Spontaneous Torque on an Inhomogeneous Chiral Body out of Thermal Equilibrium

TL;DR

This paper investigates how inhomogeneous chiral bodies experience spontaneous torque when out of thermal equilibrium, highlighting the effects of material reciprocity and the potential for observable terminal angular velocities.

Contribution

It extends previous work by analyzing the spontaneous torque on chiral bodies out of thermal equilibrium, including the effects of quantum friction and thermalization.

Findings

Spontaneous torque appears on chiral bodies out of thermal equilibrium.

A terminal angular velocity can be achieved and is potentially observable.

Quantum frictional effects influence the dynamics of rotating chiral bodies.

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.