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.

作为一个有效的理论，相对论流体动力学是由对称性固定的，最高可达一组输运系数。人们投入了大量精力来显式计算这些系数。在这里，我们采用了一种更通用的方法，使用 bootstrap 技术来排除与微观因果关系不一致的理论。剩下的是传递系数空间中的通用凸几何，我们称之为水面体。所有一致理论的景观必然位于水面体的内部或边缘。我们分析性地构建了水面体的横截面，这些横截面对应于出现在声音和扩散模式的色散关系中的输运系数边界，用于没有随机波动的理论。