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In mathematics, a Hopf algebra, ''H'', is quasitriangular〔Montgomery & Schneider (2002), (p. 72 ).〕 if there exists an invertible element, ''R'', of such that : * for all , where is the coproduct on ''H'', and the linear map is given by , : *, : *, where , , and , where , , and , are algebra morphisms determined by : : : ''R'' is called the R-matrix. As a consequence of the properties of quasitriangularity, the R-matrix, ''R'', is a solution of the Yang-Baxter equation (and so a module ''V'' of ''H'' can be used to determine quasi-invariants of braids, knots and links). Also as a consequence of the properties of quasitriangularity, ; moreover , , and . One may further show that the antipode ''S'' must be a linear isomorphism, and thus ''S2'' is an automorphism. In fact, ''S2'' is given by conjugating by an invertible element: where (cf. Ribbon Hopf algebras). It is possible to construct a quasitriangular Hopf algebra from a Hopf algebra and its dual, using the Drinfeld quantum double construction. ==Twisting== The property of being a quasi-triangular Hopf algebra is preserved by twisting via an invertible element such that and satisfying the cocycle condition : Furthermore, is invertible and the twisted antipode is given by , with the twisted comultiplication, R-matrix and co-unit change according to those defined for the quasi-triangular quasi-Hopf algebra. Such a twist is known as an admissible (or Drinfeld) twist. 抄文引用元・出典: フリー百科事典『 ウィキペディア(Wikipedia)』 ■ウィキペディアで「Quasitriangular Hopf algebra」の詳細全文を読む スポンサード リンク
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