Upcoming Seminars

Date/Place May. 30th(Tue.) 15:30-16:30 / H711
Name Norihiro Tanahashi (Osaka University)
Title Wave propagation and shock formation in the most general scalar-tensor theory
Abstract We study the wave propagation in the most general scalar-tensor theory focusing on the shock formation caused by nonlinear effects. For this study we use the Horndeski theory, which is the most general scalar-tensor theory that gives second order equations of motion. The propagation speeds of the scalar field wave and gravitational wave depend on the environment and also their own amplitudes in this theory, and it causes various phenomena which cannot be seen in GR. To study the shock formation, we focus on transport of weak discontinuity in the metric and scalar field. We find that amplitude of the discontinuity generically diverges within finite time, which corresponds to shock formation. It turns out that the canonical scalar field and the scalar DBI model, among the theories described by the Horndeski theory, are free from such shock formation even on nontrivial background. We also observe that gravitational wave is protected against shock formation when the background has some symmetries at least. We will discuss implications of these findings.


Date/Place Jun. 6th(Tue.) 15:30-16:30 / H711
Name Hiroshi Ohki (Nara Women's University)
Title TBA
Abstract TBA


Date/Place Jun. 13th(Tue.) 15:30-16:30 / H711
Name Takashi Shimomura (University of Miyazaki)
Title TBA
Abstract TBA


Past Seminars