Progress on Old and New Themes in cosmology (PONT) 2023

2 May 2023, 08:35 → 5 May 2023, 20:00 Europe/Paris

Chambre du Trésorier (Palais des papes, Avignon)

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

The 2023 edition, the sixth in the PONT series, focused 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)

pic_small.jpg

Tuesday 2 May

1 Intro

Speaker: Christian Marinoni (Centre de Physique Théorique, Marseille)

IntroPONT2023.pdf

Gravitational Waves

2 LVK review

Speaker: Rachel Gray

PONT_2023_v3.pdf

3 PTA Review

Speaker: Golam Mohiuddin Shaifullah

4 GW Beyond-LCDM

Speaker: Tessa Baker

PONT_Avignon_May23_v2.pdf

10:45 Coffee break

5 Magnifying the gravitational-wave Universe

Speaker: Jose Maria Ezquiaga Bravo

ezquiaga_gw_lensing_pont23.pdf

6 LISA cosmology

Speaker: Chiara Caprini (Universite de Geneve (CH))

Chiara_PONT_May_23.pdf

12:25 Lunch break

Gravitational Waves: Contributed Talks

7 Gwfast and the detection of high-redshift black-hole binaries at third generation GW detectors

The science cases of third generation (3G) ground-based gravitational-wave observatories are making significant advancements, both in Europe with the Einstein Telescope, and in the US with the Cosmic Explorer. In this context, a crucial task is to deliver robust predictions for their detection rates and parameter estimation capabilities. I will present gwfast, a novel, open-source Fisher matrix code for third-generation gravitational-wave detectors, focussing on its technical novelties and scalability. I will then discuss one of the key targets of 3G detectors, namely the population of black holes at redshifts beyond the star formation peak, which constitutes an unexplored territory given the limited knowledge of the population of compact objects. I will point out that the detection of high-redshift sources (which can cover almost all stellar mass black hole binary in the universe) does not necessarily coincide with the possibility of confidently locating them, as the measurement error increases with distance. This can have a large impact on cosmology and population studies and it is important to start considering this effect. I will present a new figure of merit, produced with gwfast, to determine the confidence of a source being in a region where stellar-origin black holes are not expected.

Speaker: Michele Mancarella (University of Milan-Bicocca)

MANCARELLA_PONT2023.pdf

8 Gravitational-wave cosmology with binary black holes as dark sirens in the 3G era

In this talk, we consider the problem of measuring the flat-LCDM parameters using binary black hole coalescences observed by third-generation (3G) gravitational-wave detectors like the Einstein Telescope and Cosmic Explorer. Using simulated dark sirens together with redshift information from a realistic simulated galaxy catalog, we adopt a Bayesian framework to jointly estimate the Hubble constant $H_0$ and the matter energy density parameter $\Omega_m$ in different scenarios. Assuming a galaxy catalog complete up to $z=1$ and using dark sirens detected with a network signal-to-noise ratio greater than 300, we show that a network made of ET and two CEs can constrain $H_0$ ($\Omega_m$) to a promising 0.7% (9.0%) at 90% CI in one year of full observation. We also explore the importance of single-host dark sirens and an optimistic scenario with a galaxy catalog complete up to $z=3$.

Speaker: Danny LAGHI

DL-PONT23.pdf

9 Measuring supermassive black hole properties from binary inspirals in LISA

The future spatial interferometer LISA will probably detect a few inspirals from binary black holes (BBH) located in the vicinity of a giant supermassive black hole (SMBH). The latter leaves its imprint on the waveform via several relativistic three-body effects. I will show that by including in the waveform Doppler terms up to quadratic order in the velocity of the center-of-mass of the BBH, one is able to accurately measure the mass of the SMBH. Our method provides for example a 30% determination of the SMBH mass if the BBH orbits it with a period of 100 years.

Speaker: Adrien KUNTZ (Scuola Normale Superiore, Pisa)

presentation_kuntz.pdf

10 Constraining cosmological parameters with massive black hole binaries

In ~2034 the Laser Interferometer Space Antenna (LISA) will detect the coalescence of massive black hole binaries (MBHBs) from $10^5$ to $10^7 \rm M_{\odot}$ up to z$\sim$20. The gravitational wave (GWs) signal is expected to be accompanied by a powerful electromagnetic (EM) counterpart, from radio to X-ray, generated by the gas accreting on the binary.
GWs are standard sirens (StSis) since they carry the direct information of the luminosity distance of the source. If an EM counterpart is present, the galaxy hosting the merger can be identified and the redshift can be determined with follow-up observations, opening the possibility to test the expansion rate of the Universe.
In this talk, I will present the recent LISA forecasts to constrain cosmological parameters with multimessenger observations of MBHBs. Assuming between $\sim$7-20 StSis, LISA will be able to constrain the Hubble constant at a few percent.
Moreover, since the population of StSis extends from z$\sim$2 up to z$\sim$8, LISA will be able to constrain also the high-redshift expansion of the Universe, measuring H(z) at different pivot redshifts and to test dark-energy models in a still uncharted territory, where few other cosmological probes are present.

Speaker: Alberto Mangiagli

mangiagli_PONT23.pdf

11 Modified gravitational-wave propagation with extreme mass-ratio inspirals

Extreme mass-ratio inspirals (EMRIs) are systems consisting of a massive black hole and a stellar-mass compact object. These systems are one of the gravitational-wave (GW) sources that will be detected by the Laser Interferometer Space Antenna (LISA). By using dark sirens with galaxy catalogs, EMRIs detected by LISA have the potential to place stringent constraints on cosmological parameters $(H_0, \Omega_m, w_0, w_a)$ within the framework of general relativity (GR). However, some modified gravity theories predict deviations from GR in the propagation of GWs at cosmological distances, which have a more dominant effect than the modification of the background evolution. Such modified GW propagation effects could be characterized by the phenomenological parameter $(\Xi_0, n)$. In this work, we explore the detectability of possible deviation from GR using different EMRI populations detected by LISA. We study the constraints on modified GW propagation effect and provide limits on cosmological parameters $(H_0, \Omega_m, \Xi_0, n)$.

