Natural selection of inflationary vacuum required by infra-red
  regularity and gauge-invariance
  It has been an issue of debate whether the inflationary infrared(IR)
divergences are physical or not. Our claim is that, at least, in single-field
models, the answer is "No," and that the spurious IR divergence is originating
from the careless treatment of the gauge modes. In our previous work we have
explicitly shown that the IR divergence is absent in the genuine
gauge-invariant quantity at the leading order in the slow-roll approximation.
We extend our argument to include higher-order slow-roll corrections and the
contributions from the gravitational waves. The key issue is to assure the
gauge invariance in the choice of the initial vacuum, which is a new concept
that has not been considered in conventional calculations.
