Isgur–Wise function in a relativistic model of constituent quarks

The integral representation for Isgur–Wise function (IWF) is obtained in the framework of instant-form relativistic Hamiltonian dynamics for mesons with one heavy quark. The upper and lower limits are calculated for the slope parameter of IWF ρ2 by the model independent way. IWF is calculated for different wave functions of quarks in the meson. The difference between the limits of ρ2 equals 1/3. The constraint on the slope parameter is in a good agreement with experiments. The weak dependence of IWF on the choice of wave functions is found.