Probing Anisotropic Cosmic Birefringence with Foreground-Marginalised SPT B-mode Likelihoods

In this work, we construct foreground-marginalised versions of the SPT-3G D1 and SPTpol cosmic microwave background (CMB) B-mode polarisation likelihoods. The compression is performed using the CMB-lite framework and we use the resulting data sets to constrain anisotropic cosmic birefringence, parametrised by the amplitude of a scale-invariant anisotropic birefringence spectrum, . Using the new SPT-3G data we report a <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow> <mml:mn>95</mml:mn> <mml:mi>%</mml:mi> </mml:mrow> </mml:math> upper limit on of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow> <mml:mn>1.2</mml:mn> <mml:mo>×</mml:mo> <mml:msup> <mml:mn>10</mml:mn> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>4</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:math> , which tightens to <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow> <mml:mn>0.53</mml:mn> <mml:mo>×</mml:mo> <mml:msup> <mml:mn>10</mml:mn> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>4</mml:mn> </mml:mrow> </mml:msup> </mml:mrow> </mml:math> when imposing a prior on the amplitude of gravitational lensing based on CMB lensing reconstruction analyses. These are the tightest constraints on anisotropic birefringence from BB power spectrum measurements to-date, demonstrating the constraining power of the South Pole Telescope. The likelihoods used in this work are made publicly available at https://github.com/lbalkenhol/candl_data