Extra force in brane worlds

By carefully analyzing the geodesic motion of a test particle in the bulk of brane worlds, we identify an extra force which is recognized in a spacetime of one lower dimension as a nongravitational force acting on the particle. Such extra force acts on the particle in such a way that the conventional particle mechanics in one lower dimension is violated, thereby hinting at the higher-dimensional origin of embedded spacetime in the brane world scenario. We obtain the explicit equations describing the motion of the bulk test particle as observed in one lower dimension for general gravitating configurations in brane worlds and identify the extra nongravitational force acting on the particle measured in one lower dimension.