Understand
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.