Primordial non-Gaussianity from the DBI Galileons

Shuntaro Mizuno; Kazuya Koyama

doi:10.1103/PhysRevD.82.103518

paper

Primordial non-Gaussianity from the DBI Galileons

arXiv:1009.0677 · doi:10.1103/PhysRevD.82.103518

Abstract

We study primordial fluctuations generated during inflation in a class of models motivated by the DBI Galileons, which are extensions of the DBI action that yield second order field equations. This class of models generalises the DBI Galileons in a similar way with K-inflation. We calculate the primordial non-Gaussianity from the bispectrum of the curvature perturbations at leading order in the slow-varying approximations. We show that the estimator for the equilateral-type non-Gaussianity, $f_{NL}^{e q u i l}$ , can be applied to measure the amplitude of the primordial bispectrum even in the presence of the Galileon-like term although it gives a slightly different momentum dependence from K-inflation models. For the DBI Galileons, we find $- 0.32/ c_{s}^{2} < f_{NL}^{e q u i l} < - 0.16/ c_{s}^{2}$ and large primordial non-Gaussianities can be obtained when $c_{s}$ is much smaller than 1 as in the usual DBI inflation. In G-inflation models, where a de Sitter solution is obtained without any potentials, the non-linear parameter is given by $f_{NL}^{e q u i l} = 4.62 r^{- 2/3}$ where $r$ is the tensor to scalar ratio, giving a stringent constraint on the model.

10 pages, 1 figure. Accepted for publication in PRD

Primordial non-Gaussianity from the DBI Galileons

Abstract

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