On the 1-leg Donaldson-Thomas $\mathbb{Z}_2\times\mathbb{Z}_2$-vertex
Yijie Lin
TL;DR
This work addresses the open problem of an explicit formula for the 1-leg Donaldson-Thomas vertex of the orbifold $\mathbb{Z}_2\times\mathbb{Z}_2$. It introduces restricted pyramid configurations to encode leg-induced interlacing and identifies a unique symmetric interlacing class for staircase leg partitions $\nu=(m,m-1,\dots,1)$, enabling an explicit 1-leg $\mathbb{Z}_2\times\mathbb{Z}_2$-vertex formula via a connection to the 1-leg $\mathbb{Z}_4$-vertex using vertex-operator methods. The paper develops a detailed operator framework, proves the equality of two RPC families in the staircase case, and derives an explicit staircase formula that depends on $m\bmod 4$. It also clarifies the relation between the $\mathbb{Z}_2\times\mathbb{Z}_2$-vertex and the $\mathbb{Z}_4$-vertex, thereby establishing a concrete bridge between different orbifold DT vertices and providing a pathway for extending to more general leg partitions and higher-leg cases.
Abstract
We introduce a notion of restricted pyramid configurations for computing the 1-leg Donaldson-Thomas $\mathbb{Z}_2\times\mathbb{Z}_2$-vertex. We study a special type of restricted pyramid configurations with the prescribed 1-leg partitions, and find one unique class of them satisfying the symmetric interlacing property. This leads us to obtain an explicit formula for a class of 1-leg Donaldson-Thomas $\mathbb{Z}_2\times\mathbb{Z}_2$-vertex through establishing its connection with 1-leg Donaldson-Thomas $\mathbb{Z}_4$-vertex using the vertex operator methods of Okounkov-Reshetikhin-Vafa and Bryan-Young.
