Finding the best parametrization for cosmological models in the absence of first-principle theories is an open question. We propose a data-driven parametrization of cosmological models given by the disentangled 'latent' representation of a variational autoencoder (VAE) trained to compress cosmic microwave background (CMB) temperature power spectra. We consider a broad range of ΛCDM and...
Searches for neutrino isocurvature usually constrain a specific linear combination of isocurvature perturbations. In this talk, realistic cosmological scenarios giving rise to neutrino isocurvature are discussed. We show that in general both, neutrino and matter isocurvature perturbations are generated, whose ratio we parameterise by a newly introduced mixing angle. We obtain the first limits...
Gravitational lensing of the Cosmic Microwave Background is a very valuable cosmological signal, detected at very high significance by several experiments, and its SNR is expected to increase by a factor of 10 or so in the next decade.
At the same time, it has also become an hindrance to some important science goals of CMB experiments, most notably for best constraints on a primordial...
Introduction to gravitational waves emitted after the CMB
Precessing black-hole mergers can produce an imbalance between right- and left-handed circularly polarized gravitational waves. According to the Cosmological Principle, such chiral emission should average out to zero across all binary mergers in our Universe in order to preserve mirror-reflection symmetry at very large scales. In this talk, I will show how gravitational-wave astronomy enables...
In the talk, I will introduce a new semianalytical model (SAM) for supermassive black hole (SMBH) growth that departs from traditional EPS-based merger tree methods by directly tracking differential SMBH growth via mergers. I will show that this model reveals a clear preference for heavy SMBH seeds across diverse datasets—including recent JWST observations—except in cases of extremely...
The 4-metre Multi-Object Spectroscopic Telescope is currently being installed on the VISTA Telescope (Paranal) and will start observations of multiple science cases at the end of this year. One of the 18 experiments is the Cosmology Redshift Survey (CRS) which is composed of 4 samples: Bright Galaxies (BG, 0.15 < z < 0.4), Luminous Red Galaxies (LRG, 0.4 < z < 1.0), Quasars (QSO, 0.9 < z <...
I present a new gravity theory based on the Schouten and Codazzi tensors. Field equations are second order and generalize Einstein's equations with a well defined correspondence limit. Exact solutions with static spherical symmetry and with the Robertson-Walker metric contain extra terms with the potential to account for dark energy effects. The theory is still under development but it is...
Cosmological model selection, in the framework of Bayesian inference requires the calculation of the Bayesian evidence. This can often be quite challenging, especially if the underlying likelihood function is expensive to evaluate. I will show how a technique called Bayesian Optimisation, based on Gaussian Process regression, can be used to calculate this evidence in far fewer likelihood...
In this study, we explored the FLRW model within f(R,Lm) gravity, focusing on Strange Quark Matter and its role in cosmic evolution. Using 57 observational data points, we derived the best-fit H(z) curve with an impressive R^2 value of 0.9527, showing strong alignment with the ΛCDM model. The deceleration parameter q(z) highlights a smooth transition from deceleration to acceleration,...
In this study, we used the ( f(T) ) gravity framework with the energy-momentum tensor for a perfect fluid to derive key cosmological parameters, including the Hubble parameter ( H ), deceleration parameter ( q ) and Statefinder diagnostics. Model parameters were optimized using an ( R^2 ) test, resulting in ( \beta = 1.312^{+0.013}{-0.014} ), ( \xi = 1.273^{+0.0065}{-0.0071} ),...
Dark Matter (DM) is a cornerstone of the standard cosmological model, yet its fundamental nature remains elusive. Accurate numerical simulations are essential to test competing DM models against observational data. In this work, we propose a novel approach to DM simulations by replacing traditional N-body methods with Physics-Informed Kolmogorov-Arnold Networks (PIKANs). Specifically, we apply...
We assume that at a late stage of inflation, a scalar inflaton field, a thermal plasma, and a spacetime metric coexisted and interacted with each other. We expand them to the linear order around a homogeneous background and combine the perturbations into a set of gauge invariant variables. For the latter we derive evolution equations in the framework of smooth reheating. Having resolved some...
Scale hierarchies are required to reliably describe the thermodynamics of cosmological first-order phase transitions using perturbation theory. At finite temperature, such a hierarchy is provided naturally. One can then use this hierarchy to construct a three-dimensional effective field theory (EFT) that systematically includes thermal resummations to all orders.
Using this EFT framework, I...
QCD-like dark sectors may undergo a first-order chiral phase transition in the early Universe that may lead to production of stochastic gravitational wave background. We consider a class of such dark sectors that feature also dark pions as viable dark matter candidates and study the corresponding strength of the gravitational-wave signal. Importantly, the chiral phase transition is of first...
We investigate the generation of gravitational waves from scalar perturbations at second order in a matter-dominated Friedmann–Robertson–Walker (FRW) universe. Since the representation of gravitational waves in perturbation theory is gauge-dependent, identifying gauge-invariant quantities becomes essential for a physically meaningful interpretation. This leads us to define a new tensor...
