Hemispherical Power Asymmetry from Scale-Dependent Modulated Reheating

TL;DR

This paper introduces a new modulated reheating model explaining the hemispherical power asymmetry in the CMB, involving a scale-dependent modulation of the primordial perturbations via a complex scalar field.

Contribution

It presents a novel mechanism where scale-dependent modulated reheating accounts for CMB asymmetry while satisfying observational constraints.

Findings

The model can reproduce the observed hemispherical asymmetry.

It remains consistent with bounds from non-Gaussianity and quasar counts.

Predicts modifications to the spectral index and its running.

Abstract

We propose a new model for the hemispherical power asymmetry of the CMB based on modulated reheating. Non-Gaussianity from modulated reheating can be small enough to satisfy the bound from Planck if the dominant modulation of the inflaton decay rate is linear in the modulating field $\sigma$. $\sigma$ must then acquire a spatially-modulated power spectrum with a red scale-dependence. This can be achieved if the primordial perturbation of $\sigma$ is generated via tachyonic growth of a complex scalar field. Modulated reheating due to $\sigma$ then produces a spatially modulated and scale-dependent sub-dominant contribution to the adiabatic density perturbation. We show that it is possible to account for the observed asymmetry while remaining consistent with bounds from quasar number counts, non-Gaussianity and the CMB temperature quadupole. The model predicts that the adiabatic perturbation spectral index and its running will be modified by the modulated reheating component.