A Model of Inflation
  We consider a novel model of cosmic inflation. In our model one does not need any specific matter field to drive inflation, but inflation stems from the microscopic, Planck scale structure of spacetime, thus being of quantum gravitational origin. At a certain temperature spacetime performs a phase transition, where the cosmological constant drops from a huge, Planck scale value, which is about $10^{87}s^{-2}$ to its present, pretty small value $10^{-35}s^{-2}$. When the cosmological constant is large, the universe goes through a period of very rapid expansion which, however, comes to an abrupt end after the phase transition has been completed. Assuming that the cosmological constant depends on the age of the universe in an appropriate manner during the phase transition one may recover the predictions of the conventional inflationary scenario. 
Jarmo M\"akel\"a
gr-qc