Galilean symmetry in the effective theory of inflation: new shapes of non-Gaussianity

TL;DR

This paper explores how approximate Galilean symmetry in the Effective Theory of Inflation influences the shape and size of non-Gaussianities, revealing new observable signatures in the cosmic microwave background.

Contribution

It introduces a novel analysis of operators with two derivatives under Galilean symmetry, leading to new non-Gaussian shapes and larger four-point functions in inflationary models.

Findings

Three independent cubic operators with up to six derivatives produce distinct non-Gaussian shapes.

The four-point function amplitude exceeds that of models with small sound speed.

Some non-Gaussian shapes peak on flattened isosceles triangles, offering new observational signatures.

Abstract

We study the consequences of imposing an approximate Galilean symmetry on the Effective Theory of Inflation, the theory of small perturbations around the inflationary background. This approach allows us to study the effect of operators with two derivatives on each field, which can be the leading interactions due to non-renormalization properties of the Galilean Lagrangian. In this case cubic non-Gaussianities are given by three independent operators, containing up to six derivatives, two with a shape close to equilateral and one peaking on flattened isosceles triangles. The four-point function is larger than in models with small speed of sound and potentially observable with the Planck satellite.