= Nuclear-burning qualification of the helium expansion-rate response
A moderately enhanced <Hubble parameter> raises the <primordial helium mass fraction> through earlier <cosmological weak freeze-out> and less <free-neutron decay after freeze-out>, provided nuclear burning still incorporates nearly all surviving neutrons into helium-4. This provision matters: if expansion carries the gas through the nuclear-burning temperature range faster than the reaction times, <neutron-limited helium synthesis> no longer applies. More neutrons surviving the bottleneck alone does not prove more final helium in that limit.
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