Twisted representations of vertex operator algebras associated to affine Lie algebras

In this paper, we prove the categories of lower bounded twisted modules of positive integer levels for simple vertex operator algebras associated with affine Lie algebras and general automorphisms are semisimple, using the twisted generalization of Zhu's algebra for these vertex operator algebras, constructed in \cite{HY}. We also show that the category of lower bounded twisted modules for a general automorphism is equivalent to the category of lower bounded twisted modules for the corresponding diagram automorphism.Comment: 20 pages, with some minor change

Vertex algebras associated to abelian current algebras

We construct a family of vertex algebras associated to the current algebra of finite-dimensional abelian Lie algebras along with their modules and logarithmic modules. We show this family of vertex algebras and their modules are quasi-conformal and strongly $\N$-graded and verify convergence and extension property needed in the logarithmic tensor category theory for strongly graded logarithmic modules developed by Huang, Lepowsky and Zhang.Comment: 24 pages, Comments are very welcome. arXiv admin note: text overlap with arXiv:math/0206206, arXiv:1012.4193 by other author

Differential equations and logarithmic intertwining operators for strongly graded vertex algebras

We derive certain systems of differential equations for matrix elements of products and iterates of logarithmic intertwining operators among strongly graded generalized modules for a strongly graded conformal vertex algebra under suitable assumptions. Using these systems of differential equations, we verify the convergence and extension property needed in the logarithmic tensor category theory for such strongly graded generalized modules developed by Huang, Lepowsky and Zhang.Comment: 26 pages. For the sake of readability, I quote certain necessary technical definitions from earlier work of Y.-Z. Huang, J. Lepowsky and L. Zhang [arXiv:0710.2687, arXiv:1012.4193, arXiv:math/0609833

On associative algebras, modules and twisted modules for vertex operator algebras

We give a new construction of functors from the category of modules for the associative algebras $A_n(V)$ and $A_g(V)$ associated with a vertex operator algebra $V$, defined by Dong, Li and Mason, to the category of admissible $V$-modules and admissible twisted $V$-modules, respectively, using the method developed in the joint work \cite{HY1} with Y.-Z. Huang. The functors were first constructed by Dong, Li and Mason, but the importance of the new method, as in \cite{HY1}, is that we can apply the method to study objects without the commutator formula in the representation theory of vertex operator algebras

Vertex algebraic intertwining operators among generalized Verma modules for sl(2,C)^\widehat{\mathfrak{sl}(2,\mathbb{C})}

We construct vertex algebraic intertwining operators among certain generalized Verma modules for $\widehat{\mathfrak{sl}(2,\mathbb{C})}$ and calculate the corresponding fusion rules. Additionally, we show that under some conditions these intertwining operators descend to intertwining operators among one generalized Verma module and two (generally non-standard) irreducible modules. Our construction relies on the irreducibility of the maximal proper submodules of generalized Verma modules appearing in the Garland-Lepowsky resolutions of standard $\widehat{\mathfrak{sl}(2,\mathbb{C})}$-modules. We prove this irreducibility using the composition factor multiplicities of irreducible modules in Verma modules for symmetrizable Kac-Moody Lie algebras of rank $2$, given by Rocha-Caridi and Wallach.Comment: 39 pages, updated version incorporates a comment of Antun Milas, who informed us that Theorem 3.8 can be proved using a result of Rocha-Caridi and Wallac

Associative algebras for (logarithmic) twisted modules for a vertex operator algebra

We construct two associative algebras from a vertex operator algebra $V$ and a general automorphism $g$ of $V$. The first, called $g$-twisted zero-mode algebra, is a subquotient of what we call $g$-twisted universal enveloping algebra of $V$. These algebras are generalizations of the corresponding algebras introduced and studied by Frenkel-Zhu and Nagatomo-Tsuchiya in the (untwisted) case that $g$ is the identity. The other is a generalization of the $g$-twisted version of Zhu's algebra for suitable $g$-twisted modules constructed by Dong-Li-Mason when the order of $g$ is finite. We are mainly interested in $g$-twisted $V$-modules introduced by the first author in the case that $g$ is of infinite order and does not act on $V$ semisimply. In this case, twisted vertex operators in general involve the logarithm of the variable. We construct functors between categories of suitable modules for these associative algebras and categories of suitable (logarithmic) $g$-twisted $V$-modules. Using these functors, we prove that the $g$-twisted zero-mode algebra and the $g$-twisted generalization of Zhu's algebra are in fact isomorphic.Comment: 43 pages. Corrected an imprecise statement about a region in the duality property in the definition of twisted modules. Corrected the formulas in the second statement in Theorem 4.1. Added more details in the proofs of Theorem 4.1 and Theorem 5.6. Corrected a number of typos and misprints and adjusted a number of sentence

