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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:20260415T003442Z
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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