Revised theory of relaxation ultrasound attenuation in glasses

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Abstract
The effect of phonon disturbance by two-level systems on ultrasound attenuation and velocity is considered. It is shown that the phonon distribution function is substantially disturbed when the ultrasound frequency is much less than the inverse two-level system and phonon relaxation times. In such a case, the ultrasound attenuation appears to be much greater than Jäckle’s theory predicts. The transition to the phenomenological theory of ultrasound propagation is discussed. A new mechanism of phonon energy relaxation due to spectral diffusion is shown.