  The idea of spin-charge separation in cuprate superconductors has been
recently energized by Senthil and Fisher who formulated a Z_2 gauge theory and,
within its context, proposed a ``vison detection'' experiment as a test for
topological order in a sample with multiply connected geometry. Here we show
that the same experiment can be performed to test for the spin-charge
separation in U(1) [but not in SU(2)] theory and argue that vortex core
spectroscopy can in fact distinguish between the different symmetries of the
fictitious gauge field.
