Chromomagnetic and chromoelectric dipole moments of quarks in the reduced 331 model

TL;DR

This paper calculates the one-loop contributions to the top quark's chromomagnetic and electric dipole moments within the reduced 331 model, revealing significant new contributions from heavy gauge bosons and scalars, with implications for observable CP-violation effects.

Contribution

It provides the first detailed calculation of top quark dipole moments in the reduced 331 model, including off-shell gluon effects and new particle contributions, extending previous analyses in standard model extensions.

Findings

New contributions to $\u0301 ilde\mu_t(q^2)$ from $Z'$ and $V^+$ gauge bosons and $h_2$ scalar.

Dominant $_t$ contribution from $h_2$ exchange, reaching $10^{-20}$.

$_t$ is smaller than in other models, but $ ilde\mu_t(q^2)$ can be sizable.

Abstract

The one-loop contributions to the chromomagnetic dipole moment $\hat\mu_t(q^2)$ and electric dipole moment $\hat d_t(q^2)$ of the top quark are calculated within the reduced 331 model (RM331) in the general case of an off-shell gluon. It is argued that the results are gauge independent for $q^2\ne 0$ and represent valid observable quantities. In the RM331 $\hat \mu_t(q^2)$ receives new contributions from two heavy gauge bosons $Z'$ and $V^+$ and a new neutral scalar boson $h_2$, along with a new contribution from the standard model Higgs boson via flavor changing neutral currents. The latter, which are also mediated by the $Z'$ gauge boson and the scalar boson $h_2$, can give a non-vanishing $\hat d_t$ provided that there is a $CP$-violating phase. The analytical results are presented in terms of both Feynman parameter integrals and Passarino-Veltman scalar functions, which are useful to cross-check the numerical results. Both $\hat\mu_t(q^2)$ and $\hat d_t$ are numerically evaluated for parameter values still allowed by the constraints from experimental data. It is found that the new one-loop contributions of the RM331 to $\hat \mu_t(q^2)$ are of the same order of magnitude or larger than in other standard model extensions, with the dominant contribution arising from the $V^+$ gauge boson for $\|q\|$ in the 30-1000 GeV interval and a mass $m_{V}$ of the order of a few hundreds of GeVs. As for $\hat d_t(q^2)$, it receives the largest contribution from $h_2$ exchange and can reach values of the order of $10^{-20}$, which is smaller than the contributions predicted by other standard model extensions.