INSTANTONS FROM LOW-ENERGY STRING ACTIONS

We look for instanton solutions in a class of two scalar field gravity models, which includes the low energy string action in four dimension s. In models where the matter field has a potential with a false vacuu m, we find that non-singular instantons exist as long as the Dilaton f ield found in string theory has a potential with a minimum, and provid e an example of such an instanton. The class of singular instanton sol utions are also examined, and we find that depending on the parameter values, the volume factor of the Euclidean region does not always vani sh fast enough at the singularity to make the action finite. (C) 1998 Elsevier Science B.V. All rights reserved.