Improved constraints on possible variation of physical constants from H I 21-cm and molecular QSO absorption lines

Quasar (QSO) absorption spectra provide an extremely useful probe of possible cosmological variation in various physical constants. Comparison of H I 21-cm absorption with corresponding molecular (rotational) absorption spectra allows us to constrain variation in y ; a 2 g p, where a is the fine-structure constant and g p is the proton g-factor. We analyse spectra of two QSOs, PKS 14131135 and TXS 02181357, and derive values of Dy/ y at absorption redshifts of z 0: 2467 and 0. 6847 by simultaneous fitting of the H I 21-cm and molecular lines. We find Dy/ y 20: 20 ⁰: 44 10 25 and Dy/ y 20: 16 ⁰: 54 10 25 respectively, indicating an insignificantly smaller y in the past. We compare our results with other constraints from the same two QSOs given recently by Drinkwater et al. and Carilli et al. , and with our recent optical constraints, which indicated a smaller a at higher redshifts.