4th EuCAPT Annual Symposium

14 May 2024, 00:00 → 16 May 2024, 17:00 Europe/Zurich

500/1-001 - Main Auditorium (CERN)

Valerie Domcke (CERN)

The European Consortium for Astroparticle Theory (EuCAPT, https://www.eucapt.org) is a young initiative, with central hub at CERN, that aims to bring together the European community of theoretical astroparticle physicists and cosmologists. Our goals are to increase the exchange of ideas and knowledge; to coordinate scientific and training activities; to help scientists attract adequate resources for their projects; and to promote a stimulating, fair and open environment in which young scientists can thrive.     

We are delighted to announce the fourth edition of the EuCAPT annual symposium, the flagship event of our consortium, that aims to provide an interdisciplinary Europe-wide forum to discuss opportunities and challenges in Theoretical Astroparticle Physics and Cosmology. The symposium will take place at CERN, with online participation possible. We invite all scientists (PhD students, postdocs, and staff) active in these fields of research to join us remotely or in person from May 14 to 16, 2024. The symposium will feature invited presentations, and young scientists will have the opportunity to present their work with lightning talks and in a poster session. 

We invite young scientists to submit abstracts for lightning talks and posters by February 15.  There is no conference fee for this event.

Invited speakers:
Jose Luis Bernal (Institute of Physcis of Cantabria)
Simone Blasi (DESY Hamburg)
Christopher Eckner (University of Nova Gorica)
Giulio Fabbian (University of Cardiff)
Gaetan Facchinetti (Bruxelles University)
Damiano Fiorillo (Niels Bohr Institute)
Alexander Jenkins (University College London)
Juraj Klaric (Louvain University)
Valeriya Korol (Max Planck Institute for Astrophysics)
Eva-Maria Mueller (University of Sussex)
Enrico Peretti (Universite Paris Diderot)
Mathias Pierre (DESY Hamburg)
Hamsa Padmanabhan  (Geneva University)
Sarah Recchia (University of Turin)
Bogumiła Świeżewska (Warsaw University)

Conference picture: 

Tuesday, 14 May

Welcome

1 Welcome

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

EuCAPT Intro.pdf

Late Universe

Convener: Ruth Durrer

2 Galaxy clustering in the era of Stage IV surveys

Speaker: Eva-Maria Mueller

3 Line intensity mapping and the physics of cosmic reionization

Speaker: Dr Hamsa Padmanabhan (U. Geneva)

hamsa_cern_may2024.pdf

Recording

Video preview

Coffee Break

Late Universe

Convener: Ruth Durrer

4 Lensing of the Cosmic Microwave Background , synergies with galaxy surveys and AOB

Speaker: Dr Giulio Fabbian (U. Cardiff)

eucapt_2024_fabbian.pdf

Recording

Video preview

5 A model-independent test of gravity from the Weyl potential evolution

To test the vast number of modified gravity models, a systematic and comprehensive approach is necessary when analysing the data from cosmological surveys. The novel observable \hat{J}, capturing the evolution of the combined gravitational potential Ψ + Φ, provides a powerful and model-independent test of gravity. Recently, we have performed the first measurement of this observable from Dark Energy Survey data (C. Bonvin, I. Tutusaus & N. Grimm, arXiv:2312.06434), combining galaxy-galaxy lensing and galaxy clustering data. Interestingly, we find a tension with the prediction of the standard cosmological model, reaching 3.1 sigma at z=0.48. In my lightning talk, I will present this novel observable and demonstrate its remarkable capacity to test gravity in a model-independent manner.

Speaker: Nastassia Grimm

Grimm_Presentation_EUCAPT.pdf

6 Cosmology from ACT DR6 lensing cross-correlated with DES Y3 galaxies

In this work we present our pipeline for a joint analysis at the angular power spectrum level between measurements of galaxy positions from Dark Energy Survey Years 3 data release (DES Y3) and CMB lensing from the Atacama Cosmology Telescope Year 6 data release (ACT DR6) on a common area of around $4000\ \rm{deg}^2$. We show preliminary results, including several null-tests and inference on realistic mocks to achieve few percent level constraints on the amplitude of matter fluctuations. In a future work we will combine this measurement in a joint analysis with DES Y3 cosmic shear data, setting the stage for next generation cross-correlation analyses.

