Charged Nariai black holes with a dilaton

The Reissner--Nordstr\"om--de Sitter black holes of standard Einstein-Maxwell theory with a cosmological constant have no analogue in dilatonic theories with a Liouville potential. The only exception are the solutions of maximal mass, the charged Nariai solutions. We show that the structure of the solution space of the dilatonic charged Nariai black holes is quite different from that of the nondilatonic case. Its dimensionality depends on the exponential coupling constants of the dilaton. We discuss the possibility of pair creating such black holes on a suitable background. We find conditions for the existence of charged Nariai solutions in theories with general dilaton potentials, and consider specifically a massive dilaton.