29mev rates set by n freeze out bbn begins n p expt

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Unformatted text preview: + antiparticle γ + γ ⇔ e− + e+ γ + γ ⇐ e− + e+ only 2 Threshold T ~ m part .c k Examples: Tth=6x109 K for e- e+ Tth = ??? K for p+p- (homework) etc. 5/30/13 UW, ASTR 323, SP13, Eric Agol ©2013 11 Early Par8cle Produc8on through Big Bang Nucleosynthesis • Ini8ally, at the very “highest” temperatures, the universe was filled with radia8on and those par8cle- an8par8cle pairs whose Tth < T. • As T dropped, par8cle- an8par8cle pairs whose Tth≈T “froze out”, but because there is no E- threshold for par8cle annihila8on, they usually did, leaving photons. • Eventually, the universe consisted of neutrons, protons, electrons, various neutrinos (and their an8par8cles) and photons. Due to spontaneous symmetry breaking, there was an excess of ma]er over an8ma]er by 1 part in 109, so when annihila8on was complete, photons outnumbered baryons by 109 to 1. (The...
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This document was uploaded on 04/05/2014.

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