Primordial non-Gaussianity from the DBI Galileons

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, $f_{\mathrm{NL}}^{equil}$, 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 $-0.32/c_s^2<f_{\mathrm{NL}}^{equil}<-0.16/c_s^2$ 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 $f_{\mathrm{NL}}^{equil}=4.62r^{-2/3}$ where $r$ is the tensor to scalar ratio, giving a stringent constraint on the model.

10 pages, 1 figure. Accepted for publication in PRD

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• Symmetries for Galileons and DBI scalars on curved space
• Observational constraints on Galileon cosmology
• Matter perturbations in Galileon cosmology
• Primordial non-Gaussianities in general modified gravitational models of inflation
• Primordial non-Gaussianity from G-inflation
• On Classification of Models of Large Local-Type Non-Gaussianity
• A note on the role of the boundary terms for the non-Gaussianity in general k-inflation
• Cosmology of the selfaccelerating third order Galileon
• Resonant Trispectrum and a Dozen More Primordial N-point functions
• Conservation of the nonlinear curvature perturbation in generic single-field inflation
• Goldstone's Theorem and Hamiltonian of Multi-galileon Modified Gravity
• Enhanced Inflation in the Dirac-Born-Infeld framework