Amer Al-Hiyasat, MIT

Dynamics of a cold particle in a hot bath

We study the dynamics of a zero-temperature, overdamped tracer particle in a bath of Brownian particles at temperature T. At low bath densities, the tracer exhibits nonequilibrium behavior reminiscent of active particles, including wall accumulation and the emergence of ratchet currents in asymmetric potentials. As the bath density increases, these effects vanish and the tracer equilibrates to a Boltzmann distribution at temperature T. We develop an explicit model of the tracer-bath interactions that can be solved in the thermodynamic limit and determine the conditions under which this effective equilibrium picture emerges. We discuss applications to multi-temperature systems and to the dynamics of passive objects in active baths.