The double Compton process in astrophysical plasmas

Abstract

We study the double Compton (DC) process for a wide range of particle energies, extending previous treatments well beyond the soft photon limit, employing both numerical and analytical methods. This allows us to investigate the physics of the DC process up to the highly relativistic regime relevant to electromagnetic particle cascades in the early Universe and photon-dominated astrophysical plasmas. Generalized exact analytic expressions for the DC emissivity in the soft photon limit are obtained. These are compared to existing approximations, for the first time studying the ultra-relativistic regime. We also numerically integrate the full DC collision term calculating the DC emissivity at general particle energies. A careful treatment of DC infrared divergences inside astrophysical plasmas, including subtle effects related to the presence of stimulated DC emission, is discussed. The obtained results can be efficiently represented using the code DCpack, which also allows one to compute average emissivities for general incoming electron and photon distributions. This puts the modelling of the DC process inside astrophysical plasmas on a solid footing and should find applications in particular for computations of the cosmological thermalization problem in the early Universe.

arXiv comment28 pages + 6 pages appendix and references, 13 figures, to be submitted to JCAP

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• Thermalization of large energy release in the early Universe
• CMB spectral distortions from continuous large energy release
• New Horizons in Cosmology with Spectral Distortions of the Cosmic Microwave Background
• Total cross sections of $e\gamma \to eX\bar{X}$ processes with $X=\mu ,\gamma ,e$ via multiloop methods
• Comparison of numerical methods for computing the repeated Compton scattering of photons in isotropic media
• Effects of observer peculiar motion on the isotropic background frequency spectrum: from monopole to higher multipoles
• Some features of the direct and inverse double Compton effect as applied to astrophysics
• Finite time effects in single and double Compton scattering