**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;