epsilon expansion of the conductivity at the superconductor-Mott-insulator transition

We study the critical behavior of the conductivity sigma(omega) at the zero-temperature superconductor-Mott-insulator transition in d spacetime dimensions for a model of bosons with short-range interaction and no disorder. We obtain sigma(omega(n))=(4e(2)/(h) over bar)sigma(epsilon)omega(n)(1-epsilon), as predicted by the scaling theory, and the prefactor sigma(epsilon) is calculated in the epsilon expansion, to order epsilon(2) (epsilon=4-d). In two spatial dimensions (d=3), we find a value of the universal conductance sigma*=0.315(4e(2)/h), in good agreement with the known Monte Carlo results.