Impact of Warm Dark Matter on the Cosmic Neutrino Background Anisotropies

TL;DR

This paper investigates how Warm Dark Matter influences the anisotropies of the Cosmic Neutrino Background, highlighting differences from Cold Dark Matter and potential observational signatures in high-resolution neutrino sky maps.

Contribution

It demonstrates that WDM models with sterile neutrinos cause measurable differences in CνB anisotropies compared to CDM, especially at high multipole moments.

Findings

CνB anisotropies decrease at high multipoles in WDM models.

Differences between WDM and CDM become observable at scales similar to baryonic oscillations.

High-$l$ multipole measurements could distinguish WDM from CDM in future experiments.

Abstract

The Cosmic Neutrino Background (C$\nu$B) anisotropies for massive neutrinos are a unique probe of large-scale structure formation. The redshift-distance measure is completely different for massive neutrinos as compared to electromagnetic radiation. The C$\nu$B anisotropies in massive neutrinos grow in response to non-relativistic motion in gravitational potentials seeded by relatively high $k$-modes. Differences in the early phases of large-scale structure formation in Warm Dark Matter (WDM) versus Cold Dark Matter (CDM) cosmologies have an impact on the magnitude of the C$\nu$B anisotropies for contributions to the angular power spectrum that peak at high $k$-modes. We take the examples of WDM consisting of 2, 3 or 7 keV sterile neutrinos and show that the C$\nu$B anisotropies for 0.05 eV neutrinos drop off at high-$l$ multipole moment in the angular power spectrum relative to CDM. At the same angular scales that one can observe baryonic acoustical oscillations in the CMB, the C$\nu$B anisotropies begin to become sensitive to differences in WDM and CDM cosmologies. The precision measurement of high-$l$ multipoles in the C$\nu$B neutrino sky map is a potential possibility for the PTOLEMY experiment with thin film targets of spin-polarized atomic tritium superfluid that exhibit significant quantum liquid amplification for non-relativistic relic neutrino capture.