Probing vector chirality in the early Universe

TL;DR

This paper investigates the potential to detect primordial vector parity violation through galaxy spins, demonstrating that such signals can survive nonlinear evolution and be observed with upcoming surveys like DESI BGS.

Contribution

The study introduces a novel method to generate initial conditions with parity asymmetry without affecting the matter power spectrum and demonstrates the detectability of primordial vector chirality through galaxy spins.

Findings

Over 50% of initial parity asymmetry persists in late-time halo spins.

A maximum detection significance of 13σ is forecasted with DESI BGS.

Primordial vector parity violation survives nonlinear gravitational evolution.

Abstract

We explore the potential of using late-time galaxy spins to test the parity symmetry of primordial vector fossils. Using $N$-body simulations, we analyze halo spins as a reliable proxy for galaxy spins to investigate the detectability of this effect. We develop a novel approach to generate initial conditions (ICs) that have substantial parity asymmetry but do not alter the initial matter power spectrum. We construct the initial spin fields from the parity broken ICs and halo spin fields using late-time halos evolved from such ICs. Focusing on the helicity of these vector fields, we detect substantial asymmetry in the initial spin field. In addition, we find that over $50\%$ of the initial spin field's asymmetry remains in the late-time halo spin field on a range of scales. Based on mock galaxy spin fields derived from the halo spin fields, we forecast that a maximum detection at $13\sigma$ is possible with the final DESI BGS for the model considered in this analysis. Our findings demonstrate that primordial vectorial parity violation survives nonlinear gravitational evolution, and thus, can be effectively probed with galaxy spins at late times.