Statistical and Biological Physics
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One of the hallmark features of active nematics is the formation of oppositely charged, point-like, topological half-integer defects that exhibit creation/annihilation dynamics. So far, such ±1/2 defects have been found only in dense and spatially uniform active systems, and it has been argued that they are absent in dilute, phase-separated active systems. In our study, we show that phase-separated active nematics can form condensed -1/2 defects of a new kind. In stark contrast to the well-studied homogeneous case, these new defects coincide with density peaks, lack a positively charged counterpart, condense nematic fluxes, and coexist with undulating dense bands from which they are formed by a new hierarchical condensation phenomenon. more

In studies of nonequilibrium phase transitions, many different forms of local interactions have been investigated. But how do long-ranged interactions influence the critical dynamics of a colony of active agents? In order to study this question, we analyze the critical dynamics of reproducing agents subject to long-range chemical interactions and limited resources. Specifically, we study a model of chemically interacting agents, whose population dynamics are accounted for by Fisher-Kolmogorov dynamics. The chemotactic interaction is modeled by Keller-Segel like active motion, i.e., the agents are assumed to preferably move along gradients in a chemical field sourced by themselves. more