Speaker: Omar Darwish (University of Geneva)

CERN_ACTxDES.pdf

7 Probing the LCDM Universe with 21cm intensity mapping surveys

Speaker: Maria Berti (UniGE)

Eucapt_Maria_Berti.pdf

8 The Hitchhiker's Guide to the Galaxy (peculiar velocities)

In this talk, we will review what peculiar velocities are and how they can help us in better understanding both our local universe, its cosmological components and also studying relativistic effects. In particular, we will focus on the information we can extrapolate from the Pantheon+SH0ES and CosmicFlow4 datasets.

Speaker: Francesco Sorrenti (University of Geneva)

Hitchikers_presentation_Eucapt_24.pdf

9 Modified Gravity vs Dark Interactions: Settling the Dispute through the Distortion of Time

Combining measurements of the growth rate of cosmic structures with gravitational lensing is considered as the optimal way to test for deviations from General Relativity on cosmological scales. In my talk, I will demonstrate that this standard method suffers from an important limitation, since models of dark matter with additional interactions can lead to exactly the same signatures as modified gravity in these two observables. Luckily, I will show that the coming generation of large-scale structure surveys, like the Square Kilometer Array, will allow us to break this degeneracy through measurements of the distortion of time.

Speaker: Sveva Castello (University of Geneva)

SvevaCastello_EuCAPT.pdf

10 The full-sky Spherical Fourier-Bessel power spectrum in general relativity

We present a full methodology for analyzing galaxy clustering on the lightcone with the 2-point correlation in the Spherical Fourier-Bessel (SFB) formalism. SFB is a natural choice to account for all wide-angle and relativistic (GR) effects, allowing to efficiently extract information from large volume galaxy surveys.
We extend previous studies using SFB by including all projection and GR effects, developing an efficient numerical implementation that avoids the use of the Limber approximation and includes multi-bins correlations and a full non-diagonal covariance.
We investigate the impact of neglecting GR corrections in cosmological parameter constraints, focusing on Primordial Non-Gaussianity and bias parameters.
We also present a novel prescription for multi-bin correlations that allow to significantly boost the detectability of GR effects, opening a new window on general relativity testing.

Speaker: Federico Semenzato (University of Padova)

Semenzato_eucapt.pdf

Lunch Break

Particle Astrophysics

Convener: Georg Raffelt (MPI Physik, Munich)

11 Supernova 1987 neutrinos: status and prospects

Speaker: Damiano Fiorillo (Niels Bohr International Academy, Niels Bohr Institute,4 University of Copenhagen, 2100 Copenhagen, Denmark)

Recording

SlidesEUCAPT.pdf

Video preview

12 Cosmic-ray propagation

Speaker: Sarah Recchia (INAF)

CR_prop.pdf

Recording

Video preview

13 High-energy emissions from AGN and starburst galaxies

Speaker: Enrico Peretti (CNRS)

Peretti-EuCAPT.pdf

Recording

Video preview

Coffee Break

Particle Astrophysics

Convener: Georg Raffelt (MPI Physik, Munich)

14 Status of Direct Determination of Solar Neutrino Fluxes after Borexino

We determine the solar neutrino fluxes from the global analysis of the most up-to-date terrestrial and solar neutrino data including the final results of the three phases of Borexino. The analysis are performed in the framework of three-neutrino mixing with and without accounting for the solar luminosity constraint. We discuss the independence of the results on the input from the Gallium experiments. The determined fluxes are then compared with the predictions provided by the latest Standard Solar Models. We quantify the dependence of the model comparison with the assumptions about the normalization of the solar neutrino fluxes produced in the CNO-cycle as well as on the particular set of fluxes employed for the model testing.

