Atacama Cosmology Telescope: Constraints on cosmic birefringence
Toshiya Namikawa, Yilun Guan, Omar Darwish, Blake D. Sherwin, Simone Aiola, Nicholas Battaglia, James A. Beall, Daniel Becker, J. Richard Bond, Erminia Calabrese, Grace E. Chesmore, Steve K. Choi, Mark J. Devlin, Joanna Dunkley, Rolando Dünner, Anna E. Fox, Patricio A. Gallardo, Vera Gluscevic, Dongwon Han, Matthew Hasselfield, G. C. Hilton, Adam D. Hincks, Renée Hložek, Johannes Hubmayr, K. M. Huffenberger, John P. Hughes, Brian J. Koopman, Arthur Kosowsky, Thibaut Louis, Marius Lungu, Amanda MacInnis, Mathew S. Madhavacheril, Maya Mallaby-Kay, L. Maurin, Jeffrey McMahon, Kavilan Moodley, Sigurd Næss, F. Nati, Laura Newburgh, J. P. Nibarger, Michael D. Niemack, Lyman A. Page, Frank J. Qu, Naomi Robertson, A. Schillaci, Neelima Sehgal, Cristobál Sifón, Sara M. Simon, David N. Spergel, Suzanne T. Staggs, Émilie Storer, Alexander van Engelen, Jeff Van Lanen, Edward J. Wollack
Abstract
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 arc minutes and 9\ifmmode^\circ\else\textdegree\fi{}. 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 $2\ensuremath{\sigma}$ upper limit on the Chern-Simons coupling constant between axions and photons of ${g}_{\ensuremath{\alpha}\ensuremath{\gamma}}<4.0\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}2}/{H}_{I}$, where ${H}_{I}$ is the inflationary Hubble scale.