Width Difference in the B-B[over ¯] System at Next-to-Next-to-Leading Order of QCD.

We extend the theoretical prediction for the width difference ΔΓ_{q} in the mixing of neutral B mesons in the Standard Model to next-to-next-to-leading order in α_{s}. To this aim, we calculate three-loop diagrams with two |ΔB|=1 current-current operators analytically. In the matching between |ΔB|=1 and |ΔB|=2 effective theories, we regularize the infrared divergences dimensionally and take into account all relevant evanescent operators. Further elements of the calculation are the two-loop renormalization matrix Z_{ij} for the |ΔB|=2 operators and the O(α_{s}^{2}) corrections to the finite renormalization that ensures the 1/m_{b} suppression of the operator R_{0} at two-loop order. Our theoretical prediction reads ΔΓ_{s}/ΔM_{s}=(4.33±0.93)×10^{-3} if expressed in terms of the bottom mass in the MS[over ¯] scheme and ΔΓ_{s}/ΔM_{s}=(4.20±0.95)×10^{-3} for the use of the potential-subtracted mass. While the controversy on |V_{cb}| affects both ΔΓ_{s} and ΔM_{s}, the ratio ΔΓ_{s}/ΔM_{s} is not affected by the uncertainty in |V_{cb}|.

Cornering Spontaneous CP Violation with Charged-Higgs-Boson Searches.

Decades of precision measurements have firmly established the Kobayashi-Maskawa phase as the dominant source of the charge-parity (CP) violation observed in weak quark decays. However, it is still unclear whether CP violation is explicitly encoded in complex Yukawa matrices or instead stems from spontaneous symmetry breaking with underlying CP-conserving Yukawa and Higgs sectors. Here we study the latter possibility for the case of a generic two-Higgs-doublet model. We find that theoretical constraints limit the ratio t_{ß} of the vacuum expectation values (vevs) to the range 0.22≤t_{ß}≤4.5 and imply the upper bounds M_{H^{±}}≤435 GeV, M_{H_{2}^{0}}≤485 GeV and M_{H_{3}^{0}}≤545 GeV for the charged and extra neutral Higgs masses. We derive lower bounds on charged-Higgs couplings to bottom quarks which provide a strong motivation to study the nonstandard production and decay signatures pp→qbH^{±}(→q^{'}b) with all flavors q,q^{'}=u, c, t in the search for the charged Higgs boson. We further present a few benchmark scenarios with interesting discovery potential in collider analyses.

Neutral D→KK

We point out that the CP asymmetries in the decays D^{0}→K_{S}K^{*0} and D^{0}→K_{S}K[over ¯]^{*0} are potential discovery channels for charm CP violation in the standard model. We stress that no flavor tagging is necessary, the untagged CP asymmetry a_{CP}^{dir}(D[over (-)]→K_{S}K^{*0}) is essentially equal to the tagged one, so that the untagged measurement comes with a significant statistical gain. Depending on the relevant strong phase, |a_{CP}^{dir,untag}| can be as large as 0.003. The CP asymmetry is dominantly generated by exchange diagrams and does not require nonvanishing penguin amplitudes. While the CP asymmetry is smaller than in the case of D^{0}→K_{S}K_{S}, the experimental analysis is more efficient due to the prompt decay K^{*0}→K^{+}π^{-}. One may further search for favorable strong phases in the Dalitz plot in the vicinity of the K^{*0} peak.

Supersymmetric Explanation of CP Violation in K→ππ Decays.

Recent progress in the determination of hadronic matrix elements has revealed a tension between the measured value of ε_{K}^{'}/ε_{K}, which quantifies direct CP violation in K→ππ decays, and the standard-model prediction. The well-understood indirect CP violation encoded in the quantity ε_{K} typically precludes large new-physics contributions to ε_{K}^{'}/ε_{K} and challenges such an explanation of the discrepancy. We show that it is possible to cure the ε_{K}^{'}/ε_{K} anomaly in the minimal supersymmetric standard model with squark masses above 3 TeV without overshooting ε_{K}. This solution exploits two features of supersymmetry: the possibility of large isospin-breaking contributions (enhancing ε_{K}^{'}) and the Majorana nature of gluinos (permitting a suppression of ε_{K}). Our solution involves no fine-tuning of CP phases or other parameters.

Sum Rules of Charm CP Asymmetries beyond the SU(3)_{F} Limit.

We find new sum rules between direct CP asymmetries in D meson decays with coefficients that can be determined from a global fit to branching ratio data. Our sum rules eliminate the penguin topologies P and PA, which cannot be determined from branching ratios. In this way, we can make predictions about direct CP asymmetries in the standard model without ad hoc assumptions on the sizes of penguin diagrams. We consistently include first-order SU(3)_{F} breaking in the topological amplitudes extracted from the branching ratios. By confronting our sum rules with future precise data from LHCb and Belle II, one will identify or constrain new-physics contributions to P or PA. The first sum rule correlates the CP asymmetries a_{CP}^{dir} in D^{0}→K^{+}K^{-}, D^{0}→π^{+}π^{-}, and D^{0}→π^{0}π^{0}. We study the region of the a_{CP}^{dir}(D^{0}→π^{+}π^{-})-a_{CP}^{dir}(D^{0}→π^{0}π^{0}) plane allowed by current data and find that our sum rule excludes more than half of the allowed region at 95% C.L. Our second sum rule correlates the direct CP asymmetries in D^{+}→K[over ¯]^{0}K^{+}, D_{s}^{+}→K^{0}π^{+}, and D_{s}^{+}→K^{+}π^{0}.

Penguin Contributions to CP Phases in B(d,s) Decays to Charmonium.

The precision of the CP phases 2ß and 2ß(s) determined from the mixing-induced CP asymmetries in B(d)→J/ψK(S) and B(s)→J/ψϕ, respectively, is limited by the unknown long-distance contribution of a penguin diagram involving up quarks. The penguin contribution is expected to be comparable in size to the precision of the LHCb and Belle II experiments and, therefore, limits the sensitivity of the measured quantities to new physics. We analyze the infrared QCD structure of this contribution and find that all soft and collinear divergences either cancel between different diagrams or factorize into matrix elements of local four-quark operators up to terms suppressed by Λ(QCD)/m(ψ), where m(ψ) denotes the J/ψ mass. Our results, which are based on an operator product expansion, allow us to calculate the penguin-to-tree ratio P/T in terms of the matrix elements of these operators and to constrain the penguin contribution to the phase 2ß as |Δϕ(d)|≤0.68°. The penguin contribution to 2ß(s) is bounded as |Δϕ(s)(0)|≤0.97°, |Δϕ(s)(∥)|≤1.22°, and |Δϕ(s)(⊥)|≤0.99° for the case of longitudinal, parallel, and perpendicular ϕ and J/ψ polarizations, respectively. Further, we place bounds on |Δϕ(d)| for B(d)→ψ(2S)K(S) and the polarization amplitudes in B(d)→J/ψK(*). In our approach, it is further possible to constrain P/T for decays in which P/T is Cabibbo unsuppressed, and we derive upper limits on the penguin contribution to the mixing-induced CP asymmetries in B(d)→J/ψπ(0), B(d)→J/ψρ(0), B(s)→J/ψK(S), and B(s)→J/ψK(*). For all studied decay modes, we also constrain the sizes of the direct CP asymmetries.

Impact of a Higgs boson at a mass of 126 GeV on the standard model with three and four fermion generations.

We perform a comprehensive statistical analysis of the standard model (SM) with three and four generations using the latest Higgs search results from LHC and Tevatron, the electroweak precision observables measured at LEP and SLD, and the latest determinations of M(W), m(t), and α(s). For the three-generation case we analyze the tensions in the electroweak fit by removing individual observables from the fit and comparing their predicted values with the measured ones. In particular, we discuss the impact of the Higgs search results on the deviations of the electroweak precision observables from their best-fit values. Our indirect prediction of the top mass is m(t) =175.7(-2.2)(+3.0) GeV at 68.3% C.L., which is in good agreement with the direct measurement. We also plot the preferred area in the M(W)-m(t) plane. The best-fit Higgs boson mass is 126.0 GeV. For the case of the SM with a perturbative sequential fourth fermion generation (SM4) we discuss the deviations of the Higgs signal strengths from their best-fit values. The H → γγ signal strength now disagrees with its best-fit SM4 value at more than 4σ. We perform a likelihood-ratio test to compare the SM and SM4 and show that the SM4 is excluded at 5.3σ. Without the Tevatron data on H → bb the significance drops to 4.8σ.

Rare decay K+ --> pi+ nunu at the next-to-next-to-leading order in QCD.

We calculate the charm quark contribution to the rare decay Kappa(+)--> pi(+) nunu in the next-to-next-to-leading order of QCD. This new contribution reduces the theoretical uncertainty in the relevant parameter Pc from +/-10.1% down to +/-2.4%, corresponding to scale uncertainties of +/-1.3%, +/-1.0%, +/-0.006, and +/-1.2 degrees in Beta(Kappa(+) --> pi(+) nunu) and in |V(td)|, sin2(Beta), and gamma extracted from the Kappa --> pinunu system. The error in Rho(c) = 0.37 +/- 0.04 is now fully dominated by the current uncertainty of +/-3.8% in the charm quark mass m(c). We find Beta(Kappa(+) --> pi(+)nunu) = (8.0 +/- 1.1) x 10(-11), where the quoted error stems almost entirely from the present uncertainties in m(c) and the Cabibbo-Kobayashi-Maskawa elements.