Decays $Z\to\gamma\gamma$ and $Z\to gg$ in the Standard Model Extension

TL;DR

This paper investigates how certain rare Z boson decays into two photons or two gluons can occur within the Standard Model Extension due to CPT-odd interactions, which are normally forbidden in the Standard Model.

Contribution

It demonstrates that these decays, forbidden in the Standard Model, can be radiatively generated at one-loop level in the Standard Model Extension with CPT-odd terms, and are gauge invariant and divergence-free.

Findings

Decays are generated radiatively at one-loop level.

Decay widths depend only on the spatial component of the background field.

Decays are gauge invariant and ultraviolet finite.

Abstract

The $Z\to \gamma \gamma$ and $Z\to gg$ decays are studied in the context of the renormalizable version of the Standard Model Extension. The $CPT$-odd $\bar{\psi}\gamma_5 \gamma^\mu b_\mu\psi$ bilinear interaction, which involves the constant background field $b_\alpha$ and which has been a subject of interest in literature, is considered. It is shown that the $Z\to \gamma \gamma$ and $Z\to gg$ decays, which are strictly zero in the standard model, can be generated radiatively at the one-loop level. It is found that these decays are gauge invariant and free of ultraviolet divergences, and that the corresponding decay widths only depend on the spatial component of the background field $b$.