High Energy Theory Seminar: Javier Matulich

Title: The Asymptotic Structure of Higher-Dimensional Gravity: New Insights from Dimensional Reduction.

Abstract: The Bondi–van der Burg–Metzner–Sachs (BMS) group characterizes the asymptotic symmetries of gravity in asymptotically flat spacetimes. While its structure in four dimensions is well understood, the situation becomes significantly more intricate in five—and more generally, in odd—dimensions. This complexity arises from the fractional decay of the gravitational field along null directions, which obstructs a smooth conformal compactification at null infinity. In contrast, no such obstruction appears at spatial infinity, where the gravitational field decays in a standard Coulomb-like manner, independent of whether the spacetime dimension is even or odd.

After reviewing the asymptotic structure of flat spacetime, this talk will analyze the asymptotic properties of gravity in five dimensions using Hamiltonian methods. It will be shown that the corresponding algebra of asymptotic symmetries, which had not been uncovered before, constitutes a nonlinear deformation of the semidirect product of the Lorentz algebra with an Abelian algebra generated by four independent (rather than a single) arbitrary functions on the three-sphere at infinity, with nontrivial central extensions. Finally, the consequences of this novel result will be explored through a dimensional reduction scheme, aiming to deepen our understanding of  the asymptotic structure of flat spacetime.