# Progress on Old and New Themes in cosmology (PONT) 2020

Europe/Paris
Chambre du Trésorier (Palais des Papes, Avignon)

### Chambre du Trésorier

#### Palais des Papes, Avignon

Description

NEWS [28.9.2020]: The conference is confirmed for 7-11 December 2020 in person in Avignon (unless further changes). A web broadcasting will however also be put in place.
An email message is sent to all registered participants today.

NEWS [17.3.2020]: Because of the COVID-19 outbreak and in compliance with public health policies, the conference is moved to 7-11 December 2020.
An email message is sent to all registered participants today.

The conference will address 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 will be a limited number of review talks by leading experts in each field and selected contributed talks, fostering thorough debates. Some time will be allocated to discussion sessions.

Organizers:
Philippe Brax (CEA IPhT Saclay)
Chiara Caprini (CNRS APC Paris)
Marco Cirelli (CNRS LPTHE Jussieu Paris)
Christian Marinoni (CPT Marseille)

Registration
Registration Form
Participants
• Alberto Roper Pol
• Alexander Bonilla Rivera
• Alexander Dolgov
• Alexey Grobov
• Altaiqizi Marzhan
• Angelo Raffaele Fazio
• Anish Ghoshal
• Bivudutta Mishra
• Carlo Contaldi
• Chiara Caprini
• Christian Marinoni
• Christof Wetterich
• Clement STAHL
• Cristina Benso
• Dario Bettoni
• David Andriot
• Deanna Hooper
• Diego Blas Temino
• Dionysis Karagiannis
• Dominik Schwarz
• Drazen Glavan
• Elena Arbuzova
• Elena Pinetti
• Eleonora Di Valentino
• Federico Piazza
• Felix Mirabel
• Gabriel Moreau
• Goran Jarlskog
• Goran Jelic-Cizmek
• Guillermo Franco Abellán
• Harry Desmond
• Herwig Dejonghe
• Ilia Musco
• Itziar Aldecoa Tamayo
• Jacopo Ghiglieri
• Jan-Albert Viljoen
• Jean-Loic Kneur
• Johannes Herms
• Jose Beltran Jimenez
• Jose Ramon Espinosa
• José Matias-Lopes
• Juho Lankinen
• Julien Bel
• Julien Lavalle
• Justin Feng
• Kemal Gultekin
• Kenza ZEGHARI
• Laurent Chevalier
• Leong Khim Wong
• Levon Pogosian
• Ludovic Montier
• Man Ho Chan
• Marco Cirelli
• Marco Drewes
• Mariam Rashid
• MATTEO LUCCA
• Michele Frigerio
• Micol Benetti
• Miguel Zumalacarregui
• Mikhail Barabanov
• Mohamed Amine Ouahid
• Mohamed Rameez
• Nick Kaiser
• Nicola Tamanini
• Ningqiang Song
• Noemi Frusciante
• Nora NICOLAS
• Oleg Kaikov
• Oleg Lebedev
• Olivier Rousselle
• Patrick Valageas
• philippe brax
• Pierre Astier
• Pierre TAXIL
• Pierre Vanhove
• Ricardo Landim
• Riccardo Murgia
• Robert Brandenberger
• Rodrigo Calderon
• Roger Mayala
• Romain Codur
• Roy Maartens
• Sachiko Kuroyanagi
• Saurya Das
• Saurya Das
• Sebastian Garcia-Saenz
• Silvia Galli
• Simone Biondini
• Sreemanti Chakraborti
• Sébastien Clesse
• THOMAS HAMBYE
• Tien-Tien Yu
• Tokareva Anna
• Tristan Smith
• Valeri Vardanyan
• Yun-Long Zhang
• Øyvind Christiansen
Contact the organizers
• Monday, 7 December
• 09:00 12:30
Invited talks: Observational Cosmology
• 09:00
TBA 30m
Speaker: Nick Kaiser
• 09:40
TBA 30m
Speaker: Pierre Astier
• 10:20
Coffee break 20m
• 10:40
TBA 30m
Speaker: Ludovic Montier
• 11:20
TBA 30m
Speaker: Roy Maartens
• 12:00
TBA 25m
Speaker: Eleonora Di Valentino (Institut d'Astrophysique de Paris)
• 12:30 14:30
Lunch break 2h
• 14:30 15:40
Invited talks: Observational Cosmology
• 14:30
TBA 30m
• 15:10
TBA 25m
Speaker: Silvia Galli
• 15:40 18:00
Contributed talks
• 15:40
Forecast on lepton asymmetry from future CMB experiments 20m

We consider a cosmological lepton asymmetry in the form of neutrinos and impose new expected sensitivities on such asymmetry through the degeneracy parameter ($\xi_\nu$) by using some future CMB experiment configurations, such as CORE and CMB-S4. Taking the default scenario with three neutrino states, we find $\xi_\nu =0.05±0.10(±0.04)$⁠, from CORE (CMB-S4) at 95 per cent CL, respectively. Also, within this scenario, we evaluate the neutrino mass scale, obtaining that the normal hierarchy mass scheme is privileged. Our results are an update concerning on the cosmological lepton asymmetry and the neutrino mass scale within this context, from which can bring a perspective on the null hypothesis for $\xi_\nu$ (and its effects on $\Delta N_{eff}$), where perhaps, $\xi_\nu$ may take a non-null value up to 95 per cent CL from future experiments such as CMB-S4. Sensitivity results for CMB-S4 obtained here not including all expected systematic errors.

