Vortex String Formation in Black Hole Superradiance of a Dark Photon with the Higgs Mechanism

TL;DR

This paper investigates how nonlinear effects, specifically vortex string formation due to the Higgs mechanism, influence black hole superradiance of a vector boson, revealing complex dynamics and energy release patterns.

Contribution

It introduces the first nonlinear evolution study of black hole superradiance involving a vector boson acquiring mass via the Higgs mechanism, highlighting vortex string formation and energy outbursts.

Findings

Superradiant instability can cause transient symmetry restoration and vortex string formation.

The energy release during these events is primarily bosonic radiation, not gravitational waves.

The superradiant growth cycle can repeat with reduced spin-down rates.

Abstract

Black hole superradiance, which only relies on gravitational interactions, can provide a powerful probe of the existence of ultralight bosons that are weakly coupled to ordinary matter. However, as a boson cloud grows through superradiance, nonlinear effects from interactions with itself or other fields may become important. As a representative example of this, we use nonlinear evolutions to study black hole superradiance of a vector boson that attains a mass, via a coupling to a complex scalar, through the Higgs mechanism. For the cases considered, we find that the superradiant instability can lead to a transient period where the scalar field reaches its symmetry restoration value, leading to the formation of closed vortex strings, the temporary disruption of the exponential growth of the cloud, and an explosive outburst of energy. After the cloud loses sufficient mass, the superradiant growth resumes, and the cycle repeats. Thus, the black hole will be spun down but, potentially, at a much lower rate compared to when nonlinear effects are unimportant, and with the liberated energy going primarily into bosonic radiation instead of gravitational waves.