Two-loop SQCD corrections to Higgs-quark-quark couplings in the generic MSSM

In this article we compute the two-loop SQCD corrections to Higgs-quark-quark couplings in the generic MSSM generated by diagrams involving squarks and gluinos. We give analytic results for the two-loop contributions in the limit of vanishing external momenta for general SUSY masses valid in the MSSM with general flavour-structure. Working in the decoupling limit (M_SUSY >> v) we resum all chirally enhanced corrections (related to Higgs-quark-quark couplings) up to order \alpha_s^(n+1) tan(\beta)^n. This resummation allows for a more precise determination of the Yukawa coupling and CKM elements of the MSSM superpotential necessary for the study of Yukawa coupling unification. The knowledge of the Yukawa couplings of the MSSM superpotential in addition allows us to derive the effective Higgs-quark-quark couplings entering FCNC processes. These effective vertices can in addition be used for the calculation of Higgs decays into quarks as long as M_SUSY > M_Higgs holds. Furthermore, our calculation is also necessary for consistently including the chirally enhanced self-energies contributions into the calculation of FCNC processes in the MSSM beyond leading order. At two-loop order, we find an enhancement of the SUSY threshold corrections, induced by the quark self-energies, of approximately 9% for \mu=M_SUSY compared to the one-loop result. At the same time, the matching scale dependence of the effective Higgs-quark-quark couplings is significantly reduced.Comment: 35 pages, 5 figures, typos correcte

Flavour-violation in two-Higgs-doublet models

In these proceedings we review the flavour phenomenology of 2HDMs with generic Yukawa structures. We first consider the quark sector and find that despite the stringent constraints from FCNC processes large effects in tauonic B decays are still possible. We then consider lepton flavour observables, show correlations between \mu -> e\gamma and \mu^- -> e^-e^+e^- in the 2HDM of type III and give upper bounds on the lepton flavour violating B decay B_d -> \mu e.Comment: Proceedings for "The European Physical Society Conference on High Energy Physics EPS-HEP2013", 7 pages, 6 figure

Bounds on flavour violating parameters in supersymmetry

We investigate the constraints on the flavour violating parameters from the decay B --> X_s gamma, taking into account the interplay of the various sources of flavour violation in the unconstrained MSSM. We present a systematic leading logarithmic QCD analysis of these model-independent constraints, including contributions from gluinos, neutralinos, charginos, charged Higgs bosons and interferences between them. We show that two simple combinations of elements of the down squark mass matrix are stringently bounded over large parts of the parameter space where only weak assumptions on the hierarchical structure of the squark mass matrices are made. We also briefly analyse up to which values SUSY contributions, compatible with B --> X_s gamma, can enhance the Wilson coefficient C_8(m_W), which plays an important role in the phenomenology of charmless hadronic B decays.Comment: 29 pages including 22 postscript figure

1-loop SQCD corrections to the decay of top-squarks to charm and neutralino in the generic MSSM

In this article we calculate the 1-loop supersymmetric QCD (SQCD) corrections to the decay $\tilde u_1\to c \tilde\chi^0_1$ in the MSSM with generic flavour structure. This decay mode is phenomenologically important if the mass difference between the lightest squark $\tilde u_1$ (which is assumed to be mainly stop-like) and the neutralino LSP $\tilde \chi^0_1$ is smaller than the top mass. In such a scenario $\tilde u_1\to t \tilde\chi^0_1$ is kinematically not allowed and searches for $\tilde u_1\to W b \tilde\chi^0_1$ and $\tilde u_1\to c \tilde\chi^0_1$ are performed. A large decay rate for $\tilde u_1\to c \tilde\chi^0_1$ can weaken the LHC bounds from $\tilde u_1\to W b \chi^0_1$ which are usually obtained under the assumption ${\rm Br}[\tilde u_1\to W b \chi^0_1]=100\%$. We find the SQCD corrections enhance $\Gamma[\tilde u_1\to c \tilde\chi^0_1]$ by approximately 10\% if the flavour-violation originates from bilinear terms. If flavour-violation originates from trilinear terms, the effect can be $\pm 50\%$ or more, depending on the sign of $A^t$. We note that connecting a theory of SUSY breaking to LHC observables, the shift from the $\overline{\rm DR}$ to the on-shell mass is numerically very important for light stop decays.Comment: 25 pages, 7 figure

Flavor-phenomenology of two-Higgs-doublet models with generic Yukawa structure

We perform an extensive study of flavor observables in a 2HDM with generic Yukawa structure (the decoupling limit of the MSSM). We examine the effects in flavor physics and constrain the model both from tree-level processes and loop-observables. The free parameters of the model are the heavy Higgs mass, tan(\beta) and the "non-holomorphic" Yukawa couplings \epsilon^f_ij (f=u,d,\ell). In our analysis we constrain the elements \epsilon^f_ij in various ways: In a first step we give order of magnitude constraints on \epsilon^f_ij from 't Hooft's naturalness criterion. Then we constrain the Yukawa structure of the type-III 2HDM from tree-level FCNC processes (B_s,d->\mu^+\mu^-, \tau^-->\mu^-\mu^+\mu^-, etc.) and observe that all flavor off-diagonal elements except \epsilon^u_32,31 and \epsilon^u_23,13 must be very small in order to satisfy the experimental bounds. In a third step, we consider Higgs mediated loop contributions to FCNC processes (b->s,d\gamma, \mu->e\gamma, etc.) finding that also \epsilon^u_13 and \epsilon^u_23 must be very small, while the bounds on \epsilon^u_31 and \epsilon^u_32 are especially weak. Taking into account the constraints from FCNC processes we study the possible size of contributions from tree-level charged Higgs exchange. Interestingly, the unconstrained elements \epsilon^u_{32,31} enter directly the branching ratios for B->\tau\nu, B->D\tau\nu and B->D*\tau\nu and we show that the deviations from the SM predictions in these processes can be explained simultaneously. We give upper limits on the branching ratios of the lepton flavor-violating neutral B meson decays and correlate the radiative lepton decays to the corresponding neutral current lepton decays (\tau^- ->\mu^-\mu^+\mu^-, \tau^- ->e^-\mu^+\mu^- and \mu^- ->e^-e^+e^-). A detailed appendix contains all relevant information for the considered processes for general scalar-fermion-fermion couplings.Comment: 73 pages, 36 figures, 10 table