**Publication date:** Sep 2005

**Abstract:**

Perfect fluid tori with a uniform distribution of the specific angular

momentum, ell(r, θ) = const, orbiting the Kerr de Sitter black holes or

naked singularities are studied. It is well known that the structure of

equipotential surfaces of such marginally stable tori reflects the basic

properties of any tori with a general distribution of the specific

angular momentum. Closed equipotential surfaces corresponding to

stationary thick discs are allowed only in the spacetimes admitting

stable circular geodesics. The last closed surface crosses itself in the

cusp(s) enabling the outflow of matter from the torus due to the

violation of hydrostatic equilibrium. The inner cusp enables an

accretion onto the central object. The influence of the repulsive

cosmological constant, Λ > 0, on the equipotential surfaces lies in

the existence of the outer cusp (with a stabilizing effect on the thick

discs) and in the strong collimation of open equipotential surfaces

along the rotational axis. Both the effects take place near a so-called

static radius where the gravitational attraction is just balanced by the

cosmic repulsion. The outer cusp enables excretion, i.e., the outflow of

matter from the torus into the outer space. The plus-family discs (which

are always co-rotating in the black-hole backgrounds but can be counter-

rotating, even with negative energy of the fluid elements, in some

naked-singularity backgrounds) are thicker and more extended than the

minus-family ones (which are always counter-rotating in all

backgrounds). For co-rotating discs in the naked-singularity spacetimes,

the potential well between the centre of the disc and its edges at the

cusps is usually much higher than in the black-hole spacetimes. If the

parameters of naked-singularity spacetimes are very close to the

parameters of extreme black-hole spacetimes, the family of possible

disc-like configurations includes members with two isolated discs where

the inner one is always a counter-rotating accretion disc.

**Authors:**

Slaný, Petr; Stuchlík, Zdenek;