Low-l CMB Power Loss in String Inflation
  The lack of power on large scales (l < 40) might have been observed by the
PLANCK satellite. We argue that this putative feature can be explained by a
phase of fast roll at the onset of inflation. We show that in the context of
single field models what is required is an asymmetric inflection point model of
which fibre inflation is a string motivated example. We study the ability of
fibre inflation to generate a suppression of the CMB 2-point function power at
low l, finding that the potential derived from string loops is not steep enough
for this purpose. We introduce a steeper contribution to the potential, that
dominates away from the inflationary region, and show that if properly tuned it
can indeed lead to a spectrum with lack of power at large scales.
