Massive spin-2 fields on black hole spacetimes: Instability of the Schwarzschild and Kerr solutions and bounds on the graviton mass

TL;DR

This paper investigates the stability of Schwarzschild and Kerr black holes under massive spin-2 field perturbations, revealing instabilities that impose upper bounds on the graviton mass based on black hole observations.

Contribution

It demonstrates the linear instability of Schwarzschild and Kerr black holes to massive spin-2 fluctuations and derives bounds on the graviton mass from astrophysical data.

Findings

Schwarzschild black holes are linearly unstable for small tensor masses.

Kerr black holes are also unstable, including superradiant modes.

Observations constrain the graviton mass to less than 5×10^{-23} eV.

Abstract

Massive bosonic fields of arbitrary spin are predicted by general extensions of the Standard Model. It has been recently shown that there exists a family of bimetric theories of gravity - including massive gravity - which are free of Boulware-Deser ghosts at the nonlinear level. This opens up the possibility to describe consistently the dynamics of massive spin-2 particles in a gravitational field. Within this context, we develop the study of massive spin-2 fluctuations - including massive gravitons - around Schwarzschild and slowly-rotating Kerr black holes. Our work has two important outcomes. First, we show that the Schwarzschild geometry is linearly unstable for small tensor masses, against a spherically symmetric mode. Second, we provide solid evidence that the Kerr geometry is also generically unstable, both against the spherical mode and against long-lived superradiant modes. In the absence of nonlinear effects, the observation of spinning black holes bounds the graviton mass to be smaller than 5x10^{-23} eV.