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Finiteness and infiniteness results for Torelli groups of (hyper-)Kähler manifolds
Mathematische Annalen ( IF 1.4 ) Pub Date : 2021-04-12 , DOI: 10.1007/s00208-021-02174-x
Matthias Kreck , Yang Su

The Torelli group \(\mathcal T(X)\) of a closed smooth manifold X is the subgroup of the mapping class group \(\pi _0(\mathrm {Diff}^+(X))\) consisting of elements which act trivially on the integral cohomology of X. In this note we give counterexamples to Theorem 3.4 by Verbitsky (Duke Math J 162(15):2929–2986, 2013) which states that the Torelli group of simply connected Kähler manifolds of complex dimension \(\ge 3\) is finite. This is done by constructing under some mild conditions homomorphisms \(J: \mathcal T(X) \rightarrow H^3(X;\mathbb Q)\) and showing that for certain Kähler manifolds this map is non-trivial. We also give a counterexample to Theorem 3.5 (iv) in (Verbitsky in Duke Math J 162(15):2929–2986, 2013) where Verbitsky claims that the Torelli group of hyperkähler manifolds are finite. These examples are detected by the action of diffeomorphsims on \(\pi _4(X)\). Finally we confirm the finiteness result for the special case of the hyperkähler manifold \(K^{[2]}\).



中文翻译:

(超)Kähler流形的Torelli组的有限性和无限性结果

闭合光滑流形X的Torelli组\(\ mathcal T(X)\)是由元素组成的映射类组\(\ pi _0(\ mathrm {Diff} ^ +(X))\)的子组对X的积分同调微不足道。在本说明中,我们以Verbitsky的定理3.4作反例(Duke Math J 162(15):2929-2986,2013),该定理指出,简单连接复维\(\ ge 3 \)的Kähler流形的Torelli组是有限的。这是通过在某些温和条件下构造同态\(J:\ mathcal T(X)\ rightarrow H ^ 3(X; \ mathbb Q)\)来完成的并表明对于某些Kähler流形来说,这幅图是不平凡的。我们还对(Verbitsky in Duke Math J 162(15):2929-2986,2013)中的定理3.5(iv)给出了反例,其中Verbitsky声称Hyperkähler流形的Torelli组是有限的。这些示例通过diffeomorphsims对\(\ pi _4(X)\)的作用来检测。最后,我们确定了超kähler流形\(K ^ {[2]} \)的特殊情况的有限性结果。

更新日期:2021-04-12
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