Dilaton Stabilisation in D-term Inflation

Dilaton stabilisation is usually considered to pose a serious obstacle to successful D-term inflation in superstring theories. We argue that the physics of gaugino condensation is likely to be modified during the inflationary phase in such a way as to enhance the gaugino condensation scale. This enables dilaton stabilisation during inflation with the D-term still dominating the vacuum energy at the stable minimum. CERN-TH/98-181 February 1, 2008 On leave of absence from Department of Physics and Astronomy, University of Southampton, Southampton, U.K. On leave of absence from Theoretical Physics, Department of Physics, University of Oxford, Oxford, U.K. Due to its intrinsic elegance, inflation [1] has become the almost universally accepted dogma for accounting for the flatness and homogeneity of the universe. There are various classes of inflation that have been proposed, but possibly the most successful, and certainly one of the most popular versions these days is hybrid inflation [2]. In hybrid inflation, there are (at least) two fields at work: the slowly rolling inflaton field I, and a second field which we shall call ψ whose value is held at zero during inflation and whose role is to end inflation by developing a non-zero vacuum expectation value (VEV) when I passes a certain critical value I during its slow roll. With ψ = 0, the potential along the I direction is approximately flat, with the flatness lifted by a I mass which must be small enough to satisfy the slow-roll conditions for inflation. The natural framework for hybrid inflation is supersymmetry (SUSY). Supersymmetry can naturally provide flat directions along which the inflaton can roll, and additionally ensures that the scalar inflaton mass does not have quadratic divergences. The natural size of the inflaton mass in SUSY is of order the SUSY breaking scale, and the slow roll conditions and COBE constraints then determine the height of the potential during inflation V 1/4 0 to be some intermediate scale below the grand unification (GUT) scale. To be precise, during inflation we may set the field ψ = 0 so that, assuming a flat direction, the potential simplifies to: V = V0 + 1 2 mII . (1) The slow roll conditions are given by: ǫN = 1 2 MPl ( V ′ V )2 = 1 2 M Plm 4 II 2 N V 2 0 ≪ 1, (2)