Speaker: Chang Liu (L2IT / PKU)

Avignon.key

Avignon_pdf.pdf

12 Smoking guns of beyong-GR physics in binary mergers

Gravitational waves are among the ultimate tools to test fundamental
physics. The degeneracies between different effects are a serious obstacle, though, to fulfilling this goal since modified gravity often leads to smaller cumulative changes. In the present talk we will focus on some interesting new effects we can observe in the gravitational wave spectrum that differ qualitatively from the standard picture in general relativity. This includes jumps in the gravitational wave emission from merging black holes and inverse chirp signal of extreme mass-ratio inspirals. Such effects are valuable because they are a smoking gun of beyond-GR physics that can be easily traced in observations.

Speaker: Dr Daniela Doneva (University of Tuebingen)

Talk_Doneva.pdf

16:00 Coffee break

13 Gravitational wave production in higher derivative gravity

Gravity can be embedded into a renormalizable theory by means of adding quadratic in curvature terms. However, this at first leads to the presence of the Weyl ghost. It is possible to get rid of this ghost if the locality assumption is weakened and the propagator of the graviton is represented by an entire function of the d'Alembertian operator without new poles and zeros. Models of this type admit a cosmological solution describing the R^2 inflation. We study graviton production after inflation in this type of models and show that the perturbative gravitational wave production is negligible despite the presence of the higher derivative operators which could potentially cause instabilities.

Speaker: Anna Tokareva (Imperial College London)

Tokareva.pdf

14 The SGWB produced by MHD turbulence in the early universe

The stochastic gravitational wave background (SGWB) produced at the electroweak phase transition is expected to be peaking within LISA's sensitivity frequency range, being a promising test of high energy physics and beyond Standard Model extensions. The contribution of magnetohydrodynamic (MHD) turbulence to the cosmological SGWB is one of the least understood sources due to the necessity, in general, to perform large-scale numerical simulations solving MHD equations. In this talk, I will review recent numerical simulations that have addressed this issue and studied the potential detectability of the resulting SGWB and its polarization by space-based GW detectors like LISA. I will focus on magnetically dominated MHD turbulence and compare to astrophysical constraints that can provide a multi-messenger study of primordial magnetic fields. In particular, I will present the SGWB produced by decaying MHD turbulence, which has been validated by numerical simulations for a particular range of parameters. This model has been recently used to constrain the characteristics of a primordial magnetic field produced at the QCD phase transition with the common-spectrum process reported by the different pulsar timing array collaborations in the last few years.

Speaker: Dr Alberto Roper Pol (Universite de Geneve (CH))

avignon_may23.pdf

15 Real scalar phase transitions: bubble nucleation, nonperturbatively

In the Standard Model the electroweak phase transition is a crossover, but in many beyond the Standard Model theories the transition is of first order. Strong first order PTs could produce gravitational waves that might be detectable by the Laser Interferometer Space Antenna (LISA). Perturbation theory is commonly used to estimate the parameters that enter the calculation of gravitational wave spectra. However, perturbation theory is known to run into the infrared problem in the regime we are interested in and furthermore it is important to test the reliability of existing results. Here I will discuss our recent results where we studied a real singlet scalar model with a tree level potential barrier and performed nonperturbative simulations to determine the bubble nucleation rate. Our preliminary results show that higher orders in perturbation theory are necessary, and we expect our findings to allow calibration of the systematic uncertainty in perturbative results.

Speaker: Anna Kormu

PONT-Kormu.pdf

16 Reconstructing phase transitions from future LISA data

A gravitational wave background from a first order phase transition at the electroweak scale may be observable with future detectors such as LISA. While the Standard Model does not predict a first order phase transition, these occur in many BSM scenarios. Therefore, detecting a stochastic gravitational wave background could point to new physics, while a null detection could constrain or even exclude many BSM models. However, recovering the physical parameters of an underlying phase transition from a possible signal at LISA is not straightforward, partly due to other possible sources of a stochastic gravitational wave background, such as a population of white dwarf binaries. In this talk I will present our recent advances in reconstructing the phase transition parameters from mock LISA data using parameterised templates as an approximation to a more complete physical model, which greatly speeds up the process. I will also discuss how we hope to include more realistic noise sources like white dwarf binaries in our mock LISA data.

Speaker: Deanna Hooper

Hooper_pont23.pdf

17 Searching for anisotropic stochastic GW backgrounds with constellations of space-based interferometers

The anisotropies of the astrophysical stochastic gravitational-wave background (SGWB) encode an extraordinary amount of cosmological information, as they are a new unexplored tracer of the Large-Scale Structure. On the other hand, many recent studies have pointed out the difficulties of measuring these spatial fluctuations, even with a network of next-generation detectors, such as the Einstein Telescope and the Laser Interferometer Space Antenna (LISA). The two main obstacles are the shot noise and the poor angular resolution of GW instruments. The former issue is due to the discreteness of GW sources in space and time. Hence, the shot noise is intrinsic and can't be reduced or removed: the only way to alleviate its impact is to cross-correlate the SGWB with other tracers of the Large-Scale Structure. The second obstacle is the instrumental noise and, in particular, the poor localization power of GW detectors. Since a straightforward way to improve a network's angular sensitivity is to increase the distance among the detectors, a constellation of space-based instruments could be an ideal configuration to achieve the required angular resolution. After a brief introduction to SGWB anisotropies and their detection prospects, I will present the results of our recently published paper Capurri et al. 2023 ApJ 943 72, where we analyze the potential of two different detector constellations: the proposed Japanese mission DECi-hertz Interferometer Gravitational-wave Observatory (DECIGO) and a set of LISA-like detectors in heliocentric orbit. Specifically, we study the detection prospects for the SGWB anisotropies by focusing on auto- and cross-correlation signals.