Phase transitions are violent and interesting phenomena that could have occurred in the early stages of the universe. Possible perturbative techniques to study these phenomena and predict their gravitational wave background can be used in the presence of a hierarchy of scales, leading to the construction of Effective Field Theories at finite temperature by integrating out the heavier scales....
The large-scale structure of the universe provides valuable information on the fundamental
laws governing its evolution. This structure consists of a network of immense galaxy filaments,
separated by vast cosmic voids, forming an intricate pattern known as the cosmic web, which
is shaped by gravity. To study and better understand these phenomena, cosmologists employ
computational...
Motivated by analogies with the electrodynamics of media, we propose a non-local extension of Einstein’s theory of gravitation formulated within the framework of teleparallel gravity. Employing a specific localizing kernel, we analyze the local limit of the theory at both the background and linear perturbation levels, and confront it with cosmological observations. We demonstrate that the...
Combining measurements of the growth rate of cosmic structure with gravitational lensing is considered as the optimal way to test for deviations from General Relativity on cosmological scales. In my poster, I will demonstrate that this standard method suffers from an important limitation, since models of dark matter with additional interactions can lead to exactly the same signatures as...
Primordial black holes (PBHs) are a unique probe of the early Universe and offer a potential link between inflationary dynamics and dark matter. In this talk, I will present our recent work investigating PBH formation in the presence of local non-Gaussianities, exploiting a logarithmic duality relation to study a variety of inflationary mechanisms that locally deviate from slow-roll dynamics....
Scalar particles traveling faster than a subluminal gravitational wave generate gravitons via gravitational Cherenkov radiation. We investigated graviton production by the primordial plasma within the framework of modified gravity in the early Universe, generating a relic graviton background. By requiring the relic graviton background to remain consistent with the Big Bang Nucleosynthesis...
Physics-Informed Neural Networks (PINNs) have emerged as a powerful tool for solving differen-
tial equations by integrating physical laws into the learning process. This work leverages PINNs to
simulate gravitational collapse, a critical phenomenon in astrophysics and cosmology. We introduce
the Schr¨odinger-Poisson informed neural network (SPINN) which solve nonlinear...
The accelerated expansion of the Universe is canonically attributed to the Dark Energy (DE), encapsulated in the Lambda factor in the Einstein field equations of gravity, but its nature is still not understood. While observations supply strong evidence in favor of the standard model of cosmology Lambda-CDM, a plethora of different modified gravity models (MG) can still arise and describe...
In this work we reflect on the departure from the standard growth of structures induced by two seemingly different, yet comparable extensions to the standard cosmological model: modified gravity and massive neutrinos. Can current Cosmic Microwave Background anisotropy and lensing data tell the difference between a phenomenological modification in the growth of the large-scale structure,...
Based on ArXiv 2504.17680, B. Blachier, C. Ringeval (2025)
Cosmic inflation may exhibit stochastic periods during which quantum fluctuations dominate over the semi-classical evolution. Extracting observables in these regimes is a notoriously difficult program as quantum randomness makes them fully probabilistic. However, among all the possible quantum histories, the ones which are relevant...
The dynamics of neutrinos and antineutrinos within a QED plasma, around MeV temperatures (just prior to their decoupling), influences several key cosmological observables. Precision studies have become timely, and we recently computed the NLO interaction rate as a function of the neutrino momentum and flavour, finding relative corrections on the few percent level [1]. I will summarise this...
Mounting theoretical evidence suggests that the information stored in black holes suppresses their evaporation rate – a quantum effect known as memory burden. This phenomenon opens up a new window for small primordial black holes (PBHs) below $10^{15}\, \text{g}$ as viable dark matter candidates. In this talk, I will discuss observational signals from such small PBHs. Beyond constraints from...
We apply a Convolutional Neural Network (CNN) to Pulsar Timing Array residuals to identify the cosmological contribution to the Stochastic Gravitational wave Background for a variety of different cosmological models.
We find the CNN can accurately identify the cosmological contributions, and reconstruct injected signals with at least as much success as current Bayesian methods, but with...
Pulsar Timing Array (PTA) observations provide strong evidence for a stochastic gravitational wave background (SGWB), potentially originating from astrophysical sources or early universe phenomena. If the SGWB is cosmological, our relative motion with respect to the SGWB rest frame induces a kinematic anisotropy, which could dominate over intrinsic anisotropies, similar to the cosmic microwave...
Gravitational waves (GWs) can be produced by a first-order phase transition in the early Universe via the fluid perturbations induced in the primordial plasma by the expansion and collision of broken-phase bubbles. I will review the production of GWs by the anisotropic stresses of velocity and magnetic fields induced in a first-order phase transition and present analytical estimates and...
