2010/12/31 by Cristiano Germani, Alex Kehagias
Physics and Astronomy · #Black Holes and Theoretical Physics #Cosmology and Gravitation Theories #Solar and Space Plasma Dynamics #astro-ph.CO #gr-qc #hep-ph #hep-th
paper · pdf · doi:10.1103/physrevlett.106.161302
published as Phys.Rev.Lett.106:161302,2011 · 5 pages; v3: Minkowski limit of the "strong coupling scale" corrected; results unchanged; accepted in Phys. Rev. Lett. 2011
arxiv created 2011/04/01 · openalex publication_date 2011/04/20 · arxiv updated 2011/05/09 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/01
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.