Realization of new inflation

We examine cosmological phase transitions using a new approach and argue that there are many models in which the universe enters a period of exponential expansion required for an inflationary cosmology. A sufficient condition is that the interaction rates due to quantum field nonlinearities be sufficiently small compared to the expansion rate of the universe. In Coleman-Weinberg-type models this requires tuning the gauge coupling constant to a low value. In pure scalar field theories, the conditions for inflation are satisfied if the scale of symmetry breaking is of the order of the Planck scale.