### 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 generalizes 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, fNLequil, 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/cs2<fNLequil<-0. 16/cs2 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 nonlinear parameter is given by fNLequil=4.62r⊃-2⊃/3, where r is the tensor to scalar ratio, giving a stringent constraint on the model.

Original language | English |
---|---|

Article number | 103518 |

Journal | Physical Review D - Particles, Fields, Gravitation and Cosmology |

Volume | 82 |

Issue number | 10 |

DOIs | |

Publication status | Published - 2010 Nov 12 |

Externally published | Yes |

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### ASJC Scopus subject areas

- Nuclear and High Energy Physics

### Cite this

*Physical Review D - Particles, Fields, Gravitation and Cosmology*,

*82*(10), [103518]. https://doi.org/10.1103/PhysRevD.82.103518

**Primordial non-Gaussianity from the DBI Galileons.** / Mizuno, Shuntaro; Koyama, Kazuya.

Research output: Contribution to journal › Article

*Physical Review D - Particles, Fields, Gravitation and Cosmology*, vol. 82, no. 10, 103518. https://doi.org/10.1103/PhysRevD.82.103518

}

TY - JOUR

T1 - Primordial non-Gaussianity from the DBI Galileons

AU - Mizuno, Shuntaro

AU - Koyama, Kazuya

PY - 2010/11/12

Y1 - 2010/11/12

N2 - 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 generalizes 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, fNLequil, 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/cs2s 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 nonlinear parameter is given by fNLequil=4.62r⊃-2⊃/3, where r is the tensor to scalar ratio, giving a stringent constraint on the model.

AB - 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 generalizes 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, fNLequil, 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/cs2s 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 nonlinear parameter is given by fNLequil=4.62r⊃-2⊃/3, where r is the tensor to scalar ratio, giving a stringent constraint on the model.

UR - http://www.scopus.com/inward/record.url?scp=78651260477&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=78651260477&partnerID=8YFLogxK

U2 - 10.1103/PhysRevD.82.103518

DO - 10.1103/PhysRevD.82.103518

M3 - Article

AN - SCOPUS:78651260477

VL - 82

JO - Physical review D: Particles and fields

JF - Physical review D: Particles and fields

SN - 0556-2821

IS - 10

M1 - 103518

ER -