Effects of primordial fluctuations on relic neutrino simulations

TL;DR

This paper demonstrates that primordial fluctuations significantly influence relic neutrino anisotropies and abundance, emphasizing the importance of including these initial conditions in simulations for accurate future C$ u$B observations.

Contribution

The study introduces the inclusion of primordial fluctuations in neutrino initial conditions within N-1-body simulations, highlighting their impact on relic neutrino anisotropies.

Findings

Primordial fluctuations affect relic neutrino anisotropies similarly to large-scale structures.

Including primordial fluctuations alters the predicted abundance of relic neutrinos.

Proper modeling of initial conditions is crucial for future C$ u$B observational data analysis.

Abstract

After decoupling, relic neutrinos traverse the evolving gravitational imhomogeneities along their trajectories. Once they turn non-relativistic, this results in a significant amplification of the anisotropies in the cosmic neutrino background (C$\nu$B). Past studies have reconstructed the phase-space distribution of relic neutrinos from the local distribution of matter (accounting for the Milky Way halo and the surrounding large-scale structures), but have neglected the C$\nu$B anisotropies in the initial conditions of neutrino trajectories. Using our previously developed N-1-body simulation framework, we show that including these primordial fluctuations in the initial conditions can be important, as it produces similar effects on the abundance and anisotropies of the C$\nu$B as the inclusion of large-scale structures beyond the Milky Way halo. Interpretability of data from future C$\nu$B observatories like PTOLEMY therefore depends on correctly modelling these effects.