Bekenstein's model of a scalar field $\phi$ that changes the electromagnetic permeability (usually identified with ``changing $\alpha$'')predicts tiny variations of the effective fine structure constant up to very high red-shifts, $\alpha(z=3.5)/\alpha_0-1 < 10^{-10}$, when the constraints from E\"otv\"os-Dicke-Braginsky types of experiments are imposed. We generalize this model by allowing additional couplings of $\phi$ to both the dark matter candidate and to the cosmological constant. We show that in a supersymmetric generalization of Bekenstein's model, the coupling to the LSP, which is assumed to contribute significatly to the dark matter, can be up to six orders of magnitude stronger than the coupling to the baryon energy density. This allows one to evade the present limits on the non-universality of gravitational attraction due to $\phi$-exchange and at the same time accommodate the effective shift of $\alpha$ at the level of $\alpha(z=3.5)/\alpha_0-1 \sim 10^{-5}$, reported recently from observations of quasar absorption spectra.

Tuesday, October 23rd 2001, 13:10
Ernest Rutherford Physics Building, room 326