The surprising influence of late charged current weak interactions on Big Bang Nucleosynthesis

E. Grohs; G. M. Fuller

doi:10.1016/j.nuclphysb.2016.08.034

paper

The surprising influence of late charged current weak interactions on Big Bang Nucleosynthesis

arXiv:1607.02797 · doi:10.1016/j.nuclphysb.2016.08.034

Abstract

The weak interaction charged current processes ( $ν_{e} + n \leftrightarrow p + e^{-}$ , $ν ˉ_{e} + p \leftrightarrow n + e^{+}$ , $n \leftrightarrow p + e^{-} + ν ˉ_{e}$ ) interconvert neutrons and protons in the early universe and have significant influence on Big Bang Nucleosynthesis (BBN) light-element abundance yields, particulary that for $^{4} He$ . We demonstrate that the influence of these processes is still significant even when they operate well below temperatures $T \sim 0.7 MeV$ usually invoked for "weak freeze-out," and in fact down nearly into the alpha-particle formation epoch ( $T \approx 0.1 MeV$ ). This physics is correctly captured in commonly used BBN codes, though this late-time, low-temperature persistent effect of the isospin-changing weak processes, and the sensitivity of the associated rates to lepton energy distribution functions and blocking factors are not widely appreciated. We quantify this late-time influence by analyzing weak interaction rate dependence on the neutron lifetime, lepton energy distribution functions, entropy, the proton-neutron mass difference, and Hubble expansion rate. The effects we point out here render BBN a keen probe of any beyond-standard-model physics that alters lepton number/energy distributions, even subtly, in epochs of the early universe all the way down to near $T = 100 keV$ .

arXiv comment27 pages, 8 figures

The surprising influence of late charged current weak interactions on Big Bang Nucleosynthesis

Abstract

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