Search

Bilinear R-parity violation is a simple extension of the MSSM allowing for Majorana neutrino masses. One of the three neutrinos picks up mass by mixing with the neutralinos of the MSSM, while the other two neutrinos gain mass from 1-loop corrections. Once 1-loop corrections are carefully taken into account the model is able to explain solar and atmospheric neutrino data for specific though simple choices of the R-parity violating parameters., Comment: 3 pages, contribution to ICHEP2000, Osaka

The simplest unified extension of the MSSM with bi-linear R--Parity violation naturally predicts a hierarchical neutrino mass spectrum, in which one neutrino acquires mass by mixing with neutralinos, while the other two get mass radiatively. We have performed a full one-loop calculation of the neutralino-neutrino mass matrix in the bi-linear \rp MSSM, taking special care to achieve a manifestly gauge invariant calculation. Moreover we have performed the renormalization of the heaviest neutrino, needed in order to get meaningful results. The atmospheric mass scale and maximal mixing angle arise from tree-level physics, while solar neutrino scale and oscillations follow from calculable one-loop corrections. If universal supergravity assumptions are made on the soft-supersymmetry breaking terms then the atmospheric scale is calculable as a function of a single \rp violating parameter by the renormalization group evolution due to the non-zero bottom quark Yukawa coupling. The solar neutrino problem must be accounted for by the small mixing angle (SMA) MSW solution. If these assumptions are relaxed then one can implement large mixing angle solutions, either MSW or just-so. The theory predicts the lightest supersymmetic particle (LSP) decay to be observable at high-energy colliders, despite the smallness of neutrino masses indicated by experiment. This provides an independent way to test this solution of the atmospheric and solar neutrino anomalies., Comment: 46 pages, references added + several misprints corrected

Neutrinoless double beta ($\znbb$) decay is considered within bilinear R-parity breaking supersymmetry, including the full one-loop corrections to the neutrino-neutralino mass matrix. Expected rates for $\znbb$ decay in this model are discussed in light of recent atmospheric and solar neutrino data. We conclude that (a) tree-level calculations for $\znbb$ decay within the bilinear model are not reliable in the range of parameters preferred by current solar and atmospheric neutrino problems. And (b) if the solar and atmospheric neutrino problems are to be solved within bilinear R-parity violating SUSY the expected rates for $\znbb$ decay are very low; the effective Majorana neutrino mass at most 0.01 eV and typical values being one order of magnitude lower. Observing $\znbb$ decay in the next round of experiments therefore would rule out the bilinear R-parity violating supersymmetric model as an explanation for solar and atmospheric neutrino oscillations, as well as any hierarchical scheme for neutrino masses, unless new neutrino interactions are present., Comment: 1 reference added, enlarged discussion of loops

We study rare exclusive B decays based on the quark-level transition b->s(d)l^+l^-, where l=e or mu, in the context of supersymmetric theories with minimal flavour violation. We present analytic expressions for various mixing matrices in the presence of new CP-violating phases, and examine their impact on observables involving B and \bar{B} decays. An estimate is obtained for CP-violating asymmetries in B->K^(*)l^+l^- and B->rho(pi)l^+l^- decays for the dilepton invariant mass region 1.2 GeV < M_{l^+l^-}< M_{J/psi}. As a typical result, we find a CP-violating partial width asymmetry of about -6% (-5%) in the case of B->pi (B->rho) in effective supersymmetry with phases of O(1), taking into account the measurement of the inclusive b->s gamma branching fraction. On the other hand, CP asymmetries of less than 1% are predicted in the case of B->K^(*). We argue that it is not sufficient to have additional CP phases of O(1) to observe large CP-violating effects in exclusive b->s(d)l^+l^- decays., Comment: 34 pages, REVTeX, 6 figures, final version to appear in Phys. Rev. D, with some minor additions

