Superhorizon Perturbations and the Cosmic Microwave Background

TL;DR

This paper investigates how superhorizon perturbations affect the CMB temperature anisotropies, deriving constraints on their amplitude and wavelength, and examining implications for the hemispherical power asymmetry.

Contribution

It demonstrates that adiabatic superhorizon perturbations in a LCDM universe do not produce a CMB dipole and establishes bounds based on quadrupole and octupole measurements, also analyzing curvaton field fluctuations.

Findings

Superhorizon adiabatic perturbations do not generate a CMB dipole.

Constraints on amplitude and wavelength of superhorizon perturbations from CMB data.

Implications for curvaton field fluctuations and hemispherical asymmetry.

Abstract

Superhorizon perturbations induce large-scale temperature anisotropies in the cosmic microwave background (CMB) via the Grishchuk-Zel'dovich effect. We analyze the CMB temperature anisotropies generated by a single-mode adiabatic superhorizon perturbation. We show that an adiabatic superhorizon perturbation in a LCDM universe does not generate a CMB temperature dipole, and we derive constraints to the amplitude and wavelength of a superhorizon potential perturbation from measurements of the CMB quadrupole and octupole. We also consider constraints to a superhorizon fluctuation in the curvaton field, which was recently proposed as a source of the hemispherical power asymmetry in the CMB.