Lessons from black hole quasinormal modes in modified gravity

Abstract

Quasinormal modes (QNMs) of perturbed black holes have recently gained much interest because of their tight relations with the gravitational wave signals emitted during the post-merger phase of a binary black hole coalescence. One of the intriguing features of these modes is that they respect the no-hair theorem, hence they can be used to test black hole spacetimes and the underlying gravitational theory. In this paper, we exhibit three different aspects of how black hole QNMs could be altered in theories beyond Einstein's general relativity (GR). These aspects are i) the direct alterations of QNM spectra as compared with those in GR, ii) the violation of the geometric correspondence between the high-frequency QNMs and the photon geodesics around the black hole, and iii) the breaking of the isospectrality between the axial and polar gravitational perturbations. Several examples will be provided in each individual case. The prospects and possible challenges associated with future observations will be also discussed.

Linear stability of vector Horndeski black holes

“…The eikonal correspondence is thus broken at least for one of the modes. The breaking of the eikonal correspondence has been found in some modified theories of gravity, such as those with nonminimal matter-gravity couplings [89][90][91][92] or those with higher spacetime dimensions [93,94]. Therefore, observationally testing the correspondence could be a potential way of searching physics beyond GR [95].…”

Dynamical analysis of logarithmic energy-momentum squared gravity

“…[12] (see also [13]). There is a rapidly growing literature considering EMSG, see [14][15][16][17][18][19][20][21] for some cosmological applications and [22][23][24][25][26] for some other applications. EMSG theories are a special family of a Lorentz invariant and covariant generalization of GR proposed in Ref.…”