Dilaton destabilization at high temperature

Many compactifications of higher-dimensional supersymmetric theories have approximate vacuum degeneracy. The associated moduli fields are stabilized by non-perturbative effects which break supersymmetry. We show that at finite temperature the effective potential of the dilaton acquires a negative linear term. This destabilizes all moduli fields at sufficiently high temperature. We compute the corresponding critical temperature which is determined by the scale of supersymmetry breaking, the β-function associated with gaugino condensation and the curvature of the Kähler potential, Tcrit ∼ √m3/2 MP (3/β)3/4 K″-1/4. For realistic models we find Tcrit ∼ 1011 - 1012 GeV, which provides an upper bound on the temperature of the early universe. In contrast to other cosmological constraints, this upper bound cannot be circumvented by late-time entropy production. © 2004 Elsevier B.V. All rights reserved