Speaker: Joao Paulo Pinheiro (Universitat de Barcelona)

Exploring Solar Neutrino and CNO Fluxes (2).pdf

15 White dwarf cooling through neutrinos and L_mu - L_tau

Hot white dwarfs lose energy mainly in the form of neutrinos through plasmon decay from the inner part of the star. BSM physics can have visible contributions to the cooling of these compact objects. The aim of this study is to show how hot white dwarf cooling could be altered by a dark photon from the L_mu - L_tau model and explore these effects from ultra-light to heavy intermediators. This leads to very interesting constraints to this BSM model.

Speaker: Jaime Hoefken Zink

presentation_jhz_EuCAPT_2024.pdf

16 Stochastic modelling of cosmic ray sources sped up

Cosmic rays can be probed via direct detection at the Earth’s position or indirectly through diffuse emissions of gamma-rays and neutrinos produced by the interaction of cosmic rays with the interstellar medium in other parts of the Galaxy. It is commonly assumed in the modelling of galactic cosmic rays that the source density is smooth and steady. However, supernova remnants, the likely sources of cosmic rays, have a point-like and burst-like nature. This renders our predictions very sensitive to the precise positions and times of the sources. Yet observationally, those parameters are not accessible such that the source modelling must be done probabilistically. The computation of contributions to the total cosmic ray flux from individual sources is inherently parallelisable and suitable for the use of GPUs to speed up simulations. We demonstrate how these simulations can be used to constrain the energy dependence of escape from the cosmic ray accelerators and to study the energy-dependent morphology of the diffuse emission sky, relevant for observations with LHAASO, Tibet AS-gamma, IceCube and the upcoming SWGO.

Speaker: Anton Stall (Institute for Theoretical Particle Physics and Cosmology (TTK), RWTH Aachen University)

EuCAPT2024_Anton Stall.pdf

17 Constraints on the Cosmic Neutrino Background from NGC1068

We investigate IceCube's ability to constrain the neutrino relic abundance using events from the recently identified neutrino source NGC1068. Since these neutrinos have large energies $\gtrsim$ 1 TeV and have propagated through large distances, they make a great probe for overabundances of the cosmic neutrino background.

The propagation of neutrinos from NGC1068 was simulated by solving a transport equation, which takes into account the SM neutrino-neutrino interactions. The final fluxes produced are then analysed using publicly released IceCube data. Our preliminary results indicate that IceCube is able to improve the current bounds on a relic neutrino overabundance by 3 orders of magnitude compared to current experimental bounds, i.e. to less than ~ $10^9 \mathrm{cm}^{-3}$ at the $2\sigma$ confidence level.

Speaker: Jack Franklin

Eucapt_Presentation.pdf

18 New bounds on monopole abundance from cosmic magnetic fields

Magnetic monopoles are intriguing hypothetical particles and inevitable predictions of Theories of Grand Unification. They are produced during phase transitions in the early universe, but mechanisms like the Schwinger effect in strong magnetic fields could also contribute to the monopole number density. I will show how from the detection of intergalactic magnetic fields we can infer additional bounds on the magnetic monopole flux, and how even well-established limits, such as Parker bounds and limits from terrestrial experiments, are affected by the acceleration in cosmic magnetic fields. I will also discuss the implications of these bounds for minicharged monopoles and magnetic black holes as dark matter candidates.

Speaker: Daniele Perri (SISSA Trieste, Trieste)

EuCAPT2024.pdf

19 Fast particle acceleration in 3D hybrid simulations of quasi-perpendicular shocks

Understanding the conditions conducive to particle acceleration at collisionless, non-relativistic shocks is important for the origin of cosmic rays. We use hybrid (kinetic ions—fluid electrons) kinetic simulations to investigate particle acceleration and magnetic field amplification at non-relativistic, weakly magnetized, quasi-perpendicular shocks. So far, no self-consistent kinetic simulation has reported non-thermal tails at quasi-perpendicular shocks. Unlike 2D simulations, 3D runs show that protons develop a non-thermal tail spontaneously (i.e., from the thermal bath and without pre-existing magnetic turbulence). They are rapidly accelerated via shock drift acceleration up to a maximum energy determined by their escape upstream. We discuss the implications of our results for the phenomenology of heliospheric shocks, supernova remnants and radio supernovae.

