Inside the hysteresis loop: multiplicity of internal states in confined fluids.

We study the equilibrium and stability of metastable states and capillary condensation hysteresis of a Lennard-Jones fluid in cylindrical pores by means of the canonical ensemble density functional theory and gauge cell Monte Carlo simulations. We demonstrate a possibility for the existence of multiple laterally uniform internal states of equal density inside the hysteresis loop. The region of multiple states is bounded by the states of zero compressibility. The internal states can be stabilized in Monte Carlo simulations constraining the density fluctuations.