Speaker: Mr Alexander Bonilla Rivera (UFJF)
• 16:00
Cosmology from low radio frequencies with LoTSS 20m

The LOFAR Two-metre Sky Survey (LoTSS) will be the worlds largest catalogue of radio sources at low radio frequencies for the next decades. It will also have photo-z information from the cross-matching with optical and infrared surveys for most radio sources. This allows us to address cosmological questions via a new frequency window to the Universe, among them the cosmic radio dipole and the measurement of angular correlation function for shells at different redshifts. Siewert et al. have demonstrated that already the products of the LoTSS-DR1 catalogue are consistent with the Planck 2018 results. I will discuss the observational and theoretical challenges for cosmological studies of the large scale structure at low radio frequencies and will show first results from the analysis of LoTSS-DR2.

Speaker: Prof. Dominik Schwarz
• 16:20
Coffee break 20m
• 16:40
Oscillating scalar fields and the Hubble tension: a resolution with novel signatures 20m

We present a detailed investigation of a sub-dominant oscillating scalar field ('early dark energy', EDE) in the context of resolving the Hubble tension. Consistent with earlier work, but without relying on fluid approximations, we find that a scalar field frozen due to Hubble friction until log10($z_c$)∼3.5, reaching ρ$_{\rm EDE}$($z_c$)/ρ$_{\rm tot}$∼10%, and diluting faster than matter afterwards can bring cosmic microwave background (CMB), baryonic acoustic oscillations, supernovae luminosity distances, and the late-time estimate of the Hubble constant from the SH0ES collaboration into agreement. A scalar field potential which scales as $V(ϕ)∝ϕ^{2n}$ with 2≲n≲3.4 around the minimum is preferred at the 68% confidence level, and the Planck polarization places additional constraints on the dynamics of perturbations in the scalar field. In particular, the data prefers a potential which flattens at large field displacements. An MCMC analysis of mock data shows that the next-generation CMB observations (i.e., CMB-S4) can unambiguously detect the presence of the EDE at very high significance. This projected sensitivity to the EDE dynamics is mainly driven by improved measurements of the E-mode polarization. We also explore new observational signatures of EDE scalar field dynamics: (i) We find that depending on the strength of the tensor-to-scalar ratio, the presence of the EDE might imply the existence of isocurvature perturbations in the CMB. (ii) We show that a strikingly rapid, scale-dependent growth of EDE field perturbations can result from parametric resonance driven by the anharmonic oscillating field for n≈2. This instability and ensuing potentially nonlinear, spatially inhomogenoues, dynamics may provide unique signatures of this scenario.

Speaker: Prof. Tristan Smith (Swarthmore College)
• 17:00
Detecting dark matter signals by radio data of galaxy clusters 20m

Dark matter problem is a key problem in astrophysics. Recent gamma-ray and anti-proton detections suggest that dark matter annihilating via b quark channel can explain the Galactic center gamma-ray excess and the anti-proton excess simultaneously. Besides, recent studies show that radio data can also give stringent constraints for dark matter. Based on our recent studies using the radio continuum spectral data of the Ophiuchus cluster and the Abell 4038 cluster, we have figured out some potential signals of dark matter annihilation. The constrained mass range (~40-50 GeV) and annihilation channel (b quark) are consistent with the previous studies. This provides some hints for detecting dark matter signals by radio observational data.

Speaker: Dr Man Ho Chan (The Education University of Hong Kong)
• 17:20
Black Holes at Cosmic Dawn 20m

Theoretical models and observations suggest that large fractions of Pop III stars end as black holes (BHs) in High-Mass-X-ray Binaries (BH-HMXBs), which are sources of hard X-rays and synchrotron relativistic jets called Microquasars (MQs ref.1). The hard X-rays from these accreting BHs of Pop III have long free paths, pre-heat the Intergalactic Medium (IGM), and lead to a smooth end of the re-ionization epoch (ref. 2).
We will show that the relativistic jets from the remnants of Pop III stars, namely, the BH-HMXB-MQs of Pop III, produce a Synchrotron Cosmic Radio Background (CRB) that can account for the excess amplitude and bottom-flat absorption of atomic hydrogen at z~17 (78 MHz), tentatively reported by EDGES (ref. 3). In fact, the existence of a Synchrotron CRB had been inferred from the NASA ARCADE 2 Experiment (ref. 4). Recently, it was proposed that --along with the hard X-ray cosmic background-- that CRB is the smoking gun of Pop III stars (ref. 5).

References:

1) Mirabel, I.F. & Rodríguez, L.F. 1998, Nature, 392, 673-677

2) Mirabel I. F., Dijkstra M., Laurent Ph., Loeb A., Pritchard J. R., 2011, A&A, 528, A149

3) Bowman J. D., Rogers A. E. E., Monsalve R. A., Mozdzen T. J., Mahesh N., 2018, Nature, 555, 67 EP

4) Fixsen D.J., Kogut A., Levin, S. et. al. 2011, ApJ, 734, 5

5) Mirabel (2019): Review at IAU Symp. 346 (arXiv#1902.00511)

Speaker: Felix Mirabel (IAFE)
• 17:40
The synergy between CMB spectral distortions and anisotropies 20m

Despite their incredible precision, both concluded and upcoming CMB missions (such as Planck, CMB-S4, or LiteBIRD) still face several intrinsic limitations that can only be overcome with the help of complementary probes. One particularly interesting avenue to extract more information from the CMB is given by its spectral distortions (SDs). Since these distortions are created whenever the energy or number density of the CMB photons is modified, they are an ideal candidate to constrain both exotic and non-exotic energy injection scenarios. In this talk, following the novel CLASS implementation of SDs, I will provide a brief pedagogical introduction to the topic of SDs, and discuss their application to a selection of examples including decaying dark matter and primordial black holes. The presented results will show the far-reaching possibilities of combining CMB anisotropies and SDs.

