Person:

Ng, Gim Seng

The asymptotic symmetry group (ASG) at future null infinity ((I^+)) of four-dimensional de Sitter spacetimes is defined and shown to be given by the group of three-dimensional diffeomorphisms acting on (I^+). Finite charges are constructed for each choice of ASG generator together with a two-surface on (I^+). A conservation equation is derived relating the evolution of the charges with the radiation flux through (I^+).

We consider asymptotically future de Sitter spacetimes endowed with an eternal observatory. In the conventional descriptions, the conformal metric at the future boundary (I^+) is deformed by the flux of gravitational radiation. We however impose an unconventional future “Dirichlet” boundary condition requiring that the conformal metric is flat everywhere except at the conformal point where the observatory arrives at (I^+). This boundary condition violates conventional causality, but we argue the causality violations cannot be detected by any experiment in the observatory. We show that the bulk-to-bulk two-point functions obeying this future boundary condition are not realizable as operator correlation functions in any normalizable de Sitter invariant vacuum, but they do agree with those obtained by double analytic continuation from anti-de Sitter space.

We study various aspects of symmetry in four-dimensional de Sitter space (dS$_4$).