Lorentz boost and non-Gaussianity in multifield DBI inflation

Shuntaro Mizuno*, Frederico Arroja, Kazuya Koyama, Takahiro Tanaka

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

52 Citations (Scopus)


We show that higher-order actions for cosmological perturbations in the multifield Dirac-Born-Infeld (DBI) inflation model are obtained by a Lorentz boost from the rest frame of the brane to the frame where the brane is moving. We confirm that this simple method provides the same third- and fourth-order actions at leading order in slow roll and in the small sound speed limit as those obtained by the usual Arnowitt-Deser-Misner formalism. As an application, we compute the leading order connected four-point function of the primordial curvature perturbation coming from the intrinsic fourth-order contact interaction in the multifield DBI-inflation model. At third order, the interaction Hamiltonian arises purely by the boost from the second-order action in the rest frame of the brane. The boost acts on the adiabatic and entropy modes in the same way, thus there exists a symmetry between the adiabatic and entropy modes. But at fourth order this symmetry is broken due to the intrinsic fourth-order action in the rest frame and the difference between the Lagrangian and the interaction Hamiltonian. Therefore, contrary to the three-point function, the momentum dependence of the purely adiabatic component and the components including the entropic contributions are different in the four-point function. This suggests that the trispectrum can distinguish the multifield DBI-inflation model from the single field DBI-inflation model.

Original languageEnglish
Article number023530
JournalPhysical Review D - Particles, Fields, Gravitation and Cosmology
Issue number2
Publication statusPublished - 2009 Aug 6
Externally publishedYes

ASJC Scopus subject areas

  • Nuclear and High Energy Physics


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