Bounded radial geodesics around a Kerr-Sen black hole

We examine the geodesics of the Kerr-Sen black hole solution, an exact solution describing a rotating, charged, axisymmetric black hole, discovered by Sen in 1992. We show that the geodesic Hamilton-Jacobi is separable both in the Einstein and the string frame and we perform a separation of variables. Then, using the integrals, we study the radial motion from the point of view of the existence of bounded geodesics and we show that there are situations which are specific to this kind of black hole. We also compute the area of the horizon in the two frames.