The purpose of this paper is to study quadratic color Hom-Lie algebras. We present some constructions of quadratic color Hom-Lie algebras which we use to provide several examples. We describe T * -extensions and central extensions of color Hom-Lie algebras and establish some cohomological characterizations.
IntroductionThe aim of this paper is to introduce and study quadratic color Hom-Lie algebras which are graded Hom-Lie algebras with ε-symmetric, invariant and nondegenerate bilinear forms. Color Lie algebras, originally introduced in [26] and [27], can be seen as a direct generalization of Lie algebras bordering Lie superalgebras. The grading is determined by an abelian group Γ and the definition involves a bicharacter function. Hom-Lie algebras are a generalization of Lie algebras, where the classical Jacobi identity is twisted by a linear map. Quadratic Hom-Lie algebras were studied in [9]. Γ-graded Lie algebras with quadratic-algebraic structures, that is Γ-graded Lie algebras provided with homogeneous, symmetric, invariant and nondegenerate bilinear forms, have been extensively studied specially in the case where Γ = Z 2 (see for example [2,6,7,8,11,24,28]). These algebras are called homogeneous (even or odd) quadratic Lie superalgebras. One of the fundamental results connected to homogeneous quadratic Lie superalgebras is to give its inductive descriptions. The main tool used to obtain these inductive descriptions is to develop some concept of double extensions. This concept was introduced by Medina and Revoy (see [24]) to give a classification of quadratic Lie algebras. The concept of T * -extension was introduced by Bordemann [? ]. Recently a generalization to the case of quadratic (even quadratic) color Lie algebras was obtained in [25] and [33]. They mainly generalized the double extension notion and its inductive descriptions.Hom-algebraic structures appeared first as a generalization of Lie algebras in [1,12,13] were the authors studied q-deformations of Witt and Virasoro algebras. A general study and construction of Hom-Lie algebras were considered in [18], [20]. Since then, other interesting Hom-type algebraic structures of many classical structures were studied as Hom-associative algebras, Hom-Lie admissible algebras and more general G-Hom-associative algebras [21], n-ary Hom-Nambu-Lie algebras [4], Hom-Lie admissible Hom-coalgebras and Hom-Hopf algebras [22], Hom-alternative algebras, Hom-Malcev algebras and Hom-Jordan algebras [15,22,36]. Hom-algebraic structures were extended to the case of Γ-graded Lie algebras by studying Hom-Lie superalgebras and Hom-Lie admissible superalgebras in [5]. Recently, the study of Hom-Lie algebras provided with quadratic-algebraic structures was initiated by S. Benayadi and A. Makhlouf in [9] and our purpose in this paper is to generalize this study to the case of color Hom-Lie algebras.