Speaker: Luca Orusa (Princeton University)

Slides eucapt.pdf

EuCAPT community

20 EuCAPT community

Speakers: David Marsh, Silvia Pascoli (Universita e INFN, Bologna (IT))

EuCAPT_Symposium2024.pdf

Reception and Poster Session

Wednesday, 15 May

Early Universe

Convener: Mar Bastero Gil (University of Granada)

21 Baryogenesis & Leptogenesis

Speaker: Juraj Klaric (Universiteit van Amsterdam, Nikhef)

Klaric_2024_EuCAPT_BaryogenesisLeptogenesis.odp

Klaric_2024_EuCAPT_BaryogenesisLeptogenesis.pdf

Recording

simplified_Klaric_2024_EuCAPT_BaryogenesisLeptogenesis.pdf

Video preview

22 Cold-atom analogues of vacuum decay

Speaker: Dr Alexander Jenkins (University College London)

fvd-alex.pdf

fvd-alex.pptx

Recording

Video preview

Coffee Break

Early Universe

Convener: Mar Bastero Gil (University of Granada)

23 Particle creation dynamics during inflation and reheating

Speaker: Mathias Pierre

Eucapt_CERN024_MP.pdf

Recording

Video preview

24 One-loop power spectrum in ultra slow-roll inflation and implications for primordial black hole dark matter

A possible way to generate primordial black holes as candidates for the entirety of dark matter is a large power spectrum of inflationary curvature fluctuations. Recently, questions have been raised regarding the validity of perturbation theory in this context. We compute the one-loop power spectrum in ultra-slow roll inflation, including all relevant interactions for such analysis, along with counterterms that absorb the ultraviolet divergences. We compare the one-loop and tree-level contributions to the power spectrum, finding that perturbation theory remains valid in realistic ultra-slow roll models.

Speaker: Jesus Gambin Egea (Instituto de Fisica Teorica, UAM - CSIC)

Gambin_Egea_EuCapt_talk.pdf

25 Backreaction of axion-SU(2) dynamics during inflation

Nowadays, the search for primordial gravitational waves is mainly focused on the parity-odd polarization pattern in the CMB - the B-modes. A correct interpretation of B-mode measurements strongly relies on understanding their production mechanism. One intriguing scenario is gravitational waves generation by gauge fields. The tachyonic amplification of the gauge fields modes during inflation leads to significant backreaction on the background dynamics. In this talk, I will discuss how the backreaction on axion-SU(2) dynamics during inflation leads to a new dynamical attractor solution for the axion field and the vacuum expectation value of the gauge field. These findings are of particular interest to the phenomenology of axion-SU(2) inflation, redefining parts of the viable parameter space. The backreaction effects lead to characteristic oscillatory features in the primordial gravitational wave background that are potentially detectable with upcoming gravitational wave detectors.

Speaker: Oksana Iarygina (Nordita)

EuCapt_Oksana.pdf

26 Scale-invariant inflation

Fundamental scale invariance has been proposed as a new theoretical principle beyond renormalizability. Besides its highly predictive power, a scale-invariant formulation of gravity could provide a natural explanation for the long-standing hierarchy problem and interesting applications in cosmology.
We present a globally scale-invariant model of quadratic gravity and study its solutions in a spatially flat Robertson-Walker metric. The system admits a dynamical flow from an unstable to a stable fixed point, where scale symmetry gets spontaneously broken, and a mass scale — the Planck mass — is classically generated. This trajectory is compatible with an arbitrarily long stage of inflation which is investigated both at the classical level and at first order in perturbation theory. We outline some of the most recent result obtained within the framework of scale-invariant inflation.

