script 1.3 thermal evo + 1.4 recombination Flashcards
assumptions of thermal evolution
3 assump
explain reason for each, justify
particle freeze out?
collision rate< expansion
how is expansion adiabatoc
collision rate> expansion
formula for particle freeze out?
x
particle freeze out :special case fro rel particles?
N cnst
N_T = N
rel particles remain in th eq even after freeze out
particle freeze out: special case for non-rel particles?
N_T drops exponentially why?
N_T => 0
neutrinos freeze out rxn
neutrino + anti-neutrinos ==> electron + positron………. freeze out
electron + positron ==> photons freeze out then
particle freeze out: pair production vs annihilation
pair production freezes out, not enough temp for annihilation (temp drop by expansion)
decay entropy heats the photon gas, but not the neutrinos. The temperature of the photon gas is therefore higher than that of the neutrino gas.
temp before n after neutrino freezout
T’(before) = 1.4 T (after)
temp of photon gas today is 40%> temp of neutrino gas
photon to baryon ratio?
no pf photons = 10^8 no pf baryons