Spontaneous torque on an inhomogeneous chiral body out of thermal equilibrium

Abstract

In a previous paper we showed that an inhomogeneous body in vacuum will experience a spontaneous force if it is not in thermal equilibrium with its environment. This is due to the asymmetric asymptotic radiation pattern
such an object emits. We demonstrated this self-propulsive force by considering an expansion in powers of the electric susceptibility: A torque arises in first order, but only if the material constituting the body is nonreciprocal.
No force arises in first order. A force does occur for bodies made of ordinary (reciprocal) materials in second order. Here we extend these considerations to the torque. As one would expect, a spontaneous torque will also appear on an inhomogeneous chiral object if it is out of thermal equilibrium with its environment. Once a chiral body starts to rotate, it will experience a small quantum frictional torque, but much more important, unless a mechanism is provided to maintain the nonequilibrium state, is thermalization: The body will rapidly reach thermal equilibrium with the vacuum, and the angular acceleration will essentially become zero. For a small, or even a large, inhomogeneous chiral body, a terminal angular velocity will result, which seems to be in the realm
of observability.

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ORCID for Gerard Kennedy: orcid.org/0000-0003-4844-6231

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