WoU-MMA: Gravitational Wave Coupling with Inhomogeneous Plasma and Asymptotic Theory of Polarization Effects in Curved Spacetime

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Scientists have long predicted that disturbances in the fabric of spacetime, called gravitational waves (GWs), can be generated by binary stars and propagate across the Universe with speeds close to the speed of light. Recently, these waves have been detected, resulting in the 2017 Nobel Prize in Physics. This discovery opens new opportunities to study fascinating astronomical processes which so far have only been hypothesized, and may help us to better understand the Universe. Some GWs have been detected in parallel with bursts of electromagnetic radiation, and correlations between gravitational and electromagnetic signals can tell us even more than gravitational signals alone. To infer information from these correlations, we need to understand how GWs and electromagnetic radiation are coupled in plasmas surrounding GW sources. This project is aimed towards developing the first comprehensive theory to address this complicated correlation problem. The project is directly aligned with the goals of NSF's "Windows on the Universe: The Era of Multi-Messenger Astrophysics" Big Idea, because understanding of how GW waves affect a plasma is necessary for astrophysicists to interpret the origin of electromagnetic radiation from GW sources. The project bridges plasma physics and gravitational physics and a graduate student will be trained in the new multidisciplinary area at the intersection of these two fields.This project will allow a rigorous derivation of the plasma susceptibilities with respect to a combination of metric and electromagnetic oscillations. Using a variational approach, geometrical-optics equations for linear plasma waves coupled with metric oscillations will be formulated. In doing so, nonlinear (ponderomotive) forces produced by gravitational radiation will also be studied. The usual assumption of transverse polarization for the metric oscillations is not invoked, so it is expected that the estimates for the GW-plasma coupling coefficients will be significantly improved. After exploring the resulting dispersion relations, both analytically and by using particle-in-cell simulations, the energy transfer from metric oscillations to plasma will be estimated. As a spinoff, the deviation of electromagnetic rays from null geodesics in prescribed spacetime (the "spin Hall effect of light") will be rigorously calculated for a general metric for the first time.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.