Relativistic Electron Scattering and Big Bang Nucleosynthesis
  This paper is superseded by Arxiv:1911.07334. Big-bang nucleosynthesis (BBN)
is a valuable tool to constrain the physics of the early universe and is the
only probe of the radiation-dominated epoch. A fundamental assumption in BBN is
that the nuclear velocity distributions obey Maxwell-Boltzmann statistics as
they do in stars. In this letter, however, we point out that there is a
fundamental difference between stellar reaction rates and BBN reaction rates.
Specifically, the BBN epoch is characterized by a dilute baryon plasma for
which the velocity distribution of nuclei is mainly determined by the dominant
Coulomb scattering with mildly relativistic electrons. This modifies the
nuclear velocity distributions and significantly alters the thermonuclear
reaction rates, and hence, the light-element abundances. We show that this
novel result alters all previous calculations of light-element abundances from
BBN, and indeed exacerbates the discrepancies between BBN and inferred
primordial light-element abundances possibly suggesting the need for new
physics in the early universe.
