High Energy Theory Seminar - IAS - Philip Schuster, Perimeter Institute - “(Why) Is Helicity Lorentz-Invariant?”

Mon, Apr 8, 2013, 2:30 pm to 3:30 pm
Bloomberg Lecture Hall - Institute for Advanced Study
Massless particle states carry integer or half-integer spin about themomentum axis, or "helicity". Lorentz symmetry allows for helicity states to mix under boosts (like massive particle polarizations); such mixing is not understood theoretically and is not obviously well constrained by experiment. This possibility is historically known as "continuous spin"and this talk provides an informal introduction to the subject. We introduce a gauge field theory description of CSPs, and review evidence that CSPs can interact with matter via scattering amplitudes that approach familiar scalar, electromagnetic, or gravitational ones in a high-energy (and/or non-relativistic) correspondence limit. Such interactions appear thermodynamically safe. We discuss potential signatures of matter coupled to a photon-CSP and related consequences for stellar cooling. We close by identifying some directions for discovering a full interacting theory of CSPs or proving that such theories can't exist.