Dynamical friction in the primordial neutrino sea

TL;DR

This paper investigates how the primordial neutrino background causes dynamical friction on dark matter haloes, potentially affecting galaxy redshift surveys and offering a way to probe neutrino properties.

Contribution

It quantifies the dynamical friction effect of the cosmic neutrino background on dark matter haloes, highlighting its dependence on neutrino mass and halo properties.

Findings

Dynamical friction scales as m_ν^4 times relative velocity.

The effect increases with halo mass.

Galaxy surveys can detect this effect via redshift space distortions.

Abstract

Standard big bang cosmology predicts a cosmic neutrino background at $T_\nu \simeq 1.95~$K. Given the current neutrino oscillation measurements, we know most neutrinos move at large, but non-relativistic, velocities. Therefore, dark matter haloes moving in the sea of primordial neutrinos form a neutrino wake behind them, which would slow them down, due to the effect of {\it dynamical friction}. In this paper, we quantify this effect for realistic haloes, in the context of the halo model of structure formation, and show that it scales as $m_\nu^4$ $\times$ relative velocity, and monotonically grows with the halo mass. Galaxy redshift surveys can be sensitive to this effect (at $>3\sigma$ confidence level, depending on survey properties, neutrino mass and hierarchy) through redshift space distortions (RSD) of distinct galaxy populations.