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Fine tunings for inflation with simple potentials

We continue to investigate possible parameter choices for primordial inflation with simple potentials such as power-law and two-term potentials. We examine the amount of parameter tuning to make the slow-roll inflation eternal. In particular, we adopt the critical coupling for marginally eternal inflation and see whether realistic primordial inflation is attainable under such a parameter choice. It turns out that potentials with mass scale of grand unification provide, after tuning, consistent results to experimental data so that the considered tuning is allowed observationally. Namely, the primordial inflation is possibly marginal in such a setup.