Impact of Warm Dark Matter on the Cosmic Neutrino Background Anisotropies

Christopher G Tully,Gemma Zhang

doi:10.3390/universe8020118

Abstract

The Cosmic Neutrino Background (CνB) 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 CνB 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 CνB 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 CνB 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 CνB anisotropies begin to become sensitive to differences in WDM and CDM cosmologies. The precision measurement of high-l multipoles in the CνB 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.

Highlights

The “null assumption” of the cosmological principle is that the universe on large scales is homogeneous and isotropic
The nature of the non-plasma/dark matter is largely unknown with an important exception being the fraction of neutrinos which are predicted from the Cosmic Neutrino Background (CνB)
Cold dark matter is assumed to have exactly zero pressure at high redshift while warm dark matter carries some degree of non-zero radiation pressure according to its mass [3,4]

Summary

Introduction

The “null assumption” of the cosmological principle is that the universe on large scales is homogeneous and isotropic. Deviations from this assumption are, a measure of large-scale structure formation. Anisotropies in the CνB massive neutrinos are an important measure of large-scale structure formation and reveal an earlier period of dynamics than viewed at equivalent distances using optical probes. The variations on the neutrino sky are, a measure of the total matter power spectrum at redshifts relevant to CνB anisotropy growth. Depending on the model for dark matter, the total matter power spectrum can differ during the period of CνB anisotropy growth. Cold dark matter is assumed to have exactly zero pressure at high redshift while warm dark matter carries some degree of non-zero radiation pressure according to its mass [3,4]

CνB Angular Power Spectra

Quantum Amplification of Neutrino Capture

Results and Conclusions