Speaker: MATTEO LUCCA (IDP - ULB (Universite libre de Bruxelles))
• 18:15 20:15
Social events: Welcome cocktail (TBC)
• Tuesday, 8 December
• 09:00 12:30
Invited talks: Dark Matter and Dark Energy
• 09:00
TBA 30m
Speaker: Sébastien Clesse (Catholic University of Louvain)
• 09:40
Dark matter direct detection: present scenario and future prospects 30m

Profound evidence for the existence of dark matter has been collected throughout the past 100 years. However, its exact nature remains elusive. A large effort is being put into the search for direct detection of weakly interacting massive particles (WIMPs), which arise as dark matter particle candidates in various theories. The search is led by dual-phase liquid xenon time projection chambers for masses above 5 GeV/c2. The most sensitive experiment, XENON1T, probes spin-independent (SI) WIMP-nucleon interactions down to 4.1 × 10−47 cm2 for 30 GeV/c2 WIMP mass. This limit refers to the SI isoscalar channel, which, for vanishing momentum transfer q, scales quadratically with the number of nucleons A. The SI interaction thus yields the dominant nuclear response, making it the standard search channel in the field.
We will browse through the different technical approaches used in the present dark matter direct detection scenario as well as its future prospects.

Speaker: Prof. José Matias-Lopes (Coimbra University)
• 10:20
Coffee Break 20m
• 10:40
TBA 30m
Speaker: Noemi Frusciante (Instituto de Astrofísica e Ciências do Espaço)
• 11:20
TBA 30m
Speaker: Dr Harry Desmond (University of Oxford)
• 12:00
TBA 25m
Speaker: Diego Blas (KCL)
• 12:30 14:30
Lunch break 2h
• 14:30 15:40
Invited talks
• 14:30
Cosmological reconstructions of gravity 25m

We use data from cosmological survey to jointly reconstruct phenomenological functions of redshift describing departure of dark energy from the cosmological constant and possible modified gravity effects in the evolution of large scale structure. I will focus on the dependence of such reconstructions on the underlying assumptions and their implications for dark energy and modified gravity theories.

Speaker: Prof. Levon Pogosian (Simon Fraser University)
• 15:00
TBA 30m
Speaker: Tien-Tien Yu (University of Oregon (US))
• 15:40 18:00
Contributed talks
• 15:40
Ascertaining the cosmological constant using galactic superclusters in $f(R,T)$ gravity 20m

In this work we estimated the cosmological constant in a pioneering approach by using galactic superclusters in the layout of $f(R,T)$ gravity. We set $f(R,T) = R + 2\lambda T$ where $\lambda$ is the model parameter. We report that appropriate values of $\lambda$ generate cosmological constant ($\Lambda$) values in harmony with observational value of $1.1056\times10^{-52}m^{-2}$. We also delineate that for $\lambda = 0$ which corresponds to GR, yields physically unacceptable results.

Speaker: Prof. Pradyumn Kumar Sahoo (Birla Institute of Technology and Science-Pilani, Hyderabad Campus)
• 16:00
Dark matter and primordial black holes 20m

A review on the recent astronomical discoveries of black holes (BH) with masses in the range from a fraction of the solar mass up to ten billons solar masses is presented. Surprisingly such BHs are observed not only in the present day universe but also at the redshifts about ten. It is argued that all or almost all observed BHs are primordial (PBH). A mechanism of PBH production with the extended (log-normal) mass spectrum, suggested in 1993, is discussed. This mechanism successfully explains the newly made observations.

Speaker: Alexander Dolgov (NSU)
• 16:20
Coffee break 20m
• 16:40
Formation and Abundance of Primordial black holes 20m

Primordial black holes can form in the early Universe from the collapse of cosmological perturbations after the cosmological horizon crossing. They are possible candidates for the dark matter as well as for the seeds of supermassive black holes observed today in the centre of galaxies. In calculations of spherically symmetric collapse, a Lagrangian relativistic hydrodynamical code is used to follow the non linear evolution. If the perturbation is larger than a threshold depending on the equation of state and on the specific shape of the perturbation, a black hole is formed. In this talk I will discuss the dependence of PBH formation from the initial shape of the curvature profile, showing the relation with the shape of the inflationary power spectrum. This allows to compute consistently the abundance of PBHs. Depending on the model, a proper calculation shows that the abundance of PBHs might be significantly increased by several order of magnitudes compared to previous estimations.

Speaker: Dr Ilia Musco (University of Geneva)
• 17:00
Relativistic effects in dark matter evolution 20m

I'll discuss recent progress on fully relativistic treatment of dark matter evolution (thermalization, freeze-out, etc.)

Speaker: Oleg Lebedev (University of Helsinki)
• 17:20
Scalar field dark matter around supermassive Black Holes 20m

We consider scalar field models of dark matter, with a mass in the range 10^{-21} << m << 10^{-3} eV. In the nonrelativistic regime, derivative or potential self-interactions can give rise to an effective pressure that builds equilibrium configurations (solitons) in galactic halos. We extend the analysis to the relativistic regime, down to the horizon of the supermassive galactic Black Hole (BH). We discuss when the large-scale soliton is eaten by the central BH or survives on timescales much greater than the age of the Universe.

Speaker: Dr Patrick Valageas (IPhT / CEA Salcay)
• 17:40
Dark matter bound states: where do we stand? 20m

In a variety of theories, DM interacts with gauge bosons or scalars that induce long-range interactions because of repeated soft exchanges. Remarkably, the inclusion of bound-state effects for DM annihilation has been recently shown to have a large impact on the relic density and, therefore, on the parameters of a given model to be compatible with observations. At the same time, it is manifestly subtle and complicated to include bound-state dynamics in a thermal medium due to the intricate interplay between non-relativistic and thermal energy scales. Starting from a thermal field theoretic formulation of the problem, we use an effective field theory approach to describe bound-state formation and dissociation, Sommerfeld effect, DM thermal masses and interaction rates. We show the phenomenological impact of such framework for wimp-like models with mediators to the visible sector. Moreover, we discuss some shortcomings in the current rate equations that limit the validity of existing results in the literature for even simpler dark matter models.

