Tag Archives: topological recursion

Topological Recursion Meets Free Probability

Before I am getting too lazy and just re-post here information about summer schools or postdoc positions, I should of course also come back to the core of our business, namely to make progress on our main questions and to get excited about it. So there are actually two recent developments about which I am quite excited. Here is the first one, the second will come in the next post.

During the last few years there was an increasing belief that free probability (at least its higher order versions) and the theory of topological recursion should be related, maybe even just different sides of the same coin. So our communities started to have closer contacts, I started a project on this in our transregional collaborative research centre (SFB-TRR) 195, we had summer schools (here in Tübingen in 2018) and workshops (here in Münster in 2021) on possible interactions and finally there was the breakthrough paper Analytic theory of higher order free cumulants by Gaëtan Borot, Séverin Charbonnier, Elba Garcia-Failde, Felix Leid, Sergey Shadrin. This paper achieves, among other things, the solution to two of our big problems or dreams, namely:

  • Rewrite the combinatorial moment-cumulant relations into functional relations between the generating powers series; for first order this was done in Voiculescu’s famous formula relating the Cauchy and the R-transform going back to the beginnings of free probability in the 80s; for second order this was one of the main results in my paper with Benoit, Jamie and Piotr from 2007. For higher orders, however, this was wide open – and its amazing solution can now be found in the mentioned paper.
  • Is our theory of free probability only the planar (genus 0) sector of a more general theory which takes all genera into account? This is actually the idea of topological recursion, that you should consider all orders and genera and look for relations among them. I have to admit that I was always quite skeptic about defining the notion of freeness for non-planar situations – but it seems that the paper at hand provides a consistent theory for doing so; apparently also putting the notion of infinitesimial freeness into this setting.

Instead of having me mumbling more about all this, you might go right away to the paper and read its Introduction to get some more precise ideas about what this is all about and what actually is proved.

Let me also add that there is another interesting preprint, On the xy Symmetry of Correlators in Topological Recursion via Loop Insertion Operator by Alexander Hock, which also addresses the functional relations between moments and free cumulants in the g=0 case.

Mini-Workshop on Topological Recursion and Combinatorics

There will be an ACPMS mini-workshop on Friday, November 5, 15:00-19:30 (Oslo time) organised by Octavio Arizmendi Echegaray (CIMAT, Guanajuato, Mexico) and Kurusch Ebrahimi-Fard (NTNU Trondheim, Norway). This will be on topolocial recursion and combinatorics, with special emphasis also on the relation with various generalizations of free probability theory.

Title: Topological Recursion and Combinatorics

Topological recursion is a method of finding formulas for an infinite sequence of series or n-forms by means of describing them in a recursive way in terms of genus and boundary points of certain topological surfaces. While topological recursion was originally discovered in Random Matrix Theory, and could be traced back to the Harer-Zagier formula, it was until Chekhov, Eynard and Orantina (2007) that is was systematically studied. Since then it has found applications in different areas in mathematics and physics such as enumerative geometry, volumes of moduli spaces, Gromov-Witten invariants, integrable systems, geometric quantization, mirror symmetry, matrix models, knot theory and string theory. This 1/2-day series of seminar talks aims at exploring combinatorial aspects relevant to the theory of topological recursion in Random Matrix Models and to widen the bridge to free probability and its generalizations such as higher order freeness or infinitesimal freeness more transparent.

Date, time and place

  • November 5
  • 3:00pm – 7:30pm (Oslo time), 
  • Zoom (for the link write to the organisers)


  • Elba Garcia-Failde (Discussant: Reinier Kramer)
  • Séverin Charbonnier (Discussant: Octavio Arizmendi)
  • James Mingo (Discussant: Daniel Perales)
  • Jonathan Novak (Discussant: Danilo Lewański)

Titles, abstracts and schedule: