Forecasts of CMB $E$-mode anomalies for AliCPT-1

TL;DR

This paper forecasts AliCPT-1's ability to detect large-scale CMB $E$-mode anomalies, using simulations to evaluate detection prospects and the impact of combining with other experiments.

Contribution

It introduces a comprehensive forecast of AliCPT-1's sensitivity to CMB $E$-mode anomalies and assesses the benefits of joint analysis with SO for anomaly detection.

Findings

AliCPT+SO can detect dipole modulation at 99% confidence.

AliCPT alone may have biases due to limited sky coverage.

Joint analysis restores full-sky statistical properties.

Abstract

The standard $\Lambda$CDM model has been highly successful in describing cosmic microwave background (CMB) observations. Nevertheless, a set of large-scale statistical anomalies persists in temperature anisotropies across WMAP and Planck. CMB $E$-mode polarization offers an independent probe of these anomalies, circumventing the look-elsewhere effect inherent in temperature-only analyses. In this paper, we forecast the capability of the Ali CMB Polarization Telescope (AliCPT), a ground-based CMB experiment in the Northern Hemisphere, to detect such anomalies in large-scale $E$-mode polarization. Using 1000 unconstrained simulations processed with the NILC component separation method, we evaluate four anomaly estimators: dipole modulation, lack of large-angle correlations, quadrupole-octopole alignment, and point-parity asymmetry. Our analysis considers two noise levels for AliCPT, as well as a joint configuration with Simons Observatory (SO) Large Aperture Telescope (LAT). For dipole modulation, we validate the local variance estimator on modulated simulations with an input amplitude $A_d = 0.07$, and find that the combined AliCPT+SO dataset is likely to detect the injected $E$-mode modulation at a 99% confidence level. Tests of the full suite of anomaly statistics on unconstrained isotropic simulations indicate that AliCPT alone, owing to its limited sky coverage, might introduce systematic biases or enlarged uncertainties, especially for quadrupole-octopole alignment and point-parity asymmetry. The combination with SO largely restores the statistical distributions to those expected in an ideal full-sky scenario, thereby establishing a near-cosmic-variance benchmark for upcoming anomaly investigations.