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 q~, 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 q4 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. @ 1998 Published by Elsevier Science B.V. PACS: 61.2O.Qg; 05.4O.+j; 05.70.Jk; 64.60.Fr The Coulombic criticality is often studied theoreti-cally in terms of the restricted primitive model (RPM: equal number N+ and N _ of positive and negative hard spheres of equal diameter, d, with charges, fze, im-mersed in a structureless solvent of dielectric permit-tivity E; z2/e = 1 in what follows). Although there is general agreement on the existence of a liquid-gas-lik