Quantum effects, brane tension and large hierarchy in the brane-world

Semiclassical Einstein's equation with conformally invariant bulk matter fields is examined in the brane world scenario with the $S^1/Z_2$ compactification. Exact semiclassical solutions are obtained and it is suggested that, if Casimir-like energy is negative, it may be possible to take advantage of two different Randall-Sundrum scenarios by considering a positive tension for our brane and a fine-tuned tension for the hidden brane.