The SU(3) symmetric chiral quark model, which describes interactions between quarks, gluons and the Goldstone bosons, explains reasonably well many aspects of the flavor and spin structure of the proton, except for the values of f 3 /f 8 and ∆ 3 /∆ 8 . Introducing the SU(3)-breaking effect suggested by the mass difference between the strange and nonstrange quarks, we find that this discrepancy can be removed and better overall agreement obtained.

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The spin and flavor fractions of constituent quarks in the proton are obtained from their chiral fluctuations involving Goldstone bosons. SU(3) flavor symmetry breaking suggested by the mass difference between the strange and up, down quarks is included, and this improves the agreement with the data markedly.Comment: 13 pages, 1 table, no figures, LaTex, eta & eta' parts change