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′ contributions in these models there are no new free parameters beyond those already present in the Bd,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 D0→ μ+μ−, 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 Bd,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 ∆ACP, the difference between the CP asymmetries in D0→ K+K− and D0→ π+π−, 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.
Highlights
The charm case get contributions from internal down-type quarks
In the case of rare flavour changing neutral current (FCNC) processes induced by the c → u transition the effectiveness of the GIM mechanism results in so tiny branching ratios in the SM that one can consider them as null tests: their observation with a less severe degree of suppression with respect to SM would be a signal of new Physics (NP)
The short-distance SM contributions to them are both real to a very good approximation, and this is the case of the long-distance contributions. This implies that, unless NP contributions to xD and yD in a given model are in the ballpark of their values in (3.9), the best chance to search for NP in D0 − D0 mixing is through CP violation, represented by the departure of |q/p| from unity and the non-vanishing phase φ in the measured range in (3.10)
Summary
Neutral charmed mesons provide the only system where flavour oscillation of up-type quarks can occur. The short-distance SM contributions to them are both real to a very good approximation, and this is the case of the long-distance contributions This implies that, unless NP contributions to xD and yD in a given model are in the ballpark of their values in (3.9), the best chance to search for NP in D0 − D0 mixing is through CP violation, represented by the departure of |q/p| from unity and the non-vanishing phase φ in the measured range in (3.10). The experimental values in (3.9) and (3.10) provide strong constraints to the extensions of the SM in which left-right, scalar and tensor operators are present [21,22,23,24] Such operators have large hadronic matrix elements and strongly enhanced Wilson coefficients through QCD renormalization group effects, In the 331 model only the operator Q1 is involved, as in the SM, but this time its Wilson coefficient receives the contribution from tree-level Z exchange. We predict observables and correlations, as those involving |q/p| and φ
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