Searching for String Bosenovas with Gravitational Wave Detectors

Abstract

We study the phenomenology of string bosenova explosions in vector superradiance clouds around spinning black holes, focusing on the observable consequences in gravitational wave detectors and accelerometers. During the growth of the superradiance cloud, the dark gauge field might reach a critical field strength, when a network of dark photon strings is produced via a superheated phase transition. These dark photon strings will then absorb the energy in the background fields and get ejected from the cloud, with total energy as large as the rotational energy of the black hole. In this paper, we study the subsequent evolution of this dense string network, and the resulting observational consequences depending on the unknown string tension, or almost equivalently, the ratio between the quartic and the gauge coupling in the Abelian Higgs model. Strings with large tension will dissipate into gravitational waves, detectable over a wide range of frequencies, from $\sim$ nHz near supermassive black holes, to $\gtrsim 10$ MHz around stellar mass black holes. This is the first known source of high frequency gravitational waves, unconstrained by cosmological observations. The strain of this gravitational wave can be larger than $10^{-14}$ at low frequencies, lasting for longer than typical duration of experiments. Small tension strings, with total lengths in the network as large as $10^{40}$ km, can travel to the earth with appreciable rate from any black hole in the Milky Way and interact with earth based accelerometers. If the Standard Model particles are directly charged under the dark photon, e.g. B-L, this interaction leads to an acceleration of Standard Model particles that is independent of the coupling constant. We work out the spectral density of this acceleration, and project that modern accelerometers and equivalence principle tests can be sensitive to the passing of these strings.