**Publication date:** Oct 2012

**Abstract:**

We study motion of current-carrying string loops in the field of

braneworld spherically symmetric black holes and naked singularities.

The spacetime is described by the Reissner-Nordström geometry with

tidal charge b reflecting the non-local tidal effects coming from the

external dimension; both positive and negative values of the spacetime

parameter b are considered. We restrict attention to the axisymmetric

motion of string loops when the motion can be fully governed by an

appropriately defined effective potential related to the energy and

angular momentum of the string loops. In dependence on these two

constants of the motion, the string loops can be captured, trapped, or

can escape to infinity. In close vicinity of stable equilibrium points

at the centre of trapped states the motion is regular. We describe how

it is transformed to chaotic motion with growing energy of the string

loop. In the field of naked singularities the trapped states located off

the equatorial plane of the system exist and trajectories unable to

cross the equatorial plane occur, contrary to the trajectories in the

field of black holes where crossing the equatorial plane is always

admitted. We concentrate our attention to the so called transmutation

effect when the string loops are accelerated in the deep gravitational

field near the black hole or naked singularity by transforming the

oscillatory energy to the energy of the transitional motion. We

demonstrate that the influence of the tidal charge can be substantial

especially in the naked singularity spacetimes with b > 1 where the

acceleration to ultrarelativistic velocities with Lorentz factor γ

~ 100 can be reached, being more than one order higher in comparison

with those obtained in the black hole spacetimes.

**Authors:**

Stuchlík, Z.; Kološ, M.;