Taking limits in topological recursion

TL;DR

This paper establishes conditions under which topological recursion commutes with taking limits of spectral curves, ensuring analyticity and consistency in various deformation scenarios.

Contribution

It formalizes the notion of global topological recursion and provides criteria for its equivalence with local recursion, addressing a key gap in the understanding of limits.

Findings

Provided sufficient conditions for limit commutation in topological recursion

Reformulated conditions for algebraic curves based on singularity structure

Applied results to spectral curve deformations and Hurwitz numbers

Abstract

When does topological recursion applied to a family of spectral curves commute with taking limits? This problem is subtle, especially when the ramification structure of the spectral curve changes at the limit point. We provide sufficient (straightforward-to-use) conditions for checking when the commutation with limits holds, thereby closing a gap in the literature where this compatibility has been used several times without justification. This takes the form of a stronger result of analyticity of the topological recursion along suitable families. To tackle this question, we formalise the notion of global topological recursion and provide sufficient conditions for its equivalence with local topological recursion. The global version facilitates the study of analyticity and limits. For nondegenerate algebraic curves, we reformulate these conditions purely in terms of the structure of its underlying singularities. Finally, we apply this to study deformations of $ (r,s) $-spectral curves, spectral curves for weighted Hurwitz numbers, and provide several other examples and non-examples (where the commutation with limits fails).