Testing cosmological variability of the proton-to-electron mass ratio using the spectrum of PKS 0528-250

Multidimensional cosmologies allow for variations of fundamental physical constants over the course of cosmological evolution, and different versions of the theories predict different time dependences. In particular, such variations could manifest themselves as changes of the proton-to-electron mass ratio \mu=m_p/m_e over the period of ~ 10^{10} years since the moment of formation of high-redshift QSO spectra. Here we analyze a new, high-resolution spectrum of the z=2.81080 molecular hydrogen absorption system toward the quasar PKS 0528-250 to derive a new observational constraint to the time-averaged variation rate of the proton-to-electron mass ratio. We find |\dot{\mu} / \mu| < 1.5 \times 10^{-14}/year, which is much tighter than previously measured limits.