Confinement and stability of the motion of test particles in thick branes

Abstract We consider the motion of test particles in thick branes of ‘Randall–Sundrum II’-type. It is known that gravity alone cannot explain the confinement of test particles in this kind of brane. In this Letter we show that a stable confinement in a domain wall is possible by admitting a direct interaction between test particles and a scalar field. This interaction is implemented by a modification of the Lagrangian of the particle which is inspired by a Yukawa-type interaction between fermions and scalar fields.