[Jlab-seminars] Theory Seminar (Elliot Leader) Today, 2:00 p.m., F224/225

[Mary Fox]

Theory Center Seminar
Wed., June 1, 2016
2:00 p.m. (coffee at 1:45 p.m.)
CEBAF Center, /*Room F224/225 */


*The Angular Momentum Controversy: Resolution of a Conflict
Between Laser and Particle Physics*

Elliot Leader
Imperial College London

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. But that sort of thing doesn't seem to worry the Laser Physicists 
who have, for decades,  been happily measuring
physical quantities which correspond to photon orbital and spin angular 
momentum evaluated in a particular gauge. My
talk aims to reconcile the two points of view, and shows that it is the 
gauge invariant version of the canonical angular
momentum which agrees with the results of a host of laser optics 
experiments.
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