Searching for Anisotropic Cosmic Birefringence with Polarization Data from SPTpol

TL;DR

This paper searches for anisotropic cosmic birefringence using polarization data from SPTpol, setting upper limits on cosmic rotation and constraining primordial magnetic fields and Chern-Simons coupling, with no detection of a signal.

Contribution

First to place upper limits on anisotropic cosmic birefringence using SPTpol polarization data and cross-correlate with temperature fluctuations, constraining fundamental physics parameters.

Findings

No significant anisotropic birefringence detected.

Upper limit on cosmic rotation power spectrum amplitude.

Constraints on primordial magnetic fields and Chern-Simons coupling.

Abstract

We present a search for anisotropic cosmic birefringence in 500 deg$^2$ of southern sky observed at 150 GHz with the SPTpol camera on the South Pole Telescope. We reconstruct a map of cosmic polarization rotation anisotropies using higher-order correlations between the observed cosmic microwave background (CMB) $E$ and $B$ fields. We then measure the angular power spectrum of this map, which is found to be consistent with zero. The non-detection is translated into an upper limit on the amplitude of the scale-invariant cosmic rotation power spectrum, $L(L+1)C_L^{\alpha\alpha}/2\pi < 0.10 \times 10^{-4}$ rad$^2$ (0.033 deg$^2$, 95% C.L.). This upper limit can be used to place constraints on the strength of primordial magnetic fields, $B_{1 \rm Mpc} < 17 {\rm nG} $ (95% C.L.), and on the coupling constant of the Chern-Simons electromagnetic term $g_{a\gamma} < 4.0 \times 10^{-2}/H_I $ (95% C.L.), where $H_I$ is the inflationary Hubble scale. For the first time, we also cross-correlate the CMB temperature fluctuations with the reconstructed rotation angle map, a signal expected to be non-vanishing in certain theoretical scenarios, and find no detectable signal. We perform a suite of systematics and consistency checks and find no evidence for contamination.