Five-Brane Dynamics and Inflation in Heterotic M-Theory
  Generic heterotic M-theory compactifications contain five-branes wrapping non-isolated genus zero or higher genus curves in a Calabi-Yau threefold. Non-perturbative superpotentials do not depend on moduli of such five-branes.We show that fluxes and non-perturbative effects can stabilize them in a non-supersymmetric AdS vacuum. We also show that these five-branes can be stabilized in a dS vacuum, if we modify the supergravity potential energy by Fayet-Iliopoulos terms. This allows us to stabilize all heterotic M-theory moduli in a dS vacuum in the most general compactification scenarios. In addition, we demonstrate that, by this modification, one can create an inflationary potential. The inflationary phase is represented by a five-brane approaching the visible brane. We give a qualitative argument how extra states becoming light, when the five-brane comes too close, can terminate inflation. Eventually, the five-brane hits the visible brane and disappears through a small instanton transition. The post-inflationary system of moduli has simpler stability properties. It can be stabilized in a dS vacuum with a small cosmological constant. 
Evgeny I. Buchbinder