Inflation in a superstring model

A new type of inflation is presented in the heterotic E₈* E₈ superstring model. The inflation is identified with the 'Polonyi' field tau , which is related to the radius of the internal space. Radiative corrections to the gluino condensation potential are supposed to give rise to a suitable potential which is adjusted to vanish at the minimum by addition of a constant Delta V, whose magnitude is fixed by the requirement that density perturbations are of the right order. Reheating is due to the decay of the 'Polonyi' field tau and/or to the production of light particles through its oscillations. The resultant constraints upon the parameters of the potential can be satisfied without excessive fine tuning.