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Theory Center Seminar<br>
<div>Wed., June 1, 2016<br>
2:00 p.m. (coffee at 1:45 p.m.)<br>
CEBAF Center, Room L102<br>
<font color="#0f61c8"><br>
</font><b>The Angular Momentum Controversy: Resolution of a
Conflict Between Laser and Particle Physics</b><br>
<br>
Elliot Leader</div>
<div>Imperial College London<br>
<font color="#0f61c8"><br>
</font>The claim some years ago, contrary to all textbooks, that
the angular momentum of a photon (and gluon) can be split <br>
in a gauge-invariant way into an orbital and spin term, sparked a
major controversy in the Particle Physics community. <br>
A further cause of upset was the realization that the gluon
polarization in a nucleon, a supposedly physically meaningful <br>
quantity, corresponds only to the gauge-variant gluon spin derived
from Noether's theorem, evaluated in a particular <br>
gauge. But that sort of thing doesn't seem to worry the Laser
Physicists who have, for decades, been happily measuring <br>
physical quantities which correspond to photon orbital and spin
angular momentum evaluated in a particular gauge. My <br>
talk aims to reconcile the two points of view, and shows that it
is the gauge invariant version of the canonical angular <br>
momentum which agrees with the results of a host of laser optics
experiments.<br>
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