arXiv subjects
Publications and source records attributed to Y. Yamada.
We calculate the supersymmetric QCD corrections in order $α_s$ to the the widths of the Higgs boson decays $H^+ \to \st \bar\sb$ and $H^0, A^0 \to \st \bar\st, \sb \bar\sb$ in the on--shell scheme within the Minimal Supersymmetric Standard Model. We find that the QCD corrections are significant, but that the squark pair decay modes are still dominant in a wide parameter region.
We re-investigate the question whether a light higgsino-like neutralino is a viable Dark Matter candidate. To this end we compute the dominant one-loop corrections to the masses of the higgsino-like states in the minimal Supersymmetric Standard Model (MSSM), due to loops involving heavy quarks and their superpartners. We also calculate analogous corrections to the couplings of higgsino-like neutralinos to Z and Higgs bosons. In the region of parameter space leading to high higgsino purity of the lightest neutralino, these corrections can change the expected relic density by up to a factor of five in either direction. We conclude that for favorable choices of soft supersymmetry breaking parameters, a state with more than 99% higgsino purity could indeed form all cold Dark Matter in the Universe. In some cases these corrections can also increase the expected cross section for LSP scattering off spinless nuclei by up to two orders of magnitude, or reduce it to zero.
We provide a mini-guide to some of the possible manifestations of weak scale supersymmetry. For each of six scenarios we provide a brief description of the theoretical underpinnings, the adjustable parameters, a qualitative description of the associated phenomenology at future colliders, comments on how to simulate each scenario with existing event generators.
We outline several well-motivated models in which GUT boundary conditions for SUSY breaking are non-universal. The diverse phenomenological implications of the non-universality for SUSY discovery at LEP2, the Tevatron, the LHC and the NLC are sketched.
We present a complete calculation of the QCD corrections (of the order $α_s$) to the width of the decay $H^+ \to t \bar{b}$ within the Minimal Supersymmetric Standard Model. We find that the QCD corrections are quite important, and that the supersymmetric QCD corrections (due to gluino, stop and sbottom exchange) can be comparable to or even larger than the standard QCD corrections in a large region of the supersymmetric parameter space. This is mainly due to the effect of large left-right mixings of stop and sbottom. This could significantly affect the phenomenology of the $H^+$ search.
The supersymmetric one-loop contribution to the quark-lepton universality violation in the low-energy charged current weak interactions is studied. It is shown that the recent experimental data with the 1-$σ$ deviation from the universality may be explained by the existence of the light sleptons ($<220$GeV) and relatively light chargino and neutralinos ($<600$GeV) with significant gaugino components. The sign of the universality violation is briefly discussed.
We calculate the supersymmetric ${\cal O}(α_s)$ QCD corrections to the width of the decay $H^+ \rightarrow \st\bar{\sb}$ within the Minimal Supersymmetric Standard Model. We find that the QCD corrections are significant, but that they do not invalidate our previous conclusionat tree-level on the dominance of the $\st\bar{\sb}$ mode in a wide parameter region.
A systematic formulation of the higher genus expansion in topological string theory is considered. We also develop a simple way of evaluating genus zero correlation functions. At higher genera we derive some interesting formulas for the free energy in the $A_1$ and $A_2$ models. We present some evidence that topological minimal models associated with Lie algebras other than the A-D-E type do not have a consistent higher genus expansion beyond genus one. We also present some new results on the $CP^1$ model at higher genera.
We discuss topological Landau-Ginzburg theories coupled to the 2-dimensional topological gravity. We point out that the basic recursion relations for correlation functions of the 2-dimesional gravity have exactly the same form as the Gauss-Manin differential equations for the period integrals of superpotentials. Thus the one-point functions on the sphere of the Landau-Ginzburg theories are given exactly by the period integrals. We discuss various examples, A-D-E minimal models and the $c=3$ topological theories.
We discuss physical spectra and correlation functions of topological minimal models coupled to topological gravity. We first study the BRST formalism of these theories and show that their BRST operator $Q=Q_s+Q_v$ can be brought to $Q_s$ by a certain homotopy operator $U$, $UQU^{-1}=Q_s$ ($Q_s$ and $Q_v$ are the $N=2$ and diffeomorphism BRST operators, respectively). The reparametrization (anti)-ghost $b$ mixes with the supercharge operator $G$ under this transformation. Existence of this transformation enables us to use matter fields to represent cohomology classes of the operator $Q$. We explicitly construct gravitational descendants and show that they generate the higher-order KdV flows. We also evaluate genus-zero correlation functions and rederive basic recursion relations of two-dimensional topological gravity.
We analyze the properties of the q-vertex operators of U_q(sl(2)^) introduced by Frenkel and Reshetikhin. As the condition for the null vector decoupling, we derive the existence condition of the q-vertex operators ( the fusion rules ).