Pre-inflationary genesis with CMB B-mode polarization

TL;DR

This paper proposes a pre-inflationary genesis phase that modifies the primordial tensor spectrum, potentially explaining recent B-mode polarization observations and predicting a large-scale anomaly in the BB power spectrum.

Contribution

It introduces a model with a genesis phase before inflation that causes a large-scale cutoff in the tensor spectrum, aligning with observations and predicting specific polarization features.

Findings

Large-scale cutoff in tensor spectrum with $n_T ightarrow 1$

Suppression of reionization bump in BB spectrum

Potential falsifiability with Planck polarization data

Abstract

Recent B-mode polarization observation seems to imply the tensor tilt $n_T\gtrsim 1$ at large angular scale, if the primordial signal is dominated. We show that for a primordial universe, which is in a slowly expanding genesis phase before the slow-roll inflation, the primordial tensor spectrum will get a large-scale cutoff, i.e. $n_T\gtrsim 1$ at large scales while $n_T\simeq 0$ at small scale. We find that this inflationary scenario not only may be consistent with the observation, but also predicts a large-scale anomaly in BB power spectrum, i.e. due to the large suppression of tensor perturbation amplitude we will hardly see the reionization bump at low-$l$, which may be falsified by the Planck polarization data.