The polarisation of sunlight after scattering off the atmosphere was first described by Chandrasekhar using a geometrical description of Rayleigh interactions. Kosowsky later obtained similar results after extending Chandrasekhar's formalism by using Quantum Field Theory (QFT) to describe the polarisation of the Cosmological Microwave Background radiation. Here we focus on the polarisation of high energy radiation. After demonstrating why the geometrical approach fails and pointing out the need to extend Kosowsky's description, we establish the transport formalism that enables us to describe the change in gamma-ray polarisation as high energy photons propagate through space and the atmosphere. We primarily focus on Compton interactions but our approach is general enough to describe photon scattering off new particles. Finally we determine the conditions for a circularly polarised γ-ray signal to keep the same level of circular polarisation as it propagates through space or the atmosphere.
33 страницы, интересно уже хотя бы подробным изложением подхода к описанию поляризации на первых страницах.
А это мое родное тормозное излучение, и внезапно сам Стивен Вайнберг решил высказаться на 14 страниц с подробными формулами:
Soft Bremsstrahlung: https://arxiv.org/abs/1903.11168
Simple analytic formulas are considered for the energy radiated in low frequency bremsstrahlung from fully ionized gases. A formula that has been frequently cited over many years turns out to have only a limited range of validity, more narrow than for a formula derived using the Born approximation. In an attempt to find a more widely valid simple formula, a soft photon theorem is employed, which in this context implies that the differential rate of photon emission in an electron-ion collision with definite initial and final electron momenta is correctly given for sufficiently soft photons by the Born approximation, to all orders in the Coulomb potential. Corrections to the Born approximation arise because the upper limit on photon energy for this theorem to apply to a given collision becomes increasingly stringent as the scattering approaches the forward direction. A general formula is suggested that takes this into account.