I present new cosmological fits to a Hubble diagram built from supernovae and a homogeneous quasar sample spanning a redshift interval z = 0.7--3.5. The quasar distances are derived from the non-linear relation between X-ray and UV luminosities, and the sample is selected to minimize dust reddening, gas obscuration, host-galaxy contamination, and selection biases as described in the companion...
The persistent discrepancy between the locally measured Hubble constant, derived from Cepheids and Type Ia supernovae, and the value inferred from the cosmic microwave background underscores the need for independent cosmological probes. Cosmic chronometers provide a direct, model-independent measurement of the expansion history, but their accuracy is currently limited by systematic...
Despite its remarkable success, the standard cosmological model, $\Lambda$CDM, faces several serious challenges. Among them, the “Hubble tension”—the discrepancy between the value of the Hubble constant inferred from observations of the early Universe and that obtained directly from local measurements—is one of the most important problems in modern cosmology. As a possible solution to this...
We study the clustering of an optically identified galaxy cluster catalogue from the fourth data release of the Kilo Degree Survey (KiDS-1000). The photometric sample was identified by the Adaptive Matched Identifier of Clustered Objects (AMICO) algorithm and consists of 9049 clusters with $S/N\geq3.5$, in redshift range $0.1\leq z<0.8$, spread over an effective area of 838.78 deg$^2$. They...
The Distance Network provides a unified, statistically rigorous framework for a robust combined statistical analysis of a broad variety of local measurements of the Hubble constant. This approach provides full error propagation, accounting for commonalities between measurements, and statistical tests to identify possible outliers. We obtain an improved determination of the Hubble constant,...
Convergence in the value of H0 from Type Ia Supernovae
In this talk, I will review new findings that point towards a
concordant value of the Hubble constant (H0) from data based in
the SH0ES collaboration and the Chicago--Carnegie Supernova Project
using the ''SNe Ia twins method'' and using, as well, the common
''SNe Ia light curve method''.
There has been usually a discrepancy...
Recent results from the Dark Energy Spectroscopic Instrument has shifted our understanding about dark energy, preferring about 2-3 sigma evidence for evolving dark energy. The phantom crossing of the dark energy equation of state has motivated the search of new cosmological models. In this talk, I will discuss how combinations of data from Rubin Observatory LSST, Simons Observatory and SKAO...
We apply Simulation-Based Inference ('SBI') to the cosmic dipole problem for the first time, measuring the distribution of quasar counts over the sky in the infrared CatWISE2020 sample. Our SBI-based approach alleviates systematic effects arising from the WISE instrument itself and enables direct inference of the sample's dipole. We find a dipole that is twice as large as the CMB expectation...
The cosmic dipole observed in the matter distribution of galaxy surveys consistently disagrees with the kinematic expectation set by the cosmic microwave background, posing a serious challenge to the Cosmological Principle and the standard model of cosmology. However, the fidelity of the dipoles we infer rests on our understanding of the systematics present in the surveys. For many...
Recent observations have revealed the presence of cosmic structures at even very large scales in the Universe. This, along with cosmological tensions, motivates re-examination of the standard paradigm of the concordance model based on assumptions of homogeneous matter distribution at various cosmological scales. The observed large-scale matter inhomogeneities may possibly impact the background...
I perform a model-independent reconstruction of the background pre-recombination expansion history of the Universe. I find that purely early-time resolutions to the Hubble tension, satisfying the geometric CMB constraints, exist at the background level. This class of solutions requires a smooth transition around matter-radiation equality, characterized by a ≃15% expansion rate enhancement...
Fast Radio Bursts (FRBs) are millisecond radio transients with high dispersion measures, making them powerful tracers of ionized matter across cosmological distances. In this talk, I will present two complementary approaches, Bayesian analysis and machine learning, applied to a set of localized FRBs to rigorously test the consistency of the $\Lambda$CDM model at late cosmic epoch. Our results...
Detecting primordial gravitational waves (PGWs) is one of the main goals for upcoming Cosmic Microwave Background (CMB) experiments. Achieving this objective requires precise removal of the CMB gravitational lensing signal from polarisation maps -- so-called de-lensing -- as well as cleaning the maps from diffuse Galactic foregrounds. In this talk, I will present studies on influence of the...
We apply two variants of Physics-Informed Neural Networks (PINNs) to reconstruct the Type Ia supernova absolute magnitude M_B(z) from joint BAO and supernova data under four cosmological models (\LambdaCDM, CPL, GEDE, \Lambda_sCDM) and two DESI DR2 fiducial sets. A heteroscedastic single-network method tested across four constraint configurations establishes that the Etherington distance...
In general relativity, cosmic acceleration is a statement about geometry---the timelike defocusing of the comoving congruence---and the field equations source it with mass--energy combinations, not with any equation-of-state ratio. Evolving dark energy is now back at the center of cosmology, and several scenarios under active discussion---sign-switching $\Lambda_{\rm s}$CDM and AdS-to-dS...
