New constraints on the values of the fundamental constants at a look-back time of 7.3 Gyr

Abstract

The study of redshifted spectral lines can provide a measure of the fundamental constants over large look-back times. Current grand unified theories predict an evolution in these constants and astronomical observations offer the only experimental measure of the values of the constants over large timescales. Of particular interest are the dimensionless constants: the fine structure constant ($\alpha$), the proton-electron mass ratio ($\mu$), and the proton g-factor ($g_p$), since these do not require a "standard meterstick". Here we present a re-analysis of the 18 cm hydroxyl (OH) lines at $z=0.89$, which were recently detected with the MeerKAT telescope, toward the radio source PKS\,1830-211. Utilizing the previous constraint of $\Delta \mu /\mu =(-1.8\pm 1.2)\times 10^{-7}$, we obtain $\Delta (\alpha g_p^{0.27})/(\alpha g_p^{0.27})\lesssim 5.7\times 10^{-5}$, $\Delta \alpha /\alpha \lesssim 2.3\times 10^{-3}$ , and $\Delta g_p/g_p\lesssim 7.9\times 10^{-3}$. These new constraints are consistent with no evolution over a look-back time of 7.3 Gyr and provide another valuable data point in the putative evolution of the constants.

5 pages, two figures, one table, text was corrected to match the published version (A&A)

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