Lessons from black hole quasinormal modes in modified gravity

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