Recent cosmological data, including DESI DR2, highlight significant tensions within the $\Lambda$CDM paradigm. When analyzed in the context of General Relativity (GR), the latest DESI data favor a dynamical dark energy (DDE) equation of state, $w(z)$, that crosses the phantom divide line $w=-1$. However, this framework prefers a lower Hubble constant, $H_0$, than Planck 2018, thereby worsening...
Recent hints of dynamical dark energy, including a possible crossing of the phantom divide inferred from the latest cosmological data, have motivated the search for viable theoretical explanations. Scalar fields non-minimally coupled to gravity with a coupling of the form $F(\varphi)=1+\alpha\varphi^2$ are physically motivated and have emerged as promising candidates, providing a significantly...
A cosmological pseudo-scalar field provides a compelling realization of dynamical
dark energy (DE). If its coupling to photons is non-negligible, the cosmic microwave background acquires a rotation of its polarization plane, known as cosmic birefringence. We discuss pseudo-scalar models that can simultaneously account for the recent hints of evolution in the equation of state of DE and of the...
The Universal Rotation Curve provides a powerful empirical framework to investigate the distribution of luminous and dark matter in disk galaxies. By adopting normalized radial and velocity coordinates, we investigate the emergence of universal kinematic properties across galaxies with different masses and luminosities. The resulting co-added rotation curves will be analyzed through different...
The Integrated Sachs--Wolfe (ISW) effect probes the late-time evolution of gravitational potentials and provides a complementary test of the nature of dark energy. We investigate whether the redshift evolution of the ISW effect can provide new constraints on the time evolution of dark energy. We consider theoretical predictions for the standard ΛCDM cosmology and alternative w0waCDM models...
Robust hydrodynamic simulations are necessary for placing strong constraints on cosmological parameters through the analysis pipelines of observations of statistics such as galaxy clustering. However, for these purposes, the simulations need both large box size and high resolution, which is computationally prohibitive. In this work we use the connection between galaxies and their host dark...
The latest DESI DR2 BAO data favor a dynamical dark energy equation of state, reviving the question of whether late-time modifications of gravity can ease the tensions of the standard model. We test a generalized exponential $f(R)$ model with massive neutrinos, which produces an effective dynamical dark energy at low redshift while recovering $\Lambda$CDM at early times. Through a Bayesian...
Effective actions with higher curvature terms can have cosmological solutions exhibiting a transient phantom regime. I will discuss a generalization of multifield cosmology in the presence of a higher curvature term, namely the Gauss-Bonnet term. I will show that in this context there are novel features of the so called rapid turn regime, in which multifield models of cosmic acceleration (i.e....
The timescape cosmology returns to first principles, to explain apparent cosmic acceleration in the statistical regime of general relativity. As inhomogeneities in density and expansion grow, they back react on the average cosmic expansion, which differs from conventional FLRW models. Crucially, dynamical spatial curvature arises as time-varying gradients of the kinetic energy of expansion,...
The persistent  tension and the improved supernova–BAO consistency under dynamical dark energy after DESI DR2 motivate rethinking how dark energy evolution is parametrized. We formulate it directly through the inertial mass density (IMD), $\rho+p$IMD, and show that an IMD evolving from a negative to an equal positive constant toward z->0 can induce a past sign change in  itself, with...
The cosmographic condition $j(z)=1$ provides the kinematical signature of the spatially flat $\Lambda$CDM model independently of any specific dark-energy or modified-gravity theory. We investigate the extent to which current observations permit departures from this condition by considering three phenomenological ``almost-$\Lambda$CDM'' cosmographic closures in which the cosmic jerk differs...
The $\Lambda$CDM model successfully explains a wide range of cosmological observations; however, persistent discrepancies most notably the $H_0$ tension between early and late time measurements challenge its completeness. No proposed extension has yet resolved this tension while retaining the overall success of $\Lambda$CDM. We have investigated whether the $H_0$ tension can be associated with...
In this work we study a scale invariant gravity theory containing two scalar fields, dust particles and a measure defined from degrees of freedom independent of the metric. The integration of the degrees of freedom that define the measure spontaneously break the scale symmetry, leaving us in the Einstein frame with an effective potential that is dependent on the density of the particles. The...
Cosmological tensions between early- and late-Universe probes, most notably the Hubble tension in $H_0$ have intensified scrutiny of the ΛCDM paradigm and motivated flexible dark-energy scenarios beyond a cosmological constant. A persistent obstacle is that the functional form of the dark-energy equation of state $w(a)$ is usually chosen by hand (e.g.wCDM or CPL), so potentially viable models...
In this seminar, I will present a novel mechanism for cosmic acceleration driven by primordial black holes with effective repulsive behavior. Using a new Swiss Cheese cosmological framework, I will discuss four black hole spacetimes—Hayward, Bardeen, Dymnikova, and de Sitter-Schwarzschild—to show that this acceleration emerges naturally from the geometry itself. The results suggest that...
