True and Quasi Long-Range Order in Malthusian Flocks

Living matter undergoes continuous turnover. The hydrodynamic theory of Malthusian flocks describes polar active matter with turnover, but its phase diagram and nonlinear scaling behavior is not well understood. Using a nonperturbative renormalization group approach, rotationally invariant to second order in derivatives, and without defects, we explicitly obtain the strong-coupling fixed point governing true long-range order, uncover a quasi long-range ordered phase, and identify a critical point similar to, but distinct from the Berezinskii-Kosterlitz-Thouless universality class at the transition.