Toward inflation models compatible with the no-boundary proposal
  In this paper, we investigate various inflation models in the context of the
no-boundary proposal. We propose that a good inflation model should satisfy
three conditions: observational constraints, plausible initial conditions, and
naturalness of the model. For various inflation models, we assign the
probability to each initial condition using the no-boundary proposal and define
a quantitative standard, typicality, to check whether the model satisfies the
observational constraints with probable initial conditions. There are three
possible ways to satisfy the typicality criterion: there was pre-inflation near
the high energy scale, the potential is finely tuned or the inflationary field
space is unbounded, or there are sufficient number of fields that contribute to
inflation. The no-boundary proposal rejects some of naive inflation models,
explains some of traditional doubts on inflation, and possibly, can have
observational consequences.
