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This paper discusses traversable wormholes in a dark-energy setting bystarting with a model due to Sung-Won Kim. This model, based on theFriedmann-Lemaitre-Robertson-Walker model, is combined with a generalizedKaluza-Klein model. It is well known that phantom dark energy can in principlesupport traversable wormholes due to the violation of the null energy condition(NEC), a necessary condition for holding a wormhole open. Since the phantomdivide constitutes a serious barrier, we retain the dark-energy assumption$a''(t)>0$ but stay below the phantom divide. To show that the violation of theNEC can only come from the fifth dimension requires a careful analysis of thescale factor $a(t)$. While needed in the overall model, certain 1-forms lackthis scale factor since the extra dimension, often assumed to be compactified,would not be affected by the cosmological expansion. The result is a viablewormhole model of the Sung-Won Kim type. Our main conclusion involvesMorris-Thorne wormholes: due to the Kaluza-Klein gravity, we obtain a completewormhole solution without crossing the phantom divide.

Dark-energy wormholes in generalized Kaluza-Klein gravity