This process reaches a critical point where electron-positron annihilations are unable to produce(*) neutrinos and early on, this process occurred at temperatures sufficient to create a "deuterium bottleneck" effect.
The outcomes from the model for this process were compared to the observed outcome by Thushari et al to establish higher precision for parameters in the Brans-Dicke gravitational theory and studies on energy density evolution during this process have been used to establish an upper bound on the tau neutrino's mass. This process reaches a critical point where electron-positron annihilations are unable to produce(*) neutrinos and early on, this process occurred at temperatures sufficient to create a "deuterium bottleneck" effect. Due to a relative dearth of neutrons, the model for this process correctly predicts that one fourth of the universe's mass should consist of helium as originally posited in a famous paper by Alpher, Bethe and Gamow. Occurring within the first three minutes, FTP, identify this process of the early universe in which the first light elements were sythesized.
The outcomes from the model for this process were compared to the observed outcome by Thushari et al to establish higher precision for parameters in the Brans-Dicke gravitational theory and studies on energy density evolution during this process have been used to establish an upper bound on the tau neutrino's mass.
Big Bang Nucleosynthesis