Sneutrino dark matter in low-scale seesaw scenarios

We consider supersymmetric models in which sneutrinos are viable dark matter candidates. These are either simple extensions of the Minimal Supersymmetric Standard Model with additional singlet superfields, such as the inverse or linear seesaw, or a model with an additional U(1) group. All of these models can accomodate the observed small neutrino masses and large mixings. We investigate the properties of sneutrinos as dark matter candidates in these scenarios. We check for phenomenological bounds, such as correct relic abundance, consistency with direct detection cross section limits and laboratory constraints, among others lepton flavour violating (LFV) charged lepton decays. While inverse and linear seesaw lead to different results for LFV, both models have very similar dark matter phenomenology, consistent with all experimental bounds. The extended gauge model shows some additional and peculiar features due to the presence of an extra gauge boson Z' and an additional light Higgs. Specifically, we point out that for sneutrino LSPs there is a strong constraint on the mass of the Z' due to the experimental bounds on the direct detection scattering cross section

A direct search for neutralino production at LEP

This is the post-print version of the Article - Copyright @ 1990 Elsevier.A search has been performed for the production of neutralinos (χ, χ′) in e+e− annihilation at energies near the Z0 pole. No evidence for these particles was found either in searches for events with two acoplanar jets, low visible energy, and missing pt (sensitive to or in searches for single-photon events (sensitive to Z0→χχ′→χχγ). Model independent upper limits (at the 95% CL) on the branching ratio for the decay mode Z0 →χχ′ of a few 10−4 are obtained for most of the range of neutralino masses that is kinematically accessible at LEP energies. Upper limits on the mixing factor of neutralinos are also placed as a function of the neutralino masses.This study was supported by the US Dept. of Energy, US National Science Foundation, UK Science and Engineering Research Council, the A.P. Sloan Foundation, the Canadian National Sciences and Engineering Research Council, the Israeli Ministry of Science, Minerva Gesellschaft, The Japanese Ministry of Education, Science and Culture, the Monbusho International Science Research Program, the American-Israeli Bi-national Science Foundation, L'insitut de Recherche Fondamentale du Comissariat a L'Energie Atomique, and the Bundesministerium fur Forschng und Technologie