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Astrophysics, Relativity, and Cosmology Seminar - Itamar Allali (Brown University) "Constraints on Light Species from DESI 2024: Neutrinos, Dark Radiation, and the Hubble Tension"

Event Type
Seminar/Symposium
Sponsor
Department of Physics
Location
Loomis 464
Virtual
wifi event
Date
Nov 20, 2024   12:00 pm  
Speaker
Itamar Allali
Contact
Deanna Frye
E-Mail
ddebord@illinois.edu
Views
49
Originating Calendar
Physics - Astrophysics, Relativity, and Cosmology Seminar

Measurements of Baryon Acoustic OScillations (BAO) provide a precise probe of the particle content of cosmology within and beyond ΛCDM, with recent updates by the Dark Energy Spectroscopic Instrument (DESI) providing for updated constraints and inferences. I will first investigate the claims from DESI, combined with the CMB data from the Planck 18 PR3 dataset and the Planck PR4+ACT DR6 lensing data, of a strong upper bound on the sum of the neutrino masses ∑mν > 0.072 eV, which would exclude the inverted neutrino hierarchy and put some tension on even the standard hierarchy. I will show that this bound gets significantly relaxed when combining the new DESI measurements with the Hillipop + Lollipop likelihoods, based on the Planck 2020 PR4 dataset, and especially with supernovae datasets such as Pantheon+ and DES-SN5YR. On a different note, I will investigate the presence of extra relativistic degrees of freedom in the early Universe, contributing to the effective number of neutrinos 𝑁eff, as Δ𝑁eff≡𝑁eff−3.044≥0, in light of the DESI data. Considering these one-parameter extensions of the ΛCDM model where dark radiation (DR) is free streaming or behaves as a perfect fluid, I will report on the significant relaxation of upper bounds on Δ𝑁eff with respect to previous BAO data from SDSS+6dFGS. I will comment on the effects of constraints from primordial element abundances. Considering also DR produced after the epoch of Big Bang Nucleosynthesis (BBN), I will discuss the impacts of these new data on the Hubble tension, and potential evidence for DR beyond ΛCDM. Lastly, I will also return to evaluating the impact of these data on neutrino mass constraints in the context of the DR models.

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