**Publication date:** Dec 2013

**Abstract:**

Equatorial circular orbits of test particles in the Kerr-anti-de Sitter

black-hole and naked-singularity spacetimes are analyzed and their

properties like the existence, orientation and stability are discussed.

Due to the attractive cosmological constant (), all particles moving

along equatorial orbits are still bound in the gravitational field of

the central object. In general, there are two families of equatorial

circular orbits. Particles moving along minus-family orbits possess

negative angular momentum and, thus, they are counterrotating from the

point of view of the locally non-rotating frames (LNRF). Particles

moving along plus-family orbits possess, in most cases, positive angular

momentum and belong to corotating particles from the point of view of

the LNRF. Nevertheless, in stationary regions inside black holes and

also near naked singularities with appropriately chosen value of the

cosmological constant and rotational parameter , there are also

counterrotating plus-family circular orbits. Moreover, in spacetimes

with , some of these orbits are characterized by negative specific

energy, indicating the bounding energy of the particle, moving along

such an orbit, higher than its rest energy. In black-hole spacetimes,

all such orbits are radially unstable, but in naked-singularity

spacetimes, stable counterrotating orbits with negative specific energy

exist.

**Authors:**

Slaný, Petr; Pokorná, Miroslava; Stuchlík, Zdeněk;