Speaker: Dr Simone Biondini (Van Swinderen Institute for Particle Physics and Gravity)
• Wednesday, 9 December
• 09:00 12:30
Invited talks: The Early Universe
• 09:00
A fresh look at the calculation of tunneling actions 30m

The calculation of tunneling actions, that control the exponential
suppression of the decay of metastable phases (like the unstable
electroweak vacuum), can be reformulated as an elementary variational
problem in field space. This alternative approach circumvents the use of
bounces in Euclidean space by introducing an auxiliary function, a
tunneling potential Vt that connects smoothly the metastable and stable
phases of the field potential V. The tunneling action is obtained as the
integral in field space of an action density that is a simple function
of Vt and V and can be considered as a generalization of the thin-wall
action to arbitrary potentials. This formalism provides new handles for
the theoretical understanding of different features of vacuum decay, can
be easily extended to include gravitational effects in an elegant way
and has a number of useful applications that I will discuss.

Speaker: Prof. Jose Ramon Espinosa (IFT-UAM/CSIC)
• 09:40
TBA 30m
Speaker: Christof Wetterich (Heidelberg University)
• 10:20
Coffee Break 20m
• 10:40
TBA 30m
Speaker: Marco Drewes (Universite Catholique de Louvain (UCL) (BE))
• 11:20
TBA 30m
Speaker: Jacopo Ghiglieri (Centre National de la Recherche Scientifique (FR))
• 12:00
TBA 30m
Speaker: Robert Brandenberger (McGill University)
• 12:30 14:30
Lunch break 2h
• 14:30 18:00
Contributed talks
• 14:30
COSMOLOGICAL CORRELATORS, IN-IN FORMALISM AND DOUBLE COPY 20m

We are investigating if the double copy structure as product of scattering amplitudes
of gauge theories applies to cosmological correlators computed, in a class of theories for
inflation, by the operatorial version of the In-In formalism of Schwinger-Keldysh. We
consider tree level momentum-space correlators involving primordial gravitational waves
with different polarizations and the scalar curvature fluctuations on a three dimensional
fixed spatial slice. The correlators are sum of terms factorized in a time dependent scalar
factor, which takes into account the curved background where energy is not conserved,
and in a so-called tensor factor, constructed by polarization tensors. In the latter we
recognize scattering amplitudes in four dimensional Minkowski space spanned by three
points gravitational amplitudes related by double copy to those of gauge theories. Our
study indicates that gravitational waves are double copy of gluons and the primordial
scalar curvature is double copy of a scalar with Higgs-like interactions.

Speaker: Prof. Angelo Raffaele Fazio (Universidad Nacional de Colombia)
• 14:50
MEMe model: a generalized coupling theory 20m

Generalized coupling theories are characterized by a nontrivial coupling between the gravitational metric and matter, which is mediated by an auxiliary rank-2 tensor. The actions generating the field equations are constructed so that these theories are equivalent to general relativity in a vacuum, and only differ from Einstein's theory within a matter distribution. This talk will focus on one of the simplest realizations of these theories, termed the MEMe model. The MEMe model admits an exact solution for the coupling for a single perfect fluid. An analysis of the evolution of homogeneous and isotropic spacetimes in the MEMe model reveals the existence of cosmic histories with both an inflationary phase and a dark era characterized by a different expansion rate. I also discuss the propagation speed of GWs through matter and some recent work on the PPN analysis for the MEMe model.

Speaker: Justin Feng (Instituto Superior Tecnico)
• 15:10
Where is the cosmic rest frame? : the local Universe and the Cosmological principle 20m

The dipole anisotropy of the CMB is believed to be due to our motion with respect to the CMB rest frame' at 369 km/s. This should also cause a dipolar modulation in the number counts of distant sources, through aberration & Doppler boosting. We test this with various all-sky catalogues: NVSS & SUMSS radio galaxies, WISE galaxies & quasars, as well as GAIA-unWISE AGNs, consistently finding a significantly larger dipole than expected (implying velocities >1000 km/s) with statistical significance upto 3.3 sigma. These observations indicate a bulk flow between the matter & radiation rest frames in the local Universe, extending out to scales larger than is expected in LCDM. An observational effect of such a bulk flow would be a scale-dependent dipolar modulation in the deceleration parameter. We look for this in the SDSS-II/SNLS-III Joint lightcurve Analysis catalogue of SN Ia and find such a dipole with 3.9 sigma significance, while the evidence for isotropic acceleration simultaneously drops to 1.4 sigma. This talk will conclude by reviewing the history of supernova data fitting, focussing on statistical methods & data quality issues. Both dark energy & the Hubble tension seem to be artefacts of fitting data to an idealized model of the universe.

Speaker: Mohamed Rameez
• 15:30
Implications of microscopic black holes in neutrino telescopes, FCC and the early Universe 20m

If the length scale of possible extra dimensions is large enough, the effective Planck scale is lowered such that microscopic black holes could be produced in collisions of high-energy particles, which opens up a plethora of novel phenomena in terrestrial detectors and in the early Universe. Microscopic black holes from high-energy cosmic neutrino-nucleon collisions are characterized by unique topologies, distinct energy distributions and unusual ratios of hadronic-to-electronic energy deposition, visible through Cherenkov light echos due to delayed neutron recombination in IceCube-like detectors. In addition, these black holes evaporate through the emission of all particles that are kinematically and thermally allowed, including dark matter. This enables us to study the properties of dark sector from the missing momentum signatures at the next generation of colliders, regardless of the strength of the coupling between dark matter and the Standard Model. The dark matter produced from microscopic black hole decay in the early Universe may account for part or all the dark matter relic density today if the reheating temperature is close to the Planck scale in the bulk, which serves as a new dark matter production mechanism even in the absence of non-gravitational dark matter-Standard Model coupling.

