Big Bang nucleosynthesis and variation of quark masses

Many speculative theories of fundamental physics suggest that fundamental constants of the Standard Model may vary over coosmological time scales. The formation of light nuclei in the Early Universe is an ideal test of these sepculations because i) they occured early in the history of the universe and ii) this is understood at a fair level of precision. We study the constraints imposed by the observation of lioght element abundances on the possible variation of quark masses. For that we must track the rates and cross sections. In order to do this without introducing a lot of model dependence we rely on a combination of lattice QCD and a variety of effective field theories appropriate to different observables and energy regimes. We also discuss related topics as limits on the variation of the Higgs field expectation value imposed by BBN.