C k examples tth6x109 k for e e tth

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Unformatted text preview: ; if not, then the reactants “______ ____.” •  As the Universe expands, the temperature & density _____, so reac8on rates slow down (as density squared, and exponen8ally for T < Tcrit). •  When reac8on 8me is ______ than the age of the Universe, then the reac8on freezes out. 5/30/13 UW, ASTR 323, SP13, Eric Agol ©2013 9 Freeze- outs 1)  Ma]er produc8on (ma]er/an8- ma]er asymmetry): baryon freeze- out; γ +γ ⇔ p + p γ +γ ⇔ n + n 2) Neutron/proton freeze- out; n ⇔ p + e− + ν + 1.29MeV e 3) Big- bang nucleosynthesis: p/α freeze- out; 2p + 2n ⇔ 2D ⇔ He + 0.3MeV 4) Recombina8on: atom freeze- out p + e ⇔ H + 13.6eV − 5/30/13 UW, ASTR 323, SP13, Eric Agol ©2013 10 Par8cle Produc8on in the Radia8on Era ( When E phot ( = hν ) ≥ Ematter = mc 2 Example : when kT hν > mec 2 when kT < mec 2 ) γ + γ ⇒ particle...
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