Thursday, October 29, 2015, 16:00
WHGA Auditorium
Elliot Leader, Imperial College London
Abstract:
The claim some years ago, contrary to all textbooks, that the angular
momentum of a photon (and gluon) can be split in a gauge-invariant way
into an orbital and spin term, sparked a major controversy in the
Particle Physics community. A further cause of upset was the realization
that the gluon polarization in a nucleon, a supposedly physically
meaningful quantity, corresponds only to the gauge-variant gluon spin
derived from Noether's theorem, evaluated in a particular gauge. On the
other hand, Laser Physicists have, for decades, been happily measuring
physical quantities which correspond to orbital and spin angular
momentum evaluated in a particular gauge. This talk will explain the
origins of the controversy and suggest how one can reconcile the two
points of view.