Forecasts of constraining isotropic cosmic birefringence on AliCPT-1

TL;DR

This paper forecasts the ability of the AliCPT experiment, combined with Planck data, to measure cosmic birefringence angle with high precision, accounting for instrumental and foreground effects.

Contribution

It presents a semi-analytical forecast method for constraining isotropic cosmic birefringence using AliCPT and Planck data, including effects of foregrounds and calibration.

Findings

AliCPT can achieve a measurement uncertainty of 0.09° after one year.

Uncertainty improves to 0.026° after four years of data collection.

Foreground modeling errors can cause biases, mitigated by observing small, clean sky patches.

Abstract

Cosmic birefringence (CB) is a promising probe of parity-violating physics beyond the Standard Model, characterized by the rotation of the linear polarization plane of cosmic microwave background (CMB) photons. This effect, quantified by the birefringence angle $\beta$, generates non-zero $EB$ and $TB$ correlations that are otherwise absent in standard cosmology. However, instrumental miscalibration angles $\alpha$ can mimic this signal, necessitating a joint estimation approach. In this work, we forecast the sensitivity of the AliCPT experiment, combined with Planck HFI data, on constraining the isotropic CB angle using a semi-analytical maximum-likelihood method. We simulate observations under various foreground complexities, rotation angles, and scanning strategies, and demonstrate that AliCPT can achieve an uncertainty of $\sigma(\beta)=0.09^\circ$ with one-year data, which will improve to $0.026^\circ$ after four years' observations. We also find that neglecting or mismodeling the foreground $EB$ correlation will introduce significant biases, which can be alleviated under a clean but small sky patch.