Non-Gaussianity in Axion N-flation Models
Abstract
We study perturbations in the multifield axion N-flation model, taking account of the full cosine potential. We find significant differences from previous analyses which made a quadratic approximation to the potential. The tensor-to-scalar ratio and the scalar spectral index move to lower values, which nevertheless provide an acceptable fit to observation. Most significantly, we find that the bispectrum non-Gaussianity parameter fNL may be large, typically of order 10 for moderate values of the axion decay constant, increasing to of order 100 for decay constants slightly smaller than the Planck scale. Such a non-Gaussian fraction is detectable. We argue that this property is generic in multifield models of hilltop inflation.
- Publication:
-
Physical Review Letters
- Pub Date:
- October 2010
- DOI:
- 10.1103/PhysRevLett.105.181302
- arXiv:
- arXiv:1005.4410
- Bibcode:
- 2010PhRvL.105r1302K
- Keywords:
-
- 98.80.Cq;
- 14.80.Va;
- Particle-theory and field-theory models of the early Universe;
- Astrophysics - Cosmology and Nongalactic Astrophysics;
- High Energy Physics - Theory
- E-Print:
- 5 pages with 3 figures incorporated. v2: minor updates, new analytic formulae for spectral index and trispectrum, references added, typo corrections. v3: minor updates to match version accepted by Physical Review Letters