Constraints on scalar coupling to electromagnetism

Ioannis Antoniou

Published 2015-08-05Version 1

I review experimental and observational constraints on a possible non-minimal coupling of a scalar field to electromagnetism (dilatonic coupling). Such a coupling is motivated from recent quasar spectrum observations that indicate a possible spatial and/or temporal variation of the fine-structure constant. I consider a dilatonic coupling of the form $B_F(\phi)=1+g\phi$. The strongest bounds on $g$ come from weak equivalence principle tests which impose the constraint $g<1.6 \times 10^{-17} GeV^{-1}$. This constraint is strong enough to rule out this class of models as a cause for an observable cosmological variation of the fine structure constant unless chameleon type mechanism is present.