Multi-centered first order formalism

We propose a first order formalism for multi-centered black holes with flat three-dimensional base-space, within the stu model of N = 2, D = 4 ungauged Maxwell- Einstein supergravity. This provides a unified description of first order flows of this uni- versal sector of all models with a symmetric scalar manifold which can be obtained by dimensional reduction from five dimensions. We develop a D = 3 Cartesian formalism which suitably extends the definition of central and matter charges, as well as of black hole effective potential and first order "fake" superpotential, in order to deal with not necessarily axisimmetric solutions, and thus with multi-centered and/or (under-)rotating extremal black holes. We derive general first order flow equations for composite non-BPS and almost BPS classes, and we analyze some of their solutions, retrieving various single-centered (static or under-rotating) and multi-centered known systems. As in the t 3 model, the almost BPS class turns out to split into two general branches, and the well known almost BPS system is shown to be a particular solution of the sec- ond branch.