A DK Phase Transition in q-Deformed Yang-Mills on S^2 and Topological Strings
Daniel Jafferis, Joseph Marsano
TL;DR
The paper demonstrates a large-$N$ Douglas–Kazakov–type phase transition in q-deformed Yang–Mills theory on $S^2$ for $p>2$, driven by instanton contributions and studied in the ’t Hooft limit with a fixed $\lambda=g_{YM}^2 N$. It analyzes both $\theta=0$ and $\theta\neq 0$ cases, deriving a phase boundary in the $\lambda$–$\theta$ plane and arguing for a rich, multi-instanton structure that shapes the strong-coupling phase, including a strong-coupling saddle described by elliptic integrals. The work then turns to the chiral decomposition and the topological-string interpretation, showing that the trivial chiral block (topological string partition function) itself undergoes a phase transition at a different coupling than the full theory, signaling a breakdown of OSV-type factorization in the weak-coupling regime and revealing nonperturbative corrections to the factorization. Overall, the results reveal a nuanced phase structure in qYM on $S^2$ and its topological-string connections, with implications for understanding nonperturbative effects in OSV-like dualities and the dynamics of chiral blocks at large $N$.
Abstract
We demonstate the existence of a large $N$ phase transition with respect to the 't Hooft coupling in q-deformed Yang-Mills theory on $S^2$. The strong coupling phase is characterized by the formation of a clump of eigenvalues in the associated matrix model of Douglas-Kazakov (DK) type (hep-th/9305047). By understanding this in terms of instanton contributions to the q-deformed Yang-Mills theory, we gain some insight into the strong coupling phase as well as probe the phase diagram at nonzero values of the $θ$ angle. The Ooguri-Strominger-Vafa relation (hep-th/0405146) of this theory to topological strings on the local Calabi-Yau $\mathcal{O}(-p) \oplus \mathcal{O}(p-2) \to \mathbb{P}^1$ via a chiral decompostion at large $N$ hep-th/0411280, motivates us to investigate the phase structure of the trivial chiral block, which corresponds to the topological string partition function, for $p>2$. We find a phase transition at a different value of the coupling than in the full theory, indicating the likely presence of a rich phase structure in the sum over chiral blocks.
