论文标题

极性活性物质现场理论中的时间反向对称性违规和熵产生

Time-reversal symmetry violations and entropy production in field theories of polar active matter

论文作者

Borthne, Øyvind L., Fodor, Étienne, Cates, Michael E.

论文摘要

我们研究了流体动力维克斯克模型(HVM)和扩散羊群模型(DFM)中的稳态熵产生速率(EPR)。两种模型都显示出从各向同性气体到极性液体(羊群)相的过渡,除了行进的极性簇和可溶性间隙中的微相分化。 DFM的相图可能被认为是HVM的扩展,它包含在低密度下的额外结构,在该结构中,我们找到了一种新型的晶体相,其中高密度脊的固定六边形晶格围绕着低密度山谷。从低噪声下EPR的缩放量表的评估中,我们发现该极限中的动力学可以根据主要贡献组织为三个主要类别。真正的非平衡动力学的特征是在此限制下具有发散的EPR,并维持在零噪声下违反电流的全局时间反转对称性(TRS)。另一方面,略有平衡和有效的平衡动力学在此极限内具有有限的EPR,并且TRS仅在波动水平下被打破。对于这两种情况的后者,详细的平衡在较小的噪声限制中恢复,我们将有效的Boltzmann统计数据恢复到最低的非平凡顺序。我们进一步证明,EPR的缩放可能会根据计算时跟踪的动力变量而变化,并选择用于时间反转的协议。从动力学的数值模拟中获得的结果证实了我们得出的渐近缩放关系和我们的定量预测。

We investigate the steady-state entropy production rate (EPR) in the Hydrodynamic Vicsek Model (HVM) and Diffusive Flocking Model (DFM). Both models display a transition from an isotropic gas to a polar liquid (flocking) phase, in addition to traveling polar clusters and microphase-separation in the miscibility gap. The phase diagram of the DFM, which may be considered an extension of the HVM, contains additional structure at low densities where we find a novel crystal phase in which a stationary hexagonal lattice of high-density ridges surround low density valleys. From an assessment of the scaling of the EPR at low noise, we uncover that the dynamics in this limit may be organised into three main classes based on the dominant contribution. Truly nonequilibrium dynamics is characterised by a divergent EPR in this limit, and sustains global time-reversal symmetry (TRS) violating currents at zero noise. On the other hand, marginally nonequilibrium and effectively equilibrium dynamics have a finite EPR in this limit, and TRS is broken only at the level of fluctuations. For the latter of these two cases, detailed balance is restored in the small noise limit and we recover effective Boltzmann statistics to lowest nontrivial order. We further demonstrate that the scaling of the EPR may change depending on the dynamical variables that are tracked when it is computed, and the protocol chosen for time-reversal. Results acquired from numerical simulations of the dynamics confirm both the asymptotic scaling relations we derive and our quantitative predictions.

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