Large tensor spectrum of BICEP2 in the natural SUSY hybrid model

TL;DR

This paper proposes a two-field natural SUSY hybrid inflation model that explains the large tensor spectrum observed by BICEP2 while maintaining sub-Planckian decay constants and avoiding common inflationary problems.

Contribution

It introduces a novel two-field inflationary framework combining SUSY hybrid and natural inflation models with specific symmetries to match observational data.

Findings

Achieves the observed tensor-to-scalar ratio with sub-Planckian decay constant.

Provides 50 e-folds of inflation with vacuum energy around 2 x 10^{16} GeV.

Maintains spectral index of approximately 0.96.

Abstract

The large tensor spectrum recently observed by the BICEP2 Collaboration requires a super-Planckian field variation of the inflaton in the single-field inflationary scenario. The required slow-roll parameter \epsilon \approx 0.01 would restrict the e-folding number to around 7 in (sub-)Planckian inflationary models. To overcome such problems, we consider a two-field scenario based on the natural assisted supersymmetric (SUSY) hybrid model ("natural SUSY hybrid inflation" [1]), which combines the SUSY hybrid and the natural inflation models. The axionic inflaton field from the natural inflation sector can admit the right values for the tensor spectrum as well as a spectral index of 0.96 with a decay constant smaller than the Planck scale, f \lesssim M_P. On the other hand, the vacuum energy of 2 x 10^{16} GeV with 50 e-folds is provided by the inflaton coming from the SUSY hybrid sector, avoiding the eta problem. These are achieved by introducing both the U(1)_R and a shift symmetry, and employing the minimal Kahler potential.