In the present Rapid Communication we calculate the density matrix of heat conduction based on the field theory of nonequilibrium thermodynamics, which was worked out in the last $10\text{years}$. Applying these results we can discuss the existence of the maximal temperature and a possible upper limit for its value. We point out, proposing relevant physical assumptions, that this temperature could be the so-called Planck temperature [J. A. S. Lima and M. Trodden, Phys. Rev. D 53, 4280 (1996)].

• Received 21 July 2004

DOI:https://doi.org/10.1103/PhysRevE.70.055102