Strange quark, heavy quark and gluon contents of light hadrons

The sea-quark content of baryons (such as anti ss, anti cc, anti bb ...) is calculated by a combined use of the QCD trace anomaly and a chiral quark model. The result is applied to the examination of the explicit symmetry breaking in baryons, the intrinsic heavy quarks in baryons, and the Higgs-baryon coupling constants. We find that (i) the small anti ss content, large πN sigma term (∝45 MeV) and the Gell-Mann-Okubo mass formula for baryons are consistently explained contrary to the naive argument based on the lowest-order expansion by the current quark masses. The basic point is the non-linear dependence of the physical quantities on the strange mass. (ii) The probability of finding charm in the nucleon is about 0.5%, which is relevant to the charm structure function of the nucleon at large xBj and also to the charm production in proton-nucleus collisions at large Feynman xF. (iii) Both strange and heavy quarks are equally important for the Higgs-nucleon coupling. Small but non-negligible OZI violation in baryons due to the axial anomaly plays a key role in all the above quantities. The sea-quark content of the pion and the kaon and the color-sextet quark content in the nucleon are also discussed. (orig.)