Mathematical expressions for quantum fluctuations of energy for different energy-momentum tensors

Abstract: Expressions for the quantum fluctuations of energy density have been derived for the subsystems consisting of hot relativistic gas of particles with spin-$\frac{1}{2}$ and mass $m$. Our expressions for the fluctuation depend on the form of energy-momentum tensor which in turn depend on the choice of pseudo-gauge. These results suggest that quantum fluctuations of energy should be considered seriously in the case of the very small thermodynamic systems.