Prof Subir Sarkar

Abstract:

The cosmological significance of the neutralino sector is studied for a class of models in which electroweak symmetry breaking is seeded by a gauge singlet. Extensive use is made of the renormalisation group equations to significantly reduce the parameter space, by deriving analytic expressions for all the supersymmetry-breaking couplings in terms of the universal gaugino mass $m_{1/2}$, the universal scalar mass $m_0$ and the coupling $A$. The composition of the LSP is determined exactly below the W mass, no approximations are made for sfermion masses, and all particle exchanges are considered in calculating the annihilation cross-section; the relic abundance is then obtained by an analytic approximation. We find that in these models, stable neutralinos may make a significant contribution to the dark matter in the universe.

Abstract:

We have searched for electrons scattered in the forward direction by neutrinos produced by dumping a 400 GeV/c proton beam on a copper target. We estimate the number of tau neutrinos produced from the decays of Ds mesons in the dump. The data limit the possible magnetic moment of tau neutrinos to be below 5.4×10-7 ωB. This rules out the suggestion that tau neutrinos of mass O(MeV) constitute the dark matter in the universe. © 1992.

Abstract:

There has recently been renewed interest in massive neutral dark-matter particle candidates with masses greater than ∼ 1 TeV which may be unstable. We re-evaluate the constraints on such particles from the possible effects of their decays on the spectrum of the microwave background-radiation and the primordially synthesised abundances of the light elements, from observations of the diffuse gamma-ray background radiation, and from searches for muons and neutrinos in nucleon-decay and cosmic-ray detectors. We find that such unstable neutral relics may well have the cosmological critical density if their lifetime exceeds ∼ 1016 yr. We illustrate our arguments by applying them to technicolour baryons and to "cryptons" in superstring-inspired models. © 1992.