Resonant diffusion of a gravitactic circle swimmer

by Thomas Franosch (University of Innsbruck)

Tuesday 17 Sept 2024, 15:00 → 16:00 Europe/Rome

Sala Lauree (Dipartimento di Fisica-Ed. G.Marconi)

We investigate the dynamics of a single chiral active particle subject to an external torque due to the presence of a gravitational field -- coined gravitaxis. Our computer simulations reveal an arbitrarily strong increase of the long-time diffusivity D of the gravitactic agent when the external torque γ approaches the intrinsic angular drift ω. below. We provide analytic expressions for the mean-square displacement in terms of eigenfunctions and eigenvalues of the noisy-driven-pendulum problem. The pronounced maximum in the diffusivity is then rationalized by the vanishing of the lowest eigenvalues of the Fokker-Planck equation for the angular motion as the rotational diffusion decreases and the underlying classical bifurcation is approached. A simple harmonic-oscillator picture for the barrier-dominated motion provides a quantitative description for the onset of the resonance while its range of validity is determined by the crossover to a critical-fluctuation-dominated regime.