Progress on Old and New Themes in cosmology (PONT) 2026

27 Apr 2026, 08:30 → 30 Apr 2026, 20:00 Europe/Paris

Chambre du Trésorier (Palais des papes, Avignon)

Rationale The conference addresses the cardinal issues of the dark universe today, gathering a selected number of scientists working in cosmology and astroparticle physics in the inspiring and monumental setting of Avignon. There will be both review talks by leading experts in each field and selected contributions, all aimed at encouraging in-depth debates. A certain amount of time will be devoted to discussion sessions. 

The 2026 edition, the seventh in the PONT series, will focus on the following research topics: 

- Early universe

- Late universe

- Gravitational waves

- Astrophysical messengers of new physics

Organizers  Philippe Brax (IPhT Paris-Saclay, CEA), Francesca Calore (LAPTh Annecy), Marco Cirelli (LPTHE Jussieu Paris), Christian Marinoni (CPT Marseille), Vivian Poulin (LUPM Montpellier), Nicola Tamanini (L2IT Toulouse)

Technical and Administrative Secretariat  Laura Trano    (laura.trano@cpt.univ-mrs.fr)

intro.pdf

pic_small.jpg

Monday 27 April

08:30 Registration

Early Universe

Convener: philippe brax (IPhT CEA Saclay)

1 Pontificating about inflation

Cosmic inflation has been the leading paradigm to describe our Universe’s earliest moments for the last decades. Inspired by the residence of this conference, I will pontificate about recent progress on old and new themes in inflation. While necessarily broad in scope, this presentation will revisit some of the following historical themes from a modern perspective: gauge issues, quantumness of inflationary fluctuations, model degeneracy, primordial non-Gaussianity, primordial black holes and primordial gravitational waves.

Speaker: Lucas Pinol

Pinol_Pontificating about inflation.pdf

Pinol_Pontificating about inflation.pptx

2 The ACT DR6 Cosmology Results

In March 2025, the Atacama Cosmology Telescope (ACT) released a high resolution measurement of CMB polarization, covering 19 000 square degrees at 90, 150 and 220 Ghz, three times deeper than past measurements from the Planck satellite. In this talk, I will guide the audience through the different steps of the analysis of a CMB dataset, focusing on ACT DR6, and give an overview of the main cosmological results coming from ACT DR6 data, for the standard model of cosmology and some of its extensions.

Speaker: Adrien LA POSTA

LAPOSTA.pdf

3 The South Pole Telescope: recent results and future prospects

Speaker: Lennart Balkenhol

pont26_balkenhol.pdf

10:45 Coffee break

Early Universe

Convener: philippe brax (IPhT CEA Saclay)

4 Giving color to the gravitational wave spectrum

Speaker: Diego Blas (ICREA/IFAE)

27Pont.pdf

BNQ26.pdf

5 Cosmology with next generation GW observatories

Speaker: Archisman Ghosh (Nikhef)

5.ag_pont.pdf

12:25 Lunch break

Contributed talks

Convener: Lucas Pinol

6 Inflation beyond perturbation theory

The wavefunction of the universe contains the full information about primordial fluctuations. I will show how to determine it in a non-perturbative manner in a large class of inflationary scenarios, using the example of models with small and rapid oscillations in the inflaton potential. Our study reveals a profound asymmetry between maxima and minima of the density fluctuations, and indicates that even minute oscillations give large effects on the tail of the distribution. Eventually, I will describe a qualitatively new regime in which most of the information of inflationary correlators appears in higher-order correlation functions with large n, at odds with conventional wisdom.

Speaker: Sébastien Renaux-Petel

Inflation-beyond-perturbation-theory-PONT-2026.pdf

7 de Sitter Momentum Space

In many inflationary scenarios, primordial correlation functions are encoded in late-time observables in de Sitter spacetime, where even the simplest processes already involve highly nontrivial time integrals. I will show that this difficulty can be overcome by introducing a new momentum-space representation adapted to de Sitter isometries. This construction is based on diagonalizing the Casimir operator rather than the Hamiltonian, effectively trading the usual (d+1)-dimensional Fourier space for the Kontorovich–Lebedev–Fourier (KLF) space. I will also show practical advantages of this description: quadratic dynamics provides a simple propagator analogous to flat space, and the nested time integrals turn into frequency-space integrals over meromorphic functions.

Speaker: Arthur Poisson (IAP)

PONT - Poisson.pdf

8 Dual space for cosmological correlators

The generation of primordial density inhomogeneities from the inflaton
quantum fluctuations is a crucial prediction of inflation. The correlation
functions of these quantum fluctuations, called cosmological correlators,
can be studied in a perturbative framework. These fluctuations can be
mathematically described as quantum massive fields that propagate in a de
Sitter space-time. However, this propagation has a complex time and
kinematic dependence due to broken Lorentz invariance.

In this talk, I will derive an integral transform that allows one to
express cosmological correlators in terms of their flat-space counterpart
with a suitable linear transform, and I will show how it simplifies their
dependence in kinematic variables.

Speaker: Nathan Belrhali

Belrhali_PONT_Avignon_26.pdf

9 A superposition quantum universe and its perturbations

In the quest to establish possible imprints of quantum gravity we consider so-called minisuperspace models that should be understood as a low energy limit of a full quantum gravitational theory. Starting from a bouncing minisuperspace model that resolves the big bang singularity, we will relax the assumption that the state of the quantum universe has to correspond to a single highly semiclassical state. Instead, we will consider a universe in a superposition of such states.
Faced with the question of how to extract a semiclassical scale factor that can be connected to the classical evolution of general relativity, we propose to make use of the trajectory approach to quantum mechanics. We illustrate the treatment of cosmological perturbations over a superposition background described by a trajectory and consider implications for the resulting power spectrum. Notably these spectra can exhibit features that significantly differ from the single state case.

Speaker: Lisa Mickel (Institut d'Astrophysique de Paris (IAP))

PONT_Apr2026_MickelLisa.pdf

10 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

11 B-Mesogenesis: The mechanism revisited

The B-Mesogenesis mechanism aims to explain the baryon asymmetry of the Universe and dark matter through the CP violating oscillations and subsequent decays of $B$-Mesons in the early Universe at times right before BBN, $T \simeq (5-20)\,{\rm MeV}$. In this work, we point out that the photo-disassociation process $\gamma+B^0\to B^{0\star}$ that was not accounted for in the original studies is the most effective in leading to decoherence of CP violating oscillations. By providing a first principle calculation of the mechanism and considering this process we find that the efficiency of the mechanism is reduced by a factor of $\sim 2-100$ depending upon the effective reheating temperature in the model. Furthermore, we solve for BBN within the mechanism and find that consistency with observations requires $T_{\rm RH}>5.3\,{\rm MeV}$. These two findings imply that the required CP asymmetries and branching ratios of $B$ mesons into baryons and missing energy should at least be a factor of 10 larger than it was expected. Overall, we find that the mechanism is in tension with the lack of new-physics signals in these laboratory observables and may be ruled out experimentally already.

