Parity-violating Dark Photon Halos

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 $M_{\mathrm{halo}}\sim 10^5{M}_{\odot }$ 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.

Comments: 7 pages, 3 figures