The chiral Lagrangian for Goldstone boson scattering is a power series
expansion in numbers of derivatives. Each successive term is suppressed by
powers of a scale, Λχ​, which must be less than of order 4πf/N​ where f is the Goldstone boson decay constant and N is the
number of flavors. The chiral expansion therefore breaks down at or below 4πf/N​. We argue that the breakdown of the chiral expansion is
associated with the appearance of physical states other than Goldstone bosons.
Because of crossing symmetry, some ``isospin'' channels will deviate from their
low energy behavior well before they approach the scale at which their low
energy amplitudes would violate unitarity. We argue that the estimates of
``oblique'' corrections from technicolor obtained by scaling from QCD are
untrustworthy.Comment: harvmac, 18 pages (3 figures), HUTP-92/A025, BUHEP-92-18, new version
fixes a TeX problem in little mod