United QG Seminar ：

Title: Spin foam amplitude of the black-to-white hole transition

Speaker: Dr. Cong Zhang ((University of Erlangen-Nurmberg, Germany)

Spacetime Point:
A311 Science and Technology Building
Online (202.112.92.14)
4:00am-5:30pm, Mar. 19 (Tue.)

Abstract: At the end of Hawking evaporation, as the black hole horizon approaches the Planck scale, the effects of quantum gravity become significant. Based on the conjecture that these quantum gravity effects may induce the transition of the black hole into a white hole, this transition amplitude is studied within the framework of the spin foam model. The spin foam amplitude is built on a 2-complex containing 56 vertices. The boundary state in the amplitude is selected as the Thiemann's complexifier coherent state resembling the semiclassical geometry. Taking into account the fact that triad fields of different orientations give the same intrinsic geometry of the boundary, we creatively adopt the the boundary state as the superposition of the coherent states associated with the both orientations. We employ the method of complex critical point to numerically compute the transition amplitude. Despite the numerical results, it is interestingly found that the transition amplitude is dominated by the terms allowing the change in orientation. This finding suggests that the black-to-white hole transition should be accompanied by the tunneling process of a change in orientation.