Smarr Mass formulas for BPS multicenter Black Holes

Abstract

Mass formulas for multicenter BPS 4D black holes are presented. For example, ADM mass for a two center BPS solution can be related to the intercencenter distance $r$, the angular momentum $J^2$, the dyonic charge vectors $q_i$ and the value of the scalar moduli at infinity ($z_\infty$)by $M_{ADM}^2 =A\left (1+ \alpha J^2\left(1+\frac{2M_{ADM}}{r}+\frac{A}{r^2}\right)\right)$ where $A(Q),\alpha(q_i)$ are symplectic invariant quantities ($Q$, the total charge vector) depending on the special geometry prepotential defining the theory. The formula predicts the existence of a continuos class, for fixed value of the charges, of BH's with interdistances $r\in (0,\infty)$ and $M_{ADM}\in (\infty,M_\infty)$. Smarr-like expressions incorporating the intercenter distance are obtained from it: $$ dM\equiv\Omega d J+\Phi_i d q_i+ F dr,$$ in addition to an effective angular velocity $\Omega$ and electromagnetic potentials $\Phi_i$, the equation allows to define an effective "force", $F$, acting between the centers. This effective force is always negative: at infinity we recover the familiar Newton law $F\sim 1/r^2$ while at short distances $F\sim f_0+f_1/r^2$. Similar results can be easily obtained for more general models and number of centers.