  The quantum admittance of an interacting/coupled mesoscopic system and its
series expansion are obtained by using the refermionization method. With the
help of these non-perturbative results, it is possible to study the
dependencies of the admittance according to the applied dc voltage,
temperature, and frequency without any restriction on the relative values of
these variables. Explicit expressions of the admittance are derived both in the
limits of weak and strong interactions/coupling strength, giving clear
indication of the inductive or capacitive nature of the mesoscopic system. They
help to determine the conditions under which the phase of the current with
respect to the ac voltage is positive.
