Cosmic optical activity in a Randall-Sundrum braneworld with bulk Kalb-Ramond field

Optical activity of electromagnetic waves in a string inspired Kalb-Ramond cosmological background is studied in the presence of an extra spacetime dimension. The Kalb-Ramond-electromagnetic coupling, which originates from the gauge anomaly cancelling Chem-Simons term in a string inspired model, is explicitly calculated following the Randall-Sundrum braneworld conjecture. It is shown that the Randall-Sundrum scenario leads to an enormous enhancement of the optical rotation of a plane polarized electromagnetic wave propagating on the visible brane. The absence of any experimental support in favour of such a large rotation in astrophysical experiments on distant galactic radio waves indicates an apparent conflict between the Randall-Sundrum braneworld scenario and the presence of the Kalb-Ramond antisymmetric tensor field in the background spacetime.