Effects of Lorentz violation through the γe → Wνe process in the Standard Model extension

Abstract

Physics beyond the Fermi scale could show up through deviations of the gauge couplings predicted by the electroweak Yang–Mills sector. This possibility is explored in the context of the International Linear Collider through the helicity amplitudes for the γe → Wνe reaction to which the trilinear WWγ coupling contributes. The new physics effects on this vertex are parametrized in a model-independent fashion through an effective electroweak Yang–Mills sector, which is constructed by considering two essentially different sources of new physics. In one scenario, Lorentz violation will be considered exclusively as the source of new physics effects. This type of new physics is considered in an extension of the Standard Model (SM) that is known as the SM extension (SME), which is an effective field theory that contemplates CPT and Lorentz violation in a model-independent fashion. Any source of new physics that respects the Lorentz symmetry will be considered within the general context of the well-known conventional effective SM (CESM) extension. Both the SME and CESM descriptions include gauge invariant operators of dimension higher than 4, which, in general, transform as Lorentz tensors of rank higher than zero. In the former theory, observer Lorentz invariants are constructed by contracting these operators with constant Lorentz tensors, whereas in the latter the corresponding Lorentz invariant interactions are obtained contracting such operators with products of the metric tensor. In this work, we focus on a dimension 6 Lorentz 2-tensor, , which arises from an effective SU(2)L Yang–Mills sector. Contributions to the WWγ coupling arising from dimension 4 operators are ignored since they are strongly constrained. When these operators are contracted with a constant antisymmetric background tensor, bαβ, the corresponding observer invariant belongs to the SME, whereas if they are contracted with the metric tensor, gαβ, an effective interaction in the context of the CESM is obtained. We focus our study on the possibility of experimentally distinguishing both types of new physics effects on the WWγ vertex. It is found that for a new physics scale of the same order of magnitude and under determined circumstances, both types of new physics effects will be clearly distinguished.