On functors between module categories for associative algebras and for N\mathbb{N}-graded vertex algebras

We prove that the weak associativity for modules for vertex algebras are equivalent to a residue formula for iterates of vertex operators, obtained using the weak associativity and the lower truncation property of vertex operators, together with a known formula expressing products of components of vertex operators as linear combinations of iterates of components of vertex operators. By requiring that these two formulas instead of the commutator formula hold, we construct a functor $S$ from the category of modules for Zhu's algebra of a vertex operator algebra $V$ to the category of $\mathbb{N}$-gradable weak $V$-modules. We prove that $S$ has a universal property and the functor $T$ of taking top levels of $\mathbb{N}$-gradable weak $V$-modules is a left inverse of $S$. In particular, $S$ is equal to a functor implicitly given by Zhu and explicitly constructed by Dong, Li and Mason and we obtain a new construction without using relations corresponding to the commutator formula. The hard part of this new construction is a technical theorem stating roughly that in a module for Zhu's algebra, the relation corresponding to the residue formula mentioned above can in fact be obtained from the relations corresponding to the action of Zhu's algebra.Comment: 16 pages. Four spelling typos, including one in the abstract, are corrected. Everything else is the sam

Higher level Zhu algebras and modules for vertex operator algebras

Motivated by the study of indecomposable, nonsimple modules for a vertex operator algebra $V$, we study the relationship between various types of $V$-modules and modules for the higher level Zhu algebras for $V$, denoted $A_n(V)$, for $n \in \mathbb{N}$, first introduced by Dong, Li, and Mason in 1998. We resolve some issues that arise in a few theorems previously presented when these algebras were first introduced, and give examples illustrating the need for certain modifications of the statements of those theorems. We establish that whether or not $A_{n-1}(V)$ is isomorphic to a direct summand of $A_n(V)$ affects the types of indecomposable $V$-modules which can be constructed by inducing from an $A_n(V)$-module, and in particular whether there are $V$-modules induced from $A_n(V)$-modules that were not already induced by $A_0(V)$. We give some characterizations of the $V$-modules that can be constructed from such inducings, in particular as regards their singular vectors. To illustrate these results, we discuss two examples of $A_1(V)$: when $V$ is the vertex operator algebra associated to either the Heisenberg algebra or the Virasoro algebra. For these two examples, we show how the structure of $A_1(V)$ in relationship to $A_0(V)$ determines what types of indecomposable $V$-modules can be induced from a module for the level zero versus level one Zhu algebras. We construct a family of indecomposable modules for the Virasoro vertex operator algebra that are logarithmic modules and are not highest weight modules.Comment: 27 pages; "Zhu's algebra" changed to "Zhu algebra" throughout, including title; introduction revised; typos corrected; acknowledgements added; more details given in proof of Prop. 3.14; examples of modules added in Section 4.1 for the Heisenberg; errors in Section 4.2.1 for 1st Virasoro example corrected; clarification for central charge made in Section 4.2.3 for 3rd Virasoro exampl

Braided tensor categories of admissible modules for affine Lie algebras

Using the tensor category theory developed by Lepowsky, Zhang and the second author, we construct a braided tensor category structure with a twist on a semisimple category of modules for an affine Lie algebra at an admissible level. We conjecture that this braided tensor category is rigid and thus is a ribbon category. We also give conjectures on the modularity of this category and on the equivalence with a suitable quantum group tensor category. In the special case that the affine Lie algebra is $\widehat{\mathfrak{sl}}_2$, we prove the rigidity and modularity conjectures.Comment: Comments are welcom

Adaptive Stochastic Alternating Direction Method of Multipliers

The Alternating Direction Method of Multipliers (ADMM) has been studied for years. The traditional ADMM algorithm needs to compute, at each iteration, an (empirical) expected loss function on all training examples, resulting in a computational complexity proportional to the number of training examples. To reduce the time complexity, stochastic ADMM algorithms were proposed to replace the expected function with a random loss function associated with one uniformly drawn example plus a Bregman divergence. The Bregman divergence, however, is derived from a simple second order proximal function, the half squared norm, which could be a suboptimal choice. In this paper, we present a new family of stochastic ADMM algorithms with optimal second order proximal functions, which produce a new family of adaptive subgradient methods. We theoretically prove that their regret bounds are as good as the bounds which could be achieved by the best proximal function that can be chosen in hindsight. Encouraging empirical results on a variety of real-world datasets confirm the effectiveness and efficiency of the proposed algorithms.Comment: 13 page