Speaker: Martha Ulloa Calzonzin (University of Florida)

PONT2026-BMesogenesis-MarthaUlloa.pdf

12 Beyond spontaneous baryogenesis with extra fields

We investigate the theory of spontaneous baryogenesis, considering two extensions to the scalar paradigm and proposing a vectorial and LIV version of the model. Concerning the scalar paradigm, firstly we generalize the minimal theory introducing a non-minimal coupling between the inflaton field and the scalar curvature. This modifies the effective mass squared of the inflaton and accordingly changes its decay amplitude into fermion-antifermion pairs. We show that this mechanism can significantly increase the baryon asymmetry, providing a value compatible with experimental data. In the second place, we introduce a complex scalar spectator field non-minimally coupled to gravity and interacting with the inflaton through a bilinear quadratic term. Also in this case, the overall baryogenesis process turns out to be more efficient, even though the enhancement is not yet sufficient to account for the observed matter-antimatter asymmetry. Finally, we propose a vectorial version of spontaneous baryogenesis. We reformulate the model from scratch, substituting the complex scalar field with a complex vector field. We start from the unbroken phase Lagrangian and discuss the mechanism of spontaneous symmetry breaking with a vector field, yielding a spontaneous violation of Lorentz symmetry further than $U(1)_B$. In this picture, the pseudo-Nambu-Goldstone boson arising from the $U(1)_B$-breaking is the global phase of the vector field and plays the role of the inflaton. The baryon asymmetry is then produced through the same mechanism as in the scalar model. The crucial difference lies in the mixing between fermions, here acting on their spatial momenta rather than on the masses. This provides a non-null mixing factor even for massless fermions and allows larger values of the coupling constant. The net baryon asymmetry is accordingly modified and may reproduce experimental data.

Speaker: Mattia Dubbini (Università di Camerino)

Talk_Avignon_Dubbini.pdf

13 Quasi-pole inflation in metric affine gravity

We propose a new mechanism for inflationary model building in the framework of metric-affine gravity. Such a mechanism involves an inflaton non-minimally coupled with the Holst invariant. If the non-minimal coupling function has a zero point and it is very steep at that same point, the corresponding inflaton kinetic function will feature a quasi-pole behaviour, implying a canonically normalized potential featuring an exponential plateau, regardless of the shape of the original inflaton potential. The inflationary predictions in such a region are equivalent to the ones of Starobinsky inflation.

Speaker: Antonio Racioppi (National Institute of Chemical Physics and Biophysics (EE))

Racioppi_Avignon.pdf

16:00 Coffee break

Contributed talks

Convener: Sebastien Renaux

14 Post-inflationary squeezing and the phase coherence of the CMB

In this talk, we quantitatively characterise the phase of primordial perturbations from inflation to cosmic microwave background scales. Our goal is to analyse how the phase of those perturbations evolve through the entire expansion history of the universe and to identify theoretical reference values that can be tested against future observations.
To achieve this, we study the quantum squeezing of the Mukhanov–Sasaki variable and its associated phase within a Gaussian framework, with the system evolved through the radiation- and matter-dominated eras. In each epoch, the evolution is initialised using the Deruelle–Mukhanov matching conditions, ensuring consistent tracking of the mode functions across cosmological transitions. We recover the standard result that inflation makes the phase probability distribution sharply peaked, leading to phase coherence as the mode evolves outside the horizon, and we show that this imprint persists beyond inflation.
A central result is the universality of the phase coherence value within slow-roll, single-field inflationary models, even when modes experience different numbers of e-folds, as in grand-unified compared to electroweak-scale inflation. This universality results from the essential role of reheating and the radiation era, which must be modelled consistently.
Overall, this provides an exact theoretical reference for the phase variance, to be tested against future observations of phase coherence in the cosmic microwave background, E-mode polarisation, and large-scale structure.

Speaker: Siméon Vareilles

PONT_SV.pptx

15 Bayesian Optimisation for efficient cosmological model selection and parameter inference

The formalism of Bayesian model selection provides an elegant way of ranking different physical models in terms of how compatible they are with a given set of observed data. However, its practical application is often hampered by the challenge of having to compute the Bayesian evidence - a multi-dimensional integral over the product of likelihood and prior probability which may become prohibitive in case of "slow", costly to evaluate likelihoods. We introduce a method to construct a fast Gaussian Process Regression based emulator of the likelihood using a Bayesian Optimisation algorithm designed specifically to provide a realistic estimate of the emulator's uncertainty and minimise the number of likelihood evaluations required in order to meet a given evidence accuracy goal. We discuss applications to cosmology and demonstrate using examples from the CMB that training the emulator to a sufficient accuracy takes a factor of $O(10^3)$ fewer direct likelihood evaluations compared to traditional methods such as MCMC or nested sampling. Parameter posteriors are naturally obtained as a by-product of the emulation.

Speaker: Ameek Malhotra

Malhotra_PONT_2026.pdf

16 Thermal effects on Dark Matter production during cosmic reheating

The relic abundance of Dark Matter (DM) produced via thermal freeze-in is sensitive to the thermal history during and after cosmic reheating. In minimal models, this opens up the possibility to make predictions for collider observables by combining the requirement to match the DM relic abundance with observations of the Cosmic Microwave Background (CMB). We assess the impact of thermal corrections to the rate of cosmic reheating and the rate of thermal DM production on CMB observables and the relic abundance. We find that such corrections are generally negligible in the regime where perturbation theory can be applied. We construct counter-examples where this general rule is violated.

Speaker: Mubarak Mohammed (UCLouvain-CP3)

Mubarak_PONT-Talk.pdf

17 Multimessenger phenomenology of nonperturbative quantum black holes

I will talk about certain mainstream models of quantum black holes in both loop quantum gravity and generalized uncertainty principle approaches to quantum gravity, and propose some of the multimessenger test that could reveal (or refute) their quantum nature. These tests include electromagnetic and gravitational wave-related phenomena, and I will discuss the expected results in each case if such black holes are quantum in nature.

Speaker: Prof. Saeed Rastgoo (University of Alberta)

Avignon-Rastgoo.pdf

18 Quasi-periodic oscillations as probes of new physics: spin-curvature coupling in neutron star binaries

Quasi-periodic oscillations (QPOs) observed in the X-ray emission of accreting compact objects are among the most promising astrophysical messengers of strong-field gravity. Yet, despite decades of observations, their physical origin remains debated, and the most established framework to interpret them, the relativistic precession model (RPM), shows persistent observational tensions, including a systematic preference for Schwarzschild-de Sitter (SdS) geometries over standard Schwarzschild or Reissner-Nordström solutions, with no clear physical justification for the role of a cosmological constant at such scales.

We argue that this tension points to missing physics in the RPM rather than to exotic spacetime geometries. Treating accreting matter as a collection of structureless test particles is a severe oversimplification: real accretion disks carry macroscopic angular momentum and internal structure. We incorporate this ingredient into a macroscopic precession model (MPM), based on the Mathisson-Papapetrou-Dixon equations on a Schwarzschild background, which introduces a spin-curvature coupling that modifies both the Keplerian and the radial epicyclic frequencies. Crucially, this correction naturally reproduces a SdS-like behavior, offering a physical explanation for what was previously attributed to an effective cosmological constant.

We apply the MPM to eight neutron star low-mass X-ray binaries via MCMC fits to twin kHz QPOs, finding statistically competitive or superior results with respect to the SdS framework, with consistent neutron star masses, disk boundary radii in physically plausible ranges, and a natural emergence of the observed 3:2 frequency clustering. These results suggest that QPOs carry direct information about the internal structure of orbiting matter, opening a new observational window on spin-curvature effects in strong-field regimes.

Speaker: Gabriele Bianchini (University of Camerino)

TalkPONT2026Avignon_27_4_26_v2.pdf

18:30 Welcome cocktail

Tuesday 28 April

Astrophysical messengers of new physics

Convener: Marco Cirelli (CNRS LPTHE Jussieu)

19 Cornering axions with astrophysical transients

While it is way too early to make a final judgement, it is noteworthy that searches at LHC and direct detection experiments reported null results, therefore boosting the ever growing interest in sub-GeV dark sector candidates. Owing to their high temperature and density, the cores of proto-neutron stars, remnant of core-collapse supernovae and neutron star mergers, can be factories of axions and other feebly interacting particles with mass of up to several hundreds MeV. In this talk, we will summarize the state of the art of transient-based searches, and identify open questions and future directions.

Speaker: Edoardo Vitagliano

talk_PONT2026.pdf

20 Dynamical probes of dark matter

Speaker: Julien Lavalle (LUPM (CNRS / Univ. Montpellier))

dynamical_heating_probes_of_dm_pont26_lavalle.pdf

21 Dark matter direct detection in light of the Large Magellanic Cloud

Speaker: Nassim Bozorgnia (York University, University of Alberta)

Bozorgnia-PONT.pdf

10:45 Coffee break

Astrophysical messengers of new physics

Convener: Marco Cirelli (CNRS LPTHE Jussieu)

22 Producing dark matter particles after a first-order phase transition

Speaker: Felix Kahlhoefer (Karlsruhe Institute of Technology)

Phase-in_Avignon.pdf

23 Mapping out the Dark Matter in the Milky Way with Stars

Speaker: Lina Necib (MIT)

PONT.pdf

PONT.pptx

12:25 Lunch break

Contributed talks

Convener: Nassim Bozorgnia (York University, University of Alberta)

24 Cosmological implications of the Gaia Milky Way declining rotation curve.

Although the existence of dark matter is widely accepted, its true nature remains unknown, motivating alternative explanations such as Modified Newtonian Dynamics (MOND). MOND modifies Newton’s laws for low accelerations (below $a_0$) and generally reproduces the flat rotation curves of galaxies.

However, recent Gaia data reveal a declining rotation curve in the Milky Way, which differs from the usual flat behavior. This study tests whether MOND can accomodate this decline.

A standard baryonic model of the Milky Way is first built, and an NFW dark matter model successfully fits the decline. In contrast, the standard MOND framework fails to do so.

By relaxing the baryonic parameters and using an MCMC analysis, we find that MOND could only match the data if the stellar disk is very massive, while $a_0$ is consistent with zero and limited to significantly smaller values than the standard MOND value.

Speaker: Alain BLANCHARD

Pont2026.pdf

25 Cosmological constraints on dark sectors from CMB and Lyman-alpha

In this talk, I will show how measurements of the intergalactic medium (IGM) temperature from the Lyman-α forest can be used to constrain long-lived dark sector particles. Such particles deposit energy into the IGM through decays to Standard Model states, thereby modifying the thermal history of the Universe. I will also revisit constraints on these models from Planck CMB measurements of the optical depth to reionization, and demonstrate that Lyman-α bounds provide a complementary probe to those from the CMB. The resulting model-independent constraints can be reinterpreted across a wide range of decaying dark sector scenarios, such as evaporating primordial black holes and dark photons.

Speaker: Sonali VERMA (ULB, Brussels)

PONT2026_SVerma.pdf

26 Heating the dark matter halo with dark radiation from supernovae

Supernova explosions are extreme cosmic events that may impact not only ordinary matter but also dark matter (DM) halos. In this talk, I explore the possibility that a fraction of supernova energy is released as dark radiation, which could transform a cuspy DM halo into a cored one, potentially explaining observed cores in some dwarf galaxies. Alternatively, limits on DM core sizes provide constraints on the energy channeled into light particles beyond the Standard Model (SM). Based on evaluation of energetics, one finds that even a small fraction of the total SN energy is sufficient to change the overall shape of the DM halo and transform a cuspy halo into a cored one. We evaluate some well motivated benchmark models, e.g. the dark photon and dark Higgs, to demonstrate that significant supernova emissivity of dark radiation and large DM halo opacity are achievable in realistic particle physics model. Interestingly, couplings consistent with SN1987A observations can still have a measurable impact on dwarf galaxy halos.

Speaker: Stefan Vogl (University of Freiburg)

Vogl_PONT_2026.pdf

27 Casimir pressure in the presence of axion dark matter

Axion dark matter can modify electromagnetic phenomena through its coupling to photons, leading to new signatures in precision experiments. In the presence of an external magnetic field, the axion–photon interaction acts as an effective electromagnetic source that generates oscillating fields inside a cavity. Previous work by Brax and Brun showed that this mechanism can produce both classical and quantum modifications of Casimir forces between material bodies: a classical Casimir-like pressure arising from axion-induced electromagnetic fields, which can be resonantly enhanced when the cavity modes match the axion frequency, as well as quantum corrections associated with modifications of the electromagnetic vacuum modes. In this talk, I review these results and present recent progress in modelling axion-induced Casimir forces in realistic experimental configurations. The induced electromagnetic response and the resulting pressure are computed using the Lifshitz formalism, incorporating realistic material properties such as dissipation in conducting plates and finite temperature effects. Particular emphasis will be placed on two-dimensional materials such as graphene, whose tuneable electromagnetic response and unique properties may provide additional control over the cavity resonances and the resulting Casimir signal.

Speaker: Ahmad Alachkar (CEA IPHT)

Casimir_Pressure_in_presence_of_AxionDM avignon.pdf

Casimir_Pressure_in_presence_of_AxionDM avignon.pptx

28 Piezoaxionic Detection of Axion Dark Matter with Precessing Nuclear Spins

The piezoaxionic effect enables the conversion of axion-induced spin-dependent forces in polarized nuclei into measurable voltages within piezoelectric crystals. A heterodyne detection scheme is introduced in which controlled nuclear spin precession mixes the axion oscillation frequency with the nuclear Larmor frequency. This process generates sideband signals at shifted frequencies, allowing efficient scanning of axion masses by changing the applied magnetic field. This method offers a tunable, noise-resistant approach to probing QCD axion dark matter in the MHz to GHz frequency range.

Speaker: Baraa YAHYA (IPhT (CEA-SACLAY))

PONT_CONGRESS_YAHYA

29 Light bosons from cold isolated Neutron Stars

Exotic scalars and vectors coupled to nucleons and muons can be copiously produced in cold isolated neutron stars (NSs). In these environments, the milder temperature dependence of their emissivity compared to neutrinos magnifies significantly the effect of these novel exotic particles on the cooling process of such stars. The absence of traces of exotic cooling for a well-measured sample of NSs with ages around $10^5$ years can be exploited to set stringent constraints on the coupling strength of bosons with masses $m_\phi$<1 MeV, superseding by many orders of magnitude the corresponding SN 1987A cooling bound in the given mass range. Equivalently, I will discuss how the same constraints can be also derived following a simple argument based on analytic behavior of the NS cooling process. These arguments induce the most stringent bounds on the strength of fifth forces between nucleons and muons and acting on micro- to picometer length scales.

Speaker: Alessandro Lella

2026_PONT_Lella.pdf

30 Probing Long-Lived Particles with Gravitational Wave Background Spectral Breaks

I will show that spectral features of a gravitational-wave background can directly determine Lagrangian parameters of beyond-the-Standard-Model particles, independently of the gravitational-wave production mechanism. Long-lived particles generically induce a temporary period of early matter domination in the thermal history of the Universe, which imprints two characteristic frequencies in any primordial gravitational-wave background corresponding to the onset and end of this epoch. These frequencies are determined by the initial abundance, mass, and decay rate of the dominating species. I will show that once the underlying model is specified the observed spectral features directly determine the particle mass and decay rate, allowing gravitational-wave observations to probe the Lagrangian parameters of particle physics models. As an example, I will consider the gauged $U(1)_{B-L}$ model, where matter domination can be driven either by the symmetry-breaking scalar or by a right-handed neutrino, and discuss the impact this has on leptogenesis.

Speaker: Angus Spalding (Univeristy of Southampton)

PONT26.pdf

16:00 Coffee break

Contributed talks

Convener: Julien Lavalle (LUPM (CNRS / Univ. Montpellier))

31 Topological Portals to the Dark Sector

I will present the construction and phenomenology of novel portals between the Standard Model and dark sectors, arising from topological operators in chiral perturbation theory. The first example is based on a mixed Wess–Zumino–Witten term that uniquely connects three QCD pions to two dark pions, leading to a consistent framework for light thermal inelastic dark matter with suppressed direct and indirect detection, but distinctive collider signatures. The second example is a minimal model in which gauging the topological Skyrme current naturally links a QCD-like dark sector to the Standard Model, allowing a semi-annihilation process that sets the relic abundance. The purely p-wave nature of these interactions ensures compatibility with existing constraints while offering discovery prospects at colliders and beam-dump experiments.

Speaker: Nudžeim Selimović (INFN Padova)

Avignon_Selimovic.pdf

32 Cosmic-ray antinuclei in dark matter searches: Insights from collider data

Cosmic-ray antinuclei, in particular antideuterons ($\overline{\rm D}$) and antihelion-3 (${}^3\overline{\rm He}$), are among the most promising messengers for indirect dark matter (DM) searches. Their interest arises from the strong suppression of secondary production in cosmic-ray interactions with the interstellar medium at kinetic energies $K\sim 0.1–1$ GeV/n, where the expected astrophysical background lies one to two orders of magnitude below the flux predicted in many DM scenarios. In this context, recent tentative evidence reported by the Alpha Magnetic Spectrometer (AMS-02) for candidate ${}^3\overline{\rm He}$ events—together with a comparable number of $\overline{\rm D}$—would have profound implications for cosmic-ray physics and dark matter searches if confirmed.

A major theoretical uncertainty in interpreting such signals is the formation of antinuclei, typically modeled through phenomenological coalescence prescriptions. We present a study showing that physically motivated coalescence models can simultaneously reproduce collider measurements in two distinct regimes: (anti)deuteron production in $pp$ collisions measured by ALICE at $\sqrt{s}=0.9-13$ TeV and antideuteron multiplicities in hadronic $Z$ decays measured by ALEPH. These results support an approximately universal coalescence scale and provide a robust framework for predicting antinuclei yields.

Within this framework we also investigate a recently proposed Standard Model mechanism for antihelion-3 production via displaced-vertex decays of $\overline{\Lambda}_b^0$ baryons. Using a dedicated PYTHIA tuning consistent with LEP measurements of $b$-quark fragmentation and with ALICE and ALEPH data on $\overline{\rm D}$ and ${}^3\overline{\rm He}$ production, we derive predictions for antinuclei yields from heavy-flavor decays that are compatible with current LHCb limits. We find that the contribution of beauty-hadron decays to ${}^3\overline{\rm He}$ production is subdominant relative to direct hadronization.

Our results strengthen the theoretical basis for interpreting current and upcoming cosmic-ray antinuclei searches, particularly in light of future measurements by AMS-02 and the upcoming GAPS experiment, which will provide unprecedented sensitivity to low-energy antideuterons from dark matter.

Speaker: Jordan Koechler (INFN Turin)

2026_antinuclei.pdf

33 Indirect searches for sub-GeV Dark Matter models in present and upcoming observations

Indirect searches for Dark Matter (DM) particles with mass in the MeV - GeV scale have received significant attention lately. Pair-annihilations of such DM particles in the Galaxy can give rise to MeV - GeV gamma-rays via prompt emission, sub-GeV e+e-'s in cosmic-rays, as well as a broad photon spectrum ranging from X-rays to soft gamma-rays, produced by the secondary emissions from DM induced e-(e+)'s via inverse Compton scattering, bremsstrahlung and in-flight annihilation processes. In this talk I shall focus on two realistic sub-GeV DM models, namely, the vector-portal and the scalar-portal model, and present the corresponding indirect detection constraints from existing X-rays, gamma-rays and cosmic-ray observations, based on all of the above-mentioned signals. I shall also present the prospects of the upcoming MeV photon telescope COSI to probe such signals from these DM models. I shall show that for both types of DM models new unconstrained DM parameter space can be probed at the upcoming instruments like COSI.

Speaker: Dr Arpan Kar (LPTHE, Sorbonne University, Paris)

AKar_POINT2026.pdf

34 Probing Galactic dark matter objects from the heating of exoplanetary systems

We explore the gravitational heating of exoplanetary systems by dark matter substructures of different kinds (primordial black holes -- PBHs, ultra-compact -- UCMHs, or classical subhalos). In this context, the scales of the dark objects probed are of the same order as the orbital radii of planets of interest. Distant exoplanets are quite sensitive to heating processes because less bound to their stars, and a typical signature of the presence of Galactic dark objects would be multi-planets systems with increasing inclination with increasing planetary distance to the stars, up to full ejection of the most distant ones. This allows us to set new upper bounds on the abundance of PBHs and UMCHs in the mass range $10-10^8$M$_\odot$, translating into bounds on the amplitude of the primordial power spectrum in the wavenumber range $10-1000$Mpc$^{-1}$.

Speaker: Théo Paré (LUPM)

PONT_2026_PARE_THEO.pdf

35 Hunting invisible particles with the RES-NOVA Observatory

Core-collapse Supernovae (SN) are critical astronomical events where nearly the entire star's binding energy is emitted as neutrinos. Thanks to their extreme conditions, SN are also incredible laboratories for testing new Physics and could produce a wealth of Beyond Standard Model Particles. RES-NOVA is pioneering a new approach to for the detection of SN neutrinos, introducing cryogenic detectors constructed from ultra-pure archaeological Pb. The experiment exploits Coherent Elastic Neutrino–Nucleus Scattering (CEvNS), a channel with a cross-section approximately 10^4 times larger than traditional detection modes (e.g. IBD or nu-e scattering).
Beyond SN neutrino detection, the technology is opening new opportunities in astroparticle physics: the combination of low-energy thresholds and advanced background suppression makes RES-NOVA a powerful platform for multi-messenger astronomy, dark matter searches, and the detection of axion-like particles from various sources.
In this contribution, we will report on the latest experimental progress, present results from the first detectors, and outline the near-term physics reach of RES-NOVA. This project, already underway, represents a decisive step toward establishing the next-generation neutrino and dark matter observatory.

Speaker: Nahuel Ferreiro Iachellini (University of Milano-Bicocca)

pont26.pdf

36 Observing Leptogenesis in Action with Gravitational Waves

Leptogenesis has become one of the leading theories to explain the baryon asymmetry of the universe. On the other hand the existence of non-zero but tiny neutrino masses has been established through neutrino oscillation experiments. The smallness of the neutrino masses can be understood by introducing heavy right-handed neutrinos. If such neutrinos were produced in the early universe and decayed out of equilibrium, they could generate a finite lepton asymmetry, which would subsequently be converted into the observed baryon asymmetry. However, experimental verification of this theory has remained elusive. We point out that the decay of right-handed neutrinos produces a background of gravitational waves. Detecting this background would provide direct evidence for leptogenesis and the existence of heavy right-handed neutrinos. At the end of the talk, I will discuss the prospects for detecting this gravitational wave background.

Speaker: Jan Schuette Engel (UC Berkeley)

JSE_talk.pdf

19:30 Public Science Conference

Wednesday 29 April

Gravitational Waves

Convener: Nicola TAMANINI (L2IT / CNRS)

37 Gravitational Waves from Ultra-light PBHs

Speaker: Dr Yann Gouttenoire

Gouttenoire_Avignon_2026.pdf

38 LVK cosmology results from GWTC-4

Speaker: Cezary Turski (Ghent University)

pont_presentation.pdf

39 Gravitational-Wave Lensing in the Wave-Optics Regime: Current Methods and Open Problems

Speaker: Giulia Cusin

PONT_Cusin.pdf

10:45 Coffee break

Gravitational Waves

Convener: Nicola TAMANINI (L2IT / CNRS)

40 Baryogenesis: new and old ideas

Speaker: Valerie Domcke (CERN)

baryogenesis_PONT.pdf

41 Latests Results from the Dark Energy Spectroscopic Instrument

Speaker: Alexie Leauthaud

5.alexie_DESI_Avignion_2026_2.pdf

12:25 Lunch break

Contributed talks

Convener: Diego Blas (ICREA/IFAE)

42 First measurement of the Hubble constant from gravitational wave-galaxy cross-correlations

I will present our recent work where we detected for the first time cross-correlations between gravitational wave sources and galaxies, at 5.9$\sigma$. We analysed the GWTC-3 and GLADE+ catalogs with a novel technique called Peak Sirens. We obtained the first measurement of the Hubble constant from this method, and the first bounds whatsoever on the gravitational wave clustering bias. This work opens a new window for analysing GW sources as tracers of the large scale structures.

Speaker: Isabela Santiago de Matos (University of Portsmouth)

pont_avignon_Isabela.pdf

43 Cosmology with the Angular Cross-Correlation of Galaxies and Gravitational Waves

We explore the tomographic angular cross-correlation between gravitational-wave and galaxy catalogs as a probe of late-time cosmology. Focusing on next-generation interferometers combined with the Euclid photometric survey, we forecast constraints on the Hubble constant, Matter density parameter and other cosmological parameters.

Our analysis accounts for realistic GW populations, observational uncertainties, and nuisance parameters. This method can constrain the Hubble constant to percent-level accuracy, even when marginalizing over biases and other cosmological parameters. Combining galaxy auto-correlation with GW–galaxy cross-correlation boosts sensitivity by up to a factor of $\sim10$ compared to either probe alone.

We also discuss the use of a spectroscopic redshift catalog, as well as the detectability of the clustering bias of gravitational--wave sources.

Speaker: Alessandro PEDROTTI

Presentation PONT.pdf

44 Multi-probe Cosmology with Standard Sirens: a GWxHI Cross-correlation Approach

Multi-probe techniques have proven to be powerful tools in modern cosmology.
By combining different observational tracers, they break degeneracies and provide new ways to gain insights into the large-scale structure (LSS) of the Universe and its evolution.

In this talk, we explore the potential of cross-correlation between gravitational waves (GWs) and 21cm intensity mapping from neutral hydrogen emission (HI), focusing on its role in view of future high-precision observatories, specifically Einstein Telescope (ET) and the Square Kilometer Array Observatory (SKA Observatory).

Assuming that GW and HI are different tracers of the same underlying dark matter density field, we run a tomographic full-likelihood MCMC pipeline and infer cosmological parameters from both the angular power spectrum (auto-correlation) and the angular cross-power spectrum (cross-correlation) of these probes.
We show that synergies between future GW and HI experiments will significantly improve standard-sirens measurements, thanks to increased sensitivity and high-redshift coverage, allowing us to constrain cosmological parameters to a level comparable to that of well-established alternative probes.

Speaker: Matteo Schulz

Schulz_PONT2026.pdf

45 A full, high-dimensional sampling scheme for gravitational-wave dark sirens: measuring galaxy weighting and ranking host candidates

The rapidly growing field of dark siren cosmology, driven by advances in Gravitational-Wave (GW) detection campaigns and galaxy surveys, is progressing toward independent and increasingly precise measurements of the Hubble constant. As statistical uncertainties shrink, it becomes crucial to control and eliminate emerging systematics in order to address cosmological and astrophysical challenges. An important one concerns the currently unknown probability that a compact binary merger occurs in a given host galaxy as a function of its physical properties (e.g. absolute luminosity) raised to some power, the galaxy weight.
In this work, we develop a population-based weighting scheme for host galaxies, in which the galaxy weight is treated as a population-level parameter and jointly inferred from the data within a high-dimensional space (>>100) that includes single-event, population, and cosmological parameters. We apply our framework to O5-like simulated GW events using the MICECATv2 mock galaxy catalog, and we also obtain results for real data using the single-event GW170817 together with the GLADE+ galaxy catalog.
On one hand, this approach enables a fully Bayesian ranking of the host candidates for GW events, allowing us to identify the most likely host galaxies and potentially reveal connections between their astrophysical properties and those of the hosted mergers. On the other hand, by exploiting Hamiltonian Monte Carlo algorithms, we can tackle the full hierarchical inference problem, exploring correlations across parameters at all levels, while avoiding sources of numerical systematics associated with multidimensional integrals in the total likelihood, which could soon become a limiting factor for current analysis pipelines.

Speaker: Alessandro AGAPITO (Aix-Marseille Université)

Agapito_PONT_2026.pdf

46 Resolving structure in the binary black hole mass distribution: implications for population-based cosmology

Gravitational-wave observations provide a unique window into both black hole populations and cosmology. Using the latest transient catalog, GWTC-4, we investigate the presence of structure in the primary black hole mass distribution through agnostic modelling and compare the results with parametric approaches. We show that the ability to resolve specific features in the mass spectrum plays a key role in constraining the Hubble constant. We further discuss the limitations of current analyses and propose a novel framework aimed at mitigating systematic biases in these measurements.

Speaker: Vasco GENNARI (L2IT)

PONT_Gennari.pdf

47 Spectral sirens cosmology from binary black holes populations with sharper mass features

Spectral-sirens inference enables the extraction of cosmological parameters from gravitational-wave data alone, without electromagnetic counterparts or galaxy catalogs. We introduce new parametric mass functions for the binary black hole population that capture significant structure across the mass spectrum and are moderately favoured by Bayesian evidence over simpler models. Analysing the latest gravitational-wave transient catalog, GWTC-4.0, we show that powerlaws-only population models constrain the Hubble constant to $23\%$ precision, $H_0 = 53.3^{+14.0}_{-10.8} ~\rm km \,s^{-1} \,Mpc^{-1}$ at $68\%$ confidence level. This represents a $\sim 50\%$ improvement over the corresponding binary black hole-only analysis by the LIGO-Virgo-KAGRA collaboration, achieving precision comparable to their joint analyses including neutron stars and galaxy catalogs. We further test alternative cosmological models, establishing competitive constraints on modified gravitational-wave propagation, while bounds on the dark energy equation-of-state parameters remain uninformative. Projecting to future O5 observing run, we forecast substantial improvements in $H_0$ and modified propagation parameters with larger datasets at higher redshifts. Our results highlight the strong interplay between the black hole mass distribution and inferred cosmology, underscoring the need for suitable population models to fully exploit gravitational-wave data.

