18-22 September 2017
Yerevan, Armenia
Etc/GMT+4 timezone

Null congruences crossing generic shells

19 Sep 2017, 14:40
Yerevan, Armenia

Yerevan, Armenia

Department of Physics, Alex Manoogian str. 1, Yerevan, Armenia


Mr Hovhannes Demirchian (Byurakan Astrophysical Observatory)


We present a new technique for describing geodesic congruences (for example the trajectory of a gas of photons or particles) crossing a generic light-like shell in vacuum. In particular the change in the direction of the vector field of the congruence has been derived and shown to be in agreement with the results of Barrabes and Hogan thus demonstrating the validity of this technique. For the case of null shells generated by infinitesimal BMS supertranslation type soldering, the expansion and shear tensors of the congruence have also been calculated. We derived the surface equation, for relative motion orthogonal to the congruence after it crosses the shell, proving also that the congruence is always hypersurface orthogonal and the rotation tensor is always zero. This means that the Eikonal approximation can be applied to describe it as a wave on the future, and this has been carried out for a special BMS type soldering. The conditions for focusing, defocusing and formation caustics have been studied.

Type of contribution Talk

Primary authors

Mr Hovhannes Demirchian (Byurakan Astrophysical Observatory) Prof. Martin O'Loughlin (University of Nova Gorica)

Presentation Materials