Topic: Implications of Pulsar Timing Array Observations

Speaker: Prof. Yungui Gong

Coordinates: PCFT C1124, 16:00, Thursday, December 21

Abstract: Gravitational waves (GWs) opened a new window to uncover some of the universe’s biggest mysteries and became a game-changer for astronomy. Strong evidence of the existence of the stochastic gravitational wave background (SGWB) has been reported recently by the Pulsar Timing Array (PTA) observations. While supermassive black hole binaries (SMBHBs) present a plausible explanation for the observed signal, the predicted spectral index for one-sided power spectral density of SGWB is almost 2sigma away from the observation. We discuss the modifications arising from extra scalar or vector radiations to the characteristic dimensionless strain of gravitational waves from SMBHBs and explore the possibility of detecting charges carried by supermassive black holes in modified gravity and new fundamental fields. On the other hand, scalar induced secondary gravitational waves (SIGWs) from some particular models fit the signals detected by PTAs better than GWs from SMBHBs, so we also test the consistency of the data with the universal behavior of infrared parts of SIGWs in a somewhat model-independent way.