**Publication date:** Dec 2007

**Abstract:**

Rotating black holes in the brany universe of the Randall-Sundrum type

with infinite additional dimension are described by the Kerr geometry

with a tidal charge b representing the interaction of the brany black

hole and the bulk spacetime. We investigate the role of the tidal charge

in the orbital resonance model of quasiperiodic oscillations (QPOs) in

black hole systems. The orbital Keplerian frequency ν_{K} and the radial

and vertical epicyclic frequencies ν_{r}, ν_{θ} of the equatorial,

quasicircular geodetical motion are discussed, and the local maxima of

their radial profiles related to Keplerian accretion discs are given,

assuming the inner edge of the disc located at loci of the innermost

stable circular geodesic. The resonant conditions are given for possible

direct (parametric) resonances of the oscillations with the radial and

vertical epicyclic frequencies and for some trapped oscillations of the

warped discs with resonant combinational frequencies involving the

Keplerian and radial epicyclic frequencies. It is shown, how the tidal

charge could influence matching of the observational data indicating the

3:2 frequency ratio observed in GRS 1915+105 microquasar with prediction

of the orbital resonance model. The „magic“ dimensionless black hole

spin enabling presence of strong resonant phenomena at the radius, where

ν_{K}:ν_{θ}:ν_{r} = 3:2:1, is determined in dependence on the tidal

charge. Such strong resonances could be relevant even in sources with

highly scattered resonant frequencies, as those expected in Sgr A*.

**Authors:**

Stuchlík, Zdeněk; Kotrlová, Andrea;