Multiloop realization of extended affine Lie algebras and Lie tori

Universal central extensions of twisted forms of split simple Lie algebras over rings

We give sufficient conditions for the descent construction to be the universal central extension of a twisted form of a split simple Lie algebra over a ring. In particular, the universal central extensions of twisted multiloop Lie tori are obtained by the descent construction.

Étale Descent of Derivations

We study étale descent of derivations of algebras with values in a module. The algebras under consideration are twisted forms of algebras over rings, and apply to all classes of algebras, notably associative and Lie algebras, such as the multiloop algebras that appear in the construction of extended affine Lie algebras.

Isotopy for extended affine Lie algebras and Lie tori

Centreless Lie tori have been used by E. Neher to construct all extended affine Lie algebras (EALAs). In this article, we study notions of isotopes and isotopy for centreless Lie tori, and we use these notions, along with Neher's construction, to show that there is a 1-1 correspondence between centreless Lie tori up to isotopy and families of EALAs up to isomorphism. Also, centreless Lie tori can be coordinatized by unital algebras that are in general nonassociative, and, for many types of centreless Lie tori, there are classical notions of isotopes and isotopy for the coordinate algebras. We …

Twisted semigroup algebras

We study 2-cocycle twists, or equivalently Zhang twists, of semigroup algebras over a field k. If the underlying semigroup is affine, that is abelian, cancellative and finitely generated, then Spec k[S] is an affine toric variety over k, and we refer to the twists of k[S] as quantum affine toric varieties. We show that every quantum affine toric varieties has a "dense quantum torus", in the sense that it has a localization isomorphic to a quantum torus. We study quantum affine toric varieties and show that many geometric regularity properties survive the deformation process.

Classification of quantum tori with involution

Quantum tori with graded involution appear as coordinate algebras of extended affine Lie algebras of type A_1, C and BC. We classify them in the category of algebras with involution. From this, we obtain precise information on the root systems of extended affine Lie algebras of type C.

Invariant bilinear forms of algebras given by faithfully flat descent

The existence of nondegenerate invariant bilinear forms is one of the most important tools in the study of Kac-Moody Lie algebras and extended affine Lie algebras. In practice, these forms are created, or shown to exist, either by assumption or in an ad hoc basis. The purpose of this work is to describe the nature of the space of invariant bilinear forms of certain algebras given by faithfully flat descent (which includes the affine Kac-Moody Lie algebras, as well as Azumaya algebras and multiloop algebras) within a functorial framework. This will allow us to conclude the existence, uniqueness…

量子环面与量子仿射空间中的二项式理想

Binomial ideals in quantum tori and quantum affine spaces

本文研究量子环面与量子仿射空间中的二项式理想，获得了交换多项式环已知结果的非交换类比，证明了本原理想、二项式理想的根及极小素理想均为二项式理想，并揭示了量子代数中二项式理想商的结构。

Derivations of certain algebras defined by étale descent

We give an explicit description of the Lie algebra of derivations for a class of infinite dimensional algebras which are given by étale descent. The algebras under consideration are twisted forms of central algebras over rings, and include the multiloop algebras that appear in the construction of extended affine Lie algebras.

New Lie tori from Naoi tori

We define general Lie tori which generalize original Lie tori. We show that a Naoi torus is a general Lie torus. We give examples and prove several properties of general Lie tori. We also review isotopies of Lie tori, and prove that a general Lie torus is, in fact, isotopic to an original Lie torus. Finally, we suggest a very simple way of defining a Lie torus corresponding to a locally extended affine root system R, which we call a Lie R-torus.

Unitary Lie Algebras and Lie Tori of Type BC_r, r \geq 3

A Lie G-torus of type X_r is a Lie algebra with two gradings -- one by an abelian group G and the other by the root lattice of a finite irreducible root system of type X_r. In this paper we construct a centreless Lie G-torus of type BC_r, which we call a unitary Lie G-torus, as it is a special unitary Lie algebra of a nondegenerate G-graded hermitian form of Witt index r over an associative torus with involution. We prove a structure theorem for centreless Lie G-tori of type BC_r, r \geq 3, that states that any such Lie torus is bi-isomorphic to a unitary Lie G-torus, and we determine necessar…

Lie G-Tori of Symplectic Type

We classify centerless Lie G-tori of type C_r including the most difficult case r=2 by applying techniques due to Seligman. In particular, we show that the coordinate algebra of a Lie G-torus of type C_2 is either an associative G-torus with involution or a Clifford G-torus. Our results generalize the classification of the core of the extended affine Lie algebras of type C_r by Allison and Gao.

From quantum Ore extensions to quantum tori via noncommutative UFDs

All iterated skew polynomial extensions arising from quantized universal enveloping algebras of Kac-Moody algebras are special examples of a very large, axiomatically defined class of algebras, called CGL extensions. For the purposes of constructing initial clusters for quantum cluster algebra structures on an algebra R, and classification of the automorphisms of R, one needs embeddings of R into quantum tori T which have the property that R contains the corresponding quantum affine space algebra A. We explicitly construct such an embedding A \subseteq R \subset T for each CGL extension R usin…

Structurable Tori

The classification of structurable tori with nontrivial involution, which was begun by Allison and Yoshii, is completed. New examples of structurable tori are obtained using a construction of structurable algebras from a semilinear version of cubic forms satisfying the adjoint identity. The classification uses techniques borrowed from quadratic forms over Z_2 and from the geometry of generalized quadrangles. Since structurable tori are the coordinate algebras for the centreless cores of extended affine Lie algebras of type BC_1, the results of this paper provide a classification and new exampl…