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arXiv math/0510475math.GT
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三维流形的Cochran-Harvey不变量的宇称性

The parity of the Cochran-Harvey invariants of 3-manifolds

Stefan Friedl, Taehee Kim

摘要:

给定一个整数表示群G和整数群的满态映射G,Cochran和Harvey定义了一个积分不变量序列,它可以看作是高阶Alexander多项式的次数。Cochran和Harvey证明了(稍加修改)这是一个永不递减的数列,如果G是具有空边界或环形边界的3-流形的基本群,并且这些不变量给出了Thurston范数的下界。利用一定的Cohn局部化和Reidemeister挠的对偶性,我们证明了对于一个3-流形的基本群,序列中的任何跳跃必然是偶的.这特别回答了科克伦的一个问题。此外,利用Turaev的结果,我们表明,在一个温和的额外的假设下,奇偶性的Cochran-Harvey不变量同意的奇偶性的Thurston范数。

英文摘要:

Given a finitely presented group G and an epimorphism G to the group of integers Cochran and Harvey defined a sequence of integral invariants, which can be viewed as the degrees of higher--order Alexander polynomials. Cochran and Harvey showed that (up to a minor modification) this is a never decreasing sequence of numbers if G is the fundamental group of a 3-manifold with empty or toroidal boundary, and that these invariants give lower bounds on the Thurston norm. Using a certain Cohn localization and the duality of Reidemeister torsion we show that for a fundamental group of a 3--manifold any jump in the sequence is necessarily even. This answers in particular a question of Cochran. Furthermore using results of Turaev we show that under a mild extra hypothesis the parity of the Cochran--Harvey invariant agrees with the parity of the Thurston norm.

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