Speaker: Yasutaka Koga (Rikkyo University)

Title: Photon surface and relevant phenomena

Abstract:

A photon surface is a geometrical object which generalizes the photon sphere of Schwarzschild spacetime. Due to its geometrical features, there are interesting phenomena concerning the photon surface. In this talk, after reviewing a photon surface and its stability, we disucss two theoretical phenomena connected to photon surfaces. First, the sonic point/photon surface correspondence: In the analysis of accretion and outflow of a fluid, the existence of a sonic point plays a key role for finding physical solutions. If the matter is a radiation fluid, there is a one-to-one correspondence between the sonic points and photon surfaces of the spacetime. Second, photon surface as a wormhole throat: A wormhole spacetime is constructed by truncating two spacetimes and sewing them together along their boundaries. The sewn boundary is called a throat. Such a wormhole spacetime is said to be a solution of Einstein equation if the Israel's junction conditions are satisfied with an adequate matter distribution on the throat. If the throat with the matter distribution is a pure tension brane, the corresponding boundaries of the original spacetimes must be photon surfaces.

Room: Zoom videoconference (contact justin.feng@tecnico.ulisboa.pt for URL)