Bounds on variations of the strange quark mass from Big Bang nucleosynthesis

We analyze the effect of a variation of the strange nucleon matrix element $⟨N\mathrm{\mid }{m}_s\bar{s}s\mathrm{\mid }N⟩$ on the abundances of the light elements produced in the Big Bang. For that, we vary the nucleon mass in the leading eight reactions that involve neutrons, protons and the four lightest nuclei. We use various available Big Bang nucleosynthesis codes and find that the measured deuterium and ${}^4$He abundances set strict limits on the nucleon mass variations. This translates into an upper bound of possible variations of the strange quark mass, $\mid \mathrm{\Delta }{m}_s\mathrm{/}{m}_s\mid \le 5.1\mathrm{\%}$.