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

TLDR

A nearly massless, slowly rolling scalar field φ may account for most of the current Universe’s energy density, yet couplings to ordinary matter could produce observable long‑range forces and time variation of fundamental constants. I investigate whether an approximate global symmetry can further suppress these couplings. The symmetry would allow φ to couple to the electromagnetic pseudoscalar \(F_{\mu\nu}\tilde{F}^{\mu\nu}\), rotating the polarization of radiation from distant sources. This effect is already fairly well constrained, though future improvements could enable detection of the cosmological scalar field.

Abstract

A nearly massless, slowly rolling scalar field $\ensuremath{\varphi}$ 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 $\ensuremath{\varphi}$ to the pseudoscalar ${F}_{\ensuremath{\mu}\ensuremath{\nu}}{\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{F}}^{\ensuremath{\mu}\ensuremath{\nu}}$ 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.