广义nil-Coxeter代数、余交换代数和PBW性质
Generalized nil-Coxeter algebras, cocommutative algebras, and the PBW property
摘要：
Poincare-Birkhoff-Witt（PBW）定理自从Drinfeld（1986），Lusztig（1989）和Etingof-Ginzburg（2002）关于斜群代数$H \ltimes {\rm Sym}(V)$以及其他上交换霍普夫代数$H$的变形的工作以来吸引了大量的关注。在本文中，我们表明，这样的PBW定理不需要完整的霍普夫代数结构，通过工作在更一般的设置的“余交换代数”，其中涉及一个余积，但不是counit或对极。特殊情况包括无穷小Hecke代数，以及辛反射代数，有理Cherednik代数，以及更一般的Drinfeld orbifold代数。在这种一般性，我们确定精确的条件，相当于PBW属性，包括Yetter-Drinfeld型兼容性条件和雅可比恒等式。我们还刻画了具有PBW性质的梯度形变。反过来，PBW属性有助于识别一般余交换双代数中辛反射的模拟。接下来，我们介绍了一个家庭的余交换代数以外的传统研究的设置：广义nil-Coxeter代数。这些未必是霍普夫代数，事实上，甚至不是（弱）双代数。对于相应的变形Smash积代数族，我们计算了其中心和阿贝尔化，并对所有单模进行了分类。
英文摘要：
Poincare-Birkhoff-Witt (PBW) Theorems have attracted significant attention since the work of Drinfeld (1986), Lusztig (1989), and Etingof-Ginzburg (2002) on deformations of skew group algebras $H \ltimes {\rm Sym}(V)$, as well as for other cocommutative Hopf algebras $H$. In this paper we show that such PBW theorems do not require the full Hopf algebra structure, by working in the more general setting of a "cocommutative algebra", which involves a coproduct but not a counit or antipode. Special cases include infinitesimal Hecke algebras, as well as symplectic reflection algebras, rational Cherednik algebras, and more generally, Drinfeld orbifold algebras. In this generality we identify precise conditions that are equivalent to the PBW property, including a Yetter-Drinfeld type compatibility condition and a Jacobi identity. We also characterize the graded deformations that possess the PBW property. In turn, the PBW property helps identify an analogue of symplectic reflections in general cocommutative bialgebras. Next, we introduce a family of cocommutative algebras outside the traditionally studied settings: generalized nil-Coxeter algebras. These are necessarily not Hopf algebras, in fact, not even (weak) bialgebras. For the corresponding family of deformed smash product algebras, we compute the center as well as abelianization, and classify all simple modules.
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