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arXiv 2404.06110math-phmath.DGmath.MPmath.RT
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紧支撑微分同胚群的广义正能表示

Generalized Positive Energy Representations of the Group of Compactly Supported Diffeomorphisms

Bas Janssens, Milan Niestijl

AI总结:

受广义相对论启发,本文研究了光滑流形上紧支撑微分同胚群的广义正能射影酉表示,证明了在流形连通且维数大于1时该表示在单位分量上必然平凡,并确定了紧支撑向量场李代数的连续第二上同调。

摘要:

受广义相对论中渐近对称群的启发,我们考虑光滑流形M的紧支撑微分同胚李群Diff_c(M)的射影酉表示overlineρ,该表示满足所谓的广义正能条件。特别地,这涵盖了在某种适当意义上与overlineρ生成的冯诺依曼代数上的KMS态相容的表示。我们证明,若M连通且dim(M)>1,则任何此类表示在单位分量Diff_c(M)_0上必然平凡。作为获得该结果的中间步骤,我们确定了紧支撑向量场的李代数的连续第二李代数上同调H^2_ct(X_c(M), R)。鉴于紧支撑条件,这与Gelfand-Fuks上同调有微妙不同。

英文摘要:

Motivated by asymptotic symmetry groups in general relativity, we consider projective unitary representations $\overlineρ$ of the Lie group $\mathrm{Diff}_c(M)$ of compactly supported diffeomorphisms of a smooth manifold $M$ that satisfy a so-called generalized positive energy condition. In particular, this captures representations that are in a suitable sense compatible with a KMS state on the von Neumann algebra generated by $\overlineρ$. We show that if $M$ is connected and $\dim(M) > 1$, then any such representation is necessarily trivial on the identity component $\mathrm{Diff}_c(M)_0$. As an intermediate step towards this result, we determine the continuous second Lie algebra cohomology $H^2_{\mathrm{ct}}(\mathcal{X}_c(M), \mathbb{R})$ of the Lie algebra of compactly supported vector fields. This is subtly different from Gelfand--Fuks cohomology in view of the compact support condition.

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