Li, TJ (reprint author), Chinese Acad Sci, Inst Theoret Phys, KITPC, State Key Lab Theoret Phys, Beijing 100190, Peoples R China.
We show that the quadratic inflation can be realized by the phase of a complex field with helicoid potential. Remarkably, this helicoid potential can be simply realized in minimal supergravity. The global U(1) symmetry of the Kahler potential introduces a flat direction and evades the eta problem automatically. So such inflation is technically natural. The phase excursion is super-Planckian as required by the Lyth bound, while the norm of the complex field can be suppressed in the sub-Planckian region. This model resolves the ultraviolet sensitive problem of the large field inflation; besides, it also provides a new type of monodromy inflation in supersymmetric field theory with consistent field stabilization.