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We will review the results obtained from the study of a two-dimensional system of active
dumbbells, introduced as a paradigmatic example of a system of non symmetrical brownian particles with self-propulsion.
Each dumbbell is composed by two colloids kept together
by a stiff spring, with an excluded volume interaction modeled through a Weeks-Chandler-Anderson (WCA) potential. They are immersed in an implicit solvent modeled by the
Langevin equation. The activity or self-propulsion is modeled by a constant force acting on the principal direction of the dumbbell.
We find that activity triggers a nonequilibrium phase separation if the density exceeds a critical threshold and if the Peclet number is high enough. We study the kinetics of the aggregates of dumbbells in the phase separated region. The clusters spontaneously break chiral symmetry and rotate; they also display a nematic ordering with spiral patterns. We can also determine the growth law for the size of these clusters. On the other hand, for the phase without aggregation, we determine the translational and rotational diffusion properties. Different regimes can be observed, depending on the combination of the random noise, the activity and the density of the system. Unusual increase with density of the rotational diffusion is found and explained as due to particle clustering. Large deviation functions for dumbell velocities have been finally determined showing the appearance of non-singular behaviour. |