  In the underdoped high temperature superconductors, instead of a complete
Fermi surface above Tc, only disconnected Fermi arcs appear, separated by
regions that still exhibit an energy gap. We show that in this pseudogap phase,
the energy-momentum relation of electronic excitations near E_F behaves like
the dispersion of a normal metal on the Fermi arcs, but like that of a
superconductor in the gapped regions. We argue that this dichotomy in the
dispersion is hard to reconcile with a competing order parameter, but is
consistent with pairing without condensation.
