Noncommutative deformations of type-\(A\) Kleinian singularities.

*(English)*Zbl 0807.16029Let \(k\) be an algebraically closed field of characteristic zero. The author studies noncommutative \(k\)-algebras generated by the elements \(a,b\) and \(h\) satisfying the relations \(ha - ah = a\), \(hg - bh = -b\), \(ba = v(h)\), \(ab = v(h - 1)\), where \(v(x)\) is a polynomial with coefficients in \(k\). Such an algebra denoted by \(T(v)\) is a Noetherian ring of Krull dimension one. For example, if \(v(x)\) is quadratic then \(T(v)\) is isomorphic to an infinite dimensional primitive factor of the enveloping algebra of the Lie algebra \(sl(2,k)\). The author proves that the associated graded ring of \(T(v)\) is isomorphic to the coordinate ring of type-A Kleinian singularities. In the case of the complex ground field such a singularity may be presented as the quotient of an affine complex plane by a finite cyclic subgroup of \(SL_ 2(\mathbb{C})\). It is proved that \(T(v)\) is an Auslander-Gorenstein ring and its global dimension is infinite if and only if the polynomial \(v\) has repeated roots. In case the roots of \(v\) are distinct there are only the following two possibilities. When any two roots of \(v\) differ by a nonzero integer then the global dimension of \(T(v)\) is equal to 2, otherwise it is equal to 1. Furthermore, in this case it turns out that the Grothendieck group \(K_ 0(T(v))\) is a free abelian group of rank equal to the degree of \(v\). In conclusion the author formulates some open problems related to the subject.

Reviewer: A.G.Aleksandrov (Moskva)

##### MSC:

16S80 | Deformations of associative rings |

16S15 | Finite generation, finite presentability, normal forms (diamond lemma, term-rewriting) |

14H20 | Singularities of curves, local rings |

16S30 | Universal enveloping algebras of Lie algebras |

14J70 | Hypersurfaces and algebraic geometry |

16D90 | Module categories in associative algebras |

16E20 | Grothendieck groups, \(K\)-theory, etc. |

16E10 | Homological dimension in associative algebras |

13H10 | Special types (Cohen-Macaulay, Gorenstein, Buchsbaum, etc.) |