**Weekly Seminar**

HEPCo Group

Light speed as a local observable for soft hairs

K. Hajian, METU

4 AUG 2020

14:00 - 15:00

Abstract:

In flat spacetime, Poincare group is the Lie group of linear transformations on space-time which keeps the speed of light invariant. This is the corner-stone of special relativity. However, in theories defined such that are only asymptotically flat, it has been shown that the group of physical transformations is larger than Poincare, and it is called the BMS group. I will show that this group of transformations does not keep the speed of light invariant. As a result, one can use this physical observable to distinguish geometries which are related by a BMS transformation to each other, i.e the soft hairs. Moreover, this observable is related to the gravitational memory effect which had been used as an observable for soft hairs.

In my talk, first I will review Asymptotic Symmetry Group (ASG) analysis, BMS_4 group and gravitational memory effect. Then, I will present the results of the analysis of speed of light in this context.

Skype link for emergency

SkypeLink: https://join.skype.com/cm7iyEUWJVCf