Search Talks

GW250114, with a signal-to-noise ratio of ∼80, enables the most precise single-event tests of strong-field gravity to date: setting the tightest constraints on deviations from general relativity, delivering the cleanest ringdown measurement yet, and placing stringent bounds on compact object structure. The one thing it withholds is Love: no tidal deformability is detected, with a 90% upper limit of $\tilde{\Lambda} < 34.8$, fully consistent with the Kerr prediction of vanishing tidal deformability.

The classical action, or more generally the path integral, is a convenient framework for extracting the physical consequences of symmetries. In recent years, new symmetries of gravity in asymptotically flat spacetime have been uncovered based on relations to soft theorems governing the S-matrix. I will discuss a program to understand these symmetries using a formulation in which the S-matrix is identified with the action subject to asymptotic boundary conditions. This formulation of the S-matrix is analogous to the GKP/W formulation of the AdS/CFT duality and shares many of its advantages, albeit with new subtleties due to working in asymptotically flat spacetime.

A simple multiverse model explains the late time exponential expansion of our universe without the need of a cosmological constant. Assuming that the local measurement of H_0 is correct, it also give a better fit to data than the standard LCDM model, as well as a z-dependent state parameter w(z) that is not incompatible with the latest DESI data. An (tentative) underlying microscopic theory of the multiverse model, based on W_3 and exceptional Jordan algebras may allow us to calculate the expansion rate of our universe.

Within the Effective Field Theory approach to gravity, deviations from General Relativity can be systematically described by higher-curvature operators. However, computing the resulting corrections to black hole quasinormal mode spectra remains challenging in the rapidly rotating regime, where perturbative expansions in the spin break down. Making use of recently constructed numerical rotating black hole solutions, we computed scalar quasinormal mode frequency shifts at leading order for scalar Gauss-Bonnet, dynamical Chern-Simons and Cubic Riemann corrections. We employed a pseudo-spectral collocation method to solve the perturbation equations on these backgrounds, enabling accurate computation across a broad parameter range. We observed that corrections to certain modes grow significantly as the spin approaches the near-extremal regime.

Gravitational-wave observations by LIGO and Virgo are revealing a population of merging stellar-mass binary black holes. Thus far, the broad connection between the inferred population and the physics that underlies black hole formation remains elusive. The O4a run of the LVK has more than doubled the number of binary black hole detections, and this new data is revealing new features in the population and elucidating old ones. In this talk, I survey several interesting and sometimes perplexing features and subpopulations in the population distribution. I show how they let us glean some information about the underlying formation channels and connect with transient and compact object astrophysics. As the number of detections balloons in the future, these subpopulations will be footholds to a more global understanding of binary black hole formation and the rich physics behind it.