Consistency of local and astrophysical tests of the stability of fundamental constants

Abstract

Tests of the stability of nature's fundamental constants are one of the cornerstones of the ongoing search for the new physics which is required to explain the recent acceleration of the universe. The two main settings for these tests are high-resolution spectroscopy of astrophysical systems (mainly in low-density absorption clouds along the line of sight of bright quasars) and laboratory comparisons of pairs of atomic clocks. Here we use standard chi-square techniques to perform a global analysis of all currently available data, studying both the consistency of tests of stability of different constants (specifically the fine-structure constant $\alpha$, the proton-to-electron mass ratio $\mu$ and the proton gyromagnetic ratio $g_p$) and the consistency between local laboratory and astrophysical tests. We start by doing a model-independent analysis (studying the internal consistency of the various available datasets) but also explore specific phenomenological models motivated by string theory and grand unification. Overall there is weak (one to two sigma) evidence of variations, at the level of up to a few parts per million, and reasonable agreement between laboratory and astrophysical tests. This result holds even if one removes from the analysis the Webb {\it et al.} archival dataset of $\alpha$ measurements. Forthcoming astrophysical facilities, such as the ESPRESSO spectrograph, should be able to confirm or rule out these hints.