Speaker: Giulia Capurri (SISSA)

capurri_pont2023.pdf

18 Searching for the Stochastic Gravitational-Wave Background with Ground-Based Detectors

As of today, the Advanced LIGO and Virgo gravitational-wave (GW) detectors have cataloged nearly 100 GW detections from various compact object mergers. These discoveries began the endeavors to search for other kinds of GW sources. Among these, the Stochastic Gravitational-Wave Background (SGWB), arising as the superposition of individually undetectable cosmological and/or astrophysical sources, is one of the potential sources to observe with the network of ground-based GW observatories in the coming years. A cosmologically produced SGWB would carry unique signatures from the earliest epochs in the evolution of the Universe. Likewise, an astrophysical background would provide information about the astrophysical sources that generated it. To a first approximation, the SGWB is assumed to be isotropic; one could determine its statistical properties by observing any part of the sky. However, these backgrounds can be anisotropic as well. Therefore, searches for both isotropic and anisotropic SGWB have been conducted. In this overview talk, I will explain the search methods and the results from the most up-to-date quests for the SGWB using the LIGO-Virgo-KAGRA third observing run. In addition, I will outline the new analysis and searches planned for the upcoming runs of these detectors and the exciting results expected from these probes.

Speaker: Jishnu Suresh (Université catholique de Louvain)

Jishnu_Pont23.pdf

Welcome Cocktail

Conférence Grand Public

Wednesday 3 May

Early Universe

19 Probing inflation: precision physics, exploratory physics, and formal aspects

Speaker: Sébastien Renaux-Petel (IAP - CNRS)

Renaux-Petel.pdf

20 EFT Constraints on Inflationary Scenarios

Speaker: Giovanni Cabass (Institute for Advanced Study)

talk_pont.pdf

21 CMB review

Speaker: Dr Matthieu TRISTRAM (CNRS)

tristram23 Future Science with the CMB.pdf

10:45 Coffee break

22 Cosmological tests of gravity

Speaker: Kazuya Koyama

koyama.pdf

Early Universe: Contributed talks

23 Resonant Features in Inflation Beyond Perturbation Theory

Inflationary perturbations are mostly Gaussian, with non-Gaussian features usually calculated using in-in perturbation theory. However, for unlikely fluctuations, non-Gaussianities can be important and the probability distribution is then better characterized in a semi-classical approximation, which takes into account classical non-linearities at the non-perturbative level.
I will apply this method to resonant inflationary models, where the inflaton potential features tiny oscillatory modulations. In the limit where these modulations are very small and for a given curvature-perturbation profile at late times, the probability distribution can be studied analytically using a saddle-point approximation. I will describe the peculiar non-perturbative features we uncover, such as the oscillations as a function of the late-times field value.

Speaker: Giovanni Tambalo

PONT_Resonant_BPT_Tambalo2.pdf

24 Robust constraints on the primordial power spectrum from mini halos and the CMB anisotropies

Although the CMB and galaxy surveys provide precise measurements of the primordial power spectrum at large scales, the small-scale power spectrum remains largely unconstrained. An enhancement in the small-scale primordial spectrum (such an spike) can lead to the formation of Ultra-Compact-Mini-Halos (UCMH) much earlier than standard halo can form. As a result, the DM annihilation signal receives a boost than can strongly impact the CMB power spectra. In this talk, I discuss how to carefully model the effect of s- and p-wave annihilations in UCMHs onto the CMB. I quantify the impact of late-time halo mergers using excursion set theory, and argue that the associated uncertainty in the boost of energy injection is limited for the CMB, but can have serious consequences for late time probes (i.e. for the 21-cm signal). Finally, I demonstrate that the derived CMB constraints on the amplitude of the small-scale spectrum are competitive with those coming from gamma-ray observations, even for p-wave processes.

Speaker: Guillermo Franco Abellán

PONT23_guillermo.pdf

12:30 Lunch Break

Early Universe: Contributed talks

25 The Cosmological Flow: a Systematic Approach to Primordial Correlators

Correlation functions of primordial density fluctuations provide an exciting probe of the physics governing the earliest moments of our Universe. However, the standard approach to compute them is technically challenging. Theoretical predictions are therefore available only in restricted classes of theories, which can completely bias the interpretation of data.

In this talk, I will present the cosmological flow: a complete method to systematically compute tree-level primordial correlators in any theory, bypassing the intricacies of Feynman diagram computations. This framework enables one to capture all effects—including e.g. the imprints of additional particles and breaking scale-invariance—for the reason that it relies on following the time evolution of these correlators from the initial quantum vacuum state to the end of inflation. I will then demonstrate the power of this approach by exposing new results in various classes of inflationary models that are difficult to track analytically, such as the strongly mixed regime of the cosmological collider—a robust probe of the field content of inflation—that requires a non-perturbative treatment of quadratic mixings.

Speaker: Denis Werth

TheCosmologicalFlow.pdf

26 Enabling Beyond-LCDM Non-Linear Matter Power Spectrum Emulation with COLA

In this talk I will outline a fast and accurate approach to introduce modified gravity (MG) consistently in Cosmological N-Body simulations, using the COLA (COmoving Lagrangian Acceleration) method, a fast and approximate method to generate non-linear realizations of the density field. The matter power spectrum computed from these simulations is shown to be in agreement with known results in the literature at all scales, i.e., from the largest scales, where relativistic effects dominate the signal, to the smallest scales, where screening is already active and shielding the fifth force introduced by the scalar field.

Speaker: Guilherme Brando de Oliveira

GB_Avignon.pdf

27 Dynamical Tunnelling-Induced Cosmological Bounce

I will present the results of arXiv:2301.02455 and arXiv:2301.08652 where it is shown that, for sufficiently low temperatures, a scalar field tunneling between two degenerate vacua on a flat FLRW background metric results in Null Energy Condition violation in the true vacuum state. The corresponding homogeneous fluid induces a cosmological bounce, after which it obtains a phantom-like equation of state and asymptotically induces De Sitter. The present mechanism is constructed without the need for exotic matter or modified gravity.

Speaker: Drew Backhouse

Drew Backhouse - PONT.pdf

28 Phase transitions in the early universe: a 2PI approach

Gravitational waves from phase transitions in the early universe pose one of our most promising probes of beyond the standard model physics. However, existing perturbative methods for false vacuum decay rate calculations are limited to weakly coupled theories. Recently, we have proposed a new, non-perturbative quasi-stationary effective action for false vacuum decay rate calculations based on the non-perturbative functional renormalization group, and in this talk I will discuss work to extend this quasi-stationary method to the language of the 2PI formalism. This work opens the door to non-perturbative decay rate calculations in strongly coupled BSM theories and new avenues for precision decay rate calculations in the standard model.

