Fundamental physics with ESPRESSO: Constraints on Bekenstein and dark energy models from astrophysical and local probes

Dynamical scalar fields in an effective four-dimensional field theory are naturally expected to couple to the rest of the theory's degrees of freedom, unless some new symmetry is postulated to suppress these couplings. In particular, a coupling to the electromagnetic sector will lead to spacetime variations of the fine-structure constant, α. Astrophysical tests of the space-time stability of α are therefore a powerful probe of new physics. Here we use ESPRESSO and other contemporary measurements of α, together with background cosmology data, local laboratory atomic clock and weak equivalence principle measurements, to place stringent constraints on the simplest examples of the two broad classes of varying α models: Bekenstein models and quintessence-type dark energy models, both of which are parametric extensions of the canonical ΛCDM model. In both cases, previously reported constraints are improved by more than a factor of ten. This improvement is largely due to the very strong local constraints, but astrophysical measurements can help to break degeneracies between cosmology and fundamental physics parameters.