| Abstract: |
More than 20 years ago, it has been noted that pseudoscalar axions are one of the best candidates for the inflaton field, since the flatness of their potential is protected against radiative corrections by a shift symmetry. This protection is employed in many concrete realizations of large field inflation. Axions have a specific coupling to gauge fields; however, such coupling has so far received little attention in connection to inflation. We show that this coupling can actually drastically change the phenomenological predictions of the most straightforward realizations of axion inflation. The signatures in the CMB anisotropies are highly distinctive and promising: a specific and large non-gaussianity of (nearly) equilateral shape, in addition to detectably large spectral tilt and and observable gravity waves at interferometers as Advanced LIGO/VIRGO. The current observational bounds imply that the coupling of a pseudo-scalar inflaton to any gauge field must be smaller than about $1/(10^{16} GeV)$; this limit is about 5 orders of magnitude stronger than the analogous limit for the coupling of the QCD axion to photons. |
