  A full Fermi surface exists in underdoped high-temperature superconductors if
the temperature T lies above the pseudogap temperature T*. Below T* only arcs
of Fermi surface survive, scaling with T/T* as T -> 0, with T* displaying
strong doping dependence. There is no accepted explanation for this behavior.
We show that generalizing the BCS theory of normal superconductivity to include
d-wave pairs and antiferromagnetism leads to the origin and doping dependence
of the T* scale, and a quantitative description of Fermi arcs. These results
place strong constraints on viable theories of high-temperature
superconductivity.
