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arXiv 1607.01966nlin.SI
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无色散可积族与GL(2,R)几何

Dispersionless integrable hierarchies and GL(2,R) geometry

E. V. Ferapontov, B. Kruglikov

摘要:

$n$维流形上的次共形或$GL(2)$几何$M$由射影余切丛$\mathbb{P} T^*M$中的次数为$n-1$的有理正规曲线场定义.已知这样的几何出现在具有消失的Wünschmann(Doubrov-Wilczynski)不变量的常微分方程的解空间上。在本文中,我们讨论了$GL(2)$结构的另一个自然来源,即无色散可积的偏微分方程族(例如dKP族)。在后一种情况下,$GL(2)$结构与层次的特征多样性(主要符号)相一致。无色散层次结构提供了文献中研究的各种特别有趣的$GL(2)$结构类的明确例子。因此,我们得到了无挠$GL(2)$结构的布莱恩特出现在异国情调的holonomy的背景下,在4维,以及完全测地线$GL(2)$结构的Krynski。后者,也被称为对合$GL(2)$结构,具有相容仿射联络(带挠)和双参数族的全测地$α$ -流形(来自无色散的Lax方程),这使得它们成为爱因斯坦-外尔几何的自然推广。我们的主要结果表明,对合$GL(2)$结构由一个无色散的可积系统控制。这建立了文希曼条件系统的可积性。

英文摘要:

Paraconformal or $GL(2)$ geometry on an $n$-dimensional manifold $M$ is defined by a field of rational normal curves of degree $n-1$ in the projectivised cotangent bundle $\mathbb{P} T^*M$. Such geometry is known to arise on solution spaces of ODEs with vanishing Wünschmann (Doubrov-Wilczynski) invariants. In this paper we discuss yet another natural source of $GL(2)$ structures, namely dispersionless integrable hierarchies of PDEs (for instance the dKP hierarchy). In the latter context, $GL(2)$ structures coincide with the characteristic variety (principal symbol) of the hierarchy. Dispersionless hierarchies provide explicit examples of various particularly interesting classes of $GL(2)$ structures studied in the literature. Thus, we obtain torsion-free $GL(2)$ structures of Bryant that appeared in the context of exotic holonomy in dimension four, as well as totally geodesic $GL(2)$ structures of Krynski. The latter, also known as involutive $GL(2)$ structures, possess a compatible affine connection (with torsion) and a two-parameter family of totally geodesic $α$-manifolds (coming from the dispersionless Lax equations), which makes them a natural generalisation of the Einstein-Weyl geometry. Our main result states that involutive $GL(2)$ structures are governed by a dispersionless integrable system. This establishes integrability of the system of Wünschmann conditions.

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