ALEPH Four-Jet Excess, RbR_b and R−R-Parity Violation

We review briefly the indications for some relatively light superpartners based on the ~$R_b$ ~anomaly and discuss the dependence of the potential increase in $R_b$ on the assumption about ~$R-$parity (non)conservation. We point out that the exotic 4-jet events reported by ALEPH may constitute a signal for supersymmetry with such a light spectrum and with explicitly broken $R-$parity. A parton level simulation shows that production of a pair of light charginos with their subsequent baryon-number violating decays (either through a stop or through a neutralino) could possibly give rise to this excess. The decay \chi^- \ra \tilde{t}_R^\ast b \ra d s b with m_{\chi^-_1} \sim 60 \gev and m_{\tilde t} \sim 52 \gev leads to signatures very close to the experimental observations.Comment: 17 pages, submited as uuencoded gz-compressed .tar file containing LATEX file and figures. Some typos fixed and the important error in the caption of Fig. 7 correcte

Lepton non-universality in BB decays and fermion mass structure

We consider the possibility that the neutral-current $B$ anomalies are due to radiative corrections generated by Yukawa interactions of quarks and leptons with new vector-like quark and lepton electroweak doublets and new Standard Model singlet scalars. We show that the restricted interactions needed can result from an underlying Abelian family symmetry and that the same symmetry can give rise to an acceptable pattern of quark and charged lepton masses and mixings, providing a bridge between the non-universality observed in the B-sector and that of the fermion mass matrices. We construct two simple models, one with a single singlet scalar in which the flavour changing comes from quark and lepton mixing and one with an additional scalar in which the flavour changing can come from both fermion and scalar mixing. We show that for the case the new quarks are much heavier than the new leptons and scalars the $B$ anomalies can be due to box diagrams with couplings in the perturbative regime consistent with the bounds coming from $B_s- \bar B_s$, $K- \bar K$ and $D- \bar D$ mixing as well as other lepton family number violating processes. The new states can be dark matter candidates and, in the two scalar model with a light scalar of O(60) GeV and vector-like lepton of O(100) GeV, there can be a simultaneous explanation of the B-anomalies, the muon anomalous magnetic moment and the dark matter abundance.Comment: Replacement contains few additional reference

Flavour Changing Neutral Currents and Inverted Sfermion Mass Hierarchy

We study the contraints on non-flavour-blind soft supersymmetry breaking terms coming from flavour and CP violating processes in the presence of hierarchical Yukawa couplings, and quantify how much these constraints are weakened in the regions of the MSSM parameter space characterized by heavy gauginos and multi-TeV sfermion masses, respectively. We also study the inverted sfermion mass hierarchy scenario in the context of D-term supersymmetry breaking, and show that generic hierarchical Yukawa couplings with arbitrary phases require first generation squarks in the few 10 TeV range.Comment: 9 pages, 6 figures. Talk given at the XLth Rencontres de Moriond on Electroweak Interactions and Unified Theories, La Thuile, Aosta Valley, Italy, 5-12 March 2005. V3: one reference correcte

Unification in models with replicated gauge groups

We examine unification of gauge couplings in four dimensional renormalizable gauge theories inspired by the latticized (deconstructed) SM or MSSM in five dimensions. The models are based on replicated gauge groups, spontaneously broken to the diagonal subgroup. The analysis is performed at one-loop level, with the contribution from the heavy vector bosons included, and compared with the analogous results in the SM or MSSM. Unification at or above the diagonal breaking scale is discussed. We find that in the considered class of extensions of the SM(MSSM) unification is possible for a wide range of unification scales and with the similar accuracy as in the SM(MSSM). Unification above the diagonal breaking scale is particularly attractive: it is a consequence of the SM(MSSM) unification, but with the unification scale depending on the number of replications of the gauge group.Comment: 19 pages, 3 figure

Neutralinos as dark matter in the minimal supergravity model

Journal ArticleA new approach to the phenomenological study of the minimal supergravity model is presented in which the model is effectively parametrized in terms of five low energy observables. Radiative corrections due to large Yukawa couplings and particle-sparticle mass splitting are included into the analysis and found to have important effects, in particular on the degree of fine tuning in the model. In this framework the neutralino relic abundance has been calculated and the cosmologically interesting range of parameters determined (after imposing all the presently available accelerator limits)