Relative mixed multiplicities and mixed Buchsbaum-Rim multiplicities

We define and study the natural multigraded extension of the relative multiplicities introduced by Simis, Ulrich and Vasconcelos. We call these new invariants relative mixed multiplicities. We show that they have a stable value equal to the mixed Buchsbaum-Rim multiplicity of Kleiman and Thorup. Furthermore, we prove that integral dependence and birationality can be detected via the vanishing of relative mixed multiplicities.