Constraints on standard and non-standard early Universe models from CMB B-mode polarization

TL;DR

This paper compares three early Universe models using CMB B-mode polarization data, constrains their parameters with current measurements, and forecasts how future experiments can better test these models.

Contribution

It introduces a comparative analysis of standard and non-standard early Universe models through B-mode polarization signatures and provides current and future constraints.

Findings

Different models produce distinguishable B-mode features.

B-mode polarization offers a clean probe unaffected by parameter degeneracies.

Current data constrains tensor-to-scalar ratio, loop quantum parameters, and cosmic string tension.

Abstract

We investigate the observational signatures of three models of the early Universe in the $B$-mode polarization of the Cosmic Microwave Background (CMB) radiation. In addition to the standard single field inflationary model, we also consider the constraints obtainable on the loop quantum cosmology model (from Loop Quantum Gravity) and on cosmic strings, expected to be copiously produced during the latter stages of Brane inflation. We first examine the observational features of the three models, and then use current $B$-mode polarization data from the BICEP and QUaD experiments to constrain their parameters. We also examine the detectability of the primordial $B$-mode signal predicted by these models and forecast the parameter constraints achievable with future CMB polarization experiments. We find that: (a) these three models of the early Universe predict different features in the CMB B-mode polarization power spectrum, which are potentially distinguishable from the CMB experiments; (b) since $B$-mode polarization measurements are mostly unaffected by parameter degeneracies, they provide the cleanest probe of these early Universe models; (c) using the BICEP and QUaD data we obtain the following parameter constraints: $r=0.02^{+0.31}_{-0.26}$ ($1\sigma$ for the tensor-to-scalar ratio in the single field inflationary model); $m < 1.36\times 10^{-8} \text{M}_{\text{pl}}$ and $k_{*} < 2.43 \times 10^{-4} \text{Mpc}^{-1}$ ($1\sigma$ for the mass and scale parameters in the loop quantum cosmology model); and $G\mu < 5.77 \times 10^{-7}$ ($1\sigma$ for the cosmic string tension); (d) future CMB observations (both satellite missions and forthcoming sub-orbital experiments) will provide much more rigorous tests of these early Universe models.