The dielectric constant of ionic solutions is known to reduce with increasing ionic
concentrations. However, the origin of this effect has not been thoroughly explored. In this
paper, we study two such possible sources: long-range Coulombic correlations and solvent
excluded-volume. Correlations originate from fluctuations of the electrostatic potential
beyond the mean-field Poisson-Boltzmann theory, evaluated by employing a field-
theoretical loop expansion of the free energy. The solvent excluded-volume, on the other …