Speaker
Description
The standard Planck ΛCDM model is well known to encounter several tensions when
confronted with various cosmological data, including the neutrino mass and the DESI BAO
tensions. The former tension refers to the neutrino mass constraint from CMB fitting being
substantially below the lower bound from neutrino oscillation experiments. In the latter, the
BAO scales measured by DESI disagree significantly with the Planck ΛCDM prediction at
redshifts below 1. To resolve these tensions, we examine a simple and natural extension of
the standard ΛCDM model, which allows relic neutrinos to have finite chemical potentials.
We confront this ΛCDMξ model, ΛCDM with neutrino mass Mν and degeneracy ξ3 as
additional parameters, with various cosmological datasets. Fitting the ΛCDMξ model to the
CMB temperature data, we find 3σ evidence for nonzero neutrino mass (Mν = 0.57 + 0.17 −
0.13 eV) and degeneracy (ξ3 = 1.13 + 0.41 − 0.19), and the O(1) neutrino degeneracy
parameter is compatible with galaxy pairwise velocity and Big Bang Nucleosynthesis (BBN)
data. Furthermore, the recent DESI BAO data strongly prefer the ΛCDMξ model to the
Planck ΛCDM model.
