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Register a new userPossible sneutrino-pair signatures with R-parity breaking
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If sneutrinos are the lightest supersymmetry partners and $R$-parity is not conserved, the process $e^+e^- to tilde {bar u} tilde { u}$ can have striking signatures due to the decay modes $tilde{ u}toell^+ell^-$ or $tilde{ u}to q bar q$. We present cross section formulas and discuss event rates and detection at the upgraded $e^+e^-$ collider LEP. Four-lepton signals should be detectable up to sneutrino mass $tilde {m}_ u = 80$ GeV and maybe beyond; four-jet signals should be detectable up to $tilde {m}_ u = 70$ GeV, but would probably be obscured thereafter by $WW$ background.
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We consider new s-channel scalar exchanges in e+e- -> ZZ,W+W- in supersymmetry with a small lepton number violation. We show that a small bilinear R-parity violating term which leads to sneutrino--Higgs mixing can give rise to a significant scalar resonance enhancement in e+e- -> ZZ,W+W-. We use the LEP2 measurements of the WW and ZZ cross-sections to place useful constraints on this scenario. We also find, under conservative assumptions on the relevant parameter space involved, that such an exchange of the sneutrino-like admixture in e+e- -> ZZ,W+W- may be accessible to a 500 GeV e+e- collider.
In a class of extensions of the minimal supersymmetric standard model with (B-L)/left-right symmetry that explains the neutrino masses, breaking R-parity symmetry is an essential and dynamical requirement for successful gauge symmetry breaking. Two consequences of these models are: (i) a new kind of R-parity breaking interaction that protects proton stability but adds new contributions to neutrinoless double beta decay and (ii) an upper bound on the extra gauge and parity symmetry breaking scale which is within the large hadron collider (LHC) energy range. We point out that an important prediction of such theories is a potentially large mixing between the right-handed charged lepton ($e^c$) and the superpartner of the right-handed gauge boson ($widetilde W_R^+$), which leads to a brand new class of R-parity violating interactions of type $widetilde{mu^c}^dagger u_mu^c e^c$ and $widetilde{d^c}^daggeru^c e^c$. We analyze the relevant constraints on the sparticle mass spectrum and the LHC signatures for the case with smuon/stau NLSP and gravitino LSP. We note the smoking gun signals for such models to be lepton flavor/number violating processes: $ppto mu^pmmu^pm e^+e^-jj$ (or $tau^pmtau^pm e^+e^-jj$) and $pptomu^pm e^pm b bar{b} jj$ (or $tau^pm e^pm b bar{b} jj$) without significant missing energy. The predicted multi-lepton final states and the flavor structure make the model be distinguishable even in the early running of the LHC.
Widths for the new flavor changing top quark decay t-->c+sneutrino or for the reversed sneutrino decay sneutrino-->t+c(bar) are calculated in the MSSM without R-parity conservation. For large tanbeta, e.g., tanbeta ~ m_t/m_b ~ 40, Br(t-->c+sneutrino) > 10^{-5} or Br(sneutrino-->t+c(bar)) > 10^{-6} in a relatively wide range of the supersymmetric parameter space as long as there is more than one non-zero R-parity violating coupling. In the best cases, with a typical squark mass around 100 GeV, we find that Br(t-->c+sneutrino) ~ 10^{-4} - 10^{-3} or Br(sneutrino-->t+c(bar)) ~ 10^{-5} - 10^{-4}. For tanbeta ~ O(1) the corresponding branching ratios for both top or sneutrino decays are too small to be measured at the LHC. Therefore, the decays t-->c+sneutrino or sneutrino-->t+c(bar) appear to be sensitive to tanbeta and may be detected at the LHC. The branching ratios of the corresponding decays to an up quark instead of a charm quark, e.g., t-->u+sneutrino or sneutrino-->t+u(bar), may also be similar.
We consider new s-channel scalar exchanges in top quark and massive gauge-bosons pair production in e+e- collisions, in supersymmetry with a small lepton number violation. We show that a soft bilinear lepton number violating term in the scalar potential which mixes the Higgs and the slepton fields can give rise to a significant scalar resonance enhancement in e+e- -> ZZ, W+W- and in e+e- -> t t(bar). The sneutrino-Higgs mixed state couples to the incoming light leptons through its sneutrino component and to either the top quark or the massive gauge bosons through its Higgs component. Such a scalar resonance in these specific production channels cannot result from trilinear Yukawa-like R-parity violation alone, and may, therefore, stand as strong evidence for the existence of R-parity violating bilinears in the supersymmetric scalar potential. We use the LEP2 measurements of the WW and ZZ cross-sections to place useful constrains on this scenario, and investigate the expectations for the sensitivity of a future linear collider to these signals. We find that signals of these scalar resonances, in particular in top-pair production, are well within the reach of linear colliders in the small lepton number violation scenario.
$R$-parity violating supersymmetric models (RPV SUSY) are becoming increasingly more appealing than its $R$-parity conserving counterpart in view of the hitherto non-observation of SUSY signals at the LHC. In this paper, we discuss RPV scenarios where neutrino masses are naturally generated, namely RPV through bilinear terms (bRPV) and the $mu$-from-$ u$ supersymmetric standard model ($mu u$SSM). The latter is characterised by a rich Higgs sector that easily accommodates a 125-GeV Higgs boson. The phenomenology of such models at the LHC is reviewed, giving emphasis on final states with displaced objects, and relevant results obtained by LHC experiments are presented. The implications for dark matter for these theoretical proposals is also addressed.
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