Speaker: Eleanor Hall

PONT.pdf

29 Modified gravity in two body problem: theoretical implications and observational constraints

General Theory of Relativity needs at least one modification - the Cosmological Constant. Yet there are possibilities for other modified theories of gravity to explain the accelerated expansion. In this talk I'm going to discuss the impact of Modified Gravity on the two-body problem. In particular, with the latest observational constraints from the galactic center, binary pulsars and the Milky and Andromeda dynamics.

Speaker: Dr David Benisty (University of Cambridge)

AvinionBenisty-1.pdf

30 Causality Constraints on Mergers beyond General Relativity

Gravitational waves emitted during a black-hole merger might differ from what General Relativity predicts due to the presence of yet unknown degrees of freedom coupled to gravity. A simple example is that of a scalar field that produces black hole hair, affecting both the inspiral and ringdown phases of black hole mergers.
We can constrain such scenarios from the point of view of fundamental principles: can black holes be altered by a scalar field in an Effective Field Theory (EFT) consistent with causality, unitarity and locality?
I will consider the requirement that the EFT produces no measurable time-advances in the propagation of scalar and graviton probes.
This forces the scalar-graviton interaction to be much weaker than what would be allowed by perturbative control, sharply narrowing the space of theories that describe testable deviations from General Relativity.

Speaker: Francesco Serra

serra-PONT-causality.pdf

16:00 Coffee break

31 Coupling metric-affine gravity to a Higgs-like scalar field

General relativity (GR) exists in different formulations. They are equivalent in pure gravity but generically lead to distinct predictions once matter is included. After a brief overview of various versions of GR, we focus on metric-affine gravity, which avoids any assumption about the vanishing of curvature, torsion, or nonmetricity. We use it to construct an action of a scalar field coupled nonminimally to gravity. It encompasses as special cases numerous previously studied models. Eliminating nonpropagating degrees of freedom, we derive an equivalent theory in the metric formulation of GR. Finally, we give a brief outlook of implications for Higgs inflation.

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

Presentation_coupling_metric_affine_scalar (2).pdf

32 Covariant Effective Action for Generalized Proca Theories

We check quantum stability of the generalized Proca theories in curved spacetime by computing the quantum gravitational corrections using Vilkovisky- Dewitt formalism. First we consider a range of the coupling constants to maximize the predictability of EFT. We find that there exists a regime where classical nonlinearity dominates while quantum corrections are still suppressed protecting EFT at scales where the Vainshtein mechanism screens the extra degrees of freedom.

References:

1. Aashish, Sandeep & Panda, Sukanta & Tinwala, Abbas & Vidyarthi, Archit. (2021). Covariant effective action for scalar tensor theories of gravity, Journal of Cosmology and Astroparticle Physics, 10 (2021) 006

2. Panda, Sukanta & Tinwala, Abbas & Vidyarthi, Archit. (2021). Covariant effective action for Generalized Proca Theories, Journal of Cosmology and Astroparticle Physics 01 (2022) 01, 062

Speaker: Dr Sukanta Panda (IISER Bhopal)

sukantapont.pdf

33 Ruling out Interacting Holographic Dark Energy with Hubble scale cutoff

Holographic dark energy with the Hubble radius as infrared cutoff is considered as a candidate to explain the late-time cosmic acceleration for 20 years and it can solve the coincidence problem. However, a nonzero equation of state is only possible if there is an interaction between dark energy and cold dark matter. In this talk I show that the resulting matter power spectrum and cosmic microwave background power spectra have a shape very far from the observed ones, thus ruling out any value for the free parameters and indicating that the assumed interacting holographic dark energy is not viable to explain the cosmic acceleration. Additionally, I will present preliminary new constraints on a general model of interacting dark energy with phenomenological interactions.

Speaker: Ricardo Landim (University of Portsmouth)

Seminar_PONT_2023.pdf

34 A cosmological model where the expansion is blind to the spatial curvature

I will present a new cosmological model in which the expansion is no longer affected by spatial curvature (i.e. Ω = 1, ∀ Ω_k), while the measure of distances still requires this curvature. The model originates from a modification of Einstein's equation in a which a term related to the topology of the Universe is added. First, I will present the main motivation for this modification, which is related to the existence of the non-relativistic limit for any topology. Then, I will present the model and discuss its consequences on the value of the spatial curvature inferred from observations, in particular with respect to the recent ``curvature tension''.

Speaker: Vigneron Quentin (Copernicus University of Toruń)

2023_05_PONT.pdf

35 Screening approach to address relativistic species as sources of cosmological perturbations

Assuming nonnegligible relativistic component densities alongside the cold dark matter of the ΛCDM model, we reformulate cosmological perturbations within the framework of the cosmic screening approach. The scheme addresses all spatial scales, provided that gravitational interactions may be studied in the weak field limit to a good approximation. As a novel feature of the formulation, delta-shaped sources responsible for the inhomogeneous gravitational field are now allowed to be relativistic so that neutrinos or warm dark matter may also be incorporated into the extended model. Analytical expressions obtained for the first-order scalar potentials reveal that, like in the case of purely nonrelativistic matter studied previously, gravitational interactions of this wider class of components are also characterized by the time-dependent screening length, associated with the exponential cutoff introduced at large distances. (arXiv:2206.13495 [gr-qc])

Speaker: Ezgi Yilmaz (CASUS)

36 Backreaction of cosmological perturbations

We investigate the backreaction of nonlinear perturbations on the global evolution of the Universe within the cosmic screening approach. To this end, we have considered the second-order scalar perturbations. An analytical study of these perturbations followed by a numerical evaluation shows that, first, the corresponding average values have a negligible backreaction effect on the Friedmann equations and, second, the second-order correction to the gravitational potential is much less than the first-order quantity. Consequently, the expansion of perturbations into orders of smallness in the cosmic screening approach is correct. [https://doi.org/10.1016/j.physletb.2023.137797]

Speaker: Prof. Alexander Zhuk (Astronomical Observatory Odessa National University (UA), Center for Advanced Systems Understanding (Germany))

Avignon conference talk short.pdf

Thursday 4 May

Late Universe

37 Status of the Hubble tension

Speaker: Dillon Brout (Harvard Smithsonian Center for Astrophysics)

BroutPONT.pdf

38 EFT of the Large Scale Structure

Speaker: Guido D'Amico (Universita degli Studi di Parma (IT))

Avignon_May23.pdf

39 Review on theoretical solutions to the H0 and S8 tensions

Speaker: Tristan Smith (Swarthmore College)

T_Smith_PONT_2023.key

10:45 Coffee break

40 The future of dark energy

Speaker: Eric Linder

LinderPONT.pdf

Late Universe: Contributed Talks

41 Cosmological tests of Einstein and Euler

The late-time modifications of the ΛCDM model can be parametrized by three functions describing the expansion history and gravitational effects on light and matter in the Large Scale Structure. I will discuss what we learned from the first joint Bayesian reconstruction of these three functions from recent cosmological observations, particularly, the implications for modified gravity theories and the well-known cosmological tensions. I will also address the challenge of distinguishing between a modification of gravity (i.e. a modified Einstein equation) from a dark sector interaction (i.e. a modified Euler equation).

