Fluctuation-dissipation dispersion relation and quality factor for slow processes.
A generalization of the Callen-Welton formula for systems with slowly varying parameters is given. Using the momentum method and the time multiscale technique, it is shown that not only the dissipation but also the dispersive contributions determine the spectral function of the fluctuations in these systems. The general formalism is illustrated for an oscillating electrical circuit, and the influence of the dispersion contributions on the quality factor of the system is discussed.
Belyi
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IZMIRAN, Troitsk, Moscow region 142190, Russia. sbelyi@izmiran.rssi.ru