The simplest unified extension of the Minimal Supersymmetric Standard Model with bi-linear R--Parity violation provides a predictive scheme for neutrino masses which can account for the observed atmospheric and solar neutrino anomalies in terms of bi-maximal neutrino mixing. The maximality of the atmospheric mixing angle arises dynamically, by minimizing the scalar potential, while the solar neutrino problem can be accounted for either by large or by small mixing oscillations. One neutrino picks up mass by mixing with neutralinos, while the degeneracy and masslessness of the other two is lifted only by loop corrections. Despite the smallness of neutrino masses R-parity violation is observable at present and future high-energy colliders, providing an unambiguous cross-check of the model., Comment: 5 pages, final version published in Phys. Rev. D61, 2000, 071703(R)

We review models where R-parity is broken, either spontaneously or explicitly. In this last case we consider the situation where R-parity is broken via bilinear terms in the superpotential. We show that although at tree level only one neutrino gets mass, at one--loop level all three neutrinos became massive. We study the conditions under which bimaximal mixing can be achieved and show that the masses can be in the correct ranges needed for solving the atmospheric and solar neutrino problems., Comment: 11 pages, 11 Figures in Postscript. Talk given at the International Workshop on Physics Beyond the Standard Model: From Theory to Experiment, Valencia, Spain, May 3-8 1999

We discuss gauge and Yukawa unification in the context of a supersymmetric model with bilinear R-parity violation. We show that this model allows $b-\tau$ Yukawa unification for any value of $\tan\beta$ while satisfying perturbativity of the couplings. We also find the $t-b-\tau$ Yukawa unification easier to achieve than in the MSSM, occurring in a wider high $\tan\beta$ region. Finaly, we also discuss the compatibility between the predicted and the measured values for $\alpha_s(M_Z)$, Comment: 8 pages, 4 Figures in Postscript. Talk given at European Network Meeting on Physics Beyond the Standard Model, Trieste, Italy, 24-27 Feb 1999. To appear in the JHEP

Minimal R-parity violating supergravity predicts a value for $alpha_s(M_Z)$ 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 $alpha_s$ 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 correlated 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 $alpha_s(M_Z)$ may naturally occur even with tau neutrino masses as small as indicated by the simplest neutrino oscillation interpretation of the atmospheric neutrino data from Super-Kamiokande., Comment: Latex, 21 pages including 2 figures

We derive the width of the Higgs boson into vector bosons. General formulas are derived both for the on-shell decay H -> VV as well for the off-shell decays, H -> V^* V and H -> V^* V^*, where V=\gamma,W,Z. For the off-shell decays the width of the decaying vector boson is properly included. The formulas are valid both for the Standard Model as well as for arbitrary extensions. As an example we study in detail the gauge-invariant effective Lagrangian models where we can have sizable enhancements over the Standard Model that could be observed at LEP., Comment: 26 pages, 15 Figures in Postscript

If supersymmetry is realized with spontaneous breaking of R-parity, there will be important consequences in several different areas which can be tested through different types of experiments. In this talk we review the phenomenological implications of these theories, with special emphasis on new signals at the present and future accelerators., Comment: 12 pages, 2 Figures in Postscript

We show that in the presence of sufficiently strong tau neutrino annihilations into majorons, the primordial nucleosynthesis constraints can not rule out tau neutrino masses in the MeV range., Comment: 7 pages, LaTeX, 4 Postscript Figures. Talk given at the International Workshop "New Worlds in Astroparticle Physics", held in Faro, Portugal, 8-10 September 1996

We discuss some rare Z decay signatures associated with extensions of the Standard Model with spontaneous lepton number violation at the electroweak scale. We show that single-photon Z decays such as $Z \to \gamma H$ and $Z \to \gamma J J$ where H is a CP-even Higgs boson and J denotes the associated CP-odd Majoron may occur with branching ratios accessible to LEP sensitivities, even though the corresponding neutrino masses can be very small, as required in order to explain the deficit of solar neutrinos., Comment: 15 pages, 10 Figures in Postscript

