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Cosmic Positron Background

Calculation of the Electron-Positron Paar Production Rate from the Cosmic Photon Background

Electron-positron pairs can be formed in the interaction of two photons. The Cosmic Photon Background (CPB) is the isotropic and persistent emission that reaches Earth from radio wavelengths to gamma-ray energies. Its strongest component is the Cosmic Microwave Background (CMB), i.e. the remnant of a hot Big Bang, and has a spectrum that exactly matches that of a blackbody with a temperature of 2.7 K. The interactions of the CPB with itself would create a sizeable amount of pairs with a remarkable unique spectrum. When the positrons lose energy, they will annihilate again with free electrons or electrons from hydrogen, which results in a gamma-ray line at 511 keV photon energies. In this thesis, this reprocessing of the CPB towards gamma-rays should be calculated from first principles, starting with the local Universe and then including the dependence of the CPB on the redshift (= age of the Universe). The amount of expected gamma-ray photons is an important benchmark for the next-generation telescopes, such as the Compton Spectrometer and Imager (COSI).

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