ΛCDM Model and Cosmic Probes: Overview

• Marco Muccino (Laboratori Nazionali di Frascati)

Room: Aula Seminari The current status of the ΛCDM cosmological model is reviewed. The main observables and model constraints obtained from cosmic probes, such as standard "candles" like supernovae, "rulers" like the cosmic microwave background radiation and baryonic acoustic oscillations (BAO), and "chronometers" like the observational Hubble rate data are discussed. In particular, the BAO data release from the Dark Energy Spectroscopic Instrument (DESI) is introduced and compared with previous BAO data sets,

Dark Radiation with Baryon Acoustic Oscillations from DESI 2024 and the H0 tension

• Alessio Notari (Universitat de Barcelona)

Room: Aula Seminari I will present a search for extra relativistic degrees of freedom, or dark radiation (DR), in the early Universe in light of the recent measurements of Baryon Acoustic Oscillations (BAO) by the DESI collaboration, contributing to the so-called effective number of neutrinos N_eff. We analyze one-parameter extensions of the LCDM model where dark radiation is free streaming or behaves as a perfect fluid, due to self-interactions. We report a significant relaxation, with respect to previous BAO data, of upper bounds on N_eff when employing Planck data (and supernovae data from Pantheon+). Applying constraints from Big Band Nucleosynthesis (BBN) leads to slightly tighter constraints, but they can be avoided if DR is produced after BBN. For fluid DR we estimate the "H0 tension” with the SH0ES measurement to be around 2.3-2.8 sigma level, and for free-streaming DR the tension is below 3 sigma, if production occurs after BBN. This lesser degree of tension motivates a combination with SH0ES in these cases, resulting in a 4.4-5 sigma evidence for dark radiation and large improvements in $\chi^2$ over LCDM (from -18 to -25).

Does dark energy really revive using DESI 2024 data

• Marco Muccino (Laboratori Nazionali di Frascati)
• Orlando Luongo (Universita di Camerino)

Room: Aula Seminari The impact of the Dark Energy Spectroscopic Instrument (DESI) 2024 data on dark energy scenarios is critically revised. Through several cosmographic analyses and assuming three typologies of dark energy models, i.e. thermodynamic, Taylor expansions, and parameterizations, Monte Carlo Markov chain analyses are computed, showing significant departures from the standard ΛCDM model. Afterwards, more refined analyses, in which a controversial data point placed at z=0.51 is removed, definitely align with the concordance standard model in analogy to previous findings. This robustly indicates possible evidence for systematic issues in the DESI catalogue. Thus, the corresponding outcome is finally compared and contrasted with recent publications toward the use of DESI 2024 data. Expectations for new data release are also debated.