On the other hand, the other local fields except the gravitational field are not always localized on the brane even in the warped geometry. Indeed, in the Randall–Sundrum model in five dimensions [2], the following facts are well known: spin 0 field is localized on a brane with positive tension which also localizes the graviton while the spin 1/2 and 3/2 fields are localized not on a brane with positive tension but on a brane with negative tension [6]. Spin 1 field is not localized neither on a brane with positive tension nor on a brane with negative tension [7]. In six space–time dimensions, the spin 1 gauge field is also localized on the brane [8]. Thus, in order to fulfill the localization of Standard Model particles on a brane with positive tension, it seems that some additional interactions except the gravitational interaction must be also introduced in the bulk. There is a lot of papers devoted to the different localization mechanisms of the bulk fields in various brane world models.
