Constraining the Variation of Fundamental Constants using 18 cm OH Lines

We describe a new technique to estimate variations in the fundamental constants using 18 cm OH absorption lines, with the advantage that all lines arise in the same species, allowing a clean comparison between the measured redshifts. In conjunction with one additional transition, it is possible to simultaneously measure changes in $\alpha$, $g_p$, and $y\equiv m_e/m_p$. We use the 1665 and 1667 MHz line redshifts in conjunction with those of HI 21 cm and mm-wave molecular absorption in a gravitational lens at $z\sim 0.68$ to constrain changes in the three parameters over the redshift range $0<z\lesssim 0.68$. While the constraints are relatively weak ($\lesssim 1$ part in ${10}^3$), this is the first simultaneous constraint on the variation of all three parameters. Either one (or more) of $\alpha$, $g_p$, and $y$ must vary with cosmological time or there must be systematic velocity offsets between the OH, ${\mathrm{H}\mathrm{C}\mathrm{O}}^{+}$, and HI absorbing clouds.