Structure Constant from Big Bang Nucleosynthesis

We put bounds on the variation of the value of the fine structure constant α, at the time of Big Bang nucleosynthesis. We study carefully all light elements up to 7Li. We correct a previous upper limit on |∆α/α| estimated from 4He primordial abundance and we find interesting new potential limits (depending on the value of the baryon-to-photon ratio) from 7Li, whose production is governed to a large extent by Coulomb barriers. The presently unclear observational situation concerning the primordial abundances preclude a better limit than |∆α/α| ∼ < 2 · 10 −2, two orders of magnitude less restrictive than previous bounds. In fact, each of the (mutually exclusive) scenarios of standard Big Bang nucleosynthesis proposed, one based on a high value of the measured deuterium primordial abundance and one based on a low value, may describe some aspects of data better if a change in α of this magnitude is assumed.