Prof Subir Sarkar

Abstract:

We derive constraints on the relic abundance of a generic particle of mass ∼ 1-1014 TeV which decays into neutrinos at cosmological epochs, using data from the Fréjus and IMB nucleon decay detectors and the Fly's Eye air-shower array. The lifetime of such unstable particles which may constitute the dark matter today is bounded to be greater than ∼ 1014-1018 yr, depending on the mass. For lifetimes shorter than the age of the universe, neutrino energy losses due to scattering and the expansion redshift become important and set limits to the ability of neutrino observatories to probe the early universe. © 1993.

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.