1. Y. Takahashi, H. Umezawa, Thermofield dynamics. Collective Phenom. 2(55) (1975). (Reprinted: J. Mod. Phys. B 10, 1755, 1996.)
2. H. Umezawa, Advanced Field Theory Macro and Thermal Physics (AIP Press, New York, Micro, 1995)
3. Run-Qin Yang, A complexity of quantum field theory states and application in thermofield double states. Phys. Rev. D 97, 066004 (2018)
4. R.A. Fisher: The Negative Binomial Distribution, Blackwell Publishing Ltd. University College London (1941)
5. M. Joseph, Hilbe: Negative Binomial Regression (Cambridge University Press, Cambridge, 2011)