Cosmological birefringence constraints on light

We calculate the birefringence in the vacuum for light at the leading and sub-leading orders for the CPT-even part of the SME. We report that all the LIV coefficients absent in the leading order, but the isotropic one, contribute to the sub-leading order birefringence. We consider models free of the first order birefringence. We then show that infrared, optical, and ultraviolet spectropolarimetry of cosmological sources bound the LIV coefficients to less than 10−16. This improves the best current bound on the parity-odd coefficients by two orders of magnitude and establishes the isotropy of the one-way light speed with the precision of 41nms.