Symmetry breaking in the creation and annihilation of defects in active living matter

Active living matter continuously creates and annihilates topological defects in a process that remains poorly understood. Here, we investigate these dynamics in two distinct active living systems—swarming bacteria and human bronchial epithelial cells. Despite their entirely different evolutionary origins, biological functions, and physical scales, both systems exhibit half-integer defects, consistent with the nematic phase. 

However, in contrast to active nematic theory, we find that defect creation and annihilation undergoes spatial spontaneous mirror‑symmetry symmetry breaking.

We propose that this phenomenon stems from a fundamental dualism between nematic structural organization and generated polar forces, which are intrinsic to living systems.