Speaker: Prof. Levon Pogosian (Simon Fraser University)

Pogosian_PONT2023.pdf

42 ΛCDM is alive and well

The concordance model in cosmology, ΛCDM, performs extremely well in accounting for most current cosmological observations with high accuracy.
However, the model faces several tensions with recent cosmological data and their increased accuracy. The discrepancy between the values of the Hubble constant H0 obtained from direct distance scale measurements and the cosmic microwave background (CMB) is the most statistically significant, but the amplitude of the matter fluctuations is also considered a serious concern.
I will review the current situation. First, I will show that the combination of several recent measurements from local probes leads to a tight constraint on the current matter density ΩM as well as on the amplitude of matter fluctuations, both in good agreement with the values deduced from the CMB. Secondly, I will treat the Hubble tension by assuming that some determinations of the value of H0 are possibly biased and statistically compare these "ΛCDM+ H0 bias" models to alternative cosmological models. I find that the former can statistically outperform the extended models proposed so far.
Finally, I illustrate that the recent Pantheon+ results combined with the inferred SH0ES value lead to a value of the reduced cosmological density parameter, 𝜔𝑚 that conflicts with the inferred CMB value for the LCDM model. The situation does not really improve with the alternative models twisted to resolve the Hubble tension.

Speaker: Prof. Alain Blanchard (IRAP, UPS, Toulouse)

Pont2023AB.pdf

12:30 Lunch Break

Late Universe: Contributed talks

43 Exploring the effects of primordial non-Gaussianity at galactic scales

In this talk, I will show you my investigation of the effect of significant small-scale primordial non-Gaussianity on structure formation and the galaxy formation process. Specifically, we explored four different types of
non-Gaussianities: positive and negative skeweness and kurtosis. Generically, we find a distinct and potentially detectable feature in the matter power spectrum around the non-linear scale. The feature might have interesting consequences for the S8 tension. We then show in particular that a positively skewed distribution with fNL of the order of 1000 at these scales, implies that typical galaxy-sized halos reach half of their
present-day mass at an earlier stage and have a quieter merging history at z < 3 than in the Gaussian case. Their environment between 0.5 and 4 viri al radii at z = 0 is less dense than in the Gaussian case. This quieter history and less dense environment has potentially
interesting consequences in terms of the formation of bulges and bars. Moreover, we show that the two most massive subhalos around their host tend to display an interesting anti-correlation of velocities, indicative of kinematic coherence. All these hints will need to be
statistically confirmed in larger-box simulations with scale-dependent non-Gaussian initial conditions, followed by hydrodynamical zoom-in simulations to explore the detailed consequences of small-scale non-Gaussianities on galaxy formation.

Speaker: Clément Stahl

PNG23.pdf

44 Constraining cosmological models with the effective field theory of large-scale structures

In this talk, I will present the paradigm of the effective field theory of large-scale structures (EFTofLSS) and how it can be used to constrain cosmological models. First I will discuss the consistency of this theory and its predictive power, and then I will present the constraints of the EFTofLSS applied to BOSS and eBOSS data on the LCDM model as well as on some alternative models that allow to resolve the cosmological tensions.

Speaker: Théo Simon

PONT_Theo_SIMON.pdf

45 Constraining spatial curvature with large-scale structure

We analyse the clustering of matter on large scales in an extension of the concordance
model that allows for spatial curvature. We develop a consistent approach to curvature and wide- angle effects on the galaxy 2-point correlation function in redshift space. In particular we derive the Alcock-Paczynski distortion of fσ8, which differs significantly from empirical models in the literature.
A key innovation is the use of the ‘Clustering Ratio’, which probes clustering in a different way to redshift-space distortions, so that their combination delivers more powerful cosmological constraints. We use this combination to constrain cosmological parameters, without CMB information. In the end we show constraints when combining with CMB and BAO data sets.

Speaker: Mr Julien BEL (Centre de Physique Théorique)

PONT_2023_jbel.pdf

46 What it takes to solve the Hubble tension through modifications of cosmological recombination

We develop a formalism exploring the existence of a data-driven solution to the Hubble tension, considering perturbative modifications around a fiducial $\Lambda$CDM cosmology. Taking as proof-of-principle the case of a time-varying electron mass and fine structure constant, we demonstrate that a modified recombination can solve the Hubble tension and lower $S_8$ to match weak lensing measurements. Once baryonic acoustic oscillation and uncalibrated supernovae data are included, however, it is not possible to fully solve the tension with perturbative modifications to recombination.

Speaker: Nanoom Lee

NanoomLee-PONT.key

47 Tensions in Cosmological Probes and Quasar Cosmology

In the current era of precision cosmology, the emergence of crucial tensions in the determination of the universe expansion has led to a twofold need to determine a criterion for combining different probes in a physically meaningful way, and to extend the mapping of the expansion of the universe to include data at redshifts not currently covered. In this talk, I will present recent compatibility estimates of cosmological data and illustrate the possibility of using Quasar as cosmological probes, which can extend the Hubble diagram of SNe to a higher redshift range (𝑧 = 2.4 - 7.5) in which the predictions of cosmological models can be distinguished. The LCDM model and some of its extensions and tensions are tested and possible incompatibility between BAO, SNe and QSO data are explored.

