  A spacetime with torsion produced by a Kalb-Ramond field coupled
gravitationally to the Maxwell field, in accordance with a recent proposal by
two of us (PM and SS), is argued to lead to an optical activity in synchrotron
radiation from cosmologically distant radio sources. We suggest that this could
qualitatively explain observational data from a large number of radio sources
displaying such polarization asymmetry (after eliminating effects of Faraday
rotation due to magnetized galactic plasma). Possible implications for
heterotic string theory are also outlined.
