title: Ultraviolet-protected inflation.
abstract: In natural inflation, the inflaton is a pseudo-Nambu-Goldstone boson which acquires a mass by explicit breaking of a global shift symmetry at scale f. In this case, for small field values, the potential is flat and stable under radiative corrections. Nevertheless, slow roll conditions enforce f ≫ M(p), making the validity of the whole scenario questionable. In this Letter, we show that a coupling of the inflaton kinetic term to the Einstein tensor allows f ≪ M(p) by enhancing the gravitational friction acting on the inflaton during inflation. This new unique interaction (a) keeps the theory perturbative in the whole inflationary trajectory, (b) preserves the tree-level shift invariance of the pseudo-Nambu-Goldstone boson, and (c) avoids the introduction of any new degrees of freedom with respect to standard natural inflation.
authors: Arnold Sommerfeld Center, Ludwig-Maximilians-University, Muenchen, Germany. cristiano.germani@lmu.de
authors: Cristiano
authors: C
authors: Germani
authors: Alex
authors: A
authors: Kehagias