Instanton effects in string cosmology Original Research Article

We consider the gauge dyonic string solution of the K3 compactified heterotic string theory in a four-dimensional cosmological context. Since for this solution Green-Schwarz as well as Chern-Simons corrections have been taken into account it contains both world-sheet and string loop 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 result with gauge neutral extreme and non-extreme cosmologies and find that the non-trivial Yang-Mills background leads to a solution without any singularities whereas for trivial Yang-Mills backgrounds some of the fields become always singular at the big bang.