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January 10, 2016

BMiSsed

There’s a general mantra that we all repeat to ourselves: gauge transformations are not symmetries; they are redundancies of our description. There is an exception, of course: gauge transformations that don’t go to the identity at infinity aren’t redundancies; they are actual symmetries.

Strominger, rather beautifully showed that BMS supertranslations (or, more precisely, a certain diagonal subgroup of BMS +\text{BMS}^+ (which act as supertranslations on +\mathcal{I}^+) and BMS \text{BMS}^- (which act as supertranslations on \mathcal{I}^-) are symmetries of the gravitational S-matrix. The corresponding conservation laws are equivalent to Weinberg’s Soft-Graviton Theorem. Similarly, in electromagnetism, the U(1)U(1) gauge transformations which don’t go to the identity on ±\mathcal{I}^\pm give rise to the Soft-Photon Theorem.

A while back, there was considerable brouhaha about Hawking’s claim that BMS symmetry had something to do with resolving the blackhole information paradox. Well, finally, a paper from Hawking, Perry and Strominger has arrived.

Cue further brouhaha

Posted by distler at 11:39 AM | Permalink | Followups (25)