Effects of CPT violation on the neutrino charge radius in the standard model extension

CPT-Odd effects on the charge radius of the neutrino are studied in the context of the Standard Model Extension. Effects of CPT violation arising from the electroweak Yang–Mills sector, characterized by the Lorentz violation coefficients [Formula: see text] and [Formula: see text], which have positive mass units, are considered. In this context, we find that the [Formula: see text] vertex is induced at the tree level through the exchange of two Z gauge bosons. Although strongly suppressed due to a factor of [Formula: see text], the process has some characteristics that make it interesting. First, the vertex function [Formula: see text] is given by three independent gauge structures, which fulfill with a Ward identity of the way [Formula: see text], which is characteristic of every neutral particle, and induce electromagnetic form factors that are independent on the gauge parameter [Formula: see text]. At this level, besides the charge and anapole, two additional nonconventional form factors are generated. Second, the charge form factor [Formula: see text] has a piece that is energy dependent, which causes [Formula: see text], so the electromagnetic properties cannot be defined for a real photon in the presence of CPT violation. Instead, the charge form factor and their associated charge radius are defined in the static limit, which is given by the kinematical conditions: [Formula: see text] and then [Formula: see text]. In the static limit, we find that [Formula: see text] and a correction to the Standard Model prediction of the neutrino charge radius given by [Formula: see text], with [Formula: see text] the angle between the spatial vectors [Formula: see text] and [Formula: see text]. Using a recently derived bound on the Lorentz violation coefficients [Formula: see text] along with some reasonable assumptions, we have obtained a small correction of [Formula: see text].