Prof Subir Sarkar

Abstract:

A recently reported anomaly in the time structure of signals in the KARMEN neutrino detector suggests the decay of a new particle $x$, produced in $\pi^+ \to \mu^+ x$ with mass $m_x=33.9$ MeV. We discuss the constraints and difficulties in interpreting $x$ as a neutrino. We show that a mainly-sterile neutrino scenario is compatible with all laboratory constraints, within narrow limits on the mixing parameters, although there are problems with astrophysical and cosmological constraints. This scenario predicts that appreciable numbers of other $x$-decay events with different origins and time structures should also be observable in the KARMEN detector. Such $x$-decay events should also be found in the LSND experiment and may be relevant to the search for $\bar\nu_\mu\to\bar\nu_e$ oscillations.

Abstract:

We discuss the cosmology of string models with perturbative supersymmetry breaking at a scale of ${\cal O}$(TeV). Such models exhibit Kaluza-Klein like spectra and contain unstable massive gravitinos/gravitons. We find that considerations of primordial nucleosynthesis constrain the maximum temperature following inflation to be not much larger than the supersymmetry breaking scale. This imposes conflicting requirements on the scalar field driving inflation, making it rather difficult to construct a consistent cosmological history for such models.