Nonreciprocal chiral active matter: Collective behavior and thermodynamics

近年来，具有非互易耦合的系统已成为人们日益关注的焦点。例子出现在广泛的领域和不同的长度和时间尺度上，从非厄米量子系统到细菌悬浮液和（活性）胶体，捕食者-猎物系统和涉及传感和通信的社会系统。最近的场论研究软非互易系统，这是本质上的平衡，揭示了新类型的集体动力学。然而，在粒子水平上对这些现象的更广泛的理解尚未得到发展。在这里，我们建议从（干）活性物质，即，手性活性粒子的混合物与非互易排列耦合的非互易系统进行调查。手性粒子是活性物质的一个重要子类。我们在这里包括相互排斥的影响，产生非平凡的集群已经在没有对齐。我们的初步工作的基础上的平均场流体动力学理论揭示了不同类型的非平衡行为，可以调整的程度的非互易性。在本项目中，我们的目标，首先，在补充，从而测试流体动力学预测的基础朗之万方程的粒子为基础的模拟，重点是非互易性引起的具体影响。这尤其包括“动态阻挫”耦合的重要情况，其中种类A的粒子想要与来自B的粒子对准，而后者想要与A反对准。在这样的条件下，基于场论的研究，我们期待着新的有趣的行为，如破缺的、依赖于时间的状态的出现。第二个主要目标是从随机热力学的量来描述集体行为，特别是时间对称性破缺的度量（与熵产生有关）。这种措施，这是由嘈杂的粒子轨迹或字段访问，最近已被证明是有用的，已经在附近的运动诱导的相分离和植绒的“简单”的活性流体。在目前的系统中，非互易性作为一个额外的非平衡源，使得热力学概念的研究更加有趣。从粒子水平开始，我们的目标是，作为一个更长远的角度来看，在与相应的数量从场水平的方法进行比较。

Recently, systems with nonreciprocal couplings have become a focus of growing interest. Examples occur in a wide range of fields and on different length and time scales, from non-Hermitian quantum systems to bacterial suspensions and (active) colloids, predator-prey systems and social systems involving sensing and communication. Recent field-theoretical studies on soft non-reciprocal systems, which are intrinsically out of equilibrium, have revealed novel types of collective dynamics. However, a broader understanding of these phenomena on the particle level has not yet been developed. Here we propose to investigate a nonreciprocal system from (dry) active matter, that is, a mixture of chiral active particles with nonreciprocal alignment couplings. Chiral particles build an important subclass of active matter. We here include the effect of mutual repulsion, yielding non-trivial clustering already in the absence of alignment. Our preliminary work based on a mean-field hydrodynamical theory reveals different types of nonequilibrium behavior which can be tuned by the degree of nonreciprocity. In the present project we aim, first, at complementing and thereby testing the hydrodynamic predictions by particle-based simulations of the underlying Langevin equations, with a focus on the specific effects induced by nonreciprocity. This includes, in particular, the important case of “dynamical frustration" coupling where particle of species A want to align with those from B, while the latter want to anti-align with A. Under such conditions we expect, based on field-theoretical studies, new intriguing behavior such as the emergence of symmetry-broken, time-dependent states. The second main goal is to characterize the collective behavior in terms of quantities from stochastic thermodynamics, in particular, measures of time-symmetry breaking (connected to entropy production). Such measures, which are accessible by the noisy particle trajectories or fields, have recently proven to be useful already for "simple" active fluids in the vicinity of motility-induced phase separation and flocking. In the present systems, nonreciprocity acts as an additional source of non-equilibrium, making an investigation of thermodynamic notions even more interesting. Starting from the particle level we aim, as a longer perspective, at a comparison with corresponding quantities from a field-level approach.