SPEAKER: Norihiro Tanahashi (DAMTP)
ABSTRACT: We study gravitational wave propagation in Lovelock theories, which are extensions of Einstein's theory by higher-curvature corrections, to examine if these theories have good properties such as causality and hyperbolicity. We study the propagation on various background spacetime, and find that initial value problem may cease to be well-posed in some case. We also show that the sound speed of gravitational wave depends on the background and it may cause shock formation in these theories. We discuss implications of these phenomena.