Speaker: Dr Micol Benetti (Istituto Nazionale di Fisica Nucleare, Scuola Superiore Meridionale)

Benetti_PONT23.pdf

48 Multipole Expansion of the Local Expansion Rate

The lack of convergence to a consensus value for the Hubble constant has triggered a search for the reliability of non-standard cosmological line elements. The question is whether metrics with a lower degree of symmetry than FRW, while remaining simple, provide a reliable description of the data in the local part of the universe where the global uniformity is violated. We address this problem by determining the multipole structure of the redshift-distance relation in the local universe. Unexpected symmetries appear, whether the spherical harmonic analysis of the local expansion rate field is performed on galaxy or SNIa samples. Implications for the determination of the $H_0$ parameter will be discussed and a proposal for a non-standard metric that accurately describes the local data will be suggested.

Speaker: Basheer KALBOUNEH

anisotropy of expansion rate2.pdf

16:00 Coffee break

49 Constraining non-standard neutrino interactions with cosmology

Neutrinos are ubiquitous in cosmology and play a significant rule throughout the history of the Universe. As a result, cosmological observations offer a unique opportunity to test the properties of neutrinos. Standard model neutrinos are expected to freestream ever since they decouple from the primordial plasma in the early Universe. There are however multiple feasible particle physics scenarios in which neutrinos can interact efficiently at (much) later times. In this talk, I explore these scenarios and discuss how they can be constrained using CMB and LSS observables. I demonstrate that there is a redshift window in which neutrinos cannot interact significantly given the Planck CMB data. Finally, I discuss how the constraints can improve with future CMB Stage-IV and galaxy clustering data.

Speaker: Petter Taule (IPhT, Saclay)

Taule.pdf

50 Antisymmetric galaxy cross-correlations

Galaxies are biased tracers of the underlying dark matter density field. If we work with a single tracer, its two-point function will be symmetric under exchange of the pair of galaxies under consideration. But if we look at two different tracers, then in principle their cross-correlation could be not symmetric (Dai et al. 2016). This locally antisymmetric signal arises naturally when the two tracers have different bias parameters, and it could provide additional information with respect to the standard power-spectrum, both on the clustering and on initial conditions. I will present the basic formalism, then build on it to add redshift space distortions and primordial non-Gaussianity. Finally, I present a way to build an estimator for this signal and to get an estimate of the signal-to-noise.

Speaker: Eleonora Vanzan (Università degli Studi di Padova)

Slides_antisymmetric.pdf

51 Measuring weak lensing with strong lensing: a proof of concept

Line-of-sight (LOS) effects in strong lensing -- weak distortions to an image induced by the presence of objects such as dark matter haloes along the LOS -- have long been considered a nuisance when it comes to analysing strong lensing images. However, it was recently proposed that LOS shear could become a cosmological observable in its own right, if it could be accurately obtained from a given image. In this talk, I show how, using a new formalism, the LOS shear can indeed be measured with percent level accuracy from simulated strong lensing images, paving the way for its use as a new cosmological probe. Based on 2210.07210.

Speaker: Dr Natalie Hogg (IPhT CEA-Saclay)

natalie_hogg_WL_with_SL_PONT.pdf

52 Mysteries under a strong lens

Extracting cosmological information from observables is a daunting task. In particular, the peculiar velocity of the observer affects a large set of observables, including redshift, time intervals and angles. In the first part of my talk, I will briefly discuss two important tensions that appeared between early and late Universe probes, which are the Hubble tension and the cosmic dipole tension, the latter of which can be translated into an observer’s peculiar velocity tension. In the second part, I will describe the effect of peculiar velocities on the determination of the Hubble constant from strongly lensed quasars, which is somewhat at the interplay of both stories.

Speaker: Charles Dalang (Queen Mary University of London)

Mysteries under a strong lens.pdf

53 Gravitational lensing induced by matter currents

In this talk I will present the effects of gravitational lensing induced by the motion of massive objects. This is a relativistic effect and is much weaker than the deflection of light by density inhomogeneities. I will first discuss the effects of gravitational lensing by density perturbations and then generalise this to other possible inhomogeneities that may exist in our Universe, vector and tensor perturbations. Then I discuss the case of an isolated moving lens, a specific form of vector perturbation. I show that while subdominant to the density term future surveys will be able to measure this effect by cross-correlating the lensing convergence field with a reconstructed cosmic-momentum field. I present details of this reconstruction from galaxy redshift surveys and from the kinetic Sunyaev-Zel’dovich effect. I conclude by presenting forecasts for the next generation of cosmological survey.

Speaker: Dr Calum Murray (APC, University Paris Cité)

MovingLenses_CMurray.pdf

54 Relativistic matter bispectrum of cosmic structures on the light cone

Upcoming surveys of cosmic structures will probe scales ranging from the nonlinear regime to scales close to the cosmological horizon. This opens up the possibility of probing the LCDM model, as well as early universe scenarios, with non-Gaussianity. Modeling the galaxy bispectrum is challenging, as it involves general relativity, radiation, and large nonlinearities. In this talk, I will present a numerical modeling of the matter bispectrum on the light cone including relativistic and radiation effects. This is a crucial step towards modeling the observable bispectra, i.e. the weak lensing bispectrum and the galaxy bispectrum.

Speaker: Thomas Montandon (University of Vienna)

montandon_avignon.pdf

Conference Cocktail & Dinner

Friday 5 May

Astrophysical messengers of fundamental physics

55 Selected aspects of the particle vs wave nature of dark matter

Speaker: Sebastian Hoof (Università degli Studi di Padova)

2023_pont_avignon_hoof.pdf

56 Probing light particles with stars

Speaker: Andrea Caputo (CERN)

PONT_Caputo.pdf

57 Dark matter in extreme astrophysical environments

Speaker: Dr Djuna Croon (IPPP Durham)

PONT23.pdf

10:45 Coffee break

58 Probing dark matter with line intensity mapping

Speaker: Alvise Raccanelli (Universita e INFN, Padova (IT))

PONT Avignon.key

59 Gamma and X-ray searches for dark matter

Speaker: Nicholas Llewellyn Rodd (CERN)

IndirectDetectionatHighEnergies.pdf

12:25 Lunch Break

Astrophysical messengers of fundamental physics

60 Dark matter - baryon interactions in the Milky Way

Speaker: Prof. Kimberly Boddy (University of Texas at Austin)

