A microscopic analogue of the BMS group

Abstract: We consider a microscopic analogue of the BMS analysis of asymptotic symmetries by analysing universal geometric structures on infinitesimal tangent light cones. Thereby, two natural microscopic symmetry groups arise: A non-trivially represented Lorentz group and a BMS-like group. The latter has a rich mathematical structure, since it contains the former as a non-canonical subgroup, next to infinitely many other Lorentz subgroups. None of those Lorentz subgroups appears to be intrinsically preferred, and hence, the microscopic BMS-like group constitutes a natural symmetry group for infinitesimal tangent light cones. We compare our investigation with the classical BMS analysis and show, that the microscopic BMS-like group is a gauge group for the bundle of null vectors. Motivated by the various applications of the original BMS group, our findings could have interesting implications: They identify a geometric structure that could be suitable for a bulk analysis of gravitational waves, they suggest a possible enlargement of the fundamental gauge group of gravity and they motivate the possibility of an interrelation between the UV structure of gauge theories, gravitational memory effects and BMS-like symmetries. Also, our results imply, that BMS-like groups arise not only as macroscopic, asymptotic symmetry groups in cosmology, but describe also a fundamental and seemingly unknown microscopic symmetry of pseudo-Riemannian geometry.