Prof Subir Sarkar

Abstract:

Discrete symmetries are commonplace in field theoretical models but pose a severe problem for cosmology since they lead to the formation of domain walls during spontaneous symmetry breaking in the early universe. However if one of the vacuua is favoured over the others, either energetically, or because of initial conditions, it will eventually come to dominate the universe. Using numerical methods, we study the evolution of the domain wall network for a variety of field configurations in two and three dimensions and quantify the rate at which the walls disappear. Good agreement is found with a recent analytic estimate of the termination of the scaling regime of the wall network.

Abstract:

We constrain proposed phenomenological models for a vacuum energy which decays with the expansion of the universe from considerations of standard big bang nucleosynthesis. Several such models which attempt to solve the cosmological age problem are disfavored or even ruled out.

Abstract:

We consider the hypothesis that the recently reported anomaly in the time structure of signals in the KARMEN experiment is due to the production of a light photino (or Zino) which decays radiatively due to violation of R-parity. Such a particle is shown to be consistent with all experimental data and with cosmological nucleosynthesis. There are difficulties with constraints from SN 1987A but these may be evaded if squarks are non-degenerate in mass.