Dark Matter from Entropy Perturbations in Curved Field Space

TL;DR

This paper proposes a novel dark matter production mechanism during inflation via entropy perturbations in negatively curved field space, allowing subhorizon modes to be excited and distinguishable observationally.

Contribution

It introduces a new scenario where negative curvature in field space enables excitation of subhorizon entropy modes, expanding dark matter production models during inflation.

Findings

Subhorizon entropy modes can be excited in negatively curved field space.

The spectral density peaks at smaller scales compared to flat field space models.

The model predicts observational signatures distinguishable from existing scenarios.

Abstract

The accumulated energy density of the excited entropy modes in multiple field inflationary scenarios can play the role of dark matter. In the usual case of a flat field space without any turning trajectory, only light superhorizon entropy modes can be excited through the gravitational instability. In the case of a negatively curved field space, we show that subhorizon entropy modes can be excited as well through the tachyonic instability induced by the negative curvature of the field space. The latter allows for production of entropy modes with masses larger than or at the order of the Hubble expansion rate during inflation, leading to a new dark matter scenario. Due to the contribution of subhorizon modes, the corresponding spectral density has a peak at a scale smaller than its counterpart in the models based on a flat field space. This difference makes our model observationally distinguishable.