  Following a recent suggestion by Weinberg, we use the large-N expansion in
QCD to discuss the decay amplitudes of tetraquarks into ordinary mesons as well
as their mixing properties. We find that the flavor structure of the tetraquark
is a crucial ingredient to determine both this mixing as well as the decays.
Although in some cases tetraquarks should be expected to be as narrow as
ordinary mesons, they may get to be even narrower, depending on this flavor
structure.
