Inflation from Flux Cascades
  When electric-type flux threads compact extra dimensions, a quantum
nucleation event can break a flux line and initiate a cascade that unwinds many
units of flux. Here, we present a novel mechanism for inflation based on this
phenomenon. From the 4D point of view, the cascade begins with the formation of
a bubble containing an open Friedmann-Robertson-Walker cosmology, but the
vacuum energy inside the bubble is initially only slightly reduced, and
subsequently decreases gradually throughout the cascade. If the initial flux
number Q_0 ~ O(100), during the cascade the universe can undergo N ~ 60 efolds
of inflationary expansion with gradually decreasing Hubble constant, producing
a nearly scale-invariant spectrum of adiabatic density perturbations with
amplitude and tilt consistent with observation, and a potentially observable
level of non-Gaussianity and tensor modes. The power spectrum has a small
oscillatory component that does not decay away during inflation, with a period
set approximately by the light-crossing time of the compact dimension(s). Since
the ingredients are fluxes threading compact dimensions, this mechanism fits
naturally into the string landscape, but does not appear to suffer from the eta
problem or require fine-tuning (beyond the usual anthropic requirement of small
vacuum energy after reheating).
