Dark photon vortex formation and dynamics

TL;DR

This paper investigates the formation and evolution of vortices in dark photon dark matter, highlighting their dynamics, phase transitions, and potential observational signatures such as gravitational waves and magnetic flux lines.

Contribution

It introduces the concept of vortex formation in dark photon clouds from superradiance and explores their evolution, dissipation, and observational implications, a novel aspect in dark matter studies.

Findings

Vortex strings form in dark photon clouds and evolve into uncorrelated loops.

Dark photon vortex dynamics resemble phase transitions in condensed matter.

Vortex evolution leads to gravitational wave and magnetic flux signatures.

Abstract

We study the formation and evolution of vortices in $U(1)$ dark photon dark matter and dark photon clouds that arise through black hole superradiance. We show how the production of both longitudinal mode and transverse mode dark photon dark matter can lead to the formation of vortices. After vortex formation, the energy stored in the dark photon dark matter will be transformed into a large number of vortex strings, eradicating the coherent dark photon dark matter field. In the case where a dark photon magnetic field is produced, bundles of vortex strings are formed in a superheated phase transition, and evolve towards a configuration consisting of many string loops that are uncorrelated on large scales, analogous to a melting phase transition in condensed matter. In the process, they dissipate via dark photon and gravitational wave emission, offering a target for experimental searches. Vortex strings were also recently shown to form in dark photon superradiance clouds around black holes, and we discuss the dynamics and observational consequences of this phenomenon with phenomenologically motivated parameters. In that case, the string loops ejected from the superradiance cloud, apart from producing gravitational waves, are also quantised magnetic flux lines and can be looked for with magnetometers. We discuss the connection between the dynamics in these scenarios and similar vortex dynamics found in type II superconductors.