Theta classes: generalized topological recursion, integrability and $\mathcal{W}$-constraints
Vincent Bouchard, Nitin K. Chidambaram, Alessandro Giacchetto, Sergey Shadrin
TL;DR
The paper proves that the generalized topological recursion on the (r,s) spectral curves computes the descendant integrals of the Θ^{r,s}-classes, linking intersection theory to integrable hierarchies. It shows the Θ^{r,s}-descendant potential Z^{r,s} is a tau function of the $r$-KdV hierarchy, with initial conditions expressed through explicit Θ-integrals, and derives explicit $\\mathcal{W}$-constraints via twist-field realizations of the $\\mathcal{W}(\\mathfrak{gl}_r)$-algebra. A second determinantal/ wave-function formalism is developed to obtain loop equations, which in special cases (notably s = r−1 and s = 1) determine Z^{r,s} uniquely through (shifted) Airy-structure frameworks; for other cases, a reduced potential remains unfixed, illustrating a nuanced landscape of integrability and constraints. The results extend known correspondences for $r$-spin, Θ-classes, and Norbury Θ-classes, and provide a unified setting for understanding how topological recursion, intersection theory, and integrable hierarchies intertwine in the (r,s) family.
Abstract
We study the intersection theory of the $Θ^{r,s}$-classes, where $r \geq 2$ and $1 \le s \le r-1$, which are cohomological field theories obtained as the top degrees of Chiodo classes. We show that the recently introduced generalized topological recursion on the $(r,s)$ spectral curves computes the descendant integrals of the $Θ^{r,s}$-classes. As a consequence, we deduce that the descendant potential of the $Θ^{r,s}$-classes is a tau function of the $r$-KdV hierarchy, generalizing the Brézin--Gross--Witten tau function (the special case $r=2$, $s=1$). We also explicitly compute the $\mathcal{W}$-constraints satisfied by the descendant potential, obtained as differential representations of the $\mathcal{W}(\mathfrak{gl}_r)$-algebra at self-dual level. This work extends previously known results on the Witten $r$-spin class, the $r$-spin $Θ$-classes (the case $s=r-1$), and the Norbury $Θ$-classes (the special case $r=2$, $s=1$).
