Variation of the fine structure constant in light of recent helium abundance measurement
Osamu Seto, Tomo Takahashi, Yo Toda
Abstract
We argue that the recent result of primordial helium-4 ($^{4}\mathrm{He}$) abundance measurement by the EMPRESS Collaboration, which has reported a smaller $^{4}\mathrm{He}$ abundance than other measurements do, can be well fitted by assuming a time-varying fine structure constant $\ensuremath{\alpha}$, which takes a slightly smaller value than the present one during big bang nucleosynthesis (BBN). We find that the EMPRESS result in combination with deuterium abundance measurement indicates $\ensuremath{-}2.6%<\mathrm{\ensuremath{\Delta}}\ensuremath{\alpha}/\ensuremath{\alpha}<\ensuremath{-}1.4%$ (68% C.L.), where $\mathrm{\ensuremath{\Delta}}\ensuremath{\alpha}$ is the difference between the values of $\ensuremath{\alpha}$ at the BBN and present epochs, while $\ensuremath{-}1.2%<\mathrm{\ensuremath{\Delta}}\ensuremath{\alpha}/\ensuremath{\alpha}<0.4%$ (68% C.L.) is obtained from other previous $^{4}\mathrm{He}$ abundance data. We also investigate its effects in the framework where the effective number of neutrino species and the lepton asymmetry, which are other typical interpretations of the EMPRESS result, are allowed to vary. Once a smaller $\ensuremath{\alpha}$ is adopted, the EMPRESS result can be explained without assuming any nonstandard values for the effective number of neutrino species and lepton asymmetry.