CHALLENGES FOR INVERTED HYBRID INFLATION

Inverted hybrid inflation (in which the inflaton field slowly rolls aw ay from the origin, giving a spectral index n less than or equal to 1) is an appealing variant of the more usually studied hybrid model. Ana lysing the model alongside the ordinary hybrid case, we show that, in order to provide the correct density perturbations consistent with the COBE measurements, the dimensionless coupling constants of the invert ed hybrid potential must be very small indeed. For example, the quarti c coupling in a typical such potential is found to be less than or equ al to 10-(12). A supersymmetric model of inverted hybrid inflation, wh ich does not involve the troublesome quartic coupling is found to lead to a potential which is unbounded from below. (C) 1997 Published by E lsevier Science B.V.