Importantly, the method does not rely on a hierarchical separation between the temperature and particle mass scales, enabling reliable calculations across the full temperature range.

Speaker: Andrija Rasovic

PLANCK_2026_Andrija_Rasovic_FTQFT.pdf

15:20 Thermoskyrmions

Skyrmions are stable and topologically non-trivial field configurations that behave like localized particles. They appear in the chiral effective theory for pions, where they correspond to the baryon states, and might also exist in the electroweak theory, in the presence of certain effective interactions.

In this talk, focusing on toy models that capture different limits of the electroweak sector of the Standard Model (SM), we will how skyrmions not classically stable at zero temperature can be stabilized by thermal effects. This motivates the study of skyrmions in the quantum effective action of the SM, where they might constitute a dark matter candidate without new physics.

Speaker: Luis Gil (Universidad de Granada)

Gil_Planck2026.pdf

15:40 → 16:20 Coffee break

16:20 → 17:40 Parallel Session: COSMO -- TH Conference Room

16:20 Non-Bunch-Davies initial conditions and gravitational relics

Gravitational particle production (GPP), i.e. the production of particles out of the expansion of the universe, is an elegant and inevitable source of particles in the early universe. In particular, it is sufficient to produce the entirety of the present abundance of the dark matter. In order to compute this abundance, a number of assumptions on the early universe are required. In this talk I will review the phenomenon of the GPP, stressing what are the required hypotheses for quantitative computations, and then I will show what happens when we break one of them. In particular, I will focus on changing the initial conditions for the evolution of these particles, which can significantly impact the final predicted abundance.

Speaker: Gabriel Massoni Salla

PLANCK_2026_GMS.pdf

16:40 Particle Production from Gravitational Inhomogeneities

In this talk I will present a new mechanism to produce particles in the early universe based on gravitational inhomogeneities. Due to breaking of Weyl invariance, inhomogeneities unavoidably lead to particle production even for massless particles. I will show how metric perturbations generated during inflation or phase transitions can reproduce the DM abundance. This mechanism of DM production is always accompanied by a stochastic gravity wave background.

Based on https://inspirehep.net/literature/2822430, https://inspirehep.net/literature/2890836 and work in progress.

Speaker: Michele Redi (Universita e INFN, Firenze (IT))

Planck26_Redi.pdf

17:00 New BBN constraints on the decay of relics into SM particles

In this presentation, I will discuss big bang nucleosynthesis bounds on relics in the early Universe which decay into pairs of SM particles. Due to final-state radiation, these SM particles will emit other SM particles, and in particular quarks and gluons will hadronize. The final products of these showers then participate in different types of interactions with the baryons in the early Universe (neutrons and protons before BBN, light elements after BBN). Depending on the lifetime of the relic and thus the time of the injection, different effects will dominate the phenomenology. On the one hand for short lifetimes, (mesonic) interconversion processes drive the neutron-to-proton ratio away from its SM value, changing the initial condition of BBN. On the other hand for longer lifetimes, first the hadronic and then the electromagnetic disintegration of the light elements become important. We present model-independent bounds on the presence of the relic $\phi$ for lifetimes $\tau_\phi \in [10^2,10^{11}]\,$s and masses ranging from a few GeV up to the PeV scale with particular emphasis on the improvements and updates compared to previous literature results. We further plan to publish the codes which enable the calculation of these bounds.

Speaker: Jonas Frerick

slides_planck_jf.pdf

17:20 New tests of parity violation in the early universe

Precise polarization measurements of the Cosmic Microwave Background (CMB) provide an opportunity to rigorously test the standard cosmological model. The correlation between $E$ and $B$ modes is expected to arise from parity-violating physics in the Universe. However, detecting these $EB$ correlations remains extremely challenging as it demands exceptionally precise polarization calibration of observational instruments. In this work, we present a novel calibration method for CMB polarimeters that circumvents the need for external polarized sources or self-calibration techniques. By cross-correlating data from two instruments observing the same region of the sky, we demonstrate that the difference between their misalignment angles can be resolved with data only, providing an assumption free calibration technique. Leveraging the high-precision polarization calibration expected for the Simons Observatory Small Aperture Telescopes, we show that can calibrate other instruments observing overlapping sky regions. We then show how this improved calibration method can be directly applied to searches for parity-violating signals such as isotropic cosmic birefringence or a chiral primordial tensor component.

