  Current-carrying string-loop dynamics is studied in the Kerr spacetimes. With
attention concentrated to the axisymmetric motion of string loops around
symmetry axis of both black-hole (BH) and naked singularity (NS) spacetimes, it
is shown that the resulting motion is governed by the presence of an outer
tension barrier and an inner angular momentum barrier that are influenced by
the BH or NS spin. We classify the string dynamics according to properties of
the energy boundary function (effective potential) for the string loop motion.
We have found that for NS there exist new types of energy boundary function,
namely those with off-equatorial minima. Conversion of the energy of the string
oscillations to the energy of the linear translational motion has been studied.
Such a transmutation effect is much more efficient in the NS spacetimes because
lack of the event horizon. For BH spacetimes efficiency of the transmutation
effect is only weakly spin dependent. Transition from regular to chaotic regime
of the string-loop dynamics is examined and used for explanation of the
string-loop motion focusing problem. Radial and vertical frequencies of small
oscillations of string loops near minima of the effective potential in the
equatorial plane are given. These can be related to high-frequency
quasi-periodic oscillations observed near black holes.
