Late-time backreaction from inflationary fluctuations of a non-minimally
  coupled massless scalar
  We consider the late time one-loop quantum backreaction from inflationary
fluctuations of a non-minimally coupled, massless scalar field. The scalar is
assumed to be a spectator field in an inflationary model with a constant
principal slow roll $\epsilon$ parameter. We regulate the infrared by matching
onto a pre-inflationary radiation era. We find a large late time backreaction
when the nonminimal coupling $\xi$ is negative (in which case the scalar
exhibits a negative mass term during inflation). The one-loop quantum
backreaction becomes significant today for moderately small non-minimal
couplings, $\xi\sim -1/20$, and it changes sign (from negative to positive) at
a recent epoch when inflation lasts not much longer than what is minimally
required, $N \gtrsim 66$. Since currently we do not have a way of treating the
classical fluid and the quantum backreaction in a self-consistent manner, we
cannot say decidely whether the backreaction from inflationary quantum
fluctuations of a non-minimally coupled scalar can mimic dark energy.