Boddy-Avignon.pdf

Astrophysical messengers of fundamental physics: Contributed talks

61 First neutrino telescope dedicated search for DM induced neutrino lines

Dark Matter particles in the Galactic Center and halo can annihilate or decay into a pair of neutrinos producing a monochromatic flux of neutrinos. The spectral feature of this signal is unique and it is not expected from any astrophysical production mechanism. Its observation would constitute a dark matter smoking gun signal. We performed the first dedicated search with a neutrino telescope for such signal, by looking at both the angular and energy information of the neutrino events. To this end, a total of five years of IceCube's DeepCore data has been used to test dark matter masses ranging from 10~GeV to 40~TeV. No significant neutrino excess was found and upper limits on the annihilation cross section, as well as lower limits on the dark matter lifetime, were set. The limits reached are of the order of $10^{−24}$ cm$^3$/s for an annihilation and up to $10^{27}$ seconds for decaying Dark Matter. Using the same data sample we also derive limits for dark matter annihilation or decay into a pair of Standard Model charged particles.

Speaker: Thomas Hambye (ULB)

NulinesAvignon2023.pdf

62 CR antinuclei predictions and their detectability in the next years

The creation of anti-nuclei in the Galaxy has been has been discussed as a possible signal of exotic production mechanisms such as primordial black hole evaporation or dark matter decay/annihilation, in addition to the conventional production from cosmic-ray (CR) interactions. Tentative observations of CR antihelium by the AMS-02 collaboration have re-energized the quest to use antinuclei to search for physics beyond the standard model.
In this talk, we show state-of-art predictions of the antinuclei spectrum from both astrophysical and standard dark matter annihilation models obtained from combined fits to high-precision antiproton data as well as CR nuclei measurements (specially B, Be, Li). Astrophysical sources are capable of producing $\mathcal{O}(1)$ antideuteron event and $\mathcal{O}(0.1)$ antihelium events over 15~years of AMS-02 observations. Standard dark matter models could potentially produce $\mathcal{O}(1)$ antihelium event, while the production of a larger antihelium flux would require more novel dark matter model building. We also discuss that annihilation/decay of a QCD-like dark sector could potentially explain the AMS-02 preliminary observations of antihelium-3 and antihelium-4.

Speaker: Pedro De la Torre Luque

PONT_DelaTorreLuque.pdf

63 Probing Axions through Tomography of Anisotropic Cosmic Birefringence

Cosmic birefringence is the in-vacuo rotation of the linear polarization plane experienced by photons of the Cosmic Microwave Background (CMB) radiation when theoretically well-motivated parity-violating extensions of Maxwell electromagnetism are considered. If the angle parametrizing such a rotation is dependent on the photon's direction, then this phenomenon is called Anisotropic Cosmic Birefringence (ACB). We have performed for the first time a tomographic treatment of the ACB, by considering photons emitted both at the recombination and reionization epoch. This allows one to extract additional and complementary information about the physical source of cosmic birefringence with respect to the isotropic case. We have focused on the case of an axion-like field $\chi$, whose coupling with the electromagnetic sector induces such a phenomenon, by using an analytical and numerical approach (which involves a modification of the $\texttt{CLASS}$ code). We have found that the anisotropic component of cosmic birefringence exhibits a peculiar behavior: an increase of the axion mass implies an enhancement of the anisotropic amplitude, allowing to probe a wider range of masses with respect to the purely isotropic case. Moreover, we have shown that at large angular scales, the interplay between the reionization and recombination contributions to ACB is sensitive to the axion mass, so that at sufficiently low multipoles, for sufficiently light masses, the reionization contribution overtakes the recombination one, making the tomographic approach to cosmic birefringence a promising tool for investigating the properties of this axion-like field.

Speaker: Alessandro Greco

Tomography_of_ACB.pdf

Tomography_of_ACB.pptx

64 Quasi-extremal primordial black holes are a viable dark matter candidate

Whether primordial black holes (PBHs) can be the totality of the dark matter has always been a contentious issue. On the one hand they represent one of the best motivated candidates to make up for this dark component, but on the other hand a plethora of constraints significantly limit their abundance over a very wide mass range. Some of the most stringent examples come from cosmological and astrophysical bounds limiting the amount of Hawking evaporation that the PBHs can emit. In this talk I will discuss how under the assumption of quasi-extremality, which can be reached by assuming that the PBHs have e.g., a strong (dark) charge, these constraints can be completely erased, thereby reopening the parameter space for very light PBHs to be the dark matter. The results obtained, although relying on a simplified model, are rather general, conservative and should be taken as a proof of principle for future, more model-specific analyses.

Speaker: Matteo Lucca (ULB)

Lucca_PBHs_DM.pdf

65 Did black holes in the very early universe induced the formation of the first Pop III stars?

I will review the evidences in the local universe for star formation caused by jets from accreting black holes (BHs). These BH “positive feedbacks” take place by the interaction of BH-jets with high-density molecular clouds (Dasyra et al. 2022). Because the global gas density in the universe evolves with redshift z as (1+z)^3, it is expected that this star formation mechanism is very important in the early universe, where massive BHs come first and grow faster than stellar populations (e.g.Neeleman et al. 2021).
Recently, has been shown that the SMBHs of 10^9 M⊙ observed in quasars up to z = 7 can result from rapidly growing BH seeds of intermediate masses (IMBHs) of 10^(3-5) M⊙, formed by direct collapse of turbulent cold flows of gas in dark matter haloes at z > 25 (Latif et al. 2022). Growing from z = 30 at Eddington limit with a radiative efficiency of 10%, these IMBH seeds can reach masses of 10^9 M⊙ at z = 7. At z = 30 the global gas density is > 10^4 times the global gas density in the local universe, and under those conditions relativistic jets from those rapidly growing IMBHs would compress the gas triggering the formation of the first massive stars of Pop III.
References:
Dasyra, K. M. et al. 2022, Nature Astronomy 6, 1077-1084
Latif, M.A. et al. 2022, Nature 607, 48–51
Neeleman, M. et al. 2021 ApJ 911, 141

Speaker: Dr Felix Mirabel (CEA-France & IAFE-Argentina)

MIRABEL @ AVUGNON (05.05.2023).pdf

16:10 Coffee break

66 Black Holes as Probes for Ultralight Dark Matter

We consider the phenomenological nightmare scenario where dark matter is only coupled gravitationally, thinking of black holes as probes. We choose to focus on wave dark matter because an oscillating massive scalar endows a black hole with hair, whose profile we study.
We examine some assumptions implicit in the existing literature, and we do so by taking a fully analytic approach. We describe the field profile for a wide range of parameters, including rotating dark matter.
We then include the self-gravity of the scalar, focusing on the case
where dark matter forms a soliton in the center of the galaxy. We discuss the consequences of imposing causal boundary conditions at the horizon, which are usually neglected.

