How does a 2D gauge theory encode string theory coupling constants?

Matrix string theory proposes that a 2D supersymmetric gauge theory describes type-IIA strings. The theory's long-distance behavior is controlled by a symmetric product orbifold CFT, perturbed by the Dijkgraaf-Verlinde-Verlinde operator whose strength was unknown. Using non-renormalization theorems—symmetries that forbid certain corrections—the authors calculated this coefficient from first principles and showed it matches the string coupling constant, validating the duality.