Quintessence and the Rest of the World: Suppressing Long-Range Interactions

A nearly massless, slowly rolling scalar field $\phi$ may provide most of the energy density of the current Universe. One potential difficulty with this idea is that couplings to ordinary matter should lead to observable long-range forces and time dependence of the constants of nature. I explore the possibility that an approximate global symmetry serves to suppress such couplings even further. Such a symmetry would allow a coupling of $\phi$ to the pseudoscalar $F_{\mu \nu }{\tilde{F}}^{\mu \nu }$ of electromagnetism, which would rotate the polarization state of radiation from distant sources. This effect is fairly well constrained, but it is conceivable that future improvements could lead to a detection of a cosmological scalar field.