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Verma modules, named after Daya-Nand Verma, are objects in the representation theory of Lie algebras, a branch of mathematics. Verma modules can be used to prove that an irreducible highest weight module with highest weight is finite-dimensional, if and only if the weight is dominant and integral. Their homomorphisms correspond to invariant differential operators over flag manifolds. ==Definition of Verma modules== The definition relies on a stack of relatively dense notation. Let be a field and denote the following: * , a semisimple Lie algebra over , with universal enveloping algebra . * , a Borel subalgebra of , with universal enveloping algebra . * , a Cartan subalgebra of . We do not consider its universal enveloping algebra. * , a fixed weight. To define the Verma module, we begin by defining some other modules: * , the one-dimensional -vector space (i.e. whose underlying set is itself) together with a -module structure such that acts as multiplication by and the positive root spaces act trivially. As is a left -module, it is consequently a left -module. * Using the Poincaré–Birkhoff–Witt theorem, there is a natural right -module structure on by right multiplication of a subalgebra. is naturally a left -module, and together with this structure, it is a -bimodule. Now we can define the Verma module (with respect to ) as : which is naturally a left -module (i.e. a representation of ). The Poincaré–Birkhoff–Witt theorem implies that the underlying vector space of is isomorphic to : where is the Lie subalgebra generated by the negative root spaces of . 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「Verma module」の詳細全文を読む スポンサード リンク
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