Abstract
Following up on a recent paper by two of us (DM and SS), demonstrating the large enhancement in observable optical activity in radiation from high red-shift sources arising from the string-based coupling of bulk Kalb–Ramond field to the Maxwell–Chern–Simons three-form on the brane in a Randall–Sundrum braneworld, we exhibit here a similar enhancement in parity-violating temperature–polarization correlations, as yet unseen, in the CMB anisotropy due to a generalized parity-violating Kalb–Ramond axion–photon interaction proposed earlier by one of us (PM). The non-observation of such correlations in CMB anisotropies would necessitate unnatural fine tuning of the Kalb–Ramond axion parameters. As a stringy realization of the Randall–Sundrum braneworld scenario is yet to be understood properly, our work indicates the need for a careful investigation to establish the connection between string-based phenomenological models and the Randall–Sundrum braneworld scenario.