Constraining the mass of dark photons and axion-like particles through black-hole superradiance (1801.01420v1)

Abstract: Ultralight bosons and axion-like particles appear naturally in different scenarios and could solve some long-standing puzzles. Their detection is challenging, and all direct methods hinge on unknown couplings to the Standard Model of particle physics. However, the universal coupling to gravity provides model-independent signatures for these fields. We explore here the superradiant instability of spinning black holes triggered in the presence of such fields. The instability taps angular momentum from and limits the maximum spin of astrophysical black holes. We compute, for the first time, the spectrum of the most unstable modes of a massive vector (Proca) field for generic black-hole spin and Proca mass. The observed stability of the inner disk of stellar-mass black holes can be used to derive \emph{direct} constraints on the mass of dark photons in the mass range $ 10^{-13}\,{\rm eV}\lesssim m_V \lesssim 3\times 10^{-12}\,{\rm eV}$. By including also higher azimuthal modes, similar constraints apply to axion-like particles in the mass range $6\times10^{-13}\,{\rm eV}\lesssim m_{\rm ALP} \lesssim 10^{-11}\, {\rm eV}$. Likewise, mass and spin distributions of supermassive BHs --~as measured through continuum fitting, K$\alpha$ iron line, or with the future space-based gravitational-wave detector LISA~-- imply indirect bounds in the mass range approximately $10^{-19}\,{\rm eV}\lesssim m_V, m_{\rm ALP} \lesssim 10^{-13}\, {\rm eV}$, for both axion-like particles and dark photons. Overall, superradiance allows to explore a region of approximately $8$ orders of magnitude in the mass of ultralight bosons.

• The paper demonstrates that black-hole superradiance can extract angular momentum, setting upper bounds on ultralight boson masses including dark photons and ALPs.
• It computes the unstable mode spectrum for Proca fields and higher azimuthal modes to derive mass constraints in the ranges ~10⁻¹³ to 3×10⁻¹² eV for dark photons and 6×10⁻¹³ to 10⁻¹¹ eV for ALPs.
• These findings establish a model-independent framework linking gravitational observations to particle physics, guiding future gravitational-wave experiments and astrophysical studies.

Constraining the Mass of Dark Photons and Axion-Like Particles through Black-Hole Superradiance

The research conducted by Cardoso et al. provides a detailed investigation into the constraints imposed on the mass of ultralight bosons, specifically dark photons (ULVs) and axion-like particles (ALPs), through the phenomenon of black-hole superradiance. This paper articulates a compelling argument rooted in the universal coupling to gravity, distinct from the specificities of coupling to the Standard Model, which is typically unknown and complicates direct detection efforts.

The paper explores the superradiant instability in spinning black holes in the presence of massive vector (Proca) fields. This effect operates by extracting angular momentum from black holes, imposing a theoretical upper bound on the spin of astrophysical black holes. The team presents, for the first time, the spectrum of the most unstable modes of such fields across a range of black-hole spins and Proca masses. This calculation crucially informs the constraints on the mass of dark photons, particularly in the mass range of $$10^{-13}\,{\rm eV} \lesssim m_V \lesssim 3\times 10^{-12}\,{\rm eV}$$.

Moreover, the investigators extend their analysis to include higher azimuthal modes, achieving analogous constraints on axion-like particles, specifically in the mass range $$6\times10^{-13}\,{\rm eV} \lesssim m_{\rm ALP} \lesssim 10^{-11}\,{\rm eV}$$. This work further contemplates the constraints derived indirectly from observations concerning supermassive black holes, measured through methods such as continuum fitting and the characterization of the K$\alpha$ iron line, as well as potential future measurements from gravitational-wave observatories like LISA. These considerations delimit the viable mass ranges for these particles down to approximately $10^{-19}\,{\rm eV}$.

The practical and theoretical implications of these findings are substantial. They provide a crucial lens through which the mass of hypothetical particles, as predicted by several theoretical frameworks including those inspired by string theory, can be bounded. By effectively utilizing observed and future limits on black-hole spin and mass, this research allows one to ensure that certain configurations of ultralight particles do not excessively drain black-hole angular momentum through superradiance, thereby violating observational data.

In terms of future directions, as advancements in gravitational-wave astrophysics continue, the integration of more precise data from such initiatives as LISA will enable further refinements to these constraints. Potential developments might also focus on incorporating more complex models that account for nonlinear backreaction effects, gravitational-wave emissions, or even boson interactions with plasma environments or other scalar configurations.

Overall, the paper by Cardoso et al. creates a framework for analyzing the potential existence of dark photons and axion-like particles using readily observable astrophysical parameters, providing a model-independent viewpoint that is purely based on gravitational interactions rather than speculative couplings which are not yet directly accessible through current experimental technology. This work epitomizes a pivotal intersection between theoretical physics and observational astrophysics, advancing our understanding of the universe at its most fundamental level.