Non-Gaussianities from isocurvature modes

TL;DR

This paper explores how isocurvature modes can generate distinctive non-Gaussianities in the CMB, offering a new way to detect and constrain these modes despite their suppressed power spectrum contributions.

Contribution

It analyzes the non-Gaussian signatures of isocurvature modes and their potential to reveal isocurvature contributions through the angular bispectrum in CMB data.

Findings

Isocurvature modes produce a rich structure of the angular bispectrum.

Non-Gaussianities can dominate over power spectrum signals in some scenarios.

Future CMB data can constrain or measure isocurvature contributions via non-Gaussianity analysis.

Abstract

This contribution discusses isocurvature modes, in particular the non-Gaussianities of local type generated by these modes. Since the isocurvature transfer functions differ from the adiabatic one, the coexistence of a primordial isocurvature mode with the usual adiabatic mode leads to a rich structure of the angular bispectrum, which can be decomposed into six elementary bispectra. Future analysis of the CMB data will enable to measure their relative weights, or at least constrain them. Non-Gaussianity thus provides a new window on isocurvature modes. This is particularly relevant for some scenarios, such as those presented here, which generate isocurvature modes whose contribution in the power spectrum is suppressed, as required by present data, but whose contribution in the non-Gaussianities could be dominant and measurable.