Stochastic and Resolvable Gravitational Waves from Ultralight Bosons

Abstract

Ultralight scalar fields around spinning black holes can trigger superradiant instabilities, forming a longlived bosonic condensate outside the horizon. We use numerical solutions of the perturbed field equations and astrophysical models of massive and stellar-mass black hole populations to compute, for the first time, the stochastic gravitational-wave background from these sources. In optimistic scenarios the background is observable by Advanced LIGO and LISA for field masses ms in the range ∼ [2 × 10 −13 , 10 [20,29,[35][36][37][38][39]: the BH spins down, transferring energy and angular momentum to a mostly dipolar boson condensate until ω R ∼ mΩ H . The energy scale is set by the boson mass m s ≡ µ , which implies that ω R ∼ µ and that the instability saturates at µ ∼ mΩ H (in units G = c = 1). The condensate is then dissipated through the emission of mostly quadrupolar GWs, with frequency set by µ. The mechanism is most effective when the boson's Compton wavelength is comparable to the BH's gravitational radius: detailed calculations show that the maximum instability rate for scalar fields corresponds to M µ 0.42 [23]. Therefore, the instability window corresponds to masses m s ∼ 10 −14 -10 −10 eV and m s ∼ 10 −19 -10 −15 eV for LIGO and LISA

Science case for the Einstein telescope

“…for particle masses of 10 −21 − 10 −11 eV), they can extract rotational kinetic energy from the black hole through "superradiance" to feed the formation of a bosonic "cloud" with mass up to ∼ 10% of the black hole [179][180][181]. These clouds annihilate over a much longer timescale than their formation, through the emission of nearly monochromatic gravitational waves which could be detected either directly or as a stochastic background from a large number of such objects throughout the Universe [182,183]. Additionally, measuring the distribution of black hole masses and spins can yield an indication of the prevalence of superradiance through light scalars.…”

Gravitational collider physics

“…There is an extensive literature on superradiance with scalar [21][22][23][36][37][38][39][40][41][42][43][44][45] and vector fields [35,[46][47][48][49][50][51][52][53][54][55][56]. We will briefly review the key features that will be relevant for the analysis in this paper.…”

Constraints on anharmonic corrections of fuzzy dark matter

“…Aside from the standard searches for axions, there is a wealth of dedicated searches and projected experiments on the lookout for ultralight axions. These include studies of the neutral hydrogen distribution in the universe [31,32], laboratory constraints based on nuclear interactions [33], variation of fundamental constants [34,35], astrophysical bounds [36][37][38], gravitational wave searches [39,40] and analysis of CMB spectral distortions [41,42]. A prominent feature of the model is the presence of anharmonic corrections over the mass -2 -…”