CMB polarization anisotropies from cosmological reionization: extension to B-modes

TL;DR

This paper enhances the modeling of CMB polarization anisotropies, especially B-modes, by incorporating detailed reionization histories into a modified Boltzmann code, improving the interpretation of future cosmological data.

Contribution

It introduces a modified CAMB code to include realistic hydrogen and helium reionization histories beyond the simple { au}-parametrization, enabling more accurate predictions of CMB polarization signatures.

Findings

Reionization history significantly affects B-mode polarization shape and amplitude.

Accurate reionization modeling improves constraints on the tensor-to-scalar ratio, r.

Next-generation data can distinguish between different reionization scenarios.

Abstract

The accurate understanding of the ionization history of the Universe plays a fundamental role in modern cosmology. It includes a phase of cosmological reionization after the standard recombination epoch, possibly associated to the early stages of structure and star formation. While the simple "{\tau}-parametrization" of the reionization process and, in particular, of its imprints on the CMB anisotropy likely represents a sufficiently accurate modelling for the interpretation of current CMB data, a great attention has been recently posed on the accurate computation of the reionization signatures in the CMB for a large variety of astrophysical scenarios and physical processes. This work is aimed at a careful characterization of the imprints introduced in the polarization anisotropy, with particular attention to the B-modes. We have implemented a modified version of CAMB, the Cosmological Boltzmann code for computing the angular power spectrum (APS) of the anisotropies of the CMB, to introduce the hydrogen and helium ionization fractions predicted in astrophysical and phenomenological reionization histories, beyond the simple {\tau}-parametrization. We compared the results obtained for these models for all the non-vanishing (in the assumed scenarios) modes of the CMB APS. The amplitude and shape of the B-mode APS depends, in particular, on the tensor-to-scalar ratio, r, and on the reionization history, thus an accurate modeling of the reionization process will have implications for the precise determination of r or to set more precise constraints on it through the joint analysis of E and B-mode polarization data available in the next future and from a mission of next generation. Considering also the limitation from potential residuals of astrophysical foregrounds, we discussed the capability of next data to disentangle between different reionization scenarios in a wide range of r.