Self-calibration of BICEP1 three-year data and constraints on astrophysical polarization rotation
Cosmic microwave background (CMB) polarimeters aspire to measure the faint B-mode signature predicted to arise from inflationary gravitational waves. They also have the potential to constrain cosmic birefringence, rotation of the polarization of the CMB arising from parity-violating physics, which would produce nonzero expectation values for the CMB's temperature to B-mode correlation (TB) and E-mode to B-mode correlation (EB) spectra. However, instrumental systematic effects can also cause these TB and EB correlations to be nonzero. In particular, an overall miscalibration of the polarization orientation of the detectors produces TB and EB spectra which are degenerate with isotropic cosmological birefringence, while also introducing a small but predictable bias on the BB spectrum. We find that Bicep1 three-year spectra, which use our standard calibration of detector polarization angles from a dielectric sheet, are consistent with a polarization rotation of α=−2.77°±0.86°(statistical)±1.3°(systematic). We have revised the estimate of systematic error on the polarization rotation angle from the two-year analysis by comparing multiple calibration methods. We also account for the (negligible) impact of measured beam systematic effects. We investigate the polarization rotation for the Bicep1 100 GHz and 150 GHz bands separately to investigate theoretical models that produce frequency-dependent cosmic birefringence. We find no evidence in the data supporting either of these models or Faraday rotation of the CMB polarization by the Milky Way galaxy's magnetic field. If we assume that there is no cosmic birefringence, we can use the TB and EB spectra to calibrate detector polarization orientations, thus reducing bias of the cosmological B-mode spectrum from leaked E-modes due to possible polarization orientation miscalibration. After applying this "self-calibration" process, we find that the upper limit on the tensor-to-scalar ratio decreases slightly, from r<0.70 to r<0.65 at 95% confidence.
Additional Information© 2014 American Physical Society. Received 22 January 2014; published 24 March 2014. BICEP1 was supported by NSF Grant No. OPP-0230438, Caltech Presidents Discovery Fund, Caltech Presidents Fund PF-471, JPL Research and Technology Development Fund, and the late J. Robinson. This analysis was supported in part by NSF CAREER Award No. AST- 1255358 and the Harvard College Observatory, and J. M. K. acknowledges support from an Alfred P. Sloan Research Fellowship. B. G. K acknowledges support from NSF PECASE Award No. AST-0548262. N. J.M.'s research was supported by an appointment to the NASA Postdoctoral Program at Goddard Space Flight Center, administered by Oak Ridge Associated Universities through a contract with NASA. M. S. acknowledges support from a grant from Joan and Irwin Jacobs. We thank the South Pole Station staff for helping make our observing seasons a success. We also thank our colleagues in the ACBAR, BOOMERANG, QUAD, BOLOCAM, SPT, WMAP and Planck experiments, as well as Kim Griest, Amit Yadav, and Casey Conger for advice and helpful discussions, and Kathy Deniston and Irene Coyle for logistical and administrative support. We thank Patrick Shopbell for computational support at Caltech and the FAS Science Division Research Computing Group at Harvard University for providing support to run all the computations for this paper on the Odyssey cluster.
Published - PhysRevD.89.062006.pdf
Submitted - 1312.7877v1.pdf