Memory effect in Yang-Mills theory

by Keijo Kajantie (Helsinki Institute of Physics (FI))

Monday 20 May 2019, 15:00 → 16:00 Europe/Zurich

4/2-037 - TH meeting room (CERN)

Send a pulse of radiation to null infinity. Memory effect is the memory of the pulse left to a system of detectors after the pulse has passed. It can be analysed for U(1) electrodynamics in terms of gauge invariant variables, electric and magnetic fields. Memory is a transverse kick, total change of transverse momentum, of a test charge. It is an obviously measurable quantity and if you work it out in a fixed gauge, you have computed a change in a gauge parameter at null infinity. These "large" gauge transformations are sometimes elevated to new symmetries of ED vacuum, but they really seem to be U(1) gauge invariance. This U(1) discussion is straightforward to generalise to classical Yang-Mills fields. Any experimental testing has to face confinement and quantum effects, even if one wants to apply memory effect ideas to classical Yang-Mills fields in dense heavy ion collisions. Finally, it may be informative to compare the U(1) ideas to gravity: there the analogue of U(1) invariance group is the set of diffeomorphisms leaving the Bondi metric invariant in a specific way near null infinity.