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A locally compact quantum group is a relatively new C *-algebraic approach toward quantum groups that generalizes the Kac-algebra, compact-quantum-group and Hopf-algebra approaches. Earlier attempts at a unifying definition of quantum groups using, for example, multiplicative unitaries have enjoyed some success but have also encountered several technical problems. One of the main features distinguishing this new approach from its predecessors is the axiomatic existence of left and right invariant weights. This gives a noncommutative analogue of left and right Haar measures on a locally compact Hausdorff group. == Definitions == Before we can even begin to properly define a locally compact quantum group, we first need to define a number of preliminary concepts and also state a few theorems. Definition (weight). Let be a C *-algebra, and let denote the set of positive elements of . A weight on is a function such that * for all , and * for all a weight on . We say that is a K.M.S. weight ('K.M.S.' stands for 'Kubo-Martin-Schwinger') on if and only if is a ''proper weight'' on and there exists a norm-continuous one-parameter group for all , and * for every , we have is a dense subset of ), then we can uniquely extend to a *-homomorphism . Theorem 3. If is a state (i.e., a positive linear functional of norm ) on , then we can uniquely extend to a state on . Definition (Locally compact quantum group). A (C *-algebraic) locally compact quantum group is an ordered pair , where is a C *-algebra and is a ''non-degenerate'' *-homomorphism called the co-multiplication, that satisfies the following four conditions: * The co-multiplication is co-associative, i.e., . * The sets and are linearly dense subsets of . * There exists a faithful K.M.S. weight on that is left-invariant, i.e., for all and . * There exists a K.M.S. weight on that is right-invariant, i.e., for all and . From the definition of a locally compact quantum group, it can be shown that the right-invariant K.M.S. weight is automatically faithful. Therefore, the faithfulness of is a redundant condition and does not need to be postulated. 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「Locally compact quantum group」の詳細全文を読む スポンサード リンク
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