Speaker: Ningqiang Song (Queen's University)
• 15:50
Coffee break 20m
• 16:10
A formulation to study formation of Bose-Einstein condensation in cosmology at the level of particle physics processes 20m

This talk will be mainly based on the paper; R. Erdem and K. Gultekin. JCAP 10 (2019) 061. By considering dynamics of a scalar Bose-Einstein condensation at microscopic level, we study the initial phase of formation of condensation in cosmology. To this end, first we introduce an effective Minkowski space formulation that enables considering only the effect of particle physics processes, excluding the effect of gravitational particle production and enabling to see cosmological evolution in an easier way. Then, by using this formulation we study a model with trilinear coupling $ϕ^2 χ$ that induces the processes χχ⟶ϕϕ. After considering the phase evolution of the produced ϕ particles, we find that they evolve towards formation of a Bose-Einstein condensate provided some conditions are satisfied. In principle, the effective Minkowski space formulation introduced in this study can be applied to particle physics processes in any spacetime that is sufficiently smooth.

Speaker: Mr Kemal Gultekin (Izmir Institute of Technology)
• 16:30
On the quantum origin of a small positive cosmological constant 20m

We show that Dark Matter consisting of ultralight bosons in a Bose-Einstein condensate induces, via its quantum potential, a small positive cosmological constant which is close to the observed value. This explains why the densities of Dark Matter and Dark Energy are approximately equal.

[NOTE ADDED MC 2020.03.03 if abstract is selected, talk scheduled for 27, 28 or 29 April (i.e. Monday, Tuesday or Wednesday, and not on Thursday the 30th April)]

Speaker: Prof. Saurya Das (University of Lethbridge)
• 16:50
Gravitational effects on particle decay 20m

The presence of a gravitational field modifies significantly particle decay rates compared to the usual Minkowski space results. Because of the lack of energy conservation, new particle processes, forbidden in Minkowski space, are to be considered leading to new Feynman diagrams even at first order. I will give a brief introduction to the problems encountered when trying to calculate decay rates using quantum field theory in curved spacetime in FLRW-spacetimes. I will focus on conceptual issues, show methods of calculation to overcome some of these issues and present some recent results when these decay rates are applied to a reheating scenario in kination epoch via gravitational particle creation.

Based on:
arXiv:1805.09620
arXiv:1904.05084
arXiv:1910.07520

Speaker: Mr Juho Lankinen (University of Turku)
• 17:10
Impact of Low Reheating Temperature and X-ray Bound Relaxation on Sterile Neutrino DM Searches in Terrestrial Experiments 20m

If we consider sterile neutrino with a O(keV) mass as Warm Dark Matter candidates, produced in the early universe through admixtures with the active neutrinos, via the Dodelson-Widrow or the Shi-Fuller mechanisms, strong constraints on the active-sterile mixing angle are imposed by the observations in the X-ray band and the measurements of the total DM abundance. These constraints, that in a standard scenario would seriously put at risk the possibility of getting a signal of the existence of such sterile neutrinos in laboratory experiments in the near future, can be largely relaxed in low reheating temperature scenarios in which $\Omega_{DM}$ is constituted by a cocktail of different candidates, among which there are also sterile neutrinos, or in the case in which the decay rate of sterile neutrinos is reduced by the action of new physics.

Speaker: Cristina Benso (MPIK, Heidelberg)
• 19:30 22:30
Social events: Banquet (TBC)
• Thursday, 10 December
• 09:00 12:30
Invited talks: Gravitational Waves
• 09:00
TBA 30m
Speaker: Sachiko Kuroyanagi (Tokyo University of Science)
• 09:40
TBA 30m
Speaker: Dr Miguel Zumalacarregui (University of California at Berkeley)
• 10:20
Coffee Break 20m
• 10:40
TBA 30m
Speaker: Nicola Tamanini (IPhT CEA/Saclay)
• 11:20
TBA 30m
Speaker: Carlo Contaldi (Imperial College London)
• 12:00
TBA 25m
Speaker: Pierre Vanhove
• 12:30 14:30
Lunch break 2h
• 14:30 18:00
Contributed talks
• 14:30
Cross-correlation of the astrophysical gravitational-wave background with galaxy clustering 20m

We investigate the correlation between the distribution of galaxies and the predicted gravitational wave background of astrophysical origin. We show that the average contribution to the background as a function of redshift can be easily constrained by cross-correlating with galaxy catalogs at different redshifts. Furthermore, the interpretation of this signal allows us to address the discrepant predictions for the autocorrelation signal available in the literature. Because we show that the impact of shot noise is negligible, our results suggest that the gravitational-wave background, when combined with near-future galaxy surveys, is a powerful probe for both gravitational-wave merger physics and cosmology.

Speaker: Valeri Vardanyan (Kavli IPMU)
• 14:50
Classical de Sitter string backgrounds and the swampland 20m

Solutions of string theory with a four-dimensional de Sitter space-time could serve as an interesting starting point to build cosmological models of the early universe, or the present one. Obtaining such solutions in a well-controlled manner is however notoriously difficult. This has recently led to various conjectures, in the context of the swampland program, that strongly constrain the existence of de Sitter solutions in string effective models, with drastic consequences regarding single field inflation or quintessence. Focusing on classical string backgrounds, these conjectures can be precisely tested, with sharp no-go theorems, as well as promising counter-examples, that could eventually serve in stringy cosmological models. We will present an overview and new results on this topic.

