Four-dimensional cosmology from dilaton coupled quantum matter in two dimensions

Abstract

The reduction of 4D Einstein gravity with $N$ minimal scalars leads to specific 2D dilaton gravity with dilaton coupled scalars. Applying s-wave and large $N$ approximation (where large $N$ quantum contribution due to dilaton itself is taken into account) we study 2D cosmology for CGHS model and for reduced Einstein gravity (in both cases with dilaton coupled scalars). Numerical study shows that in most cases we get 2D singular Universe which may correspond to big bang. Nevertheless, big crunch or non-singular Universes are also possible. For reduced 4D Einstein gravity one can regard the obtained 2D cosmology with time-dependent dilaton as 4D Kantowski-Sacks Universe of singular,non-singular or big crunch type.