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We discuss the particle horizon problem in the framework of spatiallyhomogeneous and isotropic scalar cosmologies. To this purpose we consider aFriedmann-Lemaitre-Robertson-Walker (FLRW) spacetime with possibly non-zerospatial sectional curvature (and arbitrary dimension), and assume that thecontent of the universe is a family of perfect fluids, plus a scalar field thatcan be a quintessence or a phantom (depending on the sign of the kinetic partin its action functional). We show that the occurrence of a particle horizon isunavoidable if the field is a quintessence, the spatial curvature isnon-positive and the usual energy conditions are fulfilled by the perfectfluids. As a partial converse, we present three solvable models where a phantomis present in addition to a perfect fluid, and no particle horizon~appears.

On the necessity of phantom fields for solving the horizon problem in scalar cosmologies