J.C. Romão

How to spontaneously break R parity

Abstract We demonstrate explicitly that R parity (Rp) can break spontaneously in a simple extension of the minimal supersymmetric standard model (MSSM) proposed previously. For suitable values of the parameters of the low energy theory, consistent with observation, the energy is minimum when both R parity and electroweak symmetries are spontaneously broken. The R-parity breaking scale typically lies in the phenomenologically interesting range ∼ 10 GeV-1 TeV.

Neutrino masses in supersymmetry with spontaneously broken R-parity

Abstract The neutrino mass spectrum that arises in supersymmetry models with spontaneously broken R-parity is studied in detail. We analyse the attainable values for mνe, mνμ and mντ, once all observational constraints have been incorporated, including both those that arise from collider experiments such as LEP, as well as weak interaction constraints, such as the non-observation of neutrinoless double-β decay, the limits from neutrino oscillation searches, etc. For natural choices of the parameters neutrino masses arise in a very striking pattern: while νe and νμ have masses lying in the adequate range for the explanation of the observed deficit in the solar neutrino flux via the MSW effect, the ντ mass is large enough to lead to novel signatures associated with the τ-lepton that could be seen both a LEP as well as at a tau factory. These provide an additional tool to probe the parameters characterizing the solar neutrino conversions in conventional accelerator experiments. The related processes include the single-chargino Z-decay branching ratio BR ( Z → χ τ) as large as ∼ 6 × 10−5 and single-majoron emission τ-decay branching ratios τ → μ + J as large as ∼ 10−4 corresponding to solar neutrino oscillation parameters in the non-adiabatic branch favoured by present solar neutrino data. The τ-neutrino is naturally much heavier than νμ and decays to it via majoron emission, with a lifetime short enough to obey cosmological limits.

Supersymmetry phenomenology with spontaneous R parity breaking in Z0 decays

Abstract We study some of the phenomenological implications of spontaneous R parity breaking for the decays of the Z 0 . These include new experimental signatures, e.g., the decay Z 0 → χ ± τ ± which may occur with branching ratio in the range 6×10 −5 to 10 −6 , that could be visible at LEP, and sizeable enhancements in the expected rates for zen events , with respect to those of the standard supersymmetric model. In addition, the lightest chargino χ ± may dominantly decay as χ ± → τ ± +majoron.

New Higgs signatures in supersymmetry with spontaneous broken R parity

Abstract Higgs production from Z decays in supersymmetry with spontaneous broken R parity proceeds mostly by the Bjorken process as in the standard model. However, the corresponding production rates can be weaker than in the standard model (SM), especially in the low mass region. This will substantially weaken the Higgs boson mass limits derived from LEP1. More strikingly, the main Higgs decay channel is “invisible”, over most of the mass range accessible to LEP1, leading to events with large missing energy carried by majorons. This possibility should be taken into account in the planning of Higgs boson search strategies not only at LEP but also at high energy supercolliders.

Supersymmetric signals in muon and tau decays

The spectra of the decay leptons produced in μ and τ decays could be significantly different from the standard model predictions. Such changes can be induced by majoron emission processes, characteristic of supersymmetric (SUSY) SU(2) ⊗ U(1) models with spontaneously broken R -parity. We analyse the attainable values for the corresponding branching ratios, once all observational constraints have been incorporated, including both those that arise from collider experiments such as LEP, as well as weak interaction constraints, such as the nonobservation of neutrinoless double β decay, the limits on the ν τ mass, the non-observation of neutrino oscillations, etc. We conclude that a new generation of high luminosity experiments such as a τ factory could easily study these branching ratios, even if the ν τ mass is below the attainable limit of sensitivity of the planned facilities.

Supersymmetric unification with radiative breaking of R parity

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 CERN LEP 200. {copyright} {ital 1997} {ital The American Physical Society}

Can solar neutrino oscillation parameters be probed at LEP

Abstract Supersymmetry with spontaneously broken R parity naturally leads to the explanation of the observed deficit in the solar neutrino flux via matter-enhanced νe-νμ oscillations, while mντ is large enough to lead to related signatures associated with the τ lepton. These include single chargino production in Z decays with branching ratio BR ( Z → χ τ) as large as ∼6×10−5, accessible at LEP1. The ντ is naturally much heavier than νμ and decays to it via majoron emission, with a lifetime short enough to obey cosmological limits.

Neutrino mixing with revamped A(4) flavor symmetry

This work is supported by MINECO Grant No. FPA2011-22975, and MULTIDARK Consolider CSD2009-00064, by Prometeo/2009/091 (Gen. Valenciana), and by EU ITN UNILHC PITN-GA-2009-237920. S. M. thanks DFG Grant No. WI 2639/4-1. J. C. R. also acknowledges the financial support from Grants No. CFTP-FCT UNIT 777, No. CERN/FP/123580/2011, and No. PTDC/FIS/102120/2008.

Spontaneous R-parity breaking at hadron supercolliders☆

Abstract If supersymmetry (SUSY) is realized with spontaneous breaking of R-parity, there can be large rates for single sparticle production. We make a detailed study of the rates for Drell-Yan-like single chargino and single neutralino production at a hadron supercollider. The attainable rates are promising in view of the luminosities expected at these facilities. All observational restrictions from cosmology, astrophysics and laboratory are taken into account in our analysis, including the recent LEP results as well as neutrino physics constraints.

Large pseudoscalar Yukawa couplings in the complex 2HDM

A bstractWe start by presenting the current status of a complex flavour conserving two-Higgs doublet model. We will focus on some very interesting scenarios where unexpectedly the light Higgs couplings to leptons and to b-quarks can have a large pseudoscalar component with a vanishing scalar component. Predictions for the allowed parameter space at end of the next run with a total collected luminosity of 300 fb−1 and 3000 fb−1 are also discussed. These scenarios are not excluded by present data and most probably will survive the next LHC run. However, a measurement of the mixing angle ϕτ , between the scalar and pseudoscalar component of the 125 GeV Higgs, in the decay h → τ +τ − will be able to probe many of these scenarios, even with low luminosity. Similarly, a measurement of ϕt in the vertex t¯th