We show that a non-minimal coupling of electromagnetism with background torsion can produce birefringence of the electromagnetic waves. This birefringence gives rise to a B-mode polarization of the CMB. From the bounds on B-mode from WMAP and BOOMERanG data, one can put limits on the background torsion at ξ1T1=(−3.35±2.65)×10−22GeV−1.
@article{arxiv.0908.0629,
title = {Constraints on background torsion from birefringence of CMB polarization},
author = {Moumita Das and Subhendra Mohanty and A. R. Prasanna},
journal= {arXiv preprint arXiv:0908.0629},
year = {2009}
}