Speaker: Ms Claire Aude Laure Rigouzzo (King's College London)

Planck_Rigouzzo.pdf

16:20 → 17:40 Parallel Session: DARK MATTER -- Main Auditorium

16:20 Dark Matter in Warped Extra-dimensional scenarios

Apart from its gravitational interactions, Dark Matter (DM) has remained so far elusive in laboratory searches. We revisit the case of DM interacting just gravitationally with the Standard Model (SM) particles in an extra-dimensional Randall-Sundrum scenario. After discussing several possibilities with two branes, we consider the case of three branes: the Planck brane, a TeV-PeV IR brane, where the Standard Model is located, and a GeV-TeV deep IR (DIR) one, where the DM lies. In this setup, the relic abundance of DM arises from the freeze-out mechanism, thanks to DM annihilations into radions and gravitons. Focusing on a scalar singlet DM candidate, we compute and apply current and future constraints from direct, indirect and collider-based searches. Our findings demonstrate the viability of this scenario and highlight its potential testability in upcoming experiments.

Speaker: Dr Nuria Rius Dionis (IFIC, Universitat de València - CSIC)

DM_planck26.pdf

16:40 The Flavour Structure of Dark Matter

The non-trivial flavour structure of t-channel dark matter models with fermion couplings is unavoidably constrained by flavour physics, hinting towards the presence of an underlying flavour symmetry.
In this talk, I present a systematic study of the low-energy flavour constraints affecting these models from the perspective of flavour symmetries, together with complementary bounds from collider searches and dark matter direct detection experiments.
I show that the TeV scale suggested by the freeze-out mechanism is compatible with the various probes only in specific flavour-symmetric limits, highlighting the essential role of flavour symmetries in the realisation of these models.

Speaker: Xavier Ponce Diaz (University of Basel)

XPD_DM_Flavour_Planck.pdf

17:00 Gauged Flavour for Asymmetric Dark Matter

In this talk, I will discuss different approaches to the flavour puzzle of the Standard Model and their connections to other open problems. In particular, I will focus on a model of asymmetric dark matter that simultaneously explains the origin of flavour. A subgroup of the flavour symmetry is gauged at high energies, and the observed hierarchies are reproduced through a suitable choice of this subgroup and its breaking pattern. Neutrino masses are generated via a standard seesaw mechanism, which also opens the possibility of baryogenesis through leptogenesis. I will show that sphalerons associated to the flavour group can also transfer the generated lepton asymmetry into a dark, strongly coupled sector, producing dark baryons that constitute dark matter.

Speaker: JAVIER MARTÍNEZ LIZANA (Universidad de Castilla-La Mancha)

Planck26_Lizana.pdf

17:20 Dark Matter from residual symmetry in non-Abelian Froggatt-Nielsen models

We propose a general framework to obtain a Dark Matter (DM) candidate within Froggatt–Nielsen models of flavor, without invoking ad hoc additional symmetries. The construction is based on flavor theories invariant under a non-Abelian group, where DM stability emerges as a direct consequence of the flavor structure itself. In particular, the stabilization mechanism originates from a residual subgroup of the flavor symmetry that remains unbroken after spontaneous symmetry breaking.
This approach provides an elegant connection between flavor physics and Dark Matter, where stability is not imposed, but emerges as a consequence of the underlying symmetry.

Speaker: Simone Marciano (Instituto de Fisica Corpuscular IFIC - Universitat de Valencia - CSIC)

PLANCK26_Marciano.pdf

16:20 → 17:40 Parallel Session: GRAVITATIONAL WAVES -- Council Chamber

16:20 Probing Quadratically Coupled Ultralight Dark Matter with Pulsar Timing Arrays

Ultralight dark matter may couple quadratically to Standard Model particles. Such quadratic interactions give rise to both coherent and stochastic signals in pulsar timing array (PTA) observations. In this work, we characterize these signals, including the effects of dark matter propagation in a finite-density medium, and assess the sensitivity of current and upcoming PTA observations to their detection. For coherent signals, we find that the sensitivity of current PTA observations competes with and sometimes exceeds that of other probes, such as equivalence principle tests and atomic clocks. For stochastic signals, we find that PTA sensitivities underperform equivalence principle constraints for both existing and upcoming PTA data sets.

Speaker: Xucheng Gan

Planck_2026.pdf

16:40 Gravitational Waves from Black Hole Reheating

Ultra-light primordial black holes (PBHs) provide a well-motivated source of high-frequency gravitational waves and a unique probe of the early Universe. Assuming PBHs form from the collapse of superhorizon-scale overdensities, we first determine the narrowest possible width of the resulting extended PBH mass function, taking into account critical collapse and using both Press–Schechter theory and peak theory.