Speaker: Chiara Cecchini (University of Trento, TIFPA-INFN)

Cecchini_Scale-invariant inflation .pdf

27 Black holes and gravitational waves from slow phase transitions

Slow first-order phase transitions generate large inhomogeneities that can lead to the formation of primordial black holes (PBHs). We show that the gravitational wave (GW) spectrum then consists of a primary component sourced by bubble collisions and a secondary one induced by large perturbations. The latter gives the dominant peak if $\beta/H_0 < 10$, impacting, in particular, the interpretation of the recent PTA data. The GW signal associated with a particular PBH population is stronger than in typical scenarios because of a negative non-Gaussianity of the perturbations and it has a distinguishable shape with two peaks.

Speaker: Piotr Toczek (University of Warsaw)

EuCAPT_Toczek.pdf

28 Hot Leptogenesis: A naturalness-motivated solution to baryon asymmetry

In standard leptogenesis models, the baryon asymmetry is initially produced as a lepton asymmetry via the out of equilibrium decays of the lightest right handed neutrino (RHN).

There are however constraints on the RHN mass that are in tension; the naturalness constraint on the Higgs mass from RHN loop corrections, i.e. the Vissani bound, puts a limit on the RHN mass which is lower than is generally required for leptogenesis to produce a sufficient baryon asymmetry (the Davidson-Ibarra bound).

Increasing the temperature of the RHN sector, known as a 'hot leptogenesis' model, allows for a boosting of the baryon asymmetry produced, allowing for both bounds to be reconciled.

Following on from the work of Bernal and Fong on hot leptogenesis from thermal dark matter, we give a comprehensive treatment of hot leptogenesis more generally; exploring the evolution of both sectors, the parameter space of the models, as well as possible UV origins for the initially thermally disconnected SM bath and the hot RHN sector.

Speaker: Ansh Bhatnagar (IPPP, Durham University)

Hot Leptogenesis Talk Draft 2.pdf

29 CMB spectral distortions from dark sector anisotropies

We introduce a novel approach to investigate sectors solely gravitationally coupled, characterized by significant anisotropies. These anisotropies undergo damping through gravitational interactions with the baryon-photon fluid, inducing heating in the process. The resultant injected heat leads to observable distortions in the cosmic microwave background spectrum. We provide analytic estimates for the magnitude of these distortions and outline a method to calculate them from first principles. The application of these methods extends to anisotropies arising from a domain wall/cosmic string network, a first-order phase transition, or scalar field dynamics. Our findings indicate that this method holds the potential to explore substantial regions of previously unconstrained parameter space, serving as a valuable complement to upcoming searches for gravitational waves originating from such dark sectors

Speaker: Nicklas Ramberg (Johannes gutenberg universität Mainz)

Distortions of the CMB through the Dark.pdf

Lunch Break

Dark Matter

Convener: Diego Blas (UAB/IFAE)

30 Line Intensity Mapping for new physics

Speaker: Dr Jose Luis Bernal (Institute of Physics of Cantabria, Spain)

JLB_Eucapt24.pdf

Recording

Video preview

31 21 cm and CMB as dark matter probes

Speaker: Gaëtan Facchinetti

EuCAPT_Facchinetti.pdf

Recording

Video preview

Coffee Break

Dark Matter

Convener: Diego Blas (UAB/IFAE)

32 The dark shines - Highlights of gamma-ray searches for dark matter

Speaker: Christopher Eckner (University of Nova Gorica)

EuCAPT_2024_DMwithGammaRays_Eckner.pdf

Recording

Video preview

33 X-rays constraints on sub-GeV Dark Matter

We present updated constraints on 'light' Dark Matter (DM) particles with masses between 1 MeV and 5 GeV. In this range, we can expect DM-produced pairs to upscatter low-energy ambient photons in the Milky Way via the Inverse Compton process, and produce a flux of X-rays that can be probed by a range of space observatories. Using diffuse X-ray data from XMM-Newton and realistic cosmic-ray transport parameters, we compute the strongest constraints to date on annihilating and decaying DM for 1 MeV < $m_{\rm DM}$ < 5 GeV

Speaker: Jordan Koechler (LPTHE - Sorbonne Université (France))

