近日，比利时根特大学的Michal P. Heller及其研究团队取得一项新进展。经过不懈努力，他们揭示因果关系所允许的输运系数空间。相关研究成果已于2024年10月14日在国际知名学术期刊《自然—物理学》上发表。

该研究团队采用一种更为通用的方法，即运用自助法来排除与微观因果性不一致的理论。剩下的则是在输运系数空间中的一个普遍凸几何结构，研究人员称之为“流体多面体”。所有一致理论的分布必然位于流体多面体的内部或其边缘。

研究人员针对不含随机波动的理论中，出现在声音和扩散模式色散关系中的输运系数界限，分析构建了流体多面体的横截面。

据悉，作为一种有效的理论，相对论流体力学通过对称性来确定一组输运系数。人们已投入大量精力对这些系数进行显式计算。

附：英文原文

Title: The space of transport coefficients allowed by causality

Author: Heller, Michal P., Serantes, Alexandre, Spaliski, Micha, Withers, Benjamin

Issue&Volume: 2024-10-14

Abstract: As an effective theory, relativistic hydrodynamics is fixed by symmetries up to a set of transport coefficients. A lot of effort has been devoted to explicit calculations of these coefficients. Here we adopt a more general approach, deploying bootstrap techniques to rule out theories that are inconsistent with microscopic causality. What remains is a universal convex geometry in the space of transport coefficients, which we call the hydrohedron. The landscape of all consistent theories necessarily lies inside or on the edges of the hydrohedron. We analytically construct cross-sections of the hydrohedron corresponding to bounds on transport coefficients that appear in sound and diffusion modes’ dispersion relations for theories without stochastic fluctuations.

DOI: 10.1038/s41567-024-02635-5

Source: https://www.nature.com/articles/s41567-024-02635-5