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Neutrino decoupling

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Neutrino Decoupling: In the early Universe, electrons and neutrinos are strongly coupled through scattering (ν e ↔ ν e) and annihilation (ν ν¯ ↔ e e¯). (see attached files for defined parameters)
(a) Find the redshift and temperature of neutrino decoupling.
(b) After neutrino decoupling, the Universe is filled with a cosmic neutrino background. Assuming that all 3 species of neutrinos have a mass of mν = 1 eV, and that neutrinos follow a Maxwell Boltzmann distribution since they are currently non-relativistic, how many relic neutrinos are in a cubic meter?

(see attached file for detailed problem)

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Solution Summary

Given the values of cosmological parameters observed or assumed today, we calculate the main source of opacity for neutrino collisions and calculate the age of neutrino decoupling.

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