2024_EuCAPT_Talk.pdf

34 Riding the dark matter wave: Novel limits on general dark photons from LISA Pathfinder

I will point out the possibility to perform a parametrically improved search for gauged baryon ($B$) and baryon minus lepton ($B-L$) Dark Photon Dark Matter (DPDM) using auxiliary channel data from LISA Pathfinder. In particular I will show how to use the measurement of the differential movement between the test masses (TMs) and the space craft (SC) which is nearly as sensitive as the tracking between the two TMs. TMs and SC are made from different materials and therefore have different charge-to-mass ratios for both $B-L$ and $B$. Thus, the surrounding DPDM field induces a relative acceleration of nearly constant frequency. For the case of $B-L$, I will demonstrate that LISA Pathfinder can constrain previously unexplored parameter space, providing the world leading limits in the mass range $4\cdot 10^{-19}\,\text{eV}\leq m \leq 3\cdot 10^{-17}\,\text{eV}$. This limit can easily be recast also for dark photons that arise from gauging other global symmetries of the SM.

Speaker: Jonas Frerick

DPDM_LPF_JF_EuCAPT.pdf

35 Global Fits of sub-GeV Dark Matter

Sub-GeV dark matter (DM) has been gaining significant interest in recent years, since it can account for the thermal relic abundance while evading nuclear recoil direct detection constraints. However, sub-GeV DM is still subject to a number of constraints from laboratory experiments, and from astrophysical and cosmological observations. In this work, we compare these observations with the predictions of two sub-GeV DM models (Dirac fermion and scalar DM) within frequentist and Bayesian global analyses using the Global And Modular BSM Inference Tool (GAMBIT). We infer the regions in parameter space preferred by current data, and compare with projections of near-future experiments.

Speaker: Taylor Gray (Chalmers University of Technology)

EUcapt2024.pdf

EUcapt2024.pptx

36 Burst Signals from Axion String Travelling Wave Collisions

Axion strings are a type of topological defect that arise in particle physics models with a spontaneously broken global U(1) symmetry. They are predicted to radiate massless dark matter axions, massive particles and gravitational waves. If we are to detect axion dark matter, either directly or indirectly via gravitational waves, understanding the magnitude and spectrum of this radiation is crucial. In this talk, I will summarise my most recent work (arXiv:2312.07701) which models axion string radiation using adaptive mesh refinement simulations. We investigate colliding travelling wave configurations with a Gaussian profile and the dependence of the radiation on parameters such as the amplitude of the Gaussian and the radius of curvature of the string relative to the string width.

Speaker: Amelia Drew

EuCAPT_2024_Symposium.pdf

37 Dynamical contraints on PBH clusters

In the high mass range, primordial black holes are constrained by the observed velocity dispersion of the Galactic disk, as they are expected to heat up stars through two-body encounters. These constraints have been obtained assuming that the PBHs are smoothly distributed in the DM halo. However, PBHs are expected to form bound structures under the effect of gravity; furthermore, it has been argued that they are likely to be already born in clusters. In this work, we investigate how the heating of the galactic disk constrains the abundance of PBHs when clustering is taken into account.

Speaker: Francesca Scarcella (Laboratoire Univers et Particules de Montpellier (LUPM))

DiskHeatingFS.pdf

38 EFT approach to sterile neutrino dark matter

Sterile neutrinos represent a minimal and well motivated extension of the Standard Model (SM). For masses at the keV scale, their mixing to the active neutrinos offers a minimal explanation of the dark matter (DM) density. The very same mixing inevitably leads to radiative photon emission and the non-observation of such peaked X-ray lines virtually rules out this minimal sterile neutrino DM hypothesis.
However, in this talk I will point out that in the context of the SM effective field theory with (light) sterile neutrino (nuSMEFT), higher dimensional operators can produce sterile neutrino DM in a broad range of parameter space. In particular, even in the zero mixing limit the DM density can be explained. On the other hand, nuSMEFT interactions also open the large mixing parameter space. This is because some nuSMEFT operators induce photon dipoles, which can cause destructive interference effects in the X-ray emission. I will further discuss the testability prospect of the nuSMEFT operators and show their correlations to the parameter space of the DM production.

