Primordial Non-Gaussianity in Models with Dark Matter Isocurvature Fluctuations

TL;DR

This paper explores how mixed inflationary scenarios can produce significant primordial non-Gaussianity without violating dark matter isocurvature constraints, with implications for dark matter generation mechanisms.

Contribution

It demonstrates that mixed models can generate large non-Gaussianity while remaining consistent with current isocurvature limits, especially relevant for future observational constraints.

Findings

Primordial non-Gaussianity can be large in mixed scenarios without conflicting with isocurvature constraints.

Future constraints may limit the nonlinearity parameter to $f_{NL} \\lesssim 3$.

Implications for dark matter production mechanisms are discussed.

Abstract

We investigate primordial non-Gaussianity and dark matter isocurvature fluctuations in the modulated reheating and the curvaton scenarios. In these scenarios, large non-Gaussianity can be generated, on the other hand, depending on how dark matter is produced, too large isocurvature fluctuations can also arise, which is inconsistent with current observations. In this paper, we study this issue in a mixed scenario where the curvature fluctuations can also be produced from the inflaton fluctuations as well as those from a light scalar field such as the modulus and the curvaton. We show that primordial fluctuations can be highly non-Gaussian without conflicting the current constraint on isocurvature fluctuations for such mixed scenarios. However, if the constraint on isocurvature fluctuations becomes severer as expected by the Planck satellite, $f_{\rm NL}$, a nonlinearity parameter for adiabatic fluctuations, should be very small as $f_{\rm NL} \lesssim 3$, which would give interesting implications for the generation mechanism of dark matter. Non-Gaussianity from isocurvature fluctuations is also discussed in these scenarios.