Systematic Uncertainties in Ultralight Boson Constraints from Superradiance

Author(s)

Aswathi, P.S., Sun, Ling

Abstract

Ultralight bosons are well-motivated candidates for physics beyond the Standard Model and may constitute part or all of the dark matter. Black-hole superradiance provides a powerful means of probing these particles through their gravitational interaction with rotating black holes. This mechanism has motivated a growing body of constraints from electromagnetic measurements of black-hole spins and, more recently, gravitational-wave observations. Gravitational-wave probes draw on several distinct signatures: the spins of merging binary black holes, gravitational radiation emitted by boson clouds, and potential imprints of cloud-induced changes to binary dynamics. The interpretation of these probes depends on method-specific astrophysical and theoretical assumptions, including black hole formation, natal spin, age, accretion history, population priors, and boson self-interactions. In this paper, we review the principal electromagnetic and gravitational-wave constraints derived from black-hole superradiance, with particular emphasis on their underlying assumptions and systematic uncertainties. The distinct observational signatures and systematic uncertainties of these approaches offer complementary perspectives on the viability of ultralight-boson models. In particular, their overlapping coverage around boson masses of $10^{-13}$-$10^{-12}$ eV makes this region particularly informative for comparing constraints, with attention to the assumptions underlying each result.

Figures

Reported exclusions from black-hole superradiance for scalar (left) and vector (right) ultralight bosons, under the assumptions of the respective analyses. Colors indicate methodology: electromagnetic spin measurements (pink), gravitational-wave spin measurements of individual events or populations (magenta), and searches for gravitational radiation from boson clouds (purple). Filled regions above the dashed line show two-dimensional exclusions in mass and interaction-parameter space. Horizontal bars below the dashed line show mass-only exclusions obtained in the gravity-dominated regime, with no explicit coupling dependence displayed; their vertical positions are chosen solely for legibility and carry no physical meaning. Numbered labels identify the studies listed in the table in Appendix~\ref{app:reference_table}; entries from the same paper share a number. The diagonal line in the scalar panel shows the standard QCD axion mass--decay-constant relation, $m_a f_a \simeq 5.70(6)(4)\times10^{12}\,\mu\mathrm{eV\,GeV}$~\cite{GrillidiCortona:2015jxo}. The exclusions are shown at the confidence or credibility levels reported in the original studies, which vary between results.
Caption Reported exclusions from black-hole superradiance for scalar (left) and vector (right) ultralight bosons, under the assumptions of the respective analyses. Colors indicate methodology: electromagnetic spin measurements (pink), gravitational-wave spin measurements of individual events or populations (magenta), and searches for gravitational radiation from boson clouds (purple). Filled regions above the dashed line show two-dimensional exclusions in mass and interaction-parameter space. Horizontal bars below the dashed line show mass-only exclusions obtained in the gravity-dominated regime, with no explicit coupling dependence displayed; their vertical positions are chosen solely for legibility and carry no physical meaning. Numbered labels identify the studies listed in the table in Appendix~\ref{app:reference_table}; entries from the same paper share a number. The diagonal line in the scalar panel shows the standard QCD axion mass--decay-constant relation, $m_a f_a \simeq 5.70(6)(4)\times10^{12}\,\mu\mathrm{eV\,GeV}$~\cite{GrillidiCortona:2015jxo}. The exclusions are shown at the confidence or credibility levels reported in the original studies, which vary between results.
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