Inflating without a flat potential: Viscous inflation
  Bulk viscosity leads to negative pressure, which is a key ingredient for successful inflation. We build an inflationary model where the slow-roll of the inflaton field is driven by a viscous component instead of the flat potential commonly used. Since viscosity does not contribute to the energy density of the Universe, the Hubble rate depends only on the kinetic energy of the inflaton. The power spectrum is almost scale-invariant, with a tilt depending on the slow-roll parameters defined within the model. 
Luca Visinelli
gr-qc astro-ph.CO