Joint Theory Seminar: Raj Patil

 Title: Precision Gravity: Gravitational waves using Feynman diagrams

Abstract: Observations of gravitational waves (GW) have the potential to unravel the mysteries of cosmic origins, constrain the equations of state of compact objects, and serve as a test of general relativity. To achieve these scientific goals, it is crucial to develop highly precise and accurate waveform templates to minimize systematic errors. My talk will focus on computing state-of-the-art effective two-body Hamiltonians and fluxes using techniques from quantum field theory and scattering amplitudes. These Hamiltonians and fluxes serve as fundamental building blocks for waveform templates, and dictate the accuracy of the waveform model. In particular, I will describe the effects of spinning and tidally deformed compact objects on evolution of the binary system. I will present computations of the linear-in-spin Hamiltonian at 4.5 post-Newtonian (PN) order, as well as the quadratic-in-spin Hamiltonian at 5PN order. Furthermore, I will describe oscillation modes of neutron stars (NS) induced by tidal interactions, particularly the fundamental-mode dynamical tides, which are expected to play a crucial role in constraining the NS equation of state in upcoming GW observing runs. I will discuss the computation of fluxes up to 2PN for adiabatic tidal interactions and effective Hamiltonians up to 3PN for both dynamic and adiabatic tidal interactions. The latter is particularly interesting as it requires introducing counterterms to remove divergences, leading to a renormalization group flow of the post-adiabatic Love number.