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The Atacama Cosmology Telescope: Constraints on Cosmic Birefringence

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arxiv 2001.10465 v2 pith:XZ4EXHSZ submitted 2020-01-28 astro-ph.CO hep-exhep-ph

The Atacama Cosmology Telescope: Constraints on Cosmic Birefringence

classification astro-ph.CO hep-exhep-ph
keywords birefringenceatacamaconstraintscosmiccosmologydegreespowerspectrum
verification ladder T0 review T1 audit T2 compute T3 formal T4 reserved
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We present new constraints on anisotropic birefringence of the cosmic microwave background polarization using two seasons of data from the Atacama Cosmology Telescope covering $456$ square degrees of sky. The birefringence power spectrum, measured using a curved-sky quadratic estimator, is consistent with zero. Our results provide the tightest current constraint on birefringence over a range of angular scales between $5$ arcminutes and $9$ degrees. We improve previous upper limits on the amplitude of a scale-invariant birefringence power spectrum by a factor of between $2$ and $3$. Assuming a nearly-massless axion field during inflation, our result is equivalent to a $2\,\sigma$ upper limit on the Chern-Simons coupling constant between axions and photons of $g_{\alpha\gamma}<4.0\times 10^{-2}/H_I$ where $H_I$ is the inflationary Hubble scale.

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