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 α, g_p, and y≡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∼0.68 to constrain changes in the three parameters over the redshift range 0<z≲0.68. While the constraints are relatively weak (≲1 part in 10³), this is the first simultaneous constraint on the variation of all three parameters. Either one (or more) of α, g_p, and y must vary with cosmological time or there must be systematic velocity offsets between the OH, HCO⁺, and HI absorbing clouds.