Speaker: Bruno Bucciotti (Scuola Normale Superiore di Pisa)

PONT_bucciotti.pdf

67 Ultra-Light Dark Matter: Current Constraints and Future Possibilities

‘Ultra-Light’ or ‘Fuzzy’ dark matter (ULDM) has been generating interest over recent years as a plausible alternative to weakly interacting CDM. Indeed, the lack of evidence for CDM candidates in direct-detection experiments motivates the exploration of novel dark matter models. Ultra-light scalar fields present a particularly attractive possibility due to their wave-like properties on astrophysically relevant scales. In particular, this wave behaviour has the ability to suppress structure growth on sub-galactic scales while retaining the same predictions for large-scale structure as CDM. It has been suggested that this may offer a natural solution to the so-called ‘small-scale crisis’ of CDM. In this talk I will discuss the theoretical motivations for the ULDM model, the computational tools used to simulate its dynamics, and I will summarise the diversity of halo characteristics obtained through simulations. I will also briefly touch on possible modifications to the ‘vanilla’ ULDM model which may help to alleviate current constraints.

Speaker: Emily Kendall (The University of Auckland)

PONT2023_EK.pdf

68 Exploring the Role of Self-Interacting Scalar Dark Matter in Dynamical Friction and GW Emission

We present a comprehensive study of the dynamics of self-interacting scalar dark matter around a black hole, focusing on the dynamical friction and the impact of such a force on gravitational wave emission.
Specifically, we explore the large scalar mass limit with quartic self-interactions in both subsonic and supersonic regimes. Our analysis reveals that the scalar field behaves as a perfect gas with an adiabatic index $\gamma_{\rm ad}$=2 at large radii. However, close to the Schwarzschild radius, the accretion rate is dominated by the relativistic regime. To obtain analytical results, we rely on large-radius expansions that are also linked to small-scale relativistic accretion rates.
In the subsonic regime, we find that the accretion rate for self-interacting scalar dark matter is greater than for collisionless particles, by a factor $c/c_{\rm s}≫1$, but smaller than for a perfect gas, by a factor $c_{\rm s}/c≪1$, where $c_{\rm s}$ is the speed of sound. Moreover, we show that the dynamical friction is smaller than for a perfect gas by $c_{\rm s}/c≪1$. In the supersonic regime, a Chandrasekhar term appears naturally as a correction to the friction force.
Our investigation has revealed that both of these terms induce a phase shift in gravitational wave emission, of -4PN and -5.5PN respectively. The upcoming gravitational wave detectors may provide constraints on the model, emphasizing the importance of accurately accounting for environmental effects in future studies.

Speaker: Alexis Boudon

PONTAvignon_AlexisBoudon.pdf

69 Strong electroweak phase transition and simplified dark matter models

Beyond the Standard Model physics is required to explain both dark matter and the baryon asymmetry of the universe, the latter possibly generated during a strong first-order electroweak phase transition. While many proposed models tackle these problems independently, it is interesting to inquire whether the same model can explain both. We focus on a dark matter model featuring an inert Majorana fermion that is coupled to Standard Model leptons via a scalar mediator. The latter interacts directly with the Higgs boson. We link state-of-the-art perturbative assessments of the phase transition thermodynamics with the extraction of the dark matter energy density. We discern regions of the model parameter space that reproduce the observed dark matter energy density and allow for a first-order phase transition, while evading the most stringent collider constraints.

Speaker: Philipp Schicho (Goethe University Frankfurt)

pont.23.schicho.pdf

70 Solitons and halos for self-interacting scalar dark matter

We study the formation and evolution of solitons supported by repulsive self-interactions inside extended halos, for scalar-field dark matter scenarios. We focus on the semiclassical regime where the quantum pressure is typically much smaller than the self-interactions. We present numerical simulations, with initial condtions where the halo is described by the WKB approximation for its eigenfunction coefficients. We find that when the size of the system is of the order of the Jeans length associated with the self-interactions, a central soliton quickly forms and makes about 50% of the total mass. However, if the halo is ten times greater than the Jeans length, a soliton only forms in cuspy halo where the central density is large enough to trigger the self-interactions. There is no preferred soliton mass, which suggests cosmological halos would show a large scatter for their soliton mass, depending on their assembly history.

Speaker: Raquel Galazo

ppt - PONT.pdf

71 Exploring the Dark Sector (non-abelian DM-DR interaction)

In this work we derive constraints on interacting dark matter-dark radiation models from a full-shape analysis of BOSS-DR12 galaxy clustering data, combined with Planck legacy cosmic microwave background (CMB) and baryon acoustic oscillation (BAO) measurements. We consider a set of models parameterized within the effective theory of structure formation (ETHOS), quantifying the lifting of the S8 tension in view of KiDS weak-lensing results. The most favorable scenarios point to a fraction f ∼ 10 − 100% of interacting dark matter as well as a dark radiation temperature that is smaller by a factor ξ ∼ 0.1 − 0.15 compared to the CMB, leading to a reduction of the tension to the ∼ 1σ level. The temperature dependence of the interaction rate favored by relaxing the S8 tension is realized for a weakly coupled unbroken non-Abelian SU (N ) gauge interaction in the dark sector. To map our results onto this SU (N ) model, we compute higher-order corrections due to Debye screening.We find a lower bound for the fine-structure constant for relaxing the S8 tension, consistent with upper bounds from galaxy ellipticities and compatible with self-interactions relevant for small-scale structure formation.

Speaker: Asmaa Mazoun

DM-DR_interaction_Pont_Asmaa.pdf