We determine the restrictions imposed by primordial nucleosynthesis upon a heavy tau neutrino, in the presence of nu-tau annihilations into Majorons, as expected in a wide class of particle physics models of neutrino mass. We determine the equivalent number of light neutrino species $N_{eq}$ as a function of nu-tau mass and the nu-tau-Majoron coupling $g$. We show that for theoretically plausible $g$ values $\gsim 10^{-4}$ present nucleosynthesis observations can not rule out nu-tau masses in the MeV range. Moreover, these models give $N_{eq} \leq 3$ in the nu-tau mass region 1-10 MeV, for very reasonable values of $g \geq 3 \times 10^{-4}$. The evasion of the cosmological limits brings new interest to the improvement of the present laboratory limit on the nu-tau mass which can be achieved at a tau-charm factory., Comment: 20 pages, LaTex + 6 ps figures. Discussion of the majoron couplings is clarified in new appendix. To be published in NPB

We show how R-parity can break spontaneously as a result of radiative corrections in unified N=1 supergravity models. We illustrate this with a concrete rank-four unified model, where the spontaneous breaking of R-parity is accompanied by the existence of a physical majoron. We determine the resulting supersymmetric particle mass spectrum and show that R-parity-breaking signals may be detectable at LEP200., Comment: latex file, 4 pages, 2 figures

We illustrate the sensitivities of LEP experiments to leptonic signals associated to models where supersymmetry (SUSY) is realized with spontaneous breaking of R-parity. We focus on missing transverse momentum plus acoplanar muon events arising from lightest neutralino single production $\chi \nu$ as well as pair production $\chi \chi$, followed by $\chi$ decays, where $\chi$ denotes the lightest neutralino. We show that the integrated luminosity achieved at LEP already starts probing the basic parameters of the theory. We discuss the significance of these constraints for the simplest spontaneous R-parity breaking models and their relevance for future searches of SUSY particles., Comment: 28 pages, LaTex file + 6 figures, all compressed by uufiles, also available from anonymous ftp at ftp://neutrinos.uv.es/pub/papers/ps/rpv_lep1.uu

Spontaneous violation of R parity can induce rare single photon decays of the $Z^0$ involving the emission of (nearly) massless pseudoscalar Goldstone bosons, majorons, as well as massive CP even or CP odd spin zero bosons that arise in the electroweak breaking sector of these models. We show that the majoron emitting decays can have a sizeable branching ratio of $10^{-5}$ or so, without conflicting any experimental observation from neutrino physics or particle searches. These decays may lead to interesting structures for the single photon spectrum involving either mono chromatic photons as well as continuous spectra that grow with energy. They would easily account for an excess of single photon events at high energies recently hinted at by the OPAL collaboration., Comment: 13 pages, latex file, figures not included but available by fax upon request

Talk presented at the XXIX Rencontres de Moriond, Electroweak Interactions and Unified Theories, March 12-19, 1994, Meribel, Comment: FTUV/94-28 IFIC/94-26, 6 pages + two figures (.ps files included)

We derive model-independent constraints on Higgs mass and couplings from associated signals for higher masses, accessible at LEP2. This work is motivated by the fact that, in many extensions of the standard model, the Higgs boson can have substantial "invisible" decay modes, for example, into light or massless weakly interacting Goldstone bosons associated to the spontaneous violation of lepton number below the weak scale., Comment: FTUV/93-19, 13 pag + 2 figures(not included but available upon request), Latex

The Higgs sector in spontaneously broken R Parity supersymmetry (RPSUSY) shows interesting features that require new search techniques. Both the mass spectrum and production rates may differ from the standard model and minimal supersymmetric model (MSSM) expectations. For some parameter choices, the dominant Higgs boson decay mode can even be invisible, leading to events with large missing transverse momentum carried by superweakly interacting majorons. We study the reaction $pp \ra Z + H + X$, and find that it canlead to detectable events at LHC/SSC for a large region of parameter space., Comment: Latex (Matex included), 13 pag.(figures not included), FTUV/92-30 IFIF/92-38

We refute the claims made by Chaichian and Smilga in a recent paper in Phys Rev Letters on the impossibility of spontaneous R Parity breaking. Apart from explaining their error we summarize the results of a more detailed work that demonstrates explicitly that R parity can break spontaneously at a scale anywhere in the range 10 GeV to 1 Tev in a simple extension of the minimal SUSY standard model proposed previously., Comment: 4 pages and 1 figure