Bekenstein model and the time variation of the strong coupling constant
  We propose to generalize Bekenstein model for the time variation of the fine structure "constant" $\alpha_{em}$ to QCD strong coupling constant $\alpha_S$. We find that, except for a ``fine tuned'' choice of the free parameters, the extension can not be performed trivially without being in conflict with experimental constraints and this rules out $\alpha_S$ variability. This is due largely to the huge numerical value of the QCD vacuum gluon condensate when compared to the matter density of the universe. 
N. Chamoun (1,2), S.J. Landau (1) and H. Vucetich (1) ((1)U.N.L.P., La   Plata, Argentina, (2) HIAST, Damascus, Syria)