Integer Topological Defects Reveal Antisymmetric Forces in Active Nematics

Cell layers are often categorized as contractile or extensile active, nematics but recent experiments on neural progenitor cells with induced +1 topological defects challenge this classification. In a bottom-up approach, we first study a relevant particle-level model and then analyze a continuum theory derived from it. We show that both model and theory account qualitatively for the main experimental result, i.e., accumulation of cells at the core of any type of +1 defect. We argue that cell accumulation is essentially due to two generally ignored antisymmetric active forces. We finally discuss the relevance and consequences of our findings in the context of other cellular active nematics experiments and previously proposed theories.