Thèse de doctorat
Résumé : In this thesis, several new aspects of asymptotic symmetries have been exploited.Firstly, we have shown that the asymptotic symmetries can be enhanced tosymplectic symmetries in three dimensional asymptotically Anti-de Sitter (AdS) space-time with Dirichletboundary conditions. Such enhancement providesa natural connection between the asymptotic symmetries in the far region i.e. closeto the boundary) and the near-horizon region, which leads to a consistenttreatment for both cases. The second investigation in three dimensional space-time is to study theEinstein-Maxwell theory including asymptotic symmetries, solutionspace and surface charges with asymptotically flat boundary conditionsat null infinity. This model allows one to illustrate several aspectsof the four dimensional case in a simplified setting. Afterwards, we givea parallel analysis of Einstein-Maxwell theory in the asymptotically AdScase.Another new aspect consists in demonstrating a deep connection between certainasymptotic symmetry and soft theorem. Recently, a remarkable equivalence wasfound between the Ward identity of certain residual (large) U(1) gauge transformations and the leadingpiece of the soft photon theorem. It is well known that the softphoton theorem includes also a sub-leading piece. We have proven thatthe large U(1) gauge transformation responsible for the leading soft factorcan also explain the sub-leading one.In the last part of the thesis, wewill investigate the asymptotic symmetries near the inner boundary. Asa null hypersurface, the black hole horizon can be considered as an innerboundary. The near horizon symmetries create “soft” degrees of freedom. Wehave generalised such argument to isolated horizon and have shown that those “soft” degreesof freedom of an isolated horizon are equivalent to its electric multipolemoments.