Spontaneous Lorentz Violation: The Case of Infrared QED

TL;DR

This paper explores how infrared photons in QED cause spontaneous Lorentz violation, leading to angle-dependent fermion masses and potential observable effects in decay experiments.

Contribution

It extends the 'Sky' group framework to detail properties of dressed charged particles and their Lorentz-violating mass modifications.

Findings

Fermion masses become angle-dependent due to infrared photon dressing.

Lorentz violation affects fermion dispersion relations and spin content.

Potential measurable effects in muon decay experiments.

Abstract

It is by now clear that infrared sector of QED has an intriguingly complex structure. Based on earlier pioneering works on this subject, two of us recently proposed a simple modification of QED by constructing a generalization of the $U(1)$ charge group of QED to the "Sky" group incorporating the known spontaneous Lorentz violation due to infrared photons, but still compatible in particular with locality. There it was shown that the "Sky" group is generated by the algebra of angle dependent charges and a study of its superselection sectors has revealed a manifest description of spontaneous breaking of Lorentz symmetry. We further elaborate this approach here and investigate in some detail the properties of charged particles dressed by the infrared photons. We find that Lorentz violation due to soft photons may be manifestly codified in an angle dependent fermion mass modifying therefore the fermion dispersion relations. The fact that the masses of the charged particles are not Lorentz invariant affects their spin content too.Time dilation formulae for decays should also get corrections. We speculate that these effects could be measured possibly in muon decay experiments.