Title: Gravitational Wave Effective Theory with Curvature Corrections and Bosonic Mixing
Host: Yuval Grossman
Abstract: We compute bosonic (electromagnetic, gravitational, and axion/scalar dark matter) wave mixing in curved spacetime using novel gravitational wave effective field theory techniques. Curved spacetime adds a new length scale, e.g. the Schwarzschild radius, which can significantly alter the oscillation probabilities in comparison to the standard flat spacetime computations. Thus, curved spacetime effects are analogous to the Mikheyev-Smirnov-Wolfenstein (MSW) effect for neutrinos and are “frozen-in” when the bosonic wave propagates away from the compact objects. Although we consider axions and axion-like particles (ALPs), our calculational scheme is applicable to any bosonic mixing scheme. In particular, we show how the mixing can potentially occur via the coupling between gravitational wave and the energy-momentum tensor. Such implies bosonic dark matter can mix even if all phenomenological couplings, such as the axion-photon coupling, are zero. We compute the associated oscillation probabilities and discuss some of the observational consequences, including the energy spectrum and polarization of the exiting electromagnetic and  gravitational waves.