**Publication date:** Nov 2001

**Abstract:**

The equilibrium of a charged test particle with spin located in the

Reissner-Nordström background with a nonzero cosmological constant

is investigated. The stationary equilibrium conditions resulting from

the equations of motion and the equations of spin dynamics have to be

satisfied simultaneously. It is shown that equilibrium conditions are

independent of the spin of the test particle. For uncharged particles,

they are satisfied at the so-called static radius, where gravitational

attraction is exactly compensated for by cosmological repulsion. For

charged particles, there is a variety of possible equilibria due to the

electromagnetic interaction of the particle and the background. Any

charged particle can be in an unstable equilibrium state between the

black-hole and cosmological horizons of asymptotically de Sitter

spacetimes, while sufficiently repulsed particles can be in an inner

unstable equilibrium state and an outer stable equilibrium state above

the horizon of asymptotically anti-de Sitter spacetimes. The

separation-independent equilibrium is possible in extreme

Reissner-Nordström spacetimes only.

**Authors:**

Stuchlík, Zdeněk.; Hledík, Stanislav;