抄録
It is investigated how hydrodynamic excitations affect the spectrum of various fluctuating quantities and response functions. In solid, the propagating hydrodynamic excitation in phonon gas, that is, second sound contributes to thermal conduction. The corresponding conductivity diverges if the lower limit of the momentum of the excitation decreases to zero. The density fluctuation in the hydrodynamic excitations is polydispersive and has the spectrum being proportional to the inverse frequency 1/f in the long wavelength limit. Such a fluctuation leads to the 1/f characteristic in current fluctuations which are observed only when static electric field is externally applied to conductors and semiconductors. The spectrum of 1/f characteristic in density fluctuations in hydrodynamic excitations is universal. The observation of the fluctuations in hydrodynamic excitations is possible only if a certain external field is applied.
