Peculiarity of the Coulombic criticality?

A field-theoretical approach to the restricted primitive model of charged hard spheres is proposed. It uses a scalar field phi, similar to that of the sine-Gordon theory of Coulomb gas, but allows taking into account the hard-core interactions. We observe that near criticality the effective Landau-Ginzburg-Wilson Hamiltonian obtained has a negative phi(4) coefficient. A non-perturbative RG analysis of such a Hamiltonian shows that this may lead either to a first-order transition or to an Ising-like critical behavior, the partition being formed by the tricritical surface. This may explain the theoretical wavering encountered in the literature relative to the nature of the Coulombic criticality. (C) 1998 Published by Elsevier Science B.V.