Browsing by Subject "SPHENO"
Now showing items 1-4 of 4
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(2019)We analyze supersymmetric models augmented by an extra U(1) gauge group. To avoid anomalies in these models without introducing exotics, we allow for family-dependent U(1)' charges, and choose a simple form for these, dependent on one U(1)' charge parameter only. With this choice, Z' decays into ditaus but not dileptons, weakening considerably the constraints on its mass. In the supersymmetric sector, the effect is to lower the singlino mass, allowing it to be the dark matter candidate. We investigate the dark matter constraints and collider implications of such models, with mostly singlinos, mostly Higgsinos, or a mixture of the two as the lightest supersymmetric particles. In these scenarios, Z' decays significantly into chargino or neutralino pairs, and thus indirectly into final state leptons. We devise benchmarks which, with adequate cuts, can yield signals visible at the high-luminosity LHC.
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(2020)We study the possibility of observing lepton number violation in the right-handed sneutrino sector of the next-to-minimal supersymmetric Standard Model extended with right-handed neutrinos. The scalar potential introduces a lepton number violating mass term for the right-handed sneutrinos, which generates a phase difference that results in oscillations between the sneutrino and antisneutrino. If we have light Higgsinos and right-handed sneutrinos, the sneutrino decay width is determined by the tiny Yukawa couplings, which allows the phase difference to accumulate before the sneutrino decays. We investigate the possibilities of producing sneutrino pairs resonantly through a heavy Higgs of such a model and the ability of seeing a lepton number violating signature emerging from sneutrinos at the Large Hadron Collider. We also discuss how a possible future signal of this type could be used to determine the neutrino Yukawa couplings.
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(2019)We explore a minimal supersymmetric standard model scenario extended by one pair of gauge singlets per generation. In the model, light neutrino masses and their mixings are generated via the inverse seesaw mechanism. In such a scenario, a right-handed sneutrino can be the lightest supersymmetric particle and a cold dark matter (DM) candidate. if the Casas-Ibarra parametrization is imposed on the Dirac neutrino Yukawa coupling matrix (Y-nu) to fit the neutrino oscillation data, the resulting Y-nu is highly constrained from the lepton-flavor-violating decay constraints. The smallness of Y-nu requires the sneutrino DM to coannihilate with other sparticle(s) in order to satisfy the DM relic density constraint. We study sneutrino coannihilation with winos and observe that this sneutrino-wino compressed parameter space gives rise to a novel same-sign trilepton signal for the top squark, which is more effective than the conventional top squark search channels in the present framework. We show that the choice of neutrino mass hierarchy strongly affects the signal event rate, making it easier to probe the scenario with the inverted mass hierarchy.
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(2019)A search is presented for resonant production of second-generation sleptons ((mu) over tilde (L),(nu) over tilde (mu)) via the R-parityviolating coupling. gimel'(211) to quarks, in events with two samesign muons and at least two jets in the final state. The smuon ( muon sneutrino) is expected to decay into amuon and a neutralino (chargino), which will then decay into a second muon and at least two jets. The analysis is based on the 2016 data set of proton- proton collisions at root s = 13 TeV recorded with the CMS detector at the LHC, corresponding to an integrated luminosity of 35.9 fb(-1). No significant deviation is observed with respect to standard model expectations. Upper limits on cross sections, ranging from 0.24 to 730 fb, are derived in the context of two simplified models representing the dominant signal contributions leading to a same- sign muon pair. The cross section limits are translated into coupling limits for a modified constrained minimal supersymmetric model with. gimel'(211) as the only nonzero R-parity violating coupling. The results significantly extend restrictions of the parameter space compared with previous searches for similar models.
