Exact monopole instantons and cosmological solutions in string theory from Abelian dimensional reduction

We compute the exact string vacuum backgrounds corresponding to the noncompact coset theory SU(2,1)/SU(2). The conformal field theory defined by the level k=4 results in a five-dimensional singular solution that factorizes in an asymptotic region as the linear dilaton solution and an S3 model. It presents two Abelian compact isometries that allow us to reinterpret it from a four-dimensional point of view as a stationary and magnetically charged space-time resembling in some aspects the Kerr-Newman solution of general relativity. The k=13/7 theory, on the other hand, describes a cosmological solution that interpolates between a singular phase at short times and an S1xS2 universe after some Planckian times. copyright 1997 The American Physical Society