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Events on Friday, December 11th, 2020

Academic Calendar
Study day
Time: 12:00 am
Place:
Abstract: *Note: actual end time may vary.*
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Theory Seminar (High Energy/Cosmology)
Electric-Magnetic S-matrix
Time: 2:00 pm
Place: For zoom link, sign up at:
Speaker: Sungwoo Hong, Cornell University
Abstract: In the first part of the talk, I will argue that an asymptotic multi-particle state built as a product of one-particle states is not fully general. In addition, I will show that the more general asymptotic multi-particle state carries extra quantum number, pairwise-helicity, on top of the regular labels such as momentum and spin/helicity 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 properties of the electric-magnetic S-matrix, including the extra pairwise-helicity carried by the electric-magnetic asymptotic state and the associated crossing symmetry violation, modern on-shell scattering amplitude method will be motivated as a way to construct the electric-magnetic S-matrix. Pairwise spinor-helicity variables as additional building blocks for the electric-magnetic S-matrix will then be introduced. Discussion on the general three-point amplitudes and resulting generalized spin-helicity selection rules comes next. Finally, I describe the partial-wave decomposition of the 2 to 2 electric-magnetic S-matrix, showing that the well-known results based on QM computations are reproduced with a small input about the phase shift. In particular, the helicity-flip in the lowest partial wave is shown to be a simple consequence of a generalized spin-helicity selection rule. Furthermore, the full 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.
Host: Lars Aalsma
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Department Coffee Hour
Time: 3:30 pm
Place:
Abstract: Join us weekly for an informal virtual coffee hour! Catch up with others in the department, tell us how things are going, and impress everyone with your Zoom background skills. Coffee Hour is open to any and all faculty, staff, and students in the department. Sometimes we have a topic, and we'll try to get that topic posted here in advance or sent out by email before each coffee hour.
Host: Department
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