Sterile neutrinos with masses on the $\mathrm{eV}$ scale are promising candidates to account for the origin of neutrino mass and the reactor neutrino anomalies. The mixing between sterile and active neutrinos in the early universe could result in a large abundance of relic sterile neutrinos, which depends on not only their physical mass $m_{\rm phy}$ but also their degree of thermalization,...
The axion can address the strong CP problem and also provide a promising dark matter candidate in the form of a condensate of zero-momentum modes. In addition, axion models feature an unavoidable “hot” ensemble of thermally-produced axions acting as dark radiation and thus subject to present and future constraints from the effective number of neutrinos $N_\mathrm{eff}$.
I will concentrate on...
The two-body Decaying Dark Matter (DDM) model extends the standard cold dark matter paradigm by allowing dark matter particles to decay into a massive daughter particle and a relativistic species. This scenario arises naturally in particle physics and has testable implications for cosmological observables. In this talk, I will introduce the model and present updated constraints on the dark...
I will discuss the applications of the Effective Field Theory (EFT) in cosmology.
I will review the main concepts of the EFT of Large-Scale Structure, a theoretical framework that provides a systematic analytic description of cosmological observables on large scales. I will present a general perturbative model for a tracer of matter that depends on the line-of-sight selection effects, and...
Baryonic feedback processes significantly impact weak-lensing observations at small scales, introducing uncertainties and potential biases in cosmological parameter estimates. These challenges can be mitigated by combining weak-lensing data with complementary observations, such as X-ray and Sunyaev-Zeldovich (SZ) effect measurements. In this talk, I will introduce a new baryonification method...
It is found that the DESI observation can be explained by non-minimal coupled gravity. In this talk I will show that the resulting non-minimally coupled scalar-tensor gravity theory, Thawing Gravity (TG), also presents a possible resolution to the cosmological tensions. Using the standard Bayes model comparison method, TG has moderate evidence over $\Lambda$CDM with a Bayes factor $\ln B=+1.5$...
We present a framework that for the first time allows Bayesian model comparison to be performed for field-level inference of cosmological models. We achieve this by taking a simulation-based inference (SBI) approach using neural likelihood estimation, which we couple with the learned harmonic mean estimator in order to compute the Bayesian evidence for model comparison. We apply our framework...
A locally rotationally symmetric Bianchi type-I model has been analyzed with a perfect fluid within the framework of ( f(R, \mathcal{L}_m) ) gravity. The exact field equations were derived, the variable deceleration parameter ( q(t) = \alpha - \frac{\beta}{H} ) has been used here. The cosmological parameters such as energy density, pressure, equation of state, spatial volume, the Hubble...
Intensity mapping surveys of neutral hydrogen (HI) are a new way to measure the large-scale matter distribution of our Universe at low spatial resolution over a wide range of redshifts, and thus constrain cosmological parameters such as the Universal expansion. MeerKAT can be used in a “single-dish” mode to access large cosmic scales above 1 degree that are not accessible to the...
Mapping the distribution of neutral atomic hydrogen (HI) in the Universe through its 21 cm emission line provides a powerful cosmological probe to map the large-scale structures and shed light on various cosmological phenomena. The Baryon Acoustic Oscillations at low redshifts can potentially be probed by sensitive HI intensity mapping experiments and constrain the properties of dark energy....
The large-scale distribution of neutral hydrogen in the late Universe, mapped through the hydrogen 21cm line emission using radio telescopes, holds significant potential to emerge as a key cosmological probe in the coming years. In the work that I’m going to present, we developed a Gaussian likelihood code for the 21cm intensity mapping power spectrum and the 21cm-galaxy clustering...
We develop a novel approach to constrain the Hubble parameter H0 and the primordial power spectrum amplitude As using supernovae type Ia (SNIa) data. By considering SNIa as tracers of the peculiar velocity field, we can model their distance and their covariance as a function of cosmological parameters without the need of calibrators like Cepheids; this yields a new independent probe of the...
The standard Lambda Cold Dark Matter (ΛCDM) cosmological model has proven remarkably successful in describing a broad range of observational data, ranging from the cosmic microwave background (CMB) radiation to the large-scale structure of the Universe. However, recent advances in precision cosmology have revealed persistent statistical discrepancies between independent data sets and...
\begin{abstract}
In this work, we investigate a cosmological model within the framework of ( f(Q,T) ) gravity, incorporating two-fluid dynamics composed of matter and radiation. The model is constructed using the anisotropic Bianchi type-I metric to explore the evolution of the universe in an extended gravitational theory where the non-metricity scalar ( Q ) is coupled with the trace of...
Primordial Gravitational Waves (PGWs) are a key prediction of inflation, and efforts are ongoing to detect them through CMB polarization patterns and direct interferometric detection. In this talk, I will present a novel approach to probing PGWs through their impact on Large-Scale Structure.
PGWs are often assumed to have a negligible effect on structure formation, but in our study, we show...