Speaker: Dr David Andriot (TU Wien)
• 15:10
A probe into leptophilic scalar dark matter 20m

We revisit the scalar singlet dark matter (DM) scenario with a pair of dark lepton partners which form a vector-like Dirac fermionic doublet. The extra doublet couples with the SM leptonic doublet and the scalar singet via a non-SM-like Yukawa structure. As a result, (1) since the extra fermionic states interact with other dark sector particles as well as the SM via gauge and Yukawa interactions, it gives rise to new DM annihilation processes including pair annihilation as well as coannihilation channels, allowed by the existing experimental constraints and (2) such a Yukawa structure opens up new production channels for leptonic final states giving much enhancement in cross sections to search for dark matter in the LHC. The DM freeze-out scenario becomes more interesting if a dark singlet fermion is added in the particle spectrum. In the cases of mixing between the charged dark leptons, the mixing angle gives rise to interesting features in DM coannihilation. It further dictates the dominant coannihilating partner from an ensemble of nearly degenerate dark leptons. We further show how the mixing leads to interesting signatures in the distributions of weak gauge boson mediated processes in an collider environment.

Speaker: Ms Sreemanti Chakraborti (Indian Institute of Technology, Guwahati, India)
• 15:30
Constraining Dark Matter - Dark Radiation Interactions with Lyman-alpha Data 20m

Despite its remarkable success, the standard LCDM paradigm has been challenged lately by potential tensions in the Hubble Constant measurements, as well as a slight mismatch between simulations and observations on smaller scales. This has reinvigorated interest in beyond-LCDM models, such as Dark Matter interacting with an additional dark sector. These interactions result in a suppression of the matter power spectrum on small scales, making them an ideal target to be constrained with Lyman-alpha data. In this talk I will discuss a novel parameterisation of this small-scale power suppression, which allows these models to be constrained with Lyman-alpha data without needing new, computationally-expensive hydrodynamical simulations for each set of model parameters. I will also present up-to-date constraints on these interactions and their ability to alleviate the cosmological tensions, obtained with our new method.

Speaker: Dr Deanna C. Hooper (ULB (Université libre de Bruxelles))
• 15:50
Coffee break 20m
• 16:10
Constraining Dark Matter properties with the Inter-Galactic Medium and other cosmological probes 20m

The Inter-Galactic Medium (IGM) is a very powerful tool for tracing the Dark
Matter (DM) distribution at small cosmological scales. The detailed features
of the matter power power spectrum at (sub-)galactic scales depend on the
fundamental DM nature, allowing for a direct link between theoretical models
and astrophysical observations.
I will present an efficient method for constraining both thermal and
non-thermal DM scenarios with structure formation data, based on a simple
and flexible parametrisation capable to reproduce the small-scale clustering
signal of a large set of non-standard cosmologies. I will discuss the latest
astrophysical constraints on such parametrisation, easily translatable to
bounds on the fundamental DM properties without the need to run any
specific numerical simulations. Finally, I will focus on particularly viable
non-standard scenarios, such as ultra-light axions, interacting DM, and
primordial black holes: I will discuss the most updated limits obtained
through high-resolution and high-redshift Lyman-alpha forest data alone,  as
well as in combination with other cosmological probes, such as Cosmic
Microwave Background (CMB) and Baryon Acoustic Oscillation (BAO).

Speaker: Dr Riccardo Murgia (LUPM, CNRS & Montpellier University)
• 16:30
Constraints on two-body dark matter decays and implications for the Hubble tension 20m

Despite the numerous successfull predictions of the $\Lambda$CDM model, there are still some conundrums that remain. One prominent example is the "Hubble tension", i.e. the discrepancy between the value of the Hubble constant $H_0$ as inferred from a $\Lambda$CDM fit to the Cosmic Microwave Background (CMB), and its direct measurement through cosmic distance ladder observations. This disagreement is not easily explained by any systematic error in the data, therefore an increasing attention is given to possible extensions beyond $\Lambda$CDM, which could also offer hints about the Dark Matter (DM) nature.

In this talk, I will review a scenario in which cold DM can decay into two daughter particles, one massless and one with an arbitrary mass. Current constraints on this class of scenarios are generally obtained by only focusing on the background evolution. Furthermore, there has been a lack of a combined analysis including observations of both SuperNovae type Ia (SNIa) and Baryon Acoustic Oscillations (BAOs). I will show how the inclusion of both datasets significantly changes the bounds, and the implications for the Hubble tension. Finally I will discuss the impact on the linear perturbation evolution, and present updated constraints based on the aforementioned datasets in combination with full CMB data from Planck.

Speaker: Mr Guillermo Franco Abellan (Laboratoire Univers et Particules (LUPM))
• 16:50
Cross-correlation between 21cm intensity mapping and gamma rays: a new path for particle dark matter searches 20m

Dark matter in cosmic structures is expected to produce signals originated from its particle physics nature, among which the electromagnetic emission represents a relevant opportunity, whose intensity is directly linked to the amount of dark matter in galaxies and clusters. On the other hand, this emission is very faint, thus contributing only at the unresolved level. These unresolved radiation backgrounds are isotropic at first order, but must exhibit a degree of anisotropy since they originate from clustered dark matter haloes. This fact implies also that the anisotropies in the radiation fields should be correlated to the same matter distribution in the Universe.
In this talk we propose to exploit this correlation by using the intensity mapping of the 21cm emission line of neutral hydrogen as the tracer of matter distribution, and gamma rays as the tracer of particle dark matter annihilation. Intensity mapping has the advantage of not being flux limited in the measurement of the matter distribution (as instead galaxy catalogs are) since it does not need to identify individual galaxies, and offers excellent redshift information being a line emission. We show the expected level for this cross-correlation signal and we derive forecasts for the study of this novel signature through the combination of Fermi-LAT gamma rays data and SKA intensity mapping capabilities.