We then investigate the scalar-induced gravitational-wave (SIGW) signal associated with the evaporation of these PBHs. In the idealized monochromatic mass scenario, a pronounced SIGW signal can arise through the so-called poltergeist mechanism, triggered by the sharp transition from a PBH-induced early matter-dominated era to radiation domination. We show that, even for the narrowest physically consistent extended mass function, the smoothing of this transition leads to a significant suppression of the SIGW signal. This suppression reduces the detectability of a substantial part of the ultra-light PBH parameter space by future GW observatories, while at the same time relaxing strong Big Bang nucleosynthesis bounds and reopening regions that are excluded in the monochromatic approximation. In addition, we consistently include further PBH-associated SIGW contributions generated during PBH formation, early radiation-dominated and early matter-dominated phases.

We also compute the high-frequency GW components arising from PBH binary formation and mergers, including the two-body capture channel, three-body interactions, and mergers within PBH clusters, as well as the direct Hawking emission from ultra-light PBHs, and identify the regions of parameter space in which each contribution dominates.

Speaker: Nicholas Leister

Planck_26_Leister.pdf

17:00 Are the violins tuned? Dark sector phase transition explanations for the PTA signal

Strong first-order phase transitions in a dark sector are an exciting explanation for the nanohertz gravitational wave background measured by pulsar timing arrays (PTAs). In this talk, I confront this idea with the most recent PTA data and complementary constraints. After outlining model-independent relations between the key macroscopic parameters of the transition, I discuss and compare three concrete particle physics scenarios representative of distinct model classes: an Abelian dark Higgs model with a thermally induced barrier, a two-step “flip-flop” model with two scalar singlets, and a classically conformal dark U(1)’ model with a loop-induced barrier. Using extensive parameter scans, we quantify the degree of tuning required to reproduce the PTA signal while satisfying constraints from Big Bang Nucleosynthesis, the Cosmic Microwave Background, and collider searches. We find that thermally induced and two-step transitions require significant tuning of the nucleation rate to achieve sufficiently large bubble sizes, whereas conformal models naturally realize the strong supercooling favored by current data. Finally, I outline how future PTA observations and collider experiments can discriminate between these scenarios and further constrain the underlying particle physics.

Speaker: Dr Carlo Tasillo (IFIC)

2026_05_21_Planck_Eucapt.pdf

17:20 The slingshot effect and its implications for gravitational waves, primordial black holes and dark matter

In my talk, I will present the so-called slingshot effect. It represents a general phenomenon that occurs when a localized source, such as a magnetic monopole, quark, or a D-brane, crosses a wall separating the confined (Higgsed) and unconfined (Coulomb) phases. The crossover is accompanied by a stretched string that confines the source to the wall. The string tension accelerates the source towards the wall as sort of a slingshot.

The effect can take place in different setups, such as phase transitions leading to both electric and magnetic confinement, as well as in string cosmology involving D-branes. I will discuss the role of this phenomenon in sourcing gravitational waves. Furthermore, I will show that the slingshot effect can lead to the formation of dark matter, in the form of Kaluza–Klein gravitons as well as primordial black holes.

Speaker: Maximilian Bachmaier

Slingshot_PLANCK_EuCAPT_PDF.pdf

17:40 → 18:10 Break

18:10 → 18:40 Effective field theory for thermal phase transitions

Speaker: Mikael Chala (Universidad de Granada)

presentation.pdf

18:40 → 19:10 Extending the spectrum of detectable gravitational waves

Speaker: Sebastian Ellis (University of London (GB))

SEllis_GWs_Planck2026.pdf

20:00 → 22:00 Dinner at R1

22:00 → 00:00 DJ Nacho and DJ Jeremie

DinnerParty.pdf

Friday 22 May

09:00 → 09:30 Active galactic nuclei through the prism of galaxy clusters: bounds on axion-like particles

Speaker: Denys Malyshev

Axions.pdf

09:30 → 10:00 Evolving Dark Sector and the DESI data

Speaker: Georges Obied

Obied_2026.pdf

10:00 → 10:30 News from the Pulsar Timing Array Frontier

Speaker: Kai Schmitz

schmitz_planck_2026.pdf

10:30 → 11:15 Coffee break

11:15 → 11:45 SMEFT at next-to-leading order

Speaker: Anders Eller Thomsen (University of Bern)

Planck_2026.pdf

11:45 → 12:15 Adventures in Agentic AI for Particle Physics

Speaker: David Shih

Shih_Planck_2026.pdf

12:15 → 12:45 Quantum mechanics of wave-like dark matter

Speaker: Liantao Wang

Wavelike_Planck_LTW.pdf

12:45 → 13:00 Closing session

Convener: Matthew Philip Mccullough (CERN)

PlanckClosing.pdf

18:00 → 19:30 Concert Main Auditorium

Outlook-bt54wwpt.png