Andrea Campoleoni (ULB Brussels)
Hints on quantum BMS symmetries from three dimensions
When the dimension of space-time is equal to four, the asymptotic symmetries of gravitational configurations which approach Minkowski space at infinity are given by an infinite-dimensional extension of the Poincaré group, known as the Bondi-Metzner-Sachs (BMS) group. A similar extension appears in three dimensions, where the BMS_3 group is a contraction of the Virasoro asymptotic symmetries of AdS_3 gravity. After a general introduction to BMS symmetries, we show how the latter link enable one to argue that BMS_3 symmetries should survive in the quantum theory and to build representations of this infinite-dimensional group. We also stress that including higher-spin gauge fields in three dimensions brings a further extension of the asymptotic symmetries which clarifies the link between Virasoro and BMS_3 groups: different contractions of the asymptotic symmetry algebra that accidentally give the same result in Einstein gravity indeed differ when higher spins are present.