Dynamical breaking of shift-symmetry in supergravity-based inflation

Shift-symmetry is essential to protect the flatness of the potential, even beyond the super-Planckian vacuum expectation value (VEV) for an inflaton field. The breaking of the shift-symmetry can yield potentials suitable for super-Planckian excursion of the inflaton. The aim of this paper is to illustrate that it is indeed possible to break the shift-symmetry dynamically within 4 dimensional supergravity prior to a long phase of inflation. Thanks to the shift-symmetry, the leading contribu- tion to the inflaton potential is free from the dangerous exponential factor even after its breaking, which is the main obstacle to realizing the super-Planckian inflation in supergravity. But, in our simple model, the resulting inflaton potential is a cosine type potential rather than the power-law one and it is difficult to realize a super-Planckian breaking scale unfortunately.