Research Projects

The LIGO and VIRGO detectors have detected over 300 gravitational-wave (GW) detections signals from binary coalescences of compact objects such as black holes (BHs) and neutron stars (NSs). These events offer a unique opportunity to probe the equation of state (EOS) of dense nuclear matter in NSs. Coalescence begins with the inspiral, where the two objects orbit each other at large separations. As they emit GWs, they spiral inward. During this phase, each object is tidally deformed by the gravitational field of its companion, which alters binary dynamics and modifies the GW signal. These tidal effects are especially relevant for binaries involving NSs, which have a stronger tidal response than BHs. This response depends on properties such as compactness, EOS, and composition of the star. The central objective of this project is to connect the microscopic physics of NS interiors to their macroscopic tidal dynamics during inspiral. A related goal is to determine the observational sensitivity needed to distinguish between EOS models using GW data, and to search existing and future datasets for tidal signatures. This work will employ effective worldline theory, a powerful, analytical framework in which compact objects are modeled as point particles with systematic finite-size corrections. The method uses effective field theory techniques originally developed in quantum field theory. One typically writes down an effective worldline action that governs the bulk motion of the object, with tidal deformations included through tidal-response coefficients, constrained by symmetry. These coefficients can be fixed by using scattering calculations from the complete theory, such as scattering processes studied in relativistic stellar perturbation theory for NS. This provides a consistent way to model the dynamics of tidally deformed NSs. Importantly, this approach avoids the challenges of coordinate ambiguity in general relativity and reduces the computational complexity involved in systematically computing higher-order tidal effects in traditional methods. I have already applied this framework to study tidal deformation in BHs and spherical NSs, including dissipation from BH horizons and NS fluid viscosity. A critical next step is extending this analysis to spinning NSs, where spin-tide coupling introduces qualitatively new effects. Analytical results using traditional methods conflict with numerical simulations, especially for binaries containing spinning NSs, with their spins anti-aligned w.r.t the orbital angular momentum. In earlier work, I developed an understanding of tidal deformation in Kerr BHs. The proposed project will build on and extend those methods to spinning NSs, incorporating spin-induced modifications to tidal response, dissipation, and resonances within the worldline formalism. The results will lead to improved waveforms for NS binaries, enabling stronger constraints on the EOS and the physics of dense matter through GW observations.