Photon helicity and quantum anomalies in curved spacetimes
Matteo Galaverni, Gabriele Gionti S.J.
TL;DR
This paper compares different photon helicity definitions in curved spacetime, explores how quantum anomalies affect helicity conservation, and derives the associated Noether current from invariant Lagrangians.
Contribution
It provides a systematic comparison of photon helicity definitions and derives the Noether current related to duality transformations in curved spacetime.
Findings
Quantum anomalies can break helicity conservation in curved spacetime.
Different helicity definitions lead to distinct physical effects like polarization rotation.
The Noether current for duality symmetry is explicitly derived from invariant Lagrangians.
Abstract
We compare several definitions of photon helicity (magnetic, electric, electromagnetic) present in literature. In curved spacetime quantum anomalies can spoil helicity conservation inducing, according to these definitions, different effects on photons: either rotation of linear polarization or production of circular polarization. We derive the Noether current associated with duality transformations starting from manifestly invariant Lagrangians.
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