Probing parity violation in the early universe using galaxy spins

Junsup Shim^1*, Ue-Li Pen^1,2, Hao-Ran Yu³, Teppei Okumura^1,4

¹Astronomy and Astrophysics, Academia Sinica, Taipei, Taiwan
²Canadian Institute for Theoretical Astrophysics, University of Toronto, Toronto, Canada
³Department of Astronomy, Xiamen University, Xiamen, China
⁴Kavli Institute for the Physics and Mathematics of the Universe (WPI), he University of Tokyo, Tokyo, Japan

* Presenter:Junsup Shim, email:jsshim0312@gmail.com

Parity symmetry is a fundamental principle in physics, making its violation a key indicator of new physics beyond the standard models. In this study, we investigate the detectability of parity violation in the early universe through galaxy spins at low redshifts. Using N-body simulation, we consider halo spins as proxies for galaxy spins and explore how effectively primordial vectorial parity asymmetry is preserved. We develop a method to generate initial conditions with significant parity asymmetry without altering the initial matter power spectrum. We track the evolution of halo spin fields from these initial conditions, focusing on helicity to measure asymmetry. The results show that over 50% of the primordial asymmetry persists in the late-time halo spin field. Given the strong correlation between halo spins and galaxy spins, we expect that galaxy samples from DESI BGS could detect such signals at a significant level. Our findings suggest that galaxy spins serve as a reliable probe for testing primordial parity violation, offering a new tool for searching beyond-standard physics.

Keywords: primordial parity violation, parity asymmetry, galaxy spin, halo spin, helicity