Mini-Workshop: Theoretical implications on the first results of the Desi experiment

Friday 24 May 2024, 11:00 → 16:50 Europe/Rome

Aula Seminari (Laboratori Nazionali di Frascati (Rome), Italy)

Danilo Babusci (Istituto Nazionale di Fisica Nucleare), Federico Mescia (Istituto Nazionale di Fisica Nucleare)

Our leading model of the universe is known as Lambda CDM. It includes both a weakly interacting type of matter (cold dark matter, or CDM) and dark energy (Lambda). Both matter and dark energy shape how the universe expands – but in opposing ways. Matter and dark matter slow the expansion down, while dark energy speeds it up. The amount of each influences how our universe evolves. This model does a good job of describing results from previous experiments and how the universe looks throughout time.

But, with just its first year of data, Dark Energy Spectroscopic Instrument (DESI) has been able to analyze the expansion history of the young universe with over 99% accuracy. The data from DESI has provided unprecedented measurements of the expanding universe, offering new insights into dark energy.  When results are combined with data from other studies, there are some subtle differences with what Lambda CDM would predict. There are some hints pointing at small temporal variations in the density of dark energy.

 

As DESI gathers more information during its five-year survey, these early results will become more precise, shedding light on whether the data are pointing to different explanations for the results we observe or the need to update our model. 

11:00 → 11:45 ΛCDM Model and Cosmic Probes: Overview

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,

Speaker: Marco Muccino (Laboratori Nazionali di Frascati)

Muccino-INFN-DESI1.pdf

11:45 → 13:00 Dark Radiation with Baryon Acoustic Oscillations from DESI 2024 and the H0 tension

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).

Speaker: Alessio Notari (Universitat de Barcelona)

DESI_DR_Talk_AN.pdf

13:00 → 14:30 Lunch

Lunch

14:30 → 16:00 Does dark energy really revive using DESI 2024 data

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.

Speakers: Marco Muccino (Laboratori Nazionali di Frascati), Orlando Luongo (Universita di Camerino)

Muccino-INFN-DESI2.pdf

16:00 → 16:30 Coffee Break: Sofa room below Aula Seminari