The evolution of non-hydrodynamic slow processes near the QCD critical point is explored with the novel Hydro+ framework, which extends the conventional hydrodynamic description by coupling it to additional explicitly evolving slow modes describing long wavelength fluctuations. Their slow relaxation is controlled by critical behavior of the correlation length and is independent from gradients of matter density and pressure that control the evolution of the hydrodynamic quantities. In this exploratory study we follow the evolution of the slow modes on top of a simplified QCD matter background, allowing us to clearly distinguish, and study both separately and in combination, the main effects controlling the dynamics of critical slow modes. In particular, we show how the evolution of the slow modes depend on their wave number, the expansion of and advection by the fluid background, and the behavior of the correlation length. Non-equilibrium contributions from the slow modes to bulk matter properties that affect the bulk dynamics (entropy, pressure, temperature and chemical potential) are discussed and found to be small.

中文翻译：

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QCD 临界点附近的波动动态

新的 Hydro+ 框架探索了 QCD 临界点附近非流体动力学慢过程的演变，该框架通过将传统流体动力学描述耦合到描述长波长波动的其他明确演化的慢模式，扩展了传统的流体动力学描述。它们的缓慢弛豫由相关长度的临界行为控制，并且与控制流体动力学量演变的物质密度和压力梯度无关。在这项探索性研究中，我们在简化的 QCD 物质背景之上跟踪慢模式的演变，使我们能够清楚地区分并单独和组合研究控制临界慢模式动力学的主要影响。特别是，我们展示了慢模式的演变如何取决于它们的波数，流体背景的膨胀和平流，以及相关长度的行为。讨论了慢速模式对影响体动力学（熵、压力、温度和化学势）的体物质特性的非平衡贡献，发现它们很小。