The schedule is in Indian Standard Time (IST).
Note that: IST (CEST+3:30 hours, EDT+9:30 hours )
Day 1
Session Chair: Arpan Bhattacharyya
15:00 - 16:00
Title: Testing beyond GR physics with gravitational waves
Abstract: Gravitational waves are among the ultimate tools to test fundamental physics and can unveil further information about the nature of gravity in the regime of strong fields. The degeneracies between different effects are a serious obstacle, though, to fulfilling this goal. In addition, producing precise gravitational waveforms poses a theoretical and numerical challenge. In the present talk, we will focus on a few examples of interesting new effects we can observe in the gravitational wave spectrum that differ qualitatively from the standard picture in general relativity. We will also discuss recent advances in the efforts to model numerically binary black hole mergers beyond general relativity and the information we can infer from them using future gravitational wave observations.
16:00 - 17:00
Title: Black holes have vanishing non-linear static tides
Abstract: In this talk I will explain that four-dimensional spherically symmetric black holes have vanishing static tides (i.e., Love numbers) at full non-linear order. This is a result of an accidental symmetry of General Relativity in the static sector, which demystifies previous results about the vanishing of linear Love numbers and generalizes it to arbitrarily strong external fields.
Session Chair: Sounak Pal
(Oral Presentation)
17:00 - 17:30
Title: Tidal Deformability Beyond Einstein: Love Numbers in Quadratic EFT of Gravity
Abstract: We extend the study of static black-hole tidal Love numbers from pure General Relativity to the most general four-dimensional quadratic effective field theory (EFT) of gravity. By reconstructing the perturbed metric via tree-level one-point functions in a worldline EFT, we demonstrate that higher-curvature interactions induce non-vanishing, scale-independent tidal responses in both scalar and tensor channels. In particular, for dipole scalar perturbations, we derive a Yukawa-deformed Frobenius series, fix the ultraviolet integration constant through asymptotic matching to Wilson coefficients, and validate our results numerically in isotropic coordinates. Our findings reveal that quadratic corrections generate robust Love numbers—free of renormalization-group running—thereby offering a sharp EFT framework to test deviations from GR in forthcoming gravitational-wave observations.
(Oral Presentation)
17:30 - 18:00
Divyesh Solanki
Title: Perturbative soft graviton theorems in de Sitter space
Abstract: We consider soft graviton scattering for a theory where Einstein’s gravity is minimally coupled to a scalar field in a background de Sitter space. Employing a perturbative expansion in a large curvature length (or small cosmological constant), we compute the leading, subleading, and sub-subleading corrections to the Weinberg soft graviton amplitude for tree-level scatterings in the static patch of the de Sitter space. We observe similar universal features of the soft graviton amplitude as found in [JHEP10(2023)055] for the soft photons.
18:00 - 19:00
Title: Perturbative Computations from Curved Spacetimes
Abstract: Given the impressive results for classical observables obtained by field theoretic approaches to gravitational systems, we can ask if these tools can help us in other regimes and problems of interest. Amplitude tools are particularly well suited to derive observables for the binary system in a post-Minkowskian expansion, where they have achieved complete results to fourth order in Newton's constant. From the perspective of perturbative quantum field theory, classical solutions in general relativity are remarkable objects; they make manifest a resummation of an infinite series of Feynman diagrams encoding information to all orders in Newton’s constant. I will describe an effective field theory formalism tailored for computations about nontrivial classical backgrounds, and present the potential and hurdles in combining advantages from classical gravitational and field theoretic techniques to address questions related to the binary inspiral problem.
Day 2
Session Chair: Anand Sengupta
15:00 - 16:00
Title: Dynamical formation of regular black holes
Abstract: I will show that regular black holes arise as the unique spherically symmetric solutions of broad families of generalizations of Einstein gravity involving infinite towers of higher-curvature corrections in D≥ 5 spacetime dimensions. Our results are facilitated by the use of a class of theories that possess second-order equations on spherically symmetric metrics, but which are general enough to provide a basis for the gravitational effective action. I will argue that such regular black holes arise as the byproduct of gravitational collapse within these theories. Generically, spherical stars or shells collapse until they reach a minimum size inside the inner horizon of the black hole they create. Then, they bounce back and reappear through a white hole in a different universe, where they eventually reach their original size, restarting the process. I will also mention several ongoing research directions.
16:00 - 17:00
Davide Gerosa
Title: Stacking gravitational-wave events for testing GR: proceed with care
Abstract: Combining information from multiple gravitational-wave events is a promising strategy to squeeze more information out of the data and improve tests of general relativity in the strong-field, dynamical regime. However, this must be done carefully. Even if individual events show no sign of deviations from Einstein’s theory, the process of aggregating them can introduce substantial statistical and systematic errors. In particular, hierarchical Bayesian techniques-- standard practice in gravitational-wave population inference-- must be applied thoughtfully. In this talk, I will highlight two related pitfalls. First, the finite size of the catalog induces an intrinsic source of variance that can spuriously produce credible evidence for departures from general relativity, an effect that cannot be avoided simply by selecting “golden” high-signal-to-noise-ratio events. Second, even small waveform inaccuracies that are negligible for any single observation can accumulate across tens of events and mimic new physics. Both effects scale with catalog size and, as we demonstrate, can cause apparently significant departures from Einstein's predictions with as few as O(10) events.
Session Chair : Saptaswa Ghosh
(Oral Presentation)
17:00 - 17:30
Title: Probing dark matter spikes with multiband gravitational wave observations of intermediate-mass ratio inspirals
Abstract: We investigate the potential of multiband gravitational wave (GW) observations to constrain the properties of dark matter (DM) spikes surrounding intermediate-mass ratio inspirals (IMRIs), where a neutron star spirals into an intermediate-mass black hole (150–850 \msun). These DM spikes, formed via the adiabatic growth of black holes inside dark matter halos, exert dynamical friction on the inspiraling object, resulting in detectable phase shifts in the GW signal relative to vacuum predictions in general relativity. We use a waveform model that incorporates the effects of a dynamically evolving DM environment into standard vacuum phasing and estimate parameter uncertainties using the Fisher matrix formalism. Our analysis considers combined observations involving the proposed Indian decihertz space-based detector GWSat, along with third-generation ground-based detectors: the Einstein Telescope (ET) and Cosmic Explorer (CE). We find that GWSat provides the most stringent constraints on DM spike parameters, with uncertainties below 1%, as IMRIs spend most of their inspiral within its sensitive frequency band. For systems with detector-frame mass below 400 \msun, the addition of ET and CE further improves the estimation of chirp mass, symmetric mass ratio, luminosity distance, and the DM spike slope by over 15%, although their impact on the DM spike density remains limited. These results underscore the vital role of decihertz space-based detectors in probing dark matter environments through gravitational wave observations.
17:30 - 18:30
Title: Ringing Black Holes
Abstract: In this talk, I will discuss one of the frontiers of both theory and data analysis in gravitational wave astronomy - understanding the ringing of black holes and probing them from real data. I will review past efforts started from Chandrasekhar, Detweiler, et al in analyzing modes of black holes and explain what we currently understand in both linear and nonlinear wave properties, as well as the corresponding detection aspect. At last, I will show a few pressing problems and where we will be heading (from my point of view).