Can we explain cosmic birefringence without a new light field beyond Standard Model?

TL;DR

This paper investigates whether the observed cosmic birefringence can be explained within the Standard Model Effective Field Theory or low-energy EFT, concluding that new light particles beyond the Standard Model are likely needed if the effect is confirmed.

Contribution

The study systematically rules out EFT operators within the Standard Model framework as explanations for the observed cosmic birefringence, suggesting the necessity of new light particles beyond the Standard Model.

Findings

EFT operators cannot produce the observed ICB angle.

Neutrino-photon interactions are too weak to account for ICB.

Confirmation of ICB would imply new light particles beyond the Standard Model.

Abstract

The recent analysis of the Planck 2018 polarization data shows a nonzero isotropic cosmic birefringence (ICB) that is not explained within the $\Lambda$CDM paradigm. We then explore the question of whether the nonzero ICB is interpreted by the framework of the Standard Model Effective Field Theory (SMEFT), or at the energy scales of the cosmic microwave background, the low-energy EFT (LEFT) whose dynamical degrees of freedom are five SM quarks and all neutral and charged leptons. Our systematic study reveals that any operator in the EFT on a cosmological background would not give the reported ICB angle, which is observationally consistent with frequency independence. In particular, we estimate the size of the ICB angle generated by the effect that the cosmic microwave background photons travel through the medium of the cosmic neutrino background with parity-violating neutrino-photon interactions and find that it would be too small to explain the data. If the reported ICB angle should be confirmed, then our result would indicate the existence of a new particle that is lighter than the electroweak scale and feebly interacting with the SM particles.