### Abstract

Using the Schwinger-Keldysh path-ordering method, a favoured method for doing non-equilibrium quantum field theory, Korenman analyzed a simple model from quantum optics. We study the same model using the recently developed non-equilibrium thermo field dynamics (TFD), and make a comparison of these two methods. TFD can deal with time-dependent non-equilibrium situations caused by the initial conditions being out of equilibrium, while Korenman considered a stationary state maintained by an assumed external pumping mechanism. The explicit TFD calculation at one loop level shows the approach of the system to equilibrium which is described by the master equation derived from the self-consistent renormalization condition. Although both of the methods give practically the same dissipative coefficient in this order of approximation, we would find a larger difference between them in a higher order calculation because of the difference of unperturbative propagators. We also briefly consider the inclusion of a simple pumping mechanism for the system in TFD.

Original language | English |
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Pages (from-to) | 853-875 |

Number of pages | 23 |

Journal | Physica A: Statistical Mechanics and its Applications |

Volume | 156 |

Issue number | 3 |

DOIs | |

Publication status | Published - 1989 Apr 15 |

Externally published | Yes |

### ASJC Scopus subject areas

- Statistics and Probability
- Condensed Matter Physics

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## Cite this

*Physica A: Statistical Mechanics and its Applications*,

*156*(3), 853-875. https://doi.org/10.1016/0378-4371(89)90024-1