CMB dipole asymmetry from a fast roll phase

TL;DR

This paper proposes a spectator field model with a temporary fast roll phase during inflation to explain the CMB dipole asymmetry, satisfying current observational constraints and avoiding large non-Gaussianity.

Contribution

It introduces a novel spectator field scenario with a fast roll phase to account for CMB dipole asymmetry, consistent with observational bounds.

Findings

The model explains dipole asymmetry without large non-Gaussianity.

It satisfies constraints from quasars, quadrupole, and octupole CMB measurements.

The scenario leaves no isocurvature perturbations.

Abstract

The observed CMB (cosmic microwave background) dipole asymmetry cannot be explained by a single field model of inflation - it inevitably requires more than one field where one of the fields is responsible for amplifying the super-Hubble fluctuations beyond the pivot scale. Furthermore the current constraints on $f_NL$ and $tau_NL$ require that such an amplification cannot produce large non-Gaussianity. In this paper we propose a model to explain this dipole asymmetry from a spectator field, which is responsible for generating all the curvature perturbations, but has a temporary fast roll phase before the Hubble exit of the pivot scale. The current data prefers spectator scenario because it leaves no isocurvature perturbations. The spectator model will also satisfy the well-known constraints arising from quasars, and the quadrupole and octupole of the CMB.