Cosmic Birefringence from Large Lepton Asymmetry
Abstract
Cosmic birefringence, the rotation of the polarization plane of cosmic microwave background (CMB) photons, provides an intriguing probe of physics beyond the Standard Model. In this paper, we investigate a vector Chern-Simons coupling between the neutrino current and photons as a possible origin of isotropic cosmic birefringence. Firstly, we perform the first analysis of anisotropic cosmic birefringence induced by the neutrino current. We find that the anisotropic signal sourced by lepton-number isocurvature fluctuations can be important on large scales, whereas on small scales, the anisotropic signal induced by gravitational effects becomes dominant comparing with the axion-like particle (ALP) scenario. Secondly, we show that a large lepton asymmetry generated through the Affleck-Dine mechanism can successfully account for the observed isotropic birefringence, and discuss its possible connection to the recently reported low helium-4 abundances in Subaru EMPRESS and Atacama Cosmology Telescope (ACT).
Related
- Distinguishing the origin of cosmic birefringence: dark energy, dark matter, and neutrino asymmetry
- Alleviating CMB-BAO tension with a large cosmic birefringence angle during reionization induced by energy injection to axion-like particles
- De-lensing cosmic birefringence with joint reconstruction
- Can cosmic neutrinos induce a cosmic birefringence signal?
- Cosmic Birefringence and Axiogenesis
BibTeX
@misc{kasai2026cosmic,
title = {{Cosmic Birefringence from Large Lepton Asymmetry}},
author = {Kentaro Kasai and Ippei Obata},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.09748},
eprint = {2610.09748},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.09748},
}
RIS
TY - UNPB
TI - Cosmic Birefringence from Large Lepton Asymmetry
AU - Kentaro Kasai
AU - Ippei Obata
PY - 2026
DA - 2026/10/28
PB - arXiv
DO - 10.48550/arxiv.2610.09748
UR - https://arxiv.org/abs/2610.09748
AB - Cosmic birefringence, the rotation of the polarization plane of cosmic microwave background (CMB) photons, provides an intriguing probe of physics beyond the Standard Model. In this paper, we investigate a vector Chern-Simons coupling between the neutrino current and photons as a possible origin of isotropic cosmic birefringence. Firstly, we perform the first analysis of anisotropic cosmic birefringence induced by the neutrino current. We find that the anisotropic signal sourced by lepton-number isocurvature fluctuations can be important on large scales, whereas on small scales, the anisotropic signal induced by gravitational effects becomes dominant comparing with the axion-like particle (ALP) scenario. Secondly, we show that a large lepton asymmetry generated through the Affleck-Dine mechanism can successfully account for the observed isotropic birefringence, and discuss its possible connection to the recently reported low helium-4 abundances in Subaru EMPRESS and Atacama Cosmology Telescope (ACT).
ER -