The charm of 331

TL;DR

This paper analyzes flavor-changing neutral currents in charm within 331 models, showing potential for significant new physics effects, especially in rare decay modes and CP violation, with specific predictions and correlations to other meson decays.

Contribution

It demonstrates that 331 models predict no new free parameters beyond existing meson systems, allowing precise predictions of new physics effects in charm observables, including large enhancements in rare decay rates.

Findings

Potential 6-order magnitude enhancement of $D^0 o \mu^+ \mu^-$ decay

Correlation between charm rare decays and $B_{d,s}$, $K$ decays

331 models can explain observed CP asymmetry differences

Abstract

We perform a detailed analysis of flavour changing neutral current processes in the charm sector in the context of 331 models. As pointed out recently, in the case of $Z^\prime$ contributions in these models there are no new free parameters beyond those already present in the $B_{d,s}$ and $K$ meson systems analyzed in the past. As a result, definite ranges for new Physics (NP) effects in various charm observables could be obtained. While generally NP effects turn out to be small, in a number of observables they are much larger than the tiny effects predicted within the Standard Model. In particular we find that the branching ratio of the mode $D^0 \to \mu^+ \mu^-$, despite remaining tiny, can be enhanced by 6 orders of magnitude with respect to the SM. We work out correlations between this mode and rare $B_{d,s}$ and $K$ decays. We also discuss neutral charm meson oscillations and CP violation in the charm system. In particular, we point out that 331 models provide new weak phases that are a necessary condition to have non-vanishing CP asymmetries. In the case of $\Delta A_{CP}$, the difference between the CP asymmetries in $D^0 \to K^+ K^-$ and $D^0 \to \pi^+ \pi^-$, we find that agreement with experiment can be obtained provided that two conditions are verified: the phases in the ranges predicted in 331 models and large hadronic matrix elements.