Constraints on the electron-to-proton mass ratio variation at the epoch of reionization

Abstract

ABSTRACT Far-infrared fine-structure transitions of [C i] and [C ii] and rotational transitions of CO are used to probe hypothetical variations of the electron-to-proton mass ratio μ = me/mp at the epoch of reionization (z > 6). A constraint on Δμ/μ = (μobs − μlab)/μlab = (0.7 ± 1.2) × 10−5 (1σ) obtained at $\bar{z} = 6.31$ is the most stringent up-to-date limit on the variation of μ at such high redshift. For all available estimates of Δμ/μ ranging between z = 0 and z ∼ 1100, the epoch of recombination, a regression curve Δμ/μ = kμ(1 + z)p, with kμ = (1.6 ± 0.3) × 10−8 and p = 2.00 ± 0.03, is deduced. If confirmed, this would imply a dynamical nature of dark matter/dark energy.