Javier Ferrandis

Yukawa unified supersymmetric SO(10) model: Cosmology, rare decays, and collider searches

It has recently been pointed out that viable sparticle mass spectra can be generated in Yukawa unified SO(10) supersymmetric grand unified models consistent with radiative breaking of electroweak symmetry. Model solutions are obtained only if tan{beta}{approx}50, {mu}<0 and positive D-term contributions to scalar masses from SO(10) gauge symmetry breaking are used. In this paper, we attempt to systematize the parameter space regions where solutions are obtained. We go on to calculate the relic density of neutralinos as a function of parameter space. No regions of the parameter space explored were actually cosmologically excluded, and very reasonable relic densities were found in much of parameter space. Direct neutralino detection rates could exceed 1 event/kg/day fora{sup 73}Ge detector, for low values of GUT scale gaugino mass m{sub 1/2}. We also calculate the branching fraction for b{yields}s{gamma} decays, and find that it is beyond the 95% C.L. experimental limits in much, but not all, of the parameter space regions explored. For the Fermilab Tevatron collider, significant regions of parameter space can be explored via b{bar B}A and b{bar B}H searches. There also exist some limited regions of parameter space where a trilepton signal can be seen at TeV33. Finally, there exist significant regionsmorexa0» of parameter space where direct detection of bottom squark pair production can be made, especially for large negative values of the GUT parameter A{sub 0}.«xa0less

Impact of the muon anomalous magnetic moment on supersymmetric models

The recent measurement of aµ = gµ−2 2 by the E821 Collaboration at Brookhaven deviates from the quoted Standard Model (SM) central value prediction by 2.6�. The difference between SM theory and experiment may be easily accounted for in a variety of particle physics models employing weak scale supersymmetry (SUSY). Other supersymmetric models are distinctly disfavored. We evaluate aµ for various supersymmetric models, including minimal supergravity (mSUGRA), Yukawa unified SO(10) SUSY GUTs, models with inverted mass hierarchies (IMH), models with non-universal gaugino masses, gauge mediated SUSY breaking models (GMSB), anomaly-mediated SUSY breaking models (AMSB) and models with gaugino mediated SUSY breaking (inoMSB). Models with Yukawa coupling unification or multi-TeV first and second generation scalars are disfavored by the aµ measurement.

Charged Higgs boson and stau phenomenology in the simplest R-parity breaking model

Abstract We consider the charged scalar boson phenomenology in the simplest effective low-energy R -parity breaking model characterized by a bilinear violation of R -parity in the superpotential. This induces a mixing between staus and the charged Higgs boson. We show that the charged Higgs boson mass can be lower than expected in the MSSM, even before including radiative corrections. We also study the charged scalar boson decay branching ratios and show that the R -parity-violating decay rates can be comparable or even bigger than the R -parity conserving ones. Moreover, if the stau is the LSP it will have only decays into standard model fermions. These features could have important implications for charged supersymmetric scalar boson searches at future accelerators.

Supersymmetric SO(10) Grand Unified Models with Yukawa Unification and a Positive µ Term

Supersymmetric grand unified models based on SO(10) gauge symmetry have many desirable features, including the unification of Yukawa couplings. Including D-term contributions to scalar masses arising from the breakdown of SO(10), Yukawa coupling unification only to 30% can be achieved in models with a positive superpotential Higgs mass. The superparticle mass spectrum is highly constrained and yields relatively light top squarks and charginos. Surprisingly, the pattern of grand unified theory scale soft supersymmetry breaking masses are close to those found in the context of inverted hierarchy models.

Basis independent study of supersymmetry without R-parity and the tau-neutrino mass

In the most general R-parity violating model, including both bilinear and trilinear terms, the sneutrino receives a vacuum expectation value. We investigate the constraints on this vev following a basis independent approach, highlighting the relations between the three most popular basis. We study the prediction for the tau neutrino mass which follows from the minimization of the scalar potential in a SUGRA model with universality of the soft parameters at the GUT scale. Finally we show that the tau neutrino mass controls the R-parity violating effects both in the fermionic and scalar sectors.