Speaker: Tom BERTHEAS (L2IT, LPENS)

Bertheas_PONT2026.pdf

48 Gravitational Waves as a Probe of DESI-Motivated Modified Gravity: A Multi-Messenger Forecast

Recent DESI results, combined with other cosmological probes, have revived interest in dynamical dark energy, hinting at phantom crossing and a phantom regime at $z \gtrsim 1$. These observations have brought renewed attention to a class of modified gravity (MG) models consistent with current data but exhibiting rich phenomenology beyond $\Lambda$CDM. Several of these theories introduce a non-minimal coupling between a scalar field and gravity, which manifests in two distinct observational signatures: an alteration of the growth of large-scale structure, and a modification of the propagation of tensorial perturbations, inducing a friction term in the gravitational wave (GW) equation of motion, which in turn produces a systematic offset between GW and electromagnetic luminosity distances. This modified GW propagation offers a unique observable to discriminate among models otherwise degenerate at the background level.

We assess the capability of next-generation GW detectors to constrain these DESI-motivated MG models, comparing standard parametric approaches against a model-independent Gaussian Process (GP) reconstruction to evaluate how well each can distinguish viable MG theories from General Relativity.

To this end, we build a mock multi-messenger dataset of binary neutron star (BNS) mergers with $\gamma$-ray burst (GRB) counterparts detected by Fermi and Swift, and forecast the sensitivity of future GW networks to $d_L^{\rm GW}$ via a prior-informed Fisher matrix approach. Combined with CMB, SnIa, and BAO data to break parameter degeneracies, we show that this sample of $\sim$ 40 multi-messenger events is sufficient to deliver unprecedented constraints on the MG phenomenology motivated by DESI, providing a powerful complementary test of gravity in the late Universe.

Speaker: Andrea Cozzumbo (Gran Sasso Science Institute)

Cozzumbo_PONT2026.pdf

49 A universal scaling law for sourced inflationary gravitational waves and applications

We consider the gravitational wave (GW) background induced by arbitrary source fields that are amplified during inflation. We first conduct a very general analysis where the associated tensor spectral index $n_T$ is shown to be given, under minimal assumptions, by a simple and ready-to-use formula. Remarkably, we demonstrate that during slow-roll inflation $n_T$ becomes completely independent of the original spectrum of the source, exhibiting a universal near scale invariance. We then refine our study to the case of GWs induced by abelian gauge fields, covering the case of axion inflation. We analytically derive the amplitude of GWs and argue that they can overtake the standard inflationary GW background. We use this to constrain the values of gauge field couplings allowed by observations. This presentation is based on https://arxiv.org/abs/2510.00869 and https://arxiv.org/abs/2512.14670.

Speaker: Martin Teuscher

conference_avignon.pdf

50 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

PONT 2026 Alina Mierna.pdf

51 Unveiling the Central Engine of Core-collapse Supernovae in the Local Universe: Neutron Star or Black Hole?

Core-collapse supernovae (CC-SNe) mark the end of the life of massive stars, leaving behind a compact remnant. EM observations alone cannot resolve the astronomical conundrum of identifying the nature of CC-SNe remnant and central engine: neutron star (NS) or black hole (BH). This resolution may come through the radically new window of gravitational wave observation. Conventionally, the horizon distance of LIGO to CC-SNe is believed to be about a few Mpc. Here, a horizon distance of ~160Mpc is demonstrated for CC-SNe powered by rotating BHs, based on their ample energy reservoir described by the Kerr metric. Crucially, this shows these observation can break the degeneracy between NS and BH central engines by GW calorimetry, by a positive observation of one or a confident null detection of the other. Applied to the recent event SN2023ixf, at 6.7Mpc, by the confident null detection of a BH central engine, we identify it to be a NS, whereby the progenitor mass is below $20M_\odot$. [Based on Maurice H. P. M. van Putten, Maryam A. Abchouyeh, Massimo Della Valle, 2024 ApJL 972 L23].

Speaker: Maryam Aghaei Abchouyeh

PONT2026ـMAA.pdf

52 A model-independent cosmological test of GR using gravitational wave propagation

With an increasing number of detections, gravitational waves (GWs) from compact binary coalescences are now an established probe for tests of General Relativity (GR) on cosmological scales. A common test for deviations from GR with GWs involves constraining the ratio of luminosity distance from GWs and the standard electromagnetic (EM) luminosity distance. This usually relies on specific parametric ansatzes for this ratio, which greatly restrict the theory space one can access and can introduce bias. We present a new, model-independent method to simultaneously constrain the expansion rate of the universe and deviations from GR using dark sirens (GW events without an EM counterpart).

Speaker: Elena Colangeli (ICG - University of Portsmouth)

PONT2026.pdf

16:00 Coffee break

Contributed talks

Convener: Giulia Cusin

53 Dispersion induced friction in gravitational wave propagation

In general relativity, gravitational waves (GW) follow null geodesics, whereas in alternative theories of gravity they may propagate along timelike geodesics. Depending on the form of the dispersion relation, this can produce amplitude distortions in chirping signals. We demonstrate this effect for the case of massive gravitons, showing that dispersion modifies the amplitude of gravitational waves in a way which is complementary to standard tests that rely on phase distortions. Applying this dark siren test of gravity to selected events from the third observing run of LIGO–Virgo–KAGRA, we obtain constraints that are competitive with phase-based dispersion tests. Our formalism therefore complements existing phase analyses and paves the way for fully consistent tests of gravitational-wave dispersion using both phase and amplitude information.

Speaker: Dr Charles DALANG (Ecole Normale Supérieure)

54 Cosmology with strong gravitational lenses

When a massive foreground galaxy lies in front of another, more distant, background galaxy, strong gravitational lensing produces spectacular images such as Einstein rings. The detailed morphology of an Einstein ring depends not only on the gravitational field of the main deflector, but also on all the perturbations along the line of sight. As it turns out, both effects can be distinguished, so that Einstein rings may be considered “standardisable shapes”, from which the weak-lensing shear can be directly measured. In this talk, I will present a framework to include strong lensing in cosmological analyses. I will show that the associated signal is measurable with stage-IV galaxy surveys, with a very high signal-to-noise ratio, and I will present the very first forecasts on the measurements of cosmological parameters with this method.

Speaker: Pierre Fleury (CNRS, Laboratoire Univers et Particules de Montpellier)

2026-04-29 PONT version publique.pdf

55 Line of Sight Shear Cosmology - Verification with Hydrosimulated Strong Gravitational Lenses

Recent studies uncovered several aspects of strong gravitational lenses that make them useful tools for cosmology. One example is the weak-lensing shear induced by structures along the strong lens’s line of sight (LOS). This observable carries information about the mass distribution in the Universe and therefore represents a valuable cosmological probe.
While the theoretical feasibility of this method has been demonstrated, the practical observability and achievable precision remain largely to be assessed.
In this work, I investigate this question using realistic simulated lenses. Instead of relying solely on analytical mass models, I developed a pipeline to extract lens galaxies from state-of-the-art hydrodynamical simulations and generate mock lensed images, which are then analysed using current lens-modelling techniques. This approach allows us to test the impact of realistic mass distributions and modelling assumptions on the recovery of the LOS shear signal.
I will present the first results of this modelling effort and discuss how they inform the development of more flexible lens models capable of capturing the complexity of simulated galaxies.

