Isocurvature modes in the CMB bispectrum

TL;DR

This paper investigates the angular bispectrum of the CMB arising from correlations between adiabatic and isocurvature modes, assessing how well future CMB data can constrain these contributions and inform inflation models.

Contribution

It provides a detailed decomposition of the bispectrum into six elementary components and evaluates the potential of CMB data to measure or constrain their amplitudes.

Findings

CMB data can significantly constrain isocurvature contributions

Polarization data improves measurement precision

Constraints can inform multiple-field inflation models

Abstract

We study the angular bispectrum of local type arising from the (possibly correlated) combination of a primordial adiabatic mode with an isocurvature one. Generically, this bispectrum can be decomposed into six elementary bispectra. We estimate how precisely CMB data, including polarization, can enable us to measure or constrain the six corresponding amplitudes, considering separately the four types of isocurvature modes (CDM, baryon, neutrino density, neutrino velocity). Finally, we discuss how the model-independent constraints on the bispectrum can be combined to get constraints on the parameters of multiple-field inflation models.