New physics models of direct CP violation in charm decays

Abstract

In view of the recent LHCb measurement of ∆A CP , the difference between the time-integrated CP asymmetries in D → K + K − and D → π + π − decays, we perform a comparative study of the possible impact of New Physics degrees of freedom on the direct CP asymmetries in singly Cabibbo suppressed D meson decays. We systematically discuss scenarios with a minimal set of new degrees of freedom that have renormalizable couplings to the SM particles and that are heavy enough such that their effects on the D meson decays can be described by local operators. We take into account both constraints from low energy flavor observables, in particular D 0 −D 0 mixing, and from direct searches. While models that explain the large measured value for ∆A CP with chirally enhanced chromomagnetic penguins are least constrained, we identify a few viable models that contribute to the D meson decays at tree level or through loop induced QCD penguins. We emphasize that such models motivate direct searches at the LHC.

Colored scalars and the neutron electric dipole moment

“…A viable possibility is to deviate from the generation universality for the color octet couplings to the quark fields, or to modify the original MFV set-up of [29,37]. Thus, the authors of [43] suggested small deviation from the MFV ansatz by allowing flavor changing u ↔ c quark interactions with a neutral color octet scalar. Following ref.…”

“…where the couplings G(c → u) and X d are proportional to quark masses: was found that two operatorsÕ 1 S1 = (ūP R s)(sP R c) andÕ 1 S2 = (ū α P R s β )(s β P R c α ) contribute to the effective Hamiltonian as described in [43]. Motivated by the model of [43], we use this tree level effective (c u Φ 8 ) coupling bounded by the charm CP asymmetry.…”

“…Motivated by the model of [43], we use this tree level effective (c u Φ 8 ) coupling bounded by the charm CP asymmetry. Then we find that there is a new two-loop contribution, which we consider in the following subsection.…”

“…Sec. III is devoted to the study of NEDM contributions obtained within a modified color octet model [43] which produces CP violation in charm at tree level. In Sec.…”

Nonuniversality of indirectCPasymmetries inD→ππ,KKdecays

“…A survey of the effect of NP models that may contribute to the difference CP asymmetry has been performed in Ref. [38]. It points out that the CP violation may be generated at the tree level with models that involve flavor-changing couplings of Z, Z ′ bosons, new charged gauge bosons, flavor-changing heavy gluon, scalar octets, a scalar diquark, or a two-Higgs doublet with minimal flavor violation.…”