Baryon masses in a loop expansion with a form factor

Abstract

We show that the average multiplet masses in the baryon octet and decuplet can be fitted with an average error of only $0.5\ifmmode\pm\else\textpm\fi{}0.3\mathrm{MeV}$ in a meson loop expansion with chiral SU(6) couplings, with the hadrons treated as composite particles using a baryon-meson form factor. The form factor suppresses unphysical short distance effects and leads to a controllable expansion. We find, in contrast to the results of standard chiral perturbation theory, that pion loops are as important as kaon or eta loops as would be expected when only intermediate- and long-distance contributions are retained. We also find that the contributions of decuplet intermediate states are important in the calculation of the masses, and those states must be included explicitly in a consistent theory. These results agree with those of our recent loop-expansion analysis of the baryon magnetic moments. We show, finally, that the parts of the loop contributions that change the tree-level structure of the baryon masses are small, but largely account for the violations of the baryon mass sum rules which hold at the tree level.