Superradiance in massive vector fields with spatially varying mass

Abstract

Superradiance is a process by which massive bosonic particles can extract energy from spinning black holes, leading to the build up of a "cloud" if the particle has a Compton wavelength comparable to the black hole's Schwarzschild radius. One interesting possibility is that superradiance may occur for photons in a diffuse plasma, where they gain a small effective mass. Studies of the spin-0 case have indicated that such a build up is suppressed by a spatially varying effective mass, supposed to mimic the photons' interaction with a physically realistic plasma density profile. We carry out relativistic simulations of a massive Proca field evolving on a Kerr background, with modifications to account for the spatially varying effective mass. This allows us to treat the spin-1 case directly relevant to photons, and to study the effect of thinner disk profiles in the plasma. We find similar qualitative results to the scalar case, and so support the conclusions of that work: either a constant asymptotic mass or a shell-like plasma structure is required for superradiant growth to occur. We study thin disks and find a leakage of the superradiant cloud that suppresses its growth, concluding that thick disks are more likely to support the instability.

The problem with Proca: ghost instabilities in self-interacting vector fields

“…Since the self-interactions of BSM fields are largely unconstrained, the question of how robust superradiance is to them is important for the derived constraints and observables. For photons confined in a plasma, where an effective mass arises from environmental effects, self-interactions are an essential component of the model [7,9,[49][50][51][52][53][54]. It has been suggested that self-interactions may quench the superradiant growth before an explosion is reached, but the existing literature only applies to the perturbative regime where M µ 1 [55,56] (we employ geometrical units G = c = 1).…”

Superradiant instabilities by accretion disks in scalar-tensor theories

“…The scope of this work is to investigate whether this superradiant instabilities can arise if one considers realistic models of accreting BHs. A similar analysis was recently performed in [11] in the context of plasma-driven [12,13] superradiant instabilities of photons in GR for BHs accreting a tenuous plasma, using a spin-0 toy model (see also [14] for an extension to the Proca case, and [15,16] for a recent analysis of photon-plasma interactions in curved spacetime). It was shown in [11] that the complex geometry of accretion disks and the high values of plasma density near the BH can significantly quench the instability.…”

Dark photon superradiance quenched by dark matter

“…However, as number densities can reach extreme values in the process, the effect of interactions can be crucial, even for very weakly interacting fields. Recent studies have considered the effect of self-interactions, both for scalar and vector fields [8,9], axion-photon couplings [10,11], interactions with astrophysical plasmas [12][13][14][15][16][17][18], and models of DPs kinetically mixed with Standard Model photons [19].…”