Constraining the kinetically dominated Universe
  We present cosmological constraints from Planck 2015 data for a universe that
is kinetically dominated at very early times. We perform a Markov chain Monte
Carlo analysis to estimate parameters and use nested sampling to determine the
evidence for a model comparison of the single-field quadratic and Starobinsky
inflationary models with the standard $\Lambda$CDM cosmology. In particular we
investigate how different amounts of inflation before and after horizon exit
affect the primordial power spectrum and subsequently the power spectrum of the
cosmic microwave background. We find that the model using kinetically dominated
initial conditions for inflation performs similarly well in terms of Bayesian
evidence as a model directly starting out in the slow-roll phase, despite
having an additional parameter. The data show a slight preference for a cutoff
at large scales in the primordial and temperature power spectra.
