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PRODID:UW-Madison-Physics-Events
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SEQUENCE:1
UID:UW-Physics-Event-6183
DTSTART:20201211T200000Z
DTEND:20201211T210000Z
DTSTAMP:20210308T052437Z
LAST-MODIFIED:20201207T175140Z
LOCATION:For zoom link\, sign up at: https://groups.google.com/a/g-gro
ups.wisc.edu/d/forum/theoryseminars/join
SUMMARY:Electric-Magnetic S-matrix\, Theory Seminar (High Energy/Cosmo
logy)\, Sungwoo Hong\, Cornell University
DESCRIPTION:In the first part of the talk\, I will argue that an asymp
totic multi-particle state built as a product of one-particle states i
s not fully general. In addition\, I will show that the more general a
symptotic multi-particle state carries extra quantum number\, pairwise
-helicity\, on top of the regular labels such as momentum and spin/hel
icity of each particle. In the second part of the talk\, the S-matrix
for the scattering of electrically and magnetically charged particles
will be considered. After discussing several non-conventional properti
es of the electric-magnetic S-matrix\, including the extra pairwise-he
licity carried by the electric-magnetic asymptotic state and the assoc
iated crossing symmetry violation\, modern on-shell scattering amplitu
de method will be motivated as a way to construct the electric-magneti
c S-matrix. Pairwise spinor-helicity variables as additional building
blocks for the electric-magnetic S-matrix will then be introduced. Dis
cussion on the general three-point amplitudes and resulting generalize
d spin-helicity selection rules comes next. Finally\, I describe the p
artial-wave decomposition of the 2 to 2 electric-magnetic S-matrix\, s
howing that the well-known results based on QM computations are reprod
uced with a small input about the phase shift. In particular\, the hel
icity-flip in the lowest partial wave is shown to be a simple conseque
nce of a generalized spin-helicity selection rule. Furthermore\, the f
ull angular dependence for the higher partial waves is shown to agree
with QM results. Our work represents a remarkable success of on-shell
methods for non-perturbative physics\, especially when the Lagrangian
description fails.
URL:https://www.physics.wisc.edu/events/?id=6183
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