A Phenomenological Study Of Exotic Hadrons

In this thesis, we study the molecule bound state of DD*,DD and DΛc based on the Chiral Perturbation Theory. Also, wo study the instanton contributions to the correlator of the hybrid current gqσμvGμvaTqq. These contributions are then in-cluded in a QCD sum-rule analysis of the isoscalar 0++hybrid mass. The results give a prediction of fo(1370),fo(1500).fo(1710) and the four mesons found between 2000MeV～2300MeVBecause the naive quark modle is unable to explain the recent new hadron state, people developed many new models to study the new exotic hadrons found in experiment. The most used model are potential model and hybrid. After giving a brief talk about the hadron physics, we introduce the Effective Field Theory and Chiral Perturbation Theory. Chiral Perturbation Theory is an effective theory of QCD under low-energy. Based on the symmetrys of QCD lagrangian, scientist found the effective lagrangian. using this effective lagrangian, we do not need to calculate the non-perturbation effect between quarks and gluons. We need only to pay attention on the hadrons.After that we introduce the recent two works based on the Chiral Perturbation Theory:The first is the molecule state of meson-meson using the potential model. The resonance state X(3872) is widely believed to be a bound state of DD*. and most study of it was based on single-meson exchange potential. We study the twoπand two k meson exchange besides the singleπexchange potential. We found when added the two-meson exchange potential, although the size of potential si not change a lot, but the cutoffΛneed to form a bound state is reduced much. Without the twoπand two k meson exchange we can only found a bound-state underΛ≥1750MeV, by introducing two meson exchange, wen can low the cutoff to 1360MeV. especially only add twoπwith singleπpotential, we can low the cutoff to 1450MeV. Although this cutoff is not sanill enough, we believe the molecule bound state of DD* may exist. Beside this, we calculate the molecule type bound state of DD. There is no singleπexchange potential between them, so it is hard to bind them. With only twoπexchange potential we find a bound state under cutoffΛ≥1750MeV. This cutoff is a bit large. but this give some hints to us to calculate the state of meson and baryon.The second is the bound state of meson and baryon. Based on the result of DD, we found the potential between meson and baryon may be bigger than DD. Our results shows so. Between DΛc, we found bound state after we rise cutoff up to 1150MeV. This is a reasonable cutoff, and we believe the boudn state of DΛc may exist.At last we calculate the instanton effect in QCD sum rules for the O++Hybrid. Based on the QCD sum-rules, we added instanton effect to study hybrid current gqσμvGμvaTqq. Also we study the effect between hybrid and glueball current. And find the mixing of (uug+ddg)/(?)2(ssg) with glueball causes two states, their mass stay between region 1.4-1.8GeV(1.4-2.2GeV) and 1.8-2.2GeV(2.2-2.6GeV). This give an explanation to the crowed of fo(1370),fo(1500),fo(1710) and the four O++meson states between 2.0GeV～2.3GeV.