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Central Extensions of Root Graded Lie Algebras  [PDF]
Malihe Yousofzadeh
Mathematics , 2011,
Abstract: We study the central extensions of Lie algebras graded by an irreducible locally finite root system.
Graded Lie Algebras and dynamical systems  [PDF]
A. Vershik
Mathematics , 2002,
Abstract: The general class of the graded Lie algebras is defined. These algebras could be constructed using an arbitrary dynamical systems with discrete time and with invarinat measure. In this papers we consider the case of the central extension of Lie algebras which corresponds to the ordinary crossed product (as associative algebra) - series A. The structure of those Lie algebras is similar to Kac-Moody algebras, and these are a special case of so called algebras with continuous root system which were introduced by author with M.Saveliev in 90-th. The central extension open a new possibilty in algebraic theory of dynamical systems. The simpliest example corresponds to rotation of the circle (sine-algebra="quantum torus") and to adding of unity the additvie group of the p-adic integers.
Central extensions of null-filiform and naturally graded filiform non-Lie Leibniz algebras  [PDF]
J. K. Adashev,L. M. Camacho,B. A. Omirov
Mathematics , 2015,
Abstract: In this paper we describe central extensions of some nilpotent Leibniz algebras. Namely, central extensions of the Leibniz algebra with maximal index of nilpotency are classified. Moreover, non-split central extensions of naturally graded filiform non-Lie Leibniz algebras are described up to isomorphism. It is shown that $k$-dimensional central extensions ($k\geq 5$) of these algebras are split.
Multipoint Lax operator algebras. Almost-graded structure and central extensions  [PDF]
Martin Schlichenmaier
Mathematics , 2013, DOI: 10.1070/SM2014v205n05ABEH004396
Abstract: Recently, Lax operator algebras appeared as a new class of higher genus current type algebras. Based on I.Krichever's theory of Lax operators on algebraic curves they were introduced by I. Krichever and O. Sheinman. These algebras are almost-graded Lie algebras of currents on Riemann surfaces with marked points (in-points, out-points, and Tyurin points). In a previous joint article of the author with Sheinman the local cocycles and associated almost-graded central extensions are classified in the case of one in-point and one out-point. It was shown that the almost-graded extension is essentially unique. In this article the general case of Lax operator algebras corresponding to several in- and out-points is considered. In a first step it is shown that they are almost-graded. The grading is given by the splitting of the marked points which are non-Tyurin points into in- and out-points. Next, classification results both for local and bounded cocycles are shown. The uniqueness theorem for almost-graded central extensions follows. For this generalization additional techniques are needed which are presented in this article.
Adele residue symbol and Tate's central extension for multiloop Lie algebras  [PDF]
Oliver Braunling
Mathematics , 2012,
Abstract: We generalize the linear algebra setting of Tate's central extension to arbitrary dimension. In general, one obtains a Lie (n+1)-cocycle. We compute it explicitly. The construction is based on a Lie algebra variant of Beilinson's adelic multidimensional residue symbol, generalizing Tate's approach to the local residue symbol for 1-forms on curves.
Nonfiliform characteristically nilpotent Lie algebras  [PDF]
Jose Maria Ancochea-Bermudez,Otto Rutwig Campoamor-Stursberg
Mathematics , 2000,
Abstract: We construct large families of characteristically nilpotent Lie algebras by considering deformations of the Lie algebra g_{m,m-1}^{4} of type Q_{n},and which arises as a central extension fo the filiform Lie algebra L_{n}. By studying the graded cohomology spaces we obtain that the sill algebras are isomorphic to the nilradicals of solvable, complete Lie algebra laws. For extremal cocycles these laws are also rigid. Considering supplementary cocycles we construcy, for dimensions n>8, nonfiliform characteristically nilpotent Lie algebras and show that for certain deformations these are compatible with central extensions.
Higher genus affine algebras of Krichever - Novikov type  [PDF]
Martin Schlichenmaier
Mathematics , 2002,
Abstract: For higher genus multi-point current algebras of Krichever-Novikov type associated to a finite-dimensional Lie algebra, local Lie algebra two-cocycles are studied. They yield as central extensions almost-graded higher genus affine Lie algebras. In case that the Lie algebra is reductive a complete classification is given. For a simple Lie algebra, like in the classical situation, there is up to equivalence and rescaling only one non-trivial almost-graded central extension. The classification is extended to the algebras of meromorphic differential operators of order less or equal one on the currents algebra.
Higher Genus Affine Lie Algebras of Krichever -- Novikov Type  [PDF]
Martin Schlichenmaier
Mathematics , 2005,
Abstract: Classical affine Lie algebras appear e.g. as symmetries of infinite dimensional integrable systems and are related to certain differential equations. They are central extensions of current algebras associated to finite-dimensional Lie algebras g. In geometric terms these current algebras might be described as Lie algebra valued meromorphic functions on the Riemann sphere with two possible poles. They carry a natural grading. In this talk the generalization to higher genus compact Riemann surfaces and more poles is reviewed. In case that the Lie algebra g is reductive (e.g. g is simple, semi-simple, abelian, ...) a complete classification of (almost-) graded central extensions is given. In particular, for g simple there exists a unique non-trivial (almost-)graded extension class. The considered algebras are related to difference equations, special functions and play a role in Conformal Field Theory.
Graded filiform Lie algebras and symplectic nilmanifolds  [PDF]
Dmitri V. Millionschikov
Mathematics , 2002,
Abstract: We study symplectic (contact) structures on nilmanifolds that correspond to the filiform Lie algebras - nilpotent Lie algebras of the maximal length of the descending central sequence. We give a complete classification of filiform Lie algebras that possess a basis e_1, ..., e_n, [e_i,e_j]=c_{ij}e_{i{+}j} (N-graded Lie algebras). In particular we describe the spaces of symplectic cohomology classes for all even-dimensional algebras of the list. It is proved that a symplectic filiform Lie algebra is a filtered deformation of some N-graded symplectic filiform Lie algebra. But this condition is not sufficient. A spectral sequence is constructed in order to answer the question whether a given deformation of a N-graded symplectic filiform Lie algebra admits a symplectic structure or not. Other applications and examples are discussed.
Local cocycles and central extensions for multi-point algebras of Krichever-Novikov type  [PDF]
Martin Schlichenmaier
Mathematics , 2001,
Abstract: Multi-point algebras of Krichever Novikov type for higher genus Riemann surfaces are generalisations of the Virasoro algebra and its related algebras. Complete existence and uniqueness results for local 2-cocycles defining almost-graded central extensions of the functions algebra, the vector field algebra, and the differential operator algebra (of degree \le 1) are shown. This is applied to the higher genus, multi-point affine algebras to obtain uniqueness for almost-graded central extensions of the current algebra of a simple finite-dimensional Lie algebra. An earlier conjecture of the author concerning the central extension of the differential operator algebra induced by the semi-infinite wedge representations is proved.
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