标题： 极性 flock 对空间各向异性的敏感性 显示英文标题

标题： Susceptibility of Polar Flocks to Spatial Anisotropy

摘要： 我们通过研究二维中的活性$q$-态钟模型，考虑空间各向异性对极化群体的影响。 与平衡情况下的现象不同，我们发现，在大尺寸极限下，任何程度的各向异性都会显著改变旋转不变情况下的现象学特性，破坏长程关联，固定全局有序的方向，并将共存相的行进条带转化为一个移动的区域。 所有这些现象都发生在某个发散于$q\to\infty$极限的长度尺度之上。 因此，在足够大的$q$值下，可以在有限系统中观察到类似于维克塞尔模型的现象。 我们提供了一个标度论证，解释了为什么各向异性在被动和主动情况下会产生如此不同的效果。 显示英文摘要

摘要： We consider the effect of spatial anisotropy on polar flocks by investigating active $q$-state clock models in two dimensions. In contrast to what happens in equilibrium, we find that, in the large-size limit, any amount of anisotropy changes drastically the phenomenology of the rotationally-invariant case, destroying long-range correlations, pinning the direction of global order, and transforming the traveling bands of the coexistence phase into a single moving domain. All this happens beyond a lengthscale that diverges in the $q\to\infty$ limit. A phenomenology akin to that of the Vicsek model can thus be observed in a finite system for large enough values of $q$. We provide a scaling argument which rationalizes why anisotropy has so different effects in the passive and active cases.