Speaker: Mrs Elena Pinetti (University of Turin & INFN Turin & Sorbonne University)
• 17:10
Probing freeze-in dark matter with gamma ray telescopes 20m

Thermal freeze-in is a simple scenario of dark matter production that can however be very difficult to probe. We discuss a decaying dark matter setup in which the feeble coupling required to reproduce the observed relic abundance gives rise to transitions between dark matter components, resulting in gamma ray spectral features.

Speaker: Johannes Herms (TU Munich)
• Friday, 11 December
• 09:00 12:40
Contributed talks
• 09:00
Anisotropic cosmological models under f(R;T ) theory of gravity 20m

In the present work, we have presented and analyzed the cosmological models of the universe with an anisotropic variable parameter. We have set up the ?field equations with the space time in the form of Bianchi I metric with an f(R;T) gravity. The functional form for the f(R;T) gravity assumed to be f(R;T) = R + 2f(T), where R and T respectively the Ricci scalar and trace of energy momentum tensor. Two different models are constructed with respect to the scale factors, such as Power law scale factor and Hybrid scale factor. Moreover, the anisotropic parameter taken here in the form of hyperbolic function that further gives clarity on the behaviour of Equation of State (EOS) parameter. The models can be reduced to isotropic universe when the coefficient constant vanishes. For both the cases,the deceleration parameter, state fi?nder diagnostic pairs and energy conditions have been obtained and analyzed which provide physical plausibility of the models.

Keywords: Modified Gravity; Cosmology; Anisotropy; Equation of State; Deceleration Parameter.

Speaker: Bivudutta Mishra (BITS-Pilani, Hyderabad Campus)
• 09:20
Bounds on masses of dark matter particles in $R^2$-gravity 20m

Particle production by oscillating curvature in $R+R^2$ cosmology is considered. It is shown that the cosmological density of massive stable relics may be close to the observed density of dark matter. The proper range of mass values depends on the channel of the scalaron decay. In particular it opens the window for heavy supersymmetric particles to be viable dark matter constituents.

Speaker: Elena Arbuzova (Dubna State University and Novosibirsk State University)
• 09:40
Constraints on the growth rate using the observed power spectrum and multi-tracers 20m

The large-scale structure growth index γ provides a consistency test of the standard cosmology and is a potential indicator of modified gravity. We investigate the constraints on γ from next-generation spectroscopic surveys (like SKA, Euclid and DESI), and possible improvements from combining these using a multi-tracer technique. Using the angular power spectrum, which is observed in redshift space, we avoid the need for an Alcock-Packzynski correction. It also naturally incorporates cosmic evolution and wide angle effects, without any approximation. We include the cross-correlations between redshift bins, using a hybrid approximation
when the total number of bins is computationally unfeasible.

Speaker: Jan-Albert Viljoen (University of the Western Cape)
• 10:00
Spherical cosmological models: an alternative cosmology 20m

The properties of universes are explored that are entirely in the interior of black holes in another universe, a mother universe'. It is argued that these models offer a paradigm that may shed a new light on old cosmological problems. The geometry of such a universe is discussed including how it would appear to the observer. The Hubble parameter is direction dependent, but it is argued that the interpretation of any such dependence will be hard to separate from local inhomogeneities. The models do not originate from a big bang, but rather from an initial collapse and subsequent infall, that started probably a very long time ago, presumably much earlier than the accepted age of the universe. The relation to the concordance model is discussed and it is shown that a lot of the existing theory can be taken over into the proposed models. The universe has an edge, which is an ordinary sphere in 3 dimensions. That sphere acts as a gravitational mirror as seen from inside the universe, but it does not mirror redshift. The same object can thus be seen in direct sight and in reflection, although with different redshifts, different ages and different aspect angles. The models do not need dark energy, but they need dark matter, of course. Since the models are closed and neutrino's are nowadays believed to have mass, neutrino's can be reconsidered as candidates for the dark matter. As a bonus result from this paradigm, mass ejection from black holes is shown to be possible, which links that process to the controversial anomalous galaxy redshifts. Finally, we show that gravitational mass and inertial mass are proportional, and that the inertial acceleration scales as $c^2/M$, with $M$ a characteristic scale of the universe.

Speaker: Herwig Dejonghe (Ghent University)
• 10:20
Coffee break 20m
• 10:40
Accelerated universe from non-extensive entropy 20m

We derive the modified Friedmann equations based on non-extensive Tsallis thermodynamics. This model admits an accelerated expansion for the universe filled by ordinary matter and without needing dark energy. The age problem can also be alleviated in this model.

• 11:00
Thick Branes in Extra Dimensions and Suppressed Couplings 20m

Extra dimensions (ED) have been used as attempts to explain several phenomena in particle physics, such as the hierarchy and flavor problems. The interaction between new mediators in the bulk (vector, scalar of fermion fields) and the Standard Model (SM) particles can be naturally suppressed if one employs a single, flat ED. In this setup, the SM fields are localized in a finite width ‘fat’ brane, similar to models of Universal Extra Dimensions. A dark matter (DM) candidate is confined to a thin brane at the opposite end of the ED interval. Including brane localized kinetic terms on the fat brane for the mediator fields, the resulting coupling between the SM and these mediators can be several orders of magnitude smaller than the corresponding ones between the mediators and DM. The implications of this scenario is investigated for both vector (dark photon, DP) and scalar mediator fields in the 5-D bulk. The SM particles couple to the DP via their $B − L$ charges while the DP couples to the DM via a dark charge. Both the vector DP couplings and the corresponding Higgs portal couplings with the SM are shown to be naturally small in magnitude with a size dependent on ratio of the 5-D compactification radius and the SM brane thickness. This mechanism is also studied in 6-D. Finally, if a Dirac fermion is present in the bulk, it results (in 4-D) in two towers of Kaluza-Klein Majorana sterile neutrinos, whose mass mixing with the SM neutrinos is also suppressed. The seesaw mechanism is therefore obtained, and sterile neutrino masses of order $\mathcal{O}(1-10)$ TeV naturally explain the small SM neutrino mass.

