Parity-violating Dark Photon Halos

TL;DR

This paper introduces a novel mechanism where parity-violating interactions between dark photons and axions lead to the formation of gravitationally bound dark photon halos, potentially influencing early black hole formation.

Contribution

It proposes a new process for dark photon halo formation via axion-induced tachyonic instability and parity violation, with implications for structure formation and black hole seeds.

Findings

Dark photon halos form with masses from 10^5 to 10^11 solar masses.

Halo sizes range from 1 to 10^6 parsecs.

Vorticity during collapse may facilitate angular momentum transport.

Abstract

We propose a mechanism for the generation of gravitationally bound dark photon halos during the matter-dominated era. Coupled to an ultralight axion field through a parity-violating Chern-Simons term, dark photons can be produced by the tachyonic instability of axion coherent oscillation. The dark photons with a net helicity lead to a metric vorticity and can generate chiral substructures. For axion masses in the range $10^{-28} \, \mathrm{eV} \lesssim m_a \lesssim 10^{-22} \, \mathrm{eV}$, the resulting inhomogeneities collapse to form halos with masses spanning $M_{\rm halo} \sim 10^5 \, M_{\odot}$ to $10^{11} \, M_{\odot}$, with halo sizes ranging from $O(1)$ to $O(10^{6}) \, \mathrm{pc}$. During halo collapse, the induced vorticity could mediate efficient angular-momentum transport, which enables monolithic collapse and provides primordial seeds for the early formation of supermassive black holes.