Generation of Emissions By Fast Particles In Stochastic Media

Interaction of charged particles with each other and/or with external fields results in emission of electromagnetic radiation. This article considers the emission arising as fast (nonthermal) particles move through media with random inhomogeneities. The nature of these inhomogeneities might be rather arbitrary. One of the simplest examples of inhomogeneities is a distribution of the microscopic particles (atoms or molecules) in an amorphous substance, so the medium is inhomogeneous at microscopic scales (of the order of the mean distance between particles), perhaps remaining uniform (on average) at macroscopic scales. More frequently, however, real objects are inhomogeneous on macroscopic scales as well. The irregularities might be related to the interfaces between inhomogeneities, variations of the elemental composition, temperature, density, electric, and magnetic field. Random inhomogeneities of any of these parameters may strongly affect in various ways the generation of electromagnetic emission. For example, the presence of the density inhomogeneities implies that the dielectric permeability tensor is a random function, as well as the refractive indices of the electromagnetic eigen-modes. As a result, the eigen-modes of the uniform medium are not the same as the eigen-modes of the real inhomogeneous medium. The irregularities of the electric and magnetic fields affect primarily the motion of the fast particle (although the effect of the field fluctuations on the dielectric tensor exists as well). Below we consider one of many emission processes appearing due to or affecting by small-scale random inhomogeneities, namely, diffusive synchrotron radiation arising as fast particles are scattered by the small-scale random fields. This emission process is of exceptional importance since current models of many astrophysical objects (see, e.g., [1, 2] and references therein) imply generation of rather strong small-scale magnetic fields. The effect of the inhomogeneities on other emission processes is discussed briefly as well.