  The functional renormalization group for the effective action is used to
construct an effective hydrodynamic description of weakly interacting Bose
gases. We employ a scale-dependent parametrization of the boson fields
developed previously to start the renormalization evolution in a Cartesian
representation at high momenta and interpolate to an amplitude-phase one in the
low-momentum regime. This technique is applied to Bose gases in one, two and
three dimensions, where we study thermodynamic quantities such as the pressure
and energy per particle. The interpolation leads to a very natural description
of the Goldstone modes in the physical limit, and compares well to analytic and
Monte-Carlo simulations at zero temperature. The results show that our method
improves aspects of the description of low-dimensional systems, with stable
results for the superfluid phase in two dimensions and even in one dimension.
