Double-Running Inflaton Mass for a Flat Potential and Assisted Hilltop Inflation

We propose a scenario to flatten the inflaton potential for a small-field slow-roll inflation from the origin. In the scenario, the inflaton mass-square goes through a renormalization group running that depends on not only inflaton field but also an assisting field. Thanks to the assisting field participating in the running, the initial condition for a slow-roll inflation can be set naturally, and the inflaton potential can be flattened by the vacuum expectation value of the field. Applying this idea, we propose a scenario of inflation, dubbed here as assisted hilltop inflation, which is free from the initial condition and the flatness problems of inflation.