1306.0262 (A. Moyotl et al.)

Gauge invariant electromagnetic properties of fermions induced by CPT
violation in the Standard Model Extension    [PDF]

A. Moyotl, H. Novales-Sánchez, J. J. Toscano, E. S. Tututi

Low-energy Lorentz-invariant quantities could receive contributions from a fundamental theory producing small Lorentz-violating effects. Within the Lorentz-violating extension of quantum electrodynamics, we investigate, perturbatively, the contributions to the one-loop ffgamma vertex from the CPT-violating axial coupling of a vector background field to fermions. We find that the resulting vertex function has a larger set of Lorentz structures than the one characterizing the usual, Lorentz invariant, parametrization of the ffgamma vertex. We prove gauge invariance of the resulting one-loop expression through a set of gauge invariant nonrenormalizable operators introducing new-physics effects at the first and second orders in Lorentz violation, and which generate tree-level contributions to the ffgamma vertex. Whereas loop contributions involving parameters that violate Lorentz invariance at the first order are CPT-odd, those arising at the second order are CPT-even, so that contributions to low-energy physics are restricted to emerge for the first time at the second order. In this context, we derive a contribution to anomalous magnetic moment (AMM) of fermions, which we use to bound Lorentz violation.

View original: http://arxiv.org/abs/1306.0262