In Search of the Ideal Systems to Constrain the Variation of Fundamental Constants

Abstract

It has been realised in the last few years that strong constraints on the time-variations of dimensionless fundamental constants of physics can be derived at any redshift from QSO absorption line systems. Variations of the fine structure constant, α, the proton-to-electron mass ratio, μ, or the combination, $x = {\alpha }^{2}{g}_{\mathrm{p}}/\mu$, where g _p is the proton gyromagnetic factor, have been constrained. However, except for α, the number of lines of sight where these measurements can be performed is limited. In particular the number of known molecular and 21 cm absorbers is small. Our group has started several surveys to search for these systems. We present here a summary of the results obtained till now. In the course of these surveys, we discovered a z ∼ 3 system towards J133724.69 + 315254.55 which is close to “ideal” to constrain the variation of fundamental constants as several constants can be constrained using the same system, namely μ and $x = {\alpha }^{2}{G}_{\mathrm{p}}/\mu$. In particular** the constraint on x is particularly strong with $\Delta x/x = -(1.9 \pm 1.5) \times 1{0}^{-6}$. If combined with the constraint on μ derived recently, this yields a 3σ upper limit on the variation of α at z ∼ 3 of Δα ∕ α  <  2.2 ×10^− 6. We note that the quasar happens to be located in the northern part of the sky. Therefore the variations along the so-called “Australian dipole”, if any, seem to be restricted to a very specific direction in the universe.