Matrix models on large graphs
Nuclear Physics B
We consider the spherical limit of multi-matrix models on regular target graphs, for instance single or multiple Potts models, or lattices of arbitrary dimension. We show, to all orders in the low temperature expansion, that when the degree of the target graph Δ→∞, the free energy becomes independent of the target graph, up to simple transformations of the matter coupling constant. Furthermore, this universal free energy contains contributions only from those surfaces which are made up of "baby
... universes" glued together into trees, all non-universal and non-tree contributions being suppressed by inverse powers of Δ. Each order of the free energy is put into a simple, algebraic form.