Theory Colloquia

Magnetic scattering: pairwise little group and pairwise helicity

by Csaba Csaki (Cornell University)

Europe/Zurich
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CERN

Description

I discuss how to construct a Lorentz-invariant S-matrix for the scattering of electrically and magnetically charged particles. A key ingredient is a revision of our fundamental understanding of multi-particle representations of the Poincaré group. Surprisingly, the asymptotic states for electric-magnetic scattering transform with an additional little group phase, associated with pairs of electrically and magnetically charged particles. I will discuss the general construction of such states. The resulting "pairwise helicity" is identified with the quantized "cross product" of charges e1 g2- e2 g1 for  every charge-monopole pair, and represents the extra angular momentum stored in the asymptotic electromagnetic field. We define a new kind ofpairwise spinor-helicity variable, which serves as an additional building block for electric-magnetic scattering amplitudes. We then construct the most general 3-point S-matrix elements, as well as the full partial wave decomposition for the 2 -> 2 fermion-monopole S-matrix. In particular, we derive the famous helicity flip in the lowest partial wave as a simple consequence of a generalized spin-helicity selection rule, as well as the full angular dependence for the higher partial waves. We will also discuss a possible direction for resolving Callan's ``semiton" problem: the scattering amplitude of a positron on a GUT monopole which apparently does not have an allowed final state. We will show that using entagled pairwise helicity spinors a simple possible s-wave final state does exist.

Videoconference
TH colloquia
Zoom Meeting ID
67346292748
Host
Elena Gianolio
Alternative hosts
Zoom Recording Operations 2, Matthew Philip Mccullough, Joachim Kopp, Alexander Zhiboedov, Ghislain Magdeleine, Kyriakos Papadodimas
Passcode
80279029
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