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This is a continuation of a previous study initiated by the third author on nonlocal vertex bialgebras and smash product nonlocal vertex algebras. In this paper, we study a notion of right H -comodule nonlocal vertex algebra for a nonlocal vertex bialgebra H and give a construction of deformations of vertex algebras with a right H -comodule nonlocal vertex algebra structure and a compatible H -module nonlocal vertex algebra structure. We also give a construction of ϕ -coordinated quasi modules for smash product nonlocal vertex algebras. As an example, we give a family of quantum vertex algebras by deforming the vertex algebras associated to non-degenerate even lattices. [ABSTRACT FROM AUTHOR]

The conjugate-linear anti-involutions and unitary irreducible modules of the intermediate series over the twisted Heisenberg–Virasoro algebra are classified, respectively. We prove that any unitary irreducible module of the intermediate series over the twisted Heisenberg–Virasoro algebra is of the form A a , b , c for a ∈ ℝ , b ∈ 1 2 + − 1 ℝ and c ∈ ℂ. [ABSTRACT FROM AUTHOR]

In this paper, we study a family of infinite-dimensional Lie algebras X ˆ S , where X stands for the type: A , B , C , D , and S is an abelian group, which generalize the A , B , C , D series of trigonometric Lie algebras. Among the main results, we identify X ˆ S with what are called the covariant algebras of the affine Lie algebra L S ˆ with respect to some automorphism groups, where L S is an explicitly defined associative algebra viewed as a Lie algebra. We then show that restricted X ˆ S -modules of level ℓ naturally correspond to equivariant quasi modules for affine vertex algebras related to L S. Furthermore, for any finite cyclic group S , we completely determine the structures of these four families of Lie algebras, showing that they are essentially affine Kac-Moody Lie algebras of certain types. [ABSTRACT FROM AUTHOR]

Abstract: We develop a theory of toroidal vertex algebras and their modules, and we give a conceptual construction of toroidal vertex algebras and their modules. As an application, we associate toroidal vertex algebras and their modules to toroidal Lie algebras. [Copyright &y& Elsevier]

Abstract: We study twisted modules for (weak) quantum vertex algebras and we give a conceptual construction of (weak) quantum vertex algebras and their twisted modules. As an application we construct and classify irreducible twisted modules for a certain family of quantum vertex algebras. [Copyright &y& Elsevier]

Let sl N ˆ (C q) be the core of extended affine Lie algebra of type A N − 1 coordinated by the rational quantum 2-torus C q. In this paper, we first prove that for any complex number ℓ , the category of restricted sl N ˆ (C q) -modules of level ℓ is canonically isomorphic to the category of twisted modules for the vertex algebra V C g ˆ (ℓ , 0) arising from a conformal Lie algebra C g , where C g ˆ is isomorphic to a toroidal Lie algebra. Then we prove that for any nonnegative integer ℓ , the integrable restricted sl N ˆ (C q) -modules of level ℓ are exactly the twisted modules for the quotient vertex algebra L C g ˆ (ℓ , 0) of V C g ˆ (ℓ , 0). Finally, we classify irreducible graded twisted L C g ˆ (ℓ , 0) -modules. [ABSTRACT FROM AUTHOR]

In this paper, we introduce an infinite-dimensional Lie algebra D S for any abelian group S. If S is the additive group of integers, D S reduces to the q -Virasoro algebra D q introduced by Belov and Chaltikian in the study of lattice conformal theories. Guided by the theory of equivariant quasi modules for vertex algebras, we introduce another Lie algebra g S with S as an automorphism group and we prove that D S is isomorphic to the S -covariant algebra of the affine Lie algebra g S ˆ. We then relate restricted D S -modules of level ℓ ∈ C to equivariant quasi modules for the vertex algebra V g S ˆ (ℓ , 0) associated to g S ˆ with level ℓ. Furthermore, we establish an intrinsic connection between the q -Virasoro algebra D q and affine Kac-Moody Lie algebras. More specifically, we show that if S is a finite abelian group of order 2 l + 1 , D S is isomorphic to the affine Kac-Moody algebra of type B l (1). [ABSTRACT FROM AUTHOR]

In this paper, we continue the study on toroidal vertex algebras initiated in [15] , to study concrete toroidal vertex algebras associated to toroidal Lie algebra L r ( g ˆ ) = g ˆ ⊗ L r , where g ˆ is an untwisted affine Lie algebra and L r = C [ t 1 ± 1 , … , t r ± 1 ] . We first construct an ( r + 1 ) -toroidal vertex algebra V ( T , 0 ) and show that the category of restricted L r ( g ˆ ) -modules is canonically isomorphic to that of V ( T , 0 ) -modules. Let c denote the standard central element of g ˆ and set S c = U ( L r ( C c ) ) . We furthermore study a distinguished subalgebra of V ( T , 0 ) , denoted by V ( S c , 0 ) . We show that (graded) simple quotient toroidal vertex algebras of V ( S c , 0 ) are parametrized by a Z r -graded ring homomorphism ψ : S c → L r such that Im ψ is a Z r -graded simple S c -module. Denote by L ( ψ , 0 ) the simple quotient ( r + 1 ) -toroidal vertex algebra of V ( S c , 0 ) associated to ψ . We determine for which ψ , L ( ψ , 0 ) is an integrable L r ( g ˆ ) -module and we then classify irreducible L ( ψ , 0 ) -modules for such a ψ . For our need, we also obtain various general results. [ABSTRACT FROM AUTHOR]

In this paper, we study a certain deformation D of the Virasoro algebra that was introduced and called q -Virasoro algebra by Belov and Chaltikian, in the context of vertex algebras. Among the main results, we prove that for any complex number ℓ , the category of restricted D -modules of level ℓ is canonically isomorphic to the category of quasi modules for a certain vertex algebra of affine type. We also prove that the category of restricted D -modules of level ℓ is canonically isomorphic to the category of Z -equivariant ϕ -coordinated quasi modules for the same vertex algebra. In the process, we introduce and employ a certain infinite dimensional Lie algebra which is defined in terms of generators and relations and then identified explicitly with a subalgebra of gl ∞ . [ABSTRACT FROM AUTHOR]

In this paper we study the representation theory for certain “half lattice vertex algebras.” In particular we construct a large class of irreducible modules for these vertex algebras. We also discuss how the representation theory of these vertex algebras are related to the representation theory of some associative algebras. [Copyright &y& Elsevier]

In this paper, we study (G , χ ϕ) -equivariant ϕ -coordinated quasi modules for nonlocal vertex algebras. Among the main results, we establish several conceptual results, including a generalized commutator formula and a general construction of weak quantum vertex algebras and their (G , χ ϕ) -equivariant ϕ -coordinated quasi modules. As an application, we also construct (equivariant) ϕ -coordinated quasi modules for lattice vertex algebras by using Lepowsky's work on twisted vertex operators. [ABSTRACT FROM AUTHOR]

In this paper we introduce a new quantum algebra which specializes to the 2-toroidal Lie algebra of type A 1. We prove that this quantum toroidal algebra has a natural triangular decomposition, a (topological) Hopf algebra structure and a vertex operator realization. [ABSTRACT FROM AUTHOR]