Extremely persistent dense active fluids.

We study the dynamics of dense three-dimensional systems of active particles for large persistence times τ p at constant average self-propulsion force f . These systems are fluid counterparts of previously investigated extremely persistent systems, which in the large persistence time limit relax only on the time scale of τ p . We find that many dynamic properties of the systems we study, such as the mean-squared velocity, the self-intermediate scattering function, and the shear-stress correlation function, become τ p -independent in the large persistence time limit. In addition, the large τ p limits of many dynamic properties, such as the mean-square velocity and the relaxation times of the scattering function, and the shear-stress correlation function, depend on f as power laws with non-trivial exponents. We conjecture that these systems constitute a new class of extremely persistent active systems.