Interfacial dynamics in chiral active matter.

We construct an active field theory for a non-conserved pseudoscalar field in a uniaxial medium. Then we use this to obtain the stochastic dynamics of a domain wall separating regions of opposite chirality. This dynamics turns out to be equivalent to that of a steadily forced polymer. The steady-state probability distribution of the one-dimensional shape of the domain wall is the same as the passive Edwards-Wilkinsons model. However, surprisingly, the dynamical behaviour of the domain wall shape reveals its activity. A nonlinearity -- which by scaling arguments is marginal in one dimension -- turns out to lead to anomalous growth. We examine this numerically and using a two-loop RG calculation.