A Projected Estimate of the Reionization Optical Depth Using the CLASS Experiment's Sample-Variance Limited E-Mode Measurement

TL;DR

This paper demonstrates that the CLASS experiment can achieve a near cosmic-variance limited estimate of the reionization optical depth $ au$, significantly improving constraints on cosmological parameters through advanced foreground cleaning and likelihood analysis.

Contribution

The study introduces a power spectrum-based likelihood method tailored for the CLASS experiment, enabling near cosmic-variance limited $ au$ estimation from simulated data.

Findings

CLASS can estimate $ au$ within a factor of two of the cosmic variance limit.

The $ au$ constraint enhances the measurement of the sum of neutrino masses.

The method effectively cleans foregrounds and constrains multiple cosmological parameters.

Abstract

We analyze simulated maps of the Cosmology Large Angular Scale Surveyor (CLASS) experiment and recover a nearly cosmic-variance limited estimate of the reionization optical depth $\tau$. We use a power spectrum-based likelihood to simultaneously clean foregrounds and estimate cosmological parameters in multipole space. Using software specifically designed to constrain $\tau$, the amplitude of scalar fluctuations $A_s$, and the tensor-to-scalar ratio $r$, we demonstrate that the CLASS experiment will be able to estimate $\tau$ within a factor of two of the full-sky cosmic variance limit allowed by cosmic microwave background polarization measurements. Additionally, we discuss the role of CLASS's $\tau$ constraint in conjunction with gravitational lensing of the CMB on obtaining a $\gtrsim4\sigma$ measurement of the sum of the neutrino masses.