Some aspects of thermal inflation: The finite temperature potential and topological defects.

Currently favored extensions of the standard model typically contain {open_quote}{open_quote}flaton fields{close_quote}{close_quote} defined as fields with large vacuum expectation values (VEV{close_quote}s) and almost flat potentials. If a flaton field is trapped at the origin in the early Universe, one expects {open_quote}{open_quote}thermal inflation{close_quote}{close_quote} to take place before it rolls away to the true vacuum, because the finite-temperature correction to the potential will hold it at the origin until the temperature falls below 1 TeV or so. In the first part of the paper, that expectation is confirmed by an estimate of the finite-temperature corrections and of the tunneling rate to the true vacuum, paying careful attention to the validity of the approximations that are used. The second part of the paper considers topological defects which may be produced at the end of an era of thermal inflation. If the flaton fields associated with the era are grand unified theory (GUT) Higgs fields, then its end corresponds to the GUT phase transition. In that case monopoles (as well as GUT Higgs particles) will have to be diluted by a second era of thermal inflation. Such an era will not affect the cosmology of GUT strings, for which the crucial parameter is the stringmore » mass per unit length. Because of the flat Higgs potential, the GUT symmetry-breaking scale required for the strings to be a candidate for the origin of large scale structure and the CMB anisotropy is about three times bigger than usual, but given the uncertainties it is still compatible with the one required by the unification of the standard model gauge couplings. The cosmology of textures and of global monopoles is unaffected by the flatness of the potential. {copyright} {ital 1996 The American Physical Society.}« less