We present here the general expressions for the acceleration of massive test
particles along the symmetry axis of the Kerr metric, and then study the main
properties of this acceleration in different regions of the spacetime. In
particular, we show that there exists a region near the black hole in which the
gravitational field is repulsive. We provide possible physical interpretations
about the role of this effect in terms of the different conserved parameters.
The studies of these geodesics are important not only to understand better the
structure of the Kerr spacetime but also to its use as a possible mechanism for
the production of extragalactic jets. Our results are obtained with the help of
expressing the geodesics of the Kerr spacetime in terms of the Weyl
coordinates.Comment: revtex4, no figures and tables. Gen. Relativ. Grav. 48 (2016) 6
