A Quantum Correction to the Momentum Distribution Function of Particles
On the basis of the solution to the equation for a single-particle density matrix, the momentum distribution is obtained for a light-particle impurity placed in an ordered system of heavy particles and interacting with them with the amplitude U0. The effect of the value of U0/T0 on the functional form of the momentum distribution is investigated. It is shown that the momentum-distribution function obtained within the perturbation theory up to the terms ~(U0/T0)2 retains its form also outside the region of applicability of the perturbation theory; however, the relative magnitude of the correction is much smaller than that given by the perturbation theory.
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