Trispectrum from Co-dimension 2(n) Galileons

TL;DR

This paper explores a specific multi-field galileon model's cosmological effects, focusing on its distinctive trispectrum features and the implications of its symmetry properties on non-Gaussianities.

Contribution

It introduces a restrictive multi-field galileon theory with a purely quartic interaction, analyzing its unique trispectrum and non-Gaussianity characteristics.

Findings

Distinctive trispectrum features compared to P(X,φ) models

Absence of cubic Lagrangian does not imply small bispectrum

Symmetry considerations influence fluctuation non-Gaussianities

Abstract

A generalized theory of multi-field galileons has been recently put forward. This model stems from the ongoing effort to embed generic galileon theories within brane constructions. Such an approach has proved very useful in connecting interesting and essential features of these theories with geometric properties of the branes embedding. We investigate the cosmological implications of a very restrictive multi-field galileon theory whose leading interaction is solely quartic in the scalar field and lends itself nicely to an interesting cosmology. The trispectrum of curvature fluctuations has features which are quite distinctive with respect to their P(X,\phi) counterpart. We also show that, despite an absent cubic Lagrangian in the full theory, non-Gaussianities in this model cannot produce the combination a of small bispectrum alongside with a large trispectrum. We further expand on this point to draw a lesson on what having a symmetry in the full background independent theory entails at the level of fluctuations and vice-versa.