标题： 场重新定义及其在相对论流体力学中的影响 显示英文标题

标题： Field redefinition and its impact in relativistic hydrodynamics

摘要： 本文探讨了场重新定义对相对论流体力学中线性化扰动谱的影响。我们观察到流体力学模态的谱永远不会受到局域场重新定义的影响，然而非流体力学模态的谱会受到影响。通过适当的全阶重新定义，可以消除非流体力学模态，从而得到一个新的框架，在这个框架中谱仅包含流体力学模态。我们还观察到，由此产生的能动张量在动量空间中可能有一个收敛半径与被消除的非流体力学模态相关的无穷级数。在某些特殊情况下，场重新定义下的能动张量中的高阶项可能会抵消，这表明非流体力学模态只是流体变量选择的伪影，并没有物理意义，即使它们似乎违反了物理约束。使用一个特殊的玩具模型，我们找到了一个判据来区分物理和非物理的非流体力学模态。 显示英文摘要

摘要： In this paper, we explore the impact of field redefinition on the spectrum of linearized perturbations in relativistic hydrodynamics. We observe that the spectrum of hydrodynamics modes is never affected by the local field redefinition, however, the spectrum of the non-hydrodynamic modes is affected. Through an appropriate all-order redefinition, non-hydrodynamic modes can be eliminated, leading to a new frame where the spectrum contains only hydrodynamic modes. We also observe that the resulting stress-energy tensor may have an infinite series in momentum space, with a convergence radius linked to the eliminated non-hydrodynamic mode. In certain special cases, higher-order terms in the stress-energy tensor under field redefinition may cancel, indicating that non-hydrodynamic modes are mere artefacts of the fluid variable choice and hold no physical significance, even if they appear to violate physical constraints. Using a special toy example, we find a criterion to distinguish between physical and unphysical non-hydrodynamic modes.