Bag models of hadrons
We believe further progress in the bag model must come from a better understanding of QCD. The bag theory is basically a simple model of the vacuum. A ''perturbative'' vacuum of finite extent is found inside the bag, while the ''true'' vacuum is found outside. The formation of the bag can be viewed as a phase change between the two types of vacuum. In what sense does QCD support this view. There have been many recent attempts to characterize the QCD vacuum. Of particular relevance to the bag model is recent work by Hansson et al. They set out to determine the structure of the vacuum wave function by using a variational argument. Their ''trial'' wave function was inspired by the bag model, but their intention was to describe general features of QCD. Their work starts from the realization that with the usual perturbative model of the vacuum a J /sup PC/ = 0/sup + +/ glueball state can be made with m/sup 2/ < 0. This result implies that the simple vacuum is not the true vacuum. A negative squared mass occurs in the simple model, because the spin force between two gluons paired into a color singlet, spin scalar state is strongly attractive. The potential energy of attraction can overcome the kinetic energy needed to create the two gluons. Such a situation was encountered in the calculation of the lightest bag model 0/sup + +/ glueball (C. B. Thorn, unpublished), which leads to a state with m/sup 2/ < 0 when c.m. corrections are included (65). Hansson et al show that the perturbative vacuum can lower its energy by filling up with scalar glueballs. They calculate the energy of glueballs containing two and four gluons and find that the energy of the four-gluon state is higher. Therefore the vacuum energy reaches a minimum when the glueballs start to overlap.
- Research Organization:
- Dept. of Physics, Univ. of Utah, Salt Lake City, UT
- OSTI ID:
- 6159429
- Journal Information:
- Ann. Rev. Nucl. Part. Sci.; (United States), Vol. 33
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
BAG MODEL
HADRONS
QUANTUM CHROMODYNAMICS
DISTURBANCES
GLUEBALLS
GLUONS
KINETIC ENERGY
PHASE TRANSFORMATIONS
POTENTIAL ENERGY
SPIN
VACUUM STATES
WAVE FUNCTIONS
ANGULAR MOMENTUM
COMPOSITE MODELS
ELEMENTARY PARTICLES
ENERGY
EXTENDