1509Non-commutative Donaldson-Thomas theory and vertex operators KENTARO NAGAO In [26], we introduced a variant of non-commutative Donaldson-Thomas theory in a combinatorial way, which is related to the topological vertex by a wall-crossing phenomenon. In this paper, we (1) provide an alternative definition in a geometric way, (2) show that the two definitions agree with each other and (3) compute the invariants using the vertex operator method, following Okounkov, Reshetikhin and Vafa [29] and Young [12]. The stability parameter in the geometric definition determines the order of the vertex operators and hence we can understand the wall-crossing formula in non-commutative Donaldson-Thomas theory as the commutator relation of the vertex operators.
14N35
IntroductionLet X WD˚x 1 x 2 D x 3 L C x 4 L « be an affine toric Calabi-Yau 3-fold, which corresponds to the trapezoid with height 1, with length L C edge at the top and L at the bottom. Let Y ! X be a crepant resolution of X . Note that Y has L C 2 affine lines as torus invariant closed subvarieties (L WD L C C L ). In other words, there are L C 2 open edges in the toric graph of Y . Given an .LC2/-tuple of Young diagrams . ; / D C ; ;.1=2/ ; : : : ; Let A be a non-commutative crepant resolution of the affine toric Calabi-Yau 3-fold X . We can identify the derived category of coherent sheaves on Y and the one of A -modules by a derived equivalence. A parameter gives a Bridgeland's stability condition of this derived category, and hence a core A of a t-structure on it (Definition 1.7). In fact, we have two specific parameters such that the corresponding t-structures coincide with the ones given by Y or A respectively. Given an element in A , we can restrict it to get a sheaf on the smooth locus X sm . Since the singular locus X sing is compact, it makes sense to study those elements in A which are isomorphic to I ; outside a compact subset of X , or in other words, those elements in A which have the same asymptotic behavior as I ; . We will study the moduli spaces of such objects as noncommutative analogues of M DT . ; /. In general the ideal sheaf I ; is not an element in A , however P ; WD H 0 A I ; is always in A . We will construct the moduli space M ncDT ; ; of quotients of P ; in A as a GIT quotient (Section 5.1). Note that M ncDT . ; ∅; ∅/ is the moduli space we have studied in [24]. We define Euler characteristic version of open non-commutative Donaldson-Thomas invariants by the Euler characteristics of the connected components of M ncDT . ; ; / 2 .The torus action on Y induces a torus action on the moduli M ncDT . ; ; /. We will compute the Euler characteristic by counting the number of torus fixed points. For a generic , the core A of the t-structure is isomorphic to the category of A -modules, where A is associated with a quiver with a potential. Hence, we can describe the torus fixed point set on M ncDT . ; ; / in terms of a crystal melting model (see Okounkov, Reshetikhin and Vafa [29] and Ooguri and Yamazaki [30]), which we have studied in [26]...