Speaker: Giacomo QUEIROLO

Queirolo_PONT_pres.pdf

Queirolo_PONT_pres.pptx

56 Gravitational lensing beyond the eikonal approximation

Waves propagating through a gravitational potential exhibit wave-
optics effects when their wavelength is not significantly smaller than the lensing scales. We study the propagation of a scalar wave, governed by the Klein-Gordon equation in curved spacetime, to focus on effects on amplitude and phase, while leaving aside the issue of wave polarization which affects electromagnetic and gravitational waves.
Using the Newman-Penrose formalism, we obtain the first corrections beyond the geometric optics in the expansion in the inverse frequency. We check the analytic results by solving numerically the equations dictating the evolution of the corrections either in the vicinity of a Schwarzschild black hole or through a transparent star.

Speaker: Emma BRUYERE (IAP)

BruyerePONT2026.pdf

57 Light scalar fields on a curved background and their influence on the dynamics of galaxies.

We consider two extended theories of gravity involving non-minimally coupled scalar fields and investigate their influence on galactic scales. To do so, we linearise the equations of motion for the scalar fields, accounting for their dependence on curvature scalars. In this way, we recover known results and are able to extract the modifications over Einstein gravity due to the presence of the additional scalar field. We repeat this analysis for the case where the couplings to curvature terms are generated at the one-loop level, and these couplings are identified from a self-consistent calculation of the quantum effective action. We show in all cases that the non-minimal couplings to the Ricci scalar lead to shifts in the potential minimum of the scalar field, such that the modifications of gravity known to occur in scalar-tensor theories can arise ubiquitously in any extension of the SM with additional and sufficiently light scalar fields.

Speaker: Lukasz Bunio (University of Manchester)

PONT.pdf

PONT.pptx

58 Having Fun with Spherical Collapse: Halo Abundance in Decaying Dark Matter Models

Decaying dark matter (DDM) provides a well-motivated extension of $\Lambda$CDM, in which two-body decays -- characterized by a decay rate $\Gamma$ and velocity kick $v_k$ -- naturally suppress structure growth and lead to lower clustering amplitudes consistent with weak lensing measurements of $S_8$. Previous analyses combining Planck, BAO, and weak lensing data identified viable parameter space around $\Gamma^{-1} \sim 7$ Gyr and $v_k \sim 1250$ km/s. Extending these constraints with upcoming cluster abundance measurements from eROSITA, however, requires accurate theoretical predictions for the halo mass function in DDM cosmologies.

We show that the standard Press–Schechter formalism, even when supplied with the correct DDM linear power spectrum, systematically overpredicts the abundance of massive halos compared to DDM N-body simulations. This discrepancy arises from neglecting the distinct collapse physics of DDM, including the exponential decay of parent particles and mass loss from halos due to daughter particles receiving velocity kicks that exceed the escape velocity. We develop a spherical collapse framework that self-consistently incorporates these effects, yielding a mass-dependent critical density threshold $\delta_{\rm cr}(M)$ that increases for low-mass halos unable to retain kicked daughters. This leads to a suppression of low-mass halo abundances while recovering $\Lambda$CDM behavior at high masses. Comparing our theoretical predictions to simulations, we find that the DDM parameter space favored by Planck and weak lensing data produces substantially modified halo mass functions, indicating that eROSITA cluster counts should place significantly stronger constraints on decaying dark matter models.

Speaker: Thomas Montandon (Laboratoire Univers et Particules de Montpellier)

PONT2026-Montandon.pdf

59 Deciphering Coupled Scalar Dark Sectors through the lens of dynamical systems.

The dark sector represents the elusive nature of dark matter and dark energy. Possible sources of the dark sector have long been studied, and with recent data releases from the Dark Energy Spectroscopic Instrument (DESI), interest in scalar field sources for the dark sector has been revived. This talk presents recent work examining scalar fields sourcing the dark sector, with a focus on the effects of couplings in the kinetic and potential terms of the scalar fields’ Lagrangian. I will elaborate on the framework of dynamical systems that we use to analyse the effects of said couplings applied to two cases of interest involving coupled dark matter and dark energy scalar fields, as well as the case of a multi-field sourced dark energy.

Speaker: Saba Rahimy (Swansea University)

PONTpresi_saba_.pdf

19:00 Banquet

Thursday 30 April

Late Universe

Convener: Dr Vivian Poulin (LUPM, CNRS & U. de Montpellier, France)

60 Cosmic birefringence: a hint of new physics in cosmology and fundamental physics

Speaker: Patricia Diego Palazuelos (Max Planck Institute for Astrophysics)

PONT 2026 -- Patricia Diego.pdf

61 Status of SN Cosmology in the context of current cosmological tensions

Speaker: Mickaël RIGAULT (IP2I)

tensioncosmology_snia_and_ztf_PONT2026.pdf

62 Probing the Early Universe with JWST and Euclid

Speaker: Hakim ATEK (IAP)

Atek_PONT.pdf

10:45 Coffee break

Late Universe

Convener: Dr Vivian Poulin (LUPM, CNRS & U. de Montpellier, France)

63 Evolving Dark Energy and the Dark Energy Survey

Speaker: Marco Raveri

Presentation.pdf

64 Probing fundamental physics with spectroscopic probes of large-scale structure

Speaker: Azadeh MORADINEZHAD DIZGAH

Moradinezhad_Avignon_2026.pdf

12:25 Lunch break

Contributed talks

Convener: Alain BLANCHARD

65 Dark energy from string theory

Dark energy is currently being observed with unprecedented precision. Several cosmological models can for now fit this data. But only some of them can be obtained from string theory: this offers an interesting theoretical prior. We will review to what extent a cosmological constant or an exponential quintessence can be obtained from string theory. Eventually, we will focus on (string-motivated) quintessence coupled to (dark) matter, which has several interesting features: an effective phantom regime, with a possibly divergent e.o.s. parameter, and an Early Dark Energy behaviour.

Speaker: Dr David Andriot (LAPTh, CNRS)

Andriot.pdf

66 Interacting dark energy with dark matter entropy couplings

The persistent discrepancies between predictions of the standard cosmological model and high-precision measurements across multiple probes remain a significant challenge in modern cosmology. Over the past decade, mounting evidence for tensions in key cosmological parameters - derived through both model-dependent and independent methods - has motivated the exploration of extensions to the standard paradigm. Among the most compelling directions is the dark sector, whose fundamental nature remains largely unknown. In particular, the microphysical properties of dark matter are still poorly understood beyond its gravitational role. In this talk, I will introduce a new class of interactions between dark matter and dark energy, formulated within a relativistic fluid framework. In this scenario, dark matter carries non-trivial intrinsic entropy with scale-dependent fluctuations, encoding additional internal degrees of freedom. Coupling this entropy to a scalar-field dark energy component gives rise to distinctive signatures in the growth of cosmic structure, opening a novel window into dark sector physics and on new physics in the standard model as a way of reconciling the observed cosmological tensions.

Speaker: Elsa Teixeira (Laboratoire Univers et Particules de Montpellier, University of Montpellier)

Teixeira_PONT.pdf

67 INTERPRETABLE MACHINE LEARNING FOR DYNAMICAL DARK ENERGY MODELS

Recent cosmological observations suggest possible deviations from a cosmological constant, pointing toward a dynamical nature of dark energy. Quintessence models, which assume a slowly rolling scalar field, provide a compelling theoretical framework to explain this late time evolution in the dark energy equation of state. However, identifying the correct form of the quintessence potential remains a major challenge, due to both theoretical constraints and the vast landscape of functional possibilities. In my work, I explore the use of symbolic regression, an interpretable machine learning technique, to discover viable quintessence potentials directly from observational data. By searching over analytical expressions rather than fitting predefined forms, symbolic regression offers a data-driven approach to model selection that retains physical interpretability.

Speaker: Giulia Borghetto (University of Swansea)

PONT Interpretable Machine Learning for Dynamical Dark Energy Models.pdf

68 The expansion-rate fluctuation from Cosmicflows-4 compared to the standard model of cosmology

In the standard cosmological model, the expansion is expected to be statistically isotropic around any observer. Here, we test this prediction in the local Universe through an analysis of the expansion–rate fluctuation field reconstructed from the Cosmicflows-4 distance data.
We perform analyses up to redshift $z=0.1$ and examine not only the dipole, commonly associated with bulk flows in the standard model, but also the quadrupole component of the expansion field. This allows us to test predictions of the standard cosmological model directly, without assuming any of its ingredients in the definition of the observable being tested.
While the multipole amplitudes remain largely consistent with $\Lambda$CDM expectations, showing at most a marginal tension, the dipole and quadrupole exhibit a persistent coherence in both direction and polarity across redshift, a configuration with a probability $\lesssim 0.001\%$. This alignment hints at a possible violation of statistical isotropy, a cornerstone of the Cosmological Principle.

Speaker: Basheer KALBOUNEH

pont_conf_presentation.pdf

69 Inhomogeneity, anisotropy and axial symmetry with Szekeres cosmological models

In the current era of precision cosmology, the $\Lambda$CDM model, despite its stunning successes, appears insufficient to represent our actual Universe. Owing to the tensions occuring between theory and observations, it appears that a more precise representation of the local universe is mandatory. Since General Relativity (GR) is the best theory currently available to describe gravitation (verified up to some $10^{-15}$ precision in the weak and strong regimes), the new model should agree with its specifications. The Szekeres GR solution possesses all the nice properties allowing it to represent an inhomogeneous small scale universe becoming homogeneous (FLRW) at some large transition scale. Moreover, a number of observations, which will be described here, imply that the distribution of matter and its expansion are anisotropic roughly in the direction of the CMB dipole. Since the use of the general Szekeres model can seem tricky, due to its large degeneracy, its axially symmetric version might be more appealing. Therefore, taking advantage of both its compatibility with observations and its relative simplicity, we show how it can be used as a valuable cosmological model.

Speaker: Dr Marie-Noëlle Célérier (Observatoire de Paris-PSL)

axial Szekeres MN Celerier 2026.pdf

70 Covariant cosmography in the presence of local structures: comparing exact solutions and perturbation theory

Precision cosmology suggests that late-time inhomogeneities may no longer be treated as small corrections to the FLRW paradigm. Moreover, recent observational hints of axisymmetric anisotropies in the local expansion rate further motivate analyses beyond linear perturbation theory. Motivated by these issues, the framework called "Covariant Cosmography'' is adopted which describes the anisotropies in the local cosmic expansion rate within a fully relativistic framework and in a model-independent manner, free from a priori symmetry constraints on the underlying gravitational field and without resorting to linear perturbation theory approximations.

In this work, we address the intriguing evidence of an axisymmetric pattern in the angular anisotropies of the local cosmic expansion rate within the Covariant Cosmographic (CC) framework by considering the cosmological set-up of an off-center observer in a spherically symmetric Lemaître-Tolman-Bondi (LTB) spacetime. By estimating the amplitudes of the covariant cosmographic parameters—including the Hubble, deceleration, curvature, and jerk parameters, we compare it with the observed value. Moreover, we test luminosity-distance reconstructions with the CC parameters within this model. Finally, we compare the LTB relativistic distance for small inhomogeneities with the corresponding result derived from linear perturbation theory (LPT) in the standard cosmological model.

For moderate central contrasts ($\delta \leq 1$), LPT reproduces exact distances within $10\%$ for observers inside the structure. However, Covariant Cosmography (CC) extends this regime of validity up to $\delta \leq 2.5$. At larger radii, the situation reverses: for observers at three times the characteristic size, LPT remains accurate up to $\delta \leq 3$, while CC already exceeds $10\%$ error for $\delta \geq 1.5$. At sufficiently large distances from the structure, both methods converge to the exact solution.

This analysis is instrumental in interpreting expansion-rate anisotropies, facilitating investigations of the local Universe beyond the FLRW framework with a fully non-perturbative metric approach.

Speaker: Maharshi SARMA

Covariant Cosmography and Exact Solutions in GR (3).pdf

71 On the origin of dynamical dark energy in cosmographic parameters

A dynamical dark energy is derived from the scaling dimension two in UVIR-consistency between a bare cosmological constant with Big Bang cosmologies. The resulting Hubble expansion predicts the Hubble constant H0 to be $\sqrt{6/5}$ times the H0 in Planck-$\Lambda$CDM analysis of the CMB. Expressed equivalently in $w(a)$CDM, this new Hubble expansion predicts a phantom crossing at redshift $z=1.9$ coincident with the peak in the cosmic star-formation rate and galaxy mergers. [Based, in part, on van Putten, 2025, JHEAP Lett, 45, 195.]

Speaker: Maurice van putten (Sejong University)

Talk_Avignon.pdf

72 Measuring cosmic dipole with GRBs

We present a new analysis of cosmic dipole anisotropy using gamma-ray bursts (GRBs) as high-redshift standardizable candles. GRBs are ideal probes for testing the cosmological principle thanks to their high luminosity, wide redshift range, and nearly isotropic sky coverage. For the first time, we employ the luminosity-time (L-T) relation, corrected for redshift evolution, to standardize a sample of 176 long GRBs detected by Swift. We test for dipolar modulations using both the Dipole Fit Method and a new approach, the Anisotropic Residual Analysis Method. Both methods yield consistent results, with a statistically significant dipole signal, which will be discussed in the talk. We also show how, by incorporating a dipole term, residual correlations are eliminated, showing that the dipole model provides a better fit than standard isotropic ΛCDM.

Speaker: Jessica Santiago

PONT 2604 (2).pdf

73 CMB status and promises in mid 2026

CMB measurements keep progressing fast and contribute to cosmological advance in a major way. I propose to review the status of the field, making sure that contrary to many speakers, I fully cover the contributions and plans for SPO since I am part of it (NB: SPO = south Pole telescope+Bicep Keck). I will also review of course the status of ACT SO, and Litebird (which I am also part of). I plan to discuss the latest lensing results of Planck+SPT+ACT, as well as the tension of CMB + DESI, +Ho, +KIDS...

Speaker: Francois BOUCHET

2026.04 FRB@PONT-Avignon.pdf

16:40 Farewell coffee