Dark matter and collider signals in supersymmetric U(1)' models with nonuniversal Z ' couplings

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.Peer reviewe

Lepton flavor violating Higgs boson decay at e(+)e(-) colliders

We estimate the smallest branching ratio for the Higgs decay channel h -> mu tau, which can be probed at an e(+)e(-) collider, and compare it with the projected reach at the high-luminosity run of the LHC. Using a model-independent approach, Higgs production is considered in two separate cases. In the first case, hWW and hZZ couplings are allowed to be scaled by a factor allowed by the latest experimental limits on hWW and hZZ couplings. In the second case, we have introduced higher-dimensional effective operators for these interaction vertices. Keeping BR(h -> mu tau) as a purely phenomenological quantity, we find that this branching ratio can be probed down to approximate to 2.69 x 10(-3) and approximate to 5.83 x 10(-4), respectively, at the 250 GeV and 1000 GeV runs of an e(+)e(-) collider.Peer reviewe

Search for a compressed supersymmetric spectrum with a light Gravitino

Presence of the light gravitino as dark matter candidate in a supersymmetric (SUSY) model opens up interesting collider signatures consisting of one or more hard photons together with multiple jets and missing transverse energy from the cascade decay. We investigate such signals at the 13 TeV LHC in presence of compressed SUSY spectra, consistent with the Higgs mass as well as collider and dark matter constraints. We analyse and compare the discovery potential in different benchmark scenarios consisting of both compressed and uncompressed SUSY spectra, considering different levels of compression and intermediate decay modes. Our conclusion is that compressed spectra upto 2.5 TeV are likely to be probed even before the high luminosity run of LHC. Kinematic variables are also suggested, which offer distinction between compressed and uncompressed spectra yielding similar event rates for photons + multi-jets + $E\!\!\!\!/_T$.Comment: 32 pages, 7 figures, 4 tables. Published in JHEP, minor modifications in text and few references adde

Probing sterile neutrinos in the framework of inverse seesaw mechanism through leptoquark productions

We consider an extension of the standard model (SM) augmented by two neutral singlet fermions per generation and a leptoquark. In order to generate the light neutrino masses and mixing, we incorporate inverse seesaw mechanism. The right-handed neutrino production in this model is significantly larger than the conventional inverse seesaw scenario. We analyze the different collider signatures of this model and find that the final states associated with three or more leptons, multijet and at least one b-tagged and ( or) t-tagged jet can probe larger RH neutrino mass scale. We have also proposed a same-sign dilepton signal region associated with multiple jets and missing energy that can be used to distinguish the present scenario from the usual inverse seesaw extended SM.Peer reviewe

Singlet-triplet fermionic dark matter and LHC phenomenology

It is well known that for the pure standard model triplet fermionic WIMP-type dark matter (DM), the relic density is satisfied around 2 TeV. For such a heavy mass particle, the production cross-section at 13 TeV run of LHC will be very small. Extending the model further with a singlet fermion and a triplet scalar, DM relic density can be satisfied for even much lower masses. The lower mass DM can be copiously produced at LHC and hence the model can be tested at collider. For the present model we have studied the multi jet (>= 2 j) + missing energy ((sic)(T)) signal and show that this can be detected in the near future of the LHC 13 TeV run. We also predict that the present model is testable by the earth based DM direct detection experiments like Xenon-1T and in future by Darwin.Peer reviewe

Same-sign trilepton signal for stop quark in the presence of sneutrino dark matter

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.Peer reviewe