Holography, probe branes and isoperimetric inequalities

In many instances of holographic correspondences between a d -dimensional boundary theory and a ( d+1 )-dimensional bulk, a direct argument in the boundary theory implies that there must exist a simple and precise relation between the Euclidean on-shell action of a (d−1) -brane probing the bulk geometry and the Euclidean gravitational bulk action. This relation is crucial for the consistency of holography, yet it is non-trivial from the bulk perspective. In particular, we show that it relies on a nice isoperimetric inequality that must be satisfied in a large class of Poincaré–Einstein spaces. Remarkably, this inequality follows from theorems by Lee and Wang