Cosmological String Backgrounds from Gauged WZW Models

Abstract We discuss the four-dimensional target-space interpretation of bosonic strings based on gauge WZW models, in particular of those based on the non-compact coset space SL (2, R )×SO(1, 1). We show that these theories lead, apart from the recently broadly discussed black-hole type of backgrounds, to cosmological string backgrounds, such as an expanding Universe. Which of the two cases is realized depends on the sign of the level of the corresponding Kac-Moody algebra. We discuss various aspects of these new cosmological string backgrounds.