Brane World Solution To The Cosmological Constant Problem

We consider a model with two parallel (positive tension) 3-branes separated by a distance L in five-dimensional spacetime. If the interbrane space is anti-de Sitter, or is not precisely anti-de Sitter but contains no event horizons, the effective four-dimensional cosmological constant seen by observers on one of the branes (chosen to be the visible brane) becomes exponentially small as L grows large.