  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
redshift 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, 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 Randall-Sundrum braneworld scenario is
yet to be understood properly, our work indicates the need of a careful
investigation to establish the connection between string-based phenomenological
models and the Randall-Sundrum braneworld scenario
