We describe the formalism and the properties of the blobbed topological recursion, which provides the general solution of a set of abstract loop equations. This procedure extends the topological recursion by introducing extra terms (blobs) in the initial conditions for each multidifferential ωg,n. We apply this formalism to topological expansion of formal Hermitian matrix models (the blobs are necessary to include arbitrary interactions) and pose some open questions.This paper is a short, preliminary version of the extended electronic article [1].
Axiomatic definitionFunctional equations are encountered in the enumerative geometry of surfaces: Virasoro constraints (in matrix models and intersection theory over M g,n ), Tutte's equations (in map enumeration), cut-andjoin equations (in covering enumerations), etc. They have very similar natures, which has to do with the recursive construction of orientable surfaces. We introduced abstract loop equations in [2] as an attempt to write a universal set of equations, to which the abovementioned functional equations can be reduced, maybe after some problem-specific technical steps.
Abstract loop equations.Let U i , i ∈ I, be a finite collection of open sets that are complex one-dimensional manifolds with a distinguished point α i ∈ U i . We can take an arbitrary small neighborhood of α i as U i because our secret purpose is to speak of germs of functions and differential forms at α i . We assume that U i comes with a covering {x : U i → V i ⊆ C} that has a ramification point at α i . We also assume that all ramification points are simple, i.e., α i is a simple zero of dx, although the theory can be formulated for higher-order ramifications following [3], [4]. We then have a deck transformation ι : U i → U i , i.e., a holomorphic map such that x(ι(z)) = x(z) but ι = id (see Fig.