Wave function of the radion with a bulk scalar field

Abstract The behaviour of the distance between two branes (the ‘radion’) in a brane-world model with a bulk scalar field is investigated. We show that the BPS conditions of supergravity ensure that the dynamics of the scalar field and the radion are not independent; we derive the four-dimensional effective action, showing that the effective theory is of scalar–tensor nature, coupling the radion to four-dimensional gravity.