Mtd2 spotted this paper by Steven Weinberg that just went on arxiv. http://arxiv.org/abs/0911.3165 Asymptotically Safe Inflation Steven Weinberg 13 pages (Submitted on 16 Nov 2009) "Inflation is studied in the context of asymptotically safe theories of gravitation. It is found to be possible under several circumstances to have a long period of nearly exponential expansion that eventually comes to an end." It could be an important paper, and in any case it's kind of elegant because the inflation episode occurs naturally, by the running of constants, without having to dream up some exotic matter field. Reuter and Bonanno already proposed something along these lines. The essential arithmetic is very simple: there is evidence of the existence of a UV fixed point for gravity where the dimensionless forms of G(k) the running Newton and Lambda(k) the running dark energy constant both converge to finite values as the length scale k -> 0 But one can see by simple dimensional reasoning that their dimensionless forms are G(k)/k2 and Lambda(k)k2. So for them to go to finite limits as k->0 we must have G(k) getting very small and Lambda(k) growing enormous. That's just the thing to cause rapid expansion. The Newton constant is almost nothing, so nothing to hold the geometry together, and the cosmological constant---the dark energy that accelerates expansion---totally huge. But as inflation proceeds the scale k increases, which increases G and reduces Lambda. So the process eventually (actually quite quickly) shuts itself off.