  We consider Lorentzian wormholes with a phantom field and chiral matter
fields. The chiral fields are described by the non-linear sigma model with or
without a Skyrme term. When the gravitational coupling of the chiral fields is
increased, the wormhole geometry changes. The single throat is replaced by a
double throat with a belly inbetween. For a maximal value of the coupling, the
radii of both throats reach zero. Then the interior part pinches off, leaving a
closed universe and two (asymptotically) flat spaces. A stability analysis
shows that all wormholes threaded by chiral fields inherit the instability of
the Ellis wormhole.
