INSTANTON EFFECTS IN STRING COSMOLOGY

We consider the gauge dyonic string solution of the K3 compactified he terotic string theory in a four-dimensional cosmological context, Sinc e for this solution Green-Schwarz as well as Chern-Simons corrections have been taken into account it contains both world-sheet and string l oop corrections. The cosmological picture is obtained by rotating the world-volume of the gauge dyonic string into two space-like dimensions and compactifying those dimensions on a two torus, We compare the res ult with gauge neutral extreme and non-extreme cosmologies and find th at the non-trivial Yang-Mills background leads to a solution without a ny singularities whereas for trivial Yang-Mills backgrounds some of th e fields become always singular at the big bang. (C) 1997 Published by Elsevier Science B.V.