Landau–Ginzburg limit of black holeʼs quantum portrait: Self-similarity and critical exponent

Recently we have suggested that the microscopic quantum description of a black hole is an overpacked self-sustained Bose-condensate of N weakly-interacting soft gravitons, which obeys the rules of ʼt Hooftʼs large-N physics. In this Letter we derive an effective Landau–Ginzburg Lagrangian for the condensate and show that it becomes an exact description in a semi-classical limit that serves as the black hole analog of ʼt Hooftʼs planar limit. The role of a weakly-coupled Landau–Ginzburg order parameter is played by N. This description consistently reproduces the known properties of black holes in semi-classical limit. Hawking radiation, as the quantum depletion of the condensate, is described by the slow-roll of the field N. In the semi-classical limit, where black holes of arbitrarily small size are allowed, the equation of depletion is self-similar leading to a scaling law for the black hole size with critical exponent 13.