  The issue of chiral extrapolations in heavy quarkonium systems is discussed.
We show that the light quark mass dependence of the properties of heavy
quarkonia is not always suppressed. For quarkonia close to an open flavor
threshold, even a nonanalytic chiral extrapolation is needed. Both these
nontrivial facts are demonstrated to appear in the decay widths of the hindered
M1 transitions between the first radially excited and ground state P-wave
charmonia. The results at a pion mass of about 500 MeV could deviate from the
value at the physical pion mass by a factor of two. Our findings show the
necessity of performing chiral extrapolations for lattice simulations of heavy
quarkonium systems.
