  Despite the ubiquity of nanoconfined aqueous electrolytes, a theoretical
framework that accounts for the nonlinear coupling of water and ion
polarization is still missing. We introduce a nonlocal and nonlinear field
theory for the nanoscale polarization of ions and water and derive the
electrolyte dielectric properties as a function of salt concentration to first
order in a loop expansion. Classical molecular dynamics simulations are
favorably compared with the calculated dielectric response functions. The
theory correctly predicts the dielectric permittivity decrement with rising
salt concentration and furthermore shows that salt induces a Debye screening in
the longitudinal susceptibility but leaves the short-range water organization
remarkably unchanged.
