Bound States in Quantum Field Theory

~aP+rr@r = ~~rTorp (84) The mass m though invariant in a Lorentz transformation is not necessarily a constant of the motion, even if the density p of the particle is constant, since m includes the thermodynamic internal energy Lsee Eq. (34)7. Included in the Minkowski force is a term which predicts a force on a particle when it exists in a temperature gradient, a force associated with the entropy the particle possesses. If 8„8,T is constant throughout the volume of the particle, then this force is —$8„8,T, where 8 is the total entropy of the particle. Equation (25) may be written in a form which facilitates comparison with the methods of field theory, namely, T,= (1/4m)(F, Fp,+b„Fp,2/4), (86)