CMBR dipole from ultra large scale isocurvature perturbations

TL;DR

This paper proposes that the observed CMBR dipole could be caused by ultra large scale isocurvature perturbations generated during double inflation, offering an alternative to the peculiar motion explanation.

Contribution

It introduces a model where ultra large scale isocurvature perturbations from double inflation explain the CMBR dipole, challenging the conventional motion-based interpretation.

Findings

Ultra large scale isocurvature perturbations can account for the CMBR dipole.

Double inflation models can produce the necessary perturbations.

Alternative explanation reduces reliance on peculiar velocity assumptions.

Abstract

The observed CMBR dipole, generally interpreted as the consequence of the peculiar motion of the Sun with respect to the reference frame of the CMBR, can also be explained by the presence of ultra large scale (of the order of $100H_0^{-1}$) isocurvature perturbations. Moreover, the simplest model of inflation with several scalar fields, namely that of double inflation, with appropriate parameters, can produce such perturbations.