CONSTRAINTS ON BACKGROUND TORSION FROM BIREFRINGENCE OF CMB POLARIZATION.

We show that a nonminimal 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 CMB polarization from QUaD experiment, one can put limits on the background torsion at ξ1Ti = (2.78 ± 4.85) × 10-20 GeV-1. [ABSTRACT FROM AUTHOR]