Constraints on Changes in Fundamental Constants from a Cosmologically Distant OH Absorber or Emitter

We have detected the four 18 cm OH lines from the $z\sim 0.765$ gravitational lens toward PMN J0134–0931. The 1612 and 1720 MHz lines are in conjugate absorption and emission, providing a laboratory to test the evolution of fundamental constants over a large lookback time. We compare the HI and OH main line absorption redshifts of the different components in the $z\sim 0.765$ absorber and the $z\sim 0.685$ lens toward $\mathrm{B}0218+357$ to place stringent constraints on changes in $F\equiv g_p[{\alpha }^2/\mu {]}^{1.57}$. We obtain $[\Delta F/F]=(0.44\pm {0.36}^{\mathrm{stat}}\pm {1.0}^{\mathrm{syst}})\times {10}^{-5}$, consistent with no evolution over the redshift range $0<z\lesssim 0.7$. The measurements have a $2\sigma$ sensitivity of $[\Delta \alpha /\alpha ]<6.7\times {10}^{-6}$ or $[\Delta \mu /\mu ]<1.4\times {10}^{-5}$ to fractional changes in $\alpha$ and $\mu$ over a period of $\sim 6.5\mathrm{G}\mathrm{yr}$, half the age of the Universe. These are among the most sensitive constraints on changes in $\mu$. DOI: http://dx.doi.org/10.1103/PhysRevLett.95.261301 © 2005 The American Physical Society