Instability and backreaction of massive spin-2 fields around black holes
by
Tsung-Dao Lee Institute/N6F-N600 - Meeting Room
Tsung-Dao Lee Institute
Host: Zhen Pan
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Abstract:
Ultralight bosonic fields are compelling dark matter candidates. In particular, massive spin-2 fields can not only extract energy from rotating black holes via superradiant instabilities but also trigger a unique monopolar instability—specifically, the axisymmetric (azimuthal number m = 0) instability—which can even affect non-rotating black holes. This instability dominates in most of the parameter space and could potentially influence all black holes, from stellar-mass to supermassive. A thorough understanding of its nonlinear evolution and final state is therefore of great importance. In this work, based on ghost-free massive gravity theories (dRGT and the Hassan–Rosen bigravity theory), we employ time-domain evolution methods to systematically investigate the nonlinear dynamics of this instability in a spherically symmetric black hole background. Our results show that the final outcome of the evolution depends on the model parameters: the system can either evolve into a stable "hairy" black hole or experience a breakdown of the theory itself due to nonlinear effects. This study provides important insights into the nonlinear dynamics of massive gravity theories and paves the way for testing ultralight spin-2 dark matter models through astronomical observations.
Biography:
Zhen Zhong is a Postdoctoral Researcher at Sapienza University of Rome. He received his B.S. degree from the University of Science and Technology Beijing in 2018, his M.S. degree from Beijing Normal University in 2021, and his Ph. D. from the University of Lisbon, Portugal, in 2025. His research focuses on General Relativity, black hole physics, and nonlinear dynamics in the strong gravity regime. To date, he has published 17 papers, including two in Physical Review Letters, and over ten others in journals such as Physical Review D and the Journal of High Energy Physics.