Speaker: Stefan Sandner (IFIC)

Stefan_Sandner_EUCAPT_24.pdf

Optional Visits to CERN Experimental Sites

Thursday, 16 May

Gravitational Waves

Convener: Geraldine Servant (Deutsches Elektronen-Synchrotron (DE))

39 Implications of gravitational waves detection for stellar astrophysics

Speaker: Valeriya Korol (Max Planck Institute for Astrophysics)

EuCAPT2024_Korol.pdf

Recording

Video preview

40 Gravitational Waves from Phase Transitions

Speaker: Bogumila Swiezewska (University of Warsaw)

GWS_from_PT_BSwiezewska.pdf

Recording

Video preview

Coffee Break

Gravitational Waves

Convener: Geraldine Servant (Deutsches Elektronen-Synchrotron (DE))

41 Topological defects during cosmological phase transitions

Speaker: Dr Simone Blasi (DESY)

eucapt talk.pdf

Recording

Video preview

42 Timekeepers of the Universe: The recent gravitational wave observation and Primordial black holes

Primordial black holes (PBHs) are currently in the spotlight as they may solve several open questions in astrophysics and cosmology.
We describe an exact formalism for the computation of the abundance of PBHs in the presence of local non-gaussianity (NG).
Then, we describe the phenomenological relevance of our results for the connection between the abundance of PBHs and the
stochastic gravitational wave (GW) background related to their formation. As NGs modify the amplitude of perturbations necessary to produce a given PBHs abundance, modelling these effects is crucial to connect the PBH scenario to its signatures at current and future GWs experiments such as the recent data release by PTA collaborations

Speaker: Antonio Junior Iovino (Università di Roma "La Sapienza")

Eucapt.pdf

43 High Frequency Gravitational Wave Bounds from Galactic Neutron Stars

High-Frequency Gravitational Waves (HFGWs) constitute a unique window on the early Universe as well as exotic astrophysical objects. If the current gravitational wave experiments are more dedicated to the low frequency regime, the graviton conversion into photons in a strong magnetic field constitutes a powerful tool to probe HFGWs. In this paper, we show that neutron stars, due to their extreme magnetic field, are a perfect laboratory to study the conversion of HFGWs into photons. Using realistic models for the galactic neutron star population, we calculate for the first time the expected photon flux induced by the conversion of an isotropic stochastic gravitational wave background in the magnetosphere of the ensemble of neutron stars present in the Milky Way. We compare this photon flux to the observed one from several telescopes and derive upper limits on the stochastic gravitational wave background in the frequency range $10^8$ Hz - $10^{25}$ Hz. We find our limits to be competitive in the frequency range $10^8$ Hz - $10^{15}$ Hz.

Speaker: Virgile Dandoy (ULB)

Eucapt VDandoy.pdf

44 Signatures of ultralight bosons in the orbital eccentricity of binary black holes

It is well known that clouds of ultralight particles surrounding black holes produced by the superradiant instability can experience Landau-Zehner transitions if the black hole is part of a binary system.
We study the effect of orbital eccentricity, backreaction of the cloud onto it and observational possibilities with future gravitational-wave detectors like the Laser Interferometer Space Antenna, as well as the planned deciHertz gravitational-wave observatories. For black hole binaries with chirp masses below $10\,M_\odot$, such effects would provide strong evidence for the existence of a new particle of mass between $10^{−13}-10^{−11}\,\mathrm{eV}$.

Speaker: Matthias Koschnitzke (University of Hamburg/DESY)

SR_Presentation_EuCAPT.pdf

45 Colour breaking in the early universe: a minimal leptoquark model

The electroweak phase transition is a promising explanation for the origin of baryon asymmetry in the universe, a core problem in cosmology and particle physics.
An extension of the Standard Model is necessary to generate a strong first-order phase transition. Besides representing a target for several future-generation colliders, such Beyond the Standard Model (BSM) theories can generate - through a thermal phase transition - gravitational waves (GWs) potentially detectable by future space-based detectors, such as LISA 1, DECIGO, and BBO.