Speaker: Ricardo Landim (Technical University of Munich)
• 11:20
On elastic couplings in the dark sector and the sigma8 tension 20m

Elastic interactions between dark matter and dark energy provide promising models that alleviate the sigma8 tension in scenarios where the background remains unaffected. I will present the constraints from current data as well as the forecasts for future galaxy surveys. I will also briefly comment on couplings to baryons within these scenarios.

Speaker: Dr Jose Beltran Jimenez
• 11:40
Hubble-induced phase transitions: Walls are not forever 20m

If inflation is followed by a period of kinetic domination, as is common in quintessential inflation scenarios, internal symmetries of non-minimally coupled spectator fields will be generically broken. This generates a complex dynamics for this field and leads to the formation of defects. One of the most relevant consequences is that this mechanism will tend to produce a, potentially detectable, gravitational waves background. Interestingly, the symmetry will be eventually restored implying the eventual decay of the defects.

Speaker: Dario Bettoni
• 12:00
Coupling to matter in degenerate scalar-tensor theories 20m

Degenerate scalar-tensor theories of gravity extend general relativity by a single degree of freedom, despite their equations of motion being higher than second order, a virtue made possible by the existence of an additional constraint that removes the would-be ghost. This constraint can however be obstructed by matter fields, even when minimally coupled to the metric. In this talk I will present this issue in detail, explaining through some illustrative examples the precise ways in which the extra degree of freedom may reappear. I will next turn to the more physically relevant case of fermionic matter, and show that spin-1/2 fermions evade these issues and can thus be consistently coupled to degenerate theories of scalar-tensor gravity.

Speaker: Sebastian Garcia-Saenz (Imperial College London)
• 12:20
Minimal self-interacting dark matter models with light mediator 20m

The light mediator scenario of self-interacting dark matter is strongly constrained in many ways. After summarizing the various constraints, we discuss minimal options and models which allow to nevertheless satisfy all these constraints.

Speaker: Thomas Hambye
• 12:40 14:30
Lunch Break 1h 50m
• 14:30 17:30
Contributed talks
• 14:30
The 1/N expansion for stochastic fields in de Sitter spacetime 20m

We propose a 1/N expansion of Starobinsky and Yokoyama’s effective stochastic approach for light quantum fields on superhorizon scales in de Sitter spacetime. We explicitly compute the spectrum and the eigenfunctions of the Fokker-Planck operator for a O(N)-symmetric theory with quartic selfinteraction at leading and next-to-leading orders in this expansion. We obtain simple analytical expressions valid in various nonperturbative regimes in terms of the interaction coupling constant.

Speaker: Gabriel Moreau (Université de Montpellier)
• 14:50
Peccei-Quinn Phase Transitions with Gravitational Waves & UV Completion 20m

Attempts to solve naturalness by having 4-dimensional Quantum Field Theories to satisfy Total Asymptotic Freedom (TAF): the theory holds up to infinite energy, where all coupling constants flow to zero have become popular in recent times. Specifically we discuss a fundamental field theory of the QCD axion: all couplings flow to zero in the infinite-energy limit realizing the totally asymptotically free (TAF) scenario. Some observable quantities (such as the masses of new quarks and scalars) are predicted at low energies by the TAF requirement in terms of gauge couplings and a vector-boson mass. The axion sector is charged under an SU(2) gauge group and a dark photon appears at low energies. We discuss the dynamics of the Peccei-Quinn (PQ) phase transition for the QCD axions; in particular, we show that the PQ phase transition is strongly first order and can produce gravitational waves within the reach of future detectors. The models predict a frequency peak in the range 100-1000 Hz with an amplitude that is already within the sensitivity of LIGO & advanced LIGO and can be thoroughly tested with other future GW interferometers.

Speaker: Anish Ghoshal (L)
• 15:10
Gravitational radiation from MHD turbulence in the early universe 20m

The generation of primordial magnetic fields and its interaction with the primordial plasma during cosmological phase transitions is turbulent in nature. I will describe and discuss results of direct numerical simulations of magnetohydrodynamic (MHD) turbulence in the early universe and the resulting stochastic gravitational wave background (SGWB). In addition to the SGWB, the primordial magnetic field will evolve up to our present time and its relics can explain indirect observations of weak magnetic fields coherent on very large scales. I will apply the numerical results to magnetic fields produced at the electroweak and the QCD phase transitions and show that these signals may be detectable by the planned Laser Interferometer Space Antenna and by Pulsar Timing Array. The detection of these signals would lead to the understanding of cosmological phase transition physics, which can have consequences on the baryon asymmetry problem and on the origin seed of observed magnetic fields coherent over very large scales at the present time.

Speaker: Alberto Roper Pol
• 15:30
M-theory and the birth of the Universe 20m

The IIB matrix model has been suggested as a a particular formulation
of nonperturbative superstring theory (M-theory).
It has now been realized that an emerging classical spacetime must
reside in its large-N master field.
The master field of the Lorentzian IIB matrix model can, in principle,
give rise to the regularized-big-bang metric of general relativity.
The length parameter of the regularized-big-bang metric is then calculated
in terms of the IIB-matrix-model length scale.