Quantum back reaction in integrable cosmology

Two-dimensional dilaton gravity theories with a conserved current admit analytic integration of quantum back reaction in the semiclassical limit, yielding only a few classes of homogeneous cosmological solutions. One class of solutions describe a toy model of an inflationary universe which decays into a flat universe due to quantum back reaction, despite the apparent presence of a cosmological constant, thus providing a possible resolution of the cosmological constant problem. In another class of solutions the semiclassical approximation breaks down either initially or finally in the cosmological evolution.