nπ Phase Ambiguity of Cosmic Birefringence

Area of Science:

• Cosmology
• Particle Physics

Background:

• Cosmic birefringence is a recently observed parity-violating signal in the cosmic microwave background (CMB).
• The rotation angle of cosmic birefringence has a phase ambiguity (nπ), complicating the interpretation of its origin.

Purpose of the Study:

• To address the phase ambiguity in cosmic birefringence measurements.
• To investigate the potential origin of cosmic birefringence from axionlike particles (ALPs).
• To forecast constraints on the ambiguity parameter 'n' from current and future experiments.

Main Methods:

• Analyzing the impact of the phase ambiguity on CMB angular power spectra.
• Utilizing anisotropic cosmic birefringence and spectral shapes to break the ambiguity.
• Forecasting constraints on 'n' using E-mode and B-mode cross-power spectra.
• Investigating the reionization bump in the E-mode auto-power spectrum.

Main Results:

• The ambiguity in cosmic birefringence can be partly resolved by anisotropic signals and CMB power spectra shapes.
• Most non-zero values of 'n' can be excluded using E-B mode cross-power spectra.
• The reionization bump offers further constraints on 'n' if optical depth (τ) is independently determined.
• Low-l E-mode power spectrum changes may help resolve the tension in τ.

Conclusions:

• The phase ambiguity of cosmic birefringence is a critical factor for understanding its origin, possibly linked to ALPs.
• Future CMB experiments can significantly constrain the ambiguity parameter 'n'.
• This research offers potential solutions to existing cosmological tensions, particularly regarding optical depth measurements.