As a result, the interplay between BSM phenomenology and GWs is among the most active areas in the field of high-energy physics. Of particular interest are leptoquark (LQ) models, offering an alternative to conventional seesaw scenarios for the generation of Majorana neutrino masses at TeV scale. The presence of LQs can induce first order phase transitions with a temporary colour-breaking phase in the early universe.
With this poster, I intend to present results from the analysis of a minimal leptoquark model. In a dimensionally reduced effective theory approach 3, the model presents strong first order transitions, producing - in some scenarios - gravitational waves detectable by LISA. To our knowledge, these results provide the first evidence for the potential detection of color-breaking features in the above mentioned detectors.

The poster will be organized in 3 sections:

1. Introduction of the leptoquark model introduction and its features
2. Sketch of the pipeline implemented, and the adopted tools:
   (a) Computation of an effective potential with Dralgo 3.
   (b) Derivation of the phase structure and phase transition parameters by means of CosmoTransitions.
   (c) Derivation of the GW parameters with a dedicated python routine.
3. Illustration of the results
   (a) comparison of GW spectral peaks with detector sensitivities.
   (b) Interpretation of the various vacuum expectation value (vev) configurations identified in the two phases
   (c) correlation between collider observables.

---

1 Amaro-Seoane, P., Audley, H., Babak, S., Baker, J., Barausse, E., Bender, P., ... & Zweifel, P. (2017). Laser interferometer space antenna. arXiv preprint arXiv:1702.00786.

2 Felipe F. Freitas, João Gonçalves, António P. Morais, Roman Pasechnik, Werner Porod. On interplay between flavour anomalies and neutrino properties. Phys.Rev.D 108 (2023) 11, 115002.

3 Andreas Ekstedt, Philipp Schicho, Tuomas V.I. Tenkanen. DRalgo: A package for effective field theory approach for thermal phase transitions.Comput.Phys.Commun. 288 (2023) 108725.

Speaker: Marco Finetti (Aveiro University)

Colour breaking in the early Universe - Poster

Marco_Presentation EuCAPT 2024-05-16.pdf

46 Analytic derivation of gravitational wave spectrum from expanding string loop on domain wall

It is well known that spontaneous breaking of discrete symmetries produce topological objects called domain walls, which must decay in order not to dominate the energy density of the universe. One of the possible decay scenarios is nucleating holes bounded by cosmic strings on the walls. Once they are nucleated, the holes expand faster and faster by eating the energy of the domain walls and may radiate stochastic gravitational waves with significant energy fraction. This resembles cases of bubble collisions in cosmological 1st-order phase transition. We derive an analytic expression for the GW spectrum radiated from these string loops expanding on the walls. Remarkablly, the spectrum is found to be flat in high-frequency region, in contrast to usual bubble collisions. We also discuss the implication to the NANOGrav signal and future GW observatories.

Speaker: Dr Yu Hamada (DESY)

EuCAPT_hamada.pdf

47 Probes of reheating after non-Abelian axion-like inflation

We consider a model, where a single inflaton interacts as an axion with Yang-Mills gauge bosons. As these rapidly thermalize, the friction felt by the inflaton field is increased, leading to a self-amplifying process. The corresponding gravitational wave spectrum is enhanced by thermal contributions at large confinement scales of the Yang-Mills sector, which heats up to high temperatures, yet below the critical value.
On the other hand, the gauge bosons of the thermal bath may represent part of a dark sector. Assuming a feeble coupling to the visible sector, the stable component of the dark sector satisfies the bounds on the relic abundance, if its confinement scale takes values far below those relevant to the gravitational wave signal so that the dark sector is in a deconfined phase at the end of inflation. The reheating of the Standard Model is most efficiently actuated by dark glueballs after the confinement phase transition. The latter might represent an additional source of gravitational waves.

Speaker: Simona Procacci (University of Geneva (CH))

Procacci_eucapt24.pdf

Lunch Break

EuCAPT updates and outlook

48 EuCAPT updates and outlook

Speaker: David Marsh

EuCAPT_Symposium2024_closing.pdf

Talks and Poster Prize Ceremony

EucaptPrizes.pdf