Charm mixing in the Standard Model

In this talk we report on a study on the mixing of neutral charmed mesons and argue that, at the present stage, a CP violating weak phase of the order of some per mille can not be excluded in the Standard Model. It is shown how some, seemingly reasonable, simplifying assumptions about CKM couplings lead to the wrong conclusion that CP violation of this amount is an unambiguous indication of new physics. The presented results rely on a recent short-distance analysis of the ∆C = 2 transition, which con- firms the expectation that the dominant contribution is due to effects of flavour symmetry breaking appearing in higher orders of the Heavy Quark Expansion. We investigate meson-antimeson transitions with an intermediate state coupling to the meson’s sea quark background, present in dimension 10 and 12, using a factorisation approach to simplify the operator basis. On account of a lifting of GIM suppression by one power of ms/mc, the contribution to y = ∆Γ/2Γ is found to exceed that of the formally leading dimension six by a factor close to ten

Vacuum stability of the effective Higgs potential in the Minimal Supersymmetric Standard Model

The parameters of the Higgs potential of the Minimal Supersymmetric Standard Model (MSSM) receive large radiative corrections which lift the mass of the lightest Higgs boson to the measured value of 126 GeV. Depending on the MSSM parameters, these radiative corrections may also lead to the situation that the local minimum corresponding to the electroweak vacuum state is not the global minimum of the Higgs potential. We analyze the stability of the vacuum for the case of heavy squark masses as favored by current LHC data. To this end we first consider an effective Lagrangian obtained by integrating out the heavy squarks and then study the MSSM one-loop effective potential V_eff, which comprises all higher-dimensional Higgs couplings of the effective Lagrangian. We find that only the second method gives correct results and argue that the criterion of vacuum stability should be included in phenomenological analyses of the allowed MSSM parameter space. Discussing the cases of squark masses of 1 and 2 TeV we show that the criterion of vacuum stability excludes a portion of the MSSM parameter space in which (mu tanbeta) and A_t are large.Comment: minor changes in text and list of references, figures in eps format, matches published version; Erratum added and sent to PR

Short distance D-Dbar mixing

We review the status of Standard Model predictions for lifetimes and mixing rates of charmed mesons. It is shown that the short distance approach is able to reproduce τ (D+)/τ (D0) at leading order in the 1/mc expansion. SU(3) violating effects from interactions with the soft hadronic background are identified as the dominant contribution to the D–D mixing rate. We discuss the contribution from operators of dimension nine, which is able to enhance the neutral charm width splitting by a factor of order ten and comment on possible CP violation in mixing

Standard Model Predictions for D0-oscillations and CP-violation

We review the status of the standard model predictions for $D$-mixing and CP-violation in mixing.Comment: 5 pages; Talk at CHARM 2010, Beijing, October 201