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Multidimensional cosmologies allow for variations of fundamental physicalconstants over the course of cosmological evolution, and different versions ofthe theories predict different time dependences. In particular, such variationscould 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 ofhigh-redshift QSO spectra. Here we analyze a new, high-resolution spectrum ofthe z=2.81080 molecular hydrogen absorption system toward the quasar PKS0528-250 to derive a new observational constraint to the time-averagedvariation 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 measuredlimits.Comment: 9 pages, 2 tables, 3 figures, LaTeX (aas2pp4.sty and epsf.sty  included). To be published in Ap

Testing Cosmological Variability of the Proton‐to‐Electron Mass Ratio Using the Spectrum of PKS 0528−250