Strongly scale-dependent CMB dipolar asymmetry from super-curvature fluctuations

TL;DR

This paper explores how super-curvature fluctuations in open inflation models can naturally produce the observed scale-dependent CMB dipolar asymmetry, aligning with current data without fine-tuning.

Contribution

It introduces a three-field open inflation model with quadratic potentials and a non-trivial field-space metric that explains the scale-dependent dipolar asymmetry in the CMB.

Findings

Current data can be explained by the model

The model reproduces the observed scale dependence

No fine-tuning or special initial conditions needed

Abstract

We reconsider the observed CMB dipolar asymmetry in the context of open inflation, where a supercurvature mode might survive the bubble nucleation. If such a supercurvature mode modulates the amplitude of the curvature power spectrum, it would easily produce an asymmetry in the power spectrum. We show that current observational data can be accommodated in a three-field model, with simple quadratic potentials and a non-trivial field-space metric. Despite the presence of three fields, we believe this model is so far the simplest that can match current observations. We are able to match the observed strong scale dependence of the dipolar asymmetry, without a fine tuning of initial conditions, breaking slow roll or adding a feature to the evolution of any field.