Do Mixed States save Effective Field Theory from BICEP?
  The BICEP2 collaboration has for the first time observed the B-mode
polarization associated with inflationary gravitational waves. Their result has
some discomfiting implications for the validity of an effective theory approach
to single-field inflation since it would require an inflaton field excursion
larger than the Planck scale. We argue that if the quantum state of the
gravitons is a mixed state based on the Bunch-Davies vacuum, then the tensor to
scalar ratio r measured by BICEP is different than the quantity that enters the
Lyth bound. When this is taken into account, the tension between effective
field theory and the BICEP result is alleviated.
