Boundary terms in brane worlds

We clarify the relation between orbifold and interval pictures in 5d brane worlds. We establish this correspondence for Z2-even and Z2-odd orbifold fields. In the interval picture Gibbons-Hawking terms are necessary to fulfill consistency conditions. We show how the brane world consistency conditions arise in the interval picture. We apply the procedure to the situation where the transverse dimension is terminated by naked singularities. In particular, we find the boundary terms needed when the naive vacuum action is infinite. (author)