Left-right symmetry, supersymmetry : cosmological constraint

Unified models incorporating the right handed neutrino in a symmetric way generically possess parity symmetry. If this is broken spontaneously it results in the formation of domain walls in the early Universe, whose persistence is unwanted. We have considered several scenarios for the pressure difference resulting in intrinsic destabilisation of the walls. Requiring this to arise from small parity breaking effects beyond the tree level places an upper bound on the scale of spontaneous parity breaking, often much lower than the GUT scale. In the left-right symmetric models studied the upper bound is no higher than 10(11) GeV but a scale as low as 10(5) GeV is acceptable.