Narrow Results

The structure of the B–L minimal supersymmetric Standard Model (MSSM) theory — specifically, the relevant mass scales and soft supersymmetric breaking parameters — is discussed. The space of initial soft parameters is explored at the high scale using random statistical sampling subject to a constraint on the range of dimensionful parameters. For every chosen initial point, the complete set of renormalization group equations is solved. The low energy results are then constrained to be consistent with present experimental data. It is shown that a large set of initial conditions satisfy these constraints and lead to acceptable low energy particle physics. Each such initial point has explicit predictions, such as the exact physical sparticle spectrum which is presented for two such points. There are also statistical predictions for the masses of the sparticles and the LSP species which are displayed as histograms. Finally, the fine-tuning of the μ parameter — which is always equivalent to or smaller than in the MSSM — is discussed.

We have searched for R-parity violating supersymmetry in final states with electrons and muons, assuming a single non-zero LLĒ or coupling, in particular λ₁₂₁, λ₁₂₂ or λ′₂₁₁. In the absence of an excess in the data, upper cross-section limits are set as a function of gaugino and slepton masses.

The searches are performed on data collected with the DØ detector in Run II, at a center of mass energy of 1.96 TeV and an integrated luminosity of up to 240 pb^-1. All limits are improving significantly compared to the DØ Run I results.

We explain the orbifold compactification in string models and present a Z_12−I orbifold compactification toward supersymmetric standard models. We also point out an effective R-parity from this string construction. The VEVs of gauge singlets are chosen such that phenomenological constraints are satisfied.

We review the CP violation in the semileptonic |ΔS| = 1 τ-decays in supersymmetric extensions of the standard model (SM). We show that Within SUSY models with conserved R parity, the CP asymmetry of τ → kπν is below the current experimental limits, although it is enhanced by several order of magnitude than the SM results. We also study the impact of the lepton violation terms in SUSY models with R parity violation. We show that the CP asymmetry of τ-decay is enhanced significantly and the current experimental limits obtained by CLEO collaborations can be easily accommodated.

The fate of R-parity in supersymmetric theories is discussed in detail. We make a strong case for R-parity violation showing that the simplest theories based on the local B - L symmetry predict the spontaneous breaking of R-parity at the SUSY scale. The possible implications for the searches at the Large Hadron Collider are discussed.

We study the rare decays D⁺→π⁺ℓ⁺ℓ^-, and D⁰→ℓ⁺ℓ^-(ℓ = e, μ) in the minimal supersymmetic standard model with and without R-parity. Using the strong constraints on relevant supersymmetric parameters from mixing and decay, we examine constrained supersymmetry contributions to relevant branching ratios, direct CP violations and ratios of and decay rates. We find that both R-parity conserving LR as well as RL mass insertions and R-parity violating squark exchange couplings have huge effects on the direct CP violations of , moreover, the constrained LR and RL mass insertions still have obvious effects on the ratios of and decay rates. The direct CP asymmetries and the ratios of and decay rates are very sensitive to both moduli and phases of relevant supersymmetric parameters. In addition, the differential direct CP asymmetries of are studied in detail.