Gauge and Yukawa unification with broken R-parity

Abstract We study Yukawa coupling unification in the simplest extension of the Minimal Supersymmetric Standard Model (MSSM) which incorporates R-parity violation through a bilinear superpotential term. In contrast to what happens in the MSSM, we show that bottom-tau unification at the scale MGUT where the gauge couplings approximately unify can be achieved for any value of tan β by choosing appropriately the sneutrino vacuum expectation value. Moreover, we show that in contrast with the MSSM where large tan β solutions exist, in our case for sufficiently large sneutrino VEV ν3, large tan β becomes incompatible with bottom-tau unification.

Supersymmetric SO(10) GUT Models with Yukawa Unification and a Positive Mu Term

Supersymmetric grand unified models based on SO(10) gauge symmetry have many desirable features, including the unification of Yukawa couplings. Including D-term contributions to scalar masses arising from the breakdown of SO(10), Yukawa coupling unification only to 30% can be achieved in models with a positive superpotential Higgs mass. The superparticle mass spectrum is highly constrained and yields relatively light top squarks and charginos. Surprisingly, the pattern of grand unified theory scale soft supersymmetry breaking masses are close to those found in the context of inverted hierarchy models.

Supersymmetry breaking as the origin of flavor

We present an effective flavor model for the radiative generation of fermion masses and mixings based on a SU(5){sub V}xU(2){sub H} symmetry. We assume that the original source of flavor breaking resides in the supersymmetry-breaking sector. Flavor violation is transmitted radiatively to the fermion Yukawa couplings at low energy through finite supersymmetric threshold corrections. This model can fit the fermion mass ratios and Cabibbo-Kobayashi-Maskawa matrix elements, explain the nonobservation of proton decay, and overcome the present constraints on flavor changing processes through an approximate radiative alignment between the Yukawa and the soft trilinear sector. The model predicts relations between dimensionless fermion mass ratios in the three fermion sectors, and the quark mixing angles, vertical bar V{sub us} vertical bar{approx_equal}[m{sub d}/m{sub s}]{sup 1/2}{approx_equal}[m{sub u}/m{sub c}]{sup 1/4}{approx_equal}3[m{sub e}/m{sub {mu}}]{sup 1/2} and (1/2)vertical bar V{sub cb}/V{sub us} vertical bar{approx_equal}[m{sub s}{sup 3}/m{sub b}{sup 2}m{sub d}]{sup 1/2}{approx_equal}[m{sub c}{sup 3}/m{sub t}{sup 2}m{sub u}]{sup 1/2}{approx_equal}(1/9)[m{sub {mu}}{sup 3}/m{sub {tau}}{sup 2}m{sub e}]{sup 1/2}, which are confirmed by the experimental measurements.

Unification of gauge couplings and the tau-neutrino mass in supergravity without R-parity

Abstract Minimal R-parity violating supergravity predicts a value for α s (M Z ) smaller than in the case with conserved R-parity, and therefore closer to the experimental world average. We show that the R-parity violating effect on the α s prediction comes from the larger two-loop b-quark Yukawa contribution to the renormalization group evolution of the gauge couplings which characterizes R-parity violating supergravity. The effect is related to the tau neutrino mass and is sensitive to the initial conditions on the soft supersymmetry breaking parameters at the unification scale. We show how a few percent effect on α s (M Z ) may occur even with ν τ masses as small as indicated by the simplest neutrino oscillation interpretation of the atmospheric neutrino data from Super-Kamiokande.

Supersymmetry unification predictions for mtop, Vcb and tanβ

Abstract We study the predictions for m top , tan β and V cb in a popular texture ansatz for the fermion mass matrices. We do this both for the Minimal Supersymmetric Standard Model (MSSM) and for the simplest model (MSSM–BRpV) where a bilinear R -parity violating term is added to the superpotential. We find that taking the experimental values for m top and V cb at 99% c.l. and the GUT relations h b = h τ and V cb 2 = h c / h t within 5%, the large tan β solution, characteristic in the MSSM with bottom–tau unification, becomes disallowed. In contrast, the corresponding allowed region for the MSSM–BRpV is slightly larger. We also find that important modifications occur if we relax the texture conditions at the GUT scale. For example, if the GUT relations are imposed at 40%, the large tan β branch in the MSSM becomes fully allowed. In addition, in MSSM–BRpV the whole tan β – m top plane become allowed, finding unification at any value of tan β .