Primordial sources of gravitational waves (GWs) have traditionally been probed through their contribution to the stochastic GW background, detectable via pulsar timing arrays and ground-based laser interferometers. However, these same tensor perturbations can also leave an imprint on the cosmic microwave background (CMB) in the form of B-mode polarization. While a detection of primordial...
Since strong evidence for low-frequency gravitational waves (GWs) was delivered by pulsar-timing array experiments two years ago, its origin and source properties remain unknown. The amplitude of the stochastic GW background may be in mild tension with some black-hole population predictions in the literature, which can be resolved by a combination of a modified galaxy stellar mass function,...
Gravitational waves induce correlations in pulse-arrival times characterized by the well-known Hellings-Downs curve. If, however, there are spin-0 or spin-1 gravitational-wave modes, which may arise in alternative-gravity theories, and/or anisotropies in the gravitational-wave background, there may be different patterns of correlations. I will describe an elegant (at least I think so)...
Black holes are among the most intriguing predictions of general relativity, composed of the fabric of spacetime itself. Observations of black holes offer unique access to extreme gravity, and they enable us to address puzzles in fundamental physics ranging from dark matter to the very nature of gravity itself.
Among the compelling dark matter candidates are ultralight axion-like particles...
Tidal Love numbers describe the conservative response of compact objects to external tidal perturbations. Remarkably, within General Relativity, they are found to vanish exactly for black holes in vacuum. We begin by revisiting this vanishing property from a symmetry-based perspective. We then explore how this feature is modified when black holes are embedded in external environments,...