Large Tanβ Research Articles

The decayH 2 0 →gg within the Minimal Supersymmetric Standard Model

I present a detailed SUSY QCD calculation of the decay rate of the lightest Higgs bosonH20 into two gluons, where all quarks and scalar quarks are taken within the relevant loop diagrams. I include the mixing of all the scalar partners of the left and right handed quarks and show that their contribution is more than several tens of per cent compared to the quark contribution in the MSSM for some SUSY parameter space. Furthermore the MSSM fermionic contribution is enhanced by several factors for large tanβ and large Higgs masses. As a result, the two gluon decay rate ofH20 is much larger than the two gluon decay rate of an equal mass standard model Higgs boson. I further compare the decay mode ofH20→gg to the similar decay modes ofH20→cc andH20→bb including one loop QCD corrections and show that in some casesΓ(H20→gg) is even higher thanΓ(H20→cc), although still much smaller thanΓ(H20→bb).

Finite supersymmetric threshold corrections to CKM matrix elements in the large tan beta regime.

We evaluate the finite 1-loop threshold corrections, proportional to $tan\beta$, to the down quark mass matrix. These result in corrections to down quark masses and to Cabibbo-Kobayashi-Maskawa [CKM] matrix elements. The corrections to CKM matrix elements are the novel feature of this paper. For grand unified theories with large $\tan\beta$ these corrections may significantly alter the low energy predictions of four of the CKM matrix elements and the Jarlskog parameter J, a measure of CP violation. The angles $\alpha,\: \beta$ and $\gamma$ of the unitarity triangle and the ratio $|{V_{ub} \over V_{cb}}|$, however, are not corrected to this order. We also discuss these corrections in the light of recent models for fermion masses. Here the corrections may be useful in selecting among the various models. Moreover, if one model fits the data, it will only do so for a particular range of SUSY parameters.

Minimal supersymmetric standard model and large tan beta from SUSY trinification.

We construct a supersymmetric model based on the semisimple gauge group SU(3)[sub [ital c]][times]SU(3)[sub [ital L]][times]SU(3)[sub [ital R]] with the relation tan[beta][congruent][ital m][sub [ital t]]/[ital m][sub [ital b]] automatically arising from its structure. The model below a scale [similar to]10[sup 16] GeV naturally gives rise just to the minimal supersymmetric standard model and therefore to the presently favored values for sin[sup 2][theta][sub [ital W]] and [alpha][sub [ital s]] without fields in representations higher than the fundamental.

Magnitude of Higgs-boson-exchange CP violation in two-doublet models with large tan beta.

CP violation in neutral Higgs-boson exchange is studied in two-doublet models in an expansion in (1/${\mathrm{tan}}^{2}$\ensuremath{\beta}). The typical magnitude of various CP-violating quantities is found for large tan\ensuremath{\beta}. In particular the electric dipole moment (EDM) of the electron and the coefficient ${\mathit{c}}_{\mathit{S}}$ of the CP-violating electron-nucleon scalar-pseudoscalar operator are examined and it is found that in a simple class of two-doublet models ${\mathit{c}}_{\mathit{S}}$/${\mathit{d}}_{\mathit{e}}$ is typically O(${\mathrm{tan}}^{2}$\ensuremath{\beta}). Therefore ${\mathit{c}}_{\mathit{S}}$ is more important than ${\mathit{d}}_{\mathit{e}}$ for the EDM's of diamagnetic atoms and molecules (Hg, Xe, TlF) typically if tan\ensuremath{\beta}\ensuremath{\gtrsim}5, and for paramagnetic atoms (Cs, Tl) if tan\ensuremath{\beta}\ensuremath{\gtrsim}15. The dependence on tan\ensuremath{\beta} of the various contributions to the neutron EDM including the Weinberg three-gluon operator, and the dependence on tan\ensuremath{\beta} of the top-quark EDM are also discussed. Supersymmetric and three-doublet models are also considered.