Nonlinear interaction between wave packets of elementary particles and a crystal

It is shown that density redistribution of ultrarelativistic charged particles in a beam occurs due to interaction of a channeling particle with phonons (and other elementary excitations) of the crystal. This interaction results in appearance of the earlier considered non-linear contribution, i. e. depending on the wave function amplitude of the particle, to the refraction parameter and, as a consequence, to appearance of non-linear effects (self- focusing, self-compression, etc. during the movement of the wave packat in the medium. It is noted that the intensity of resonance γ-radiation by rather narrow beams of ultrarelativistic charged particles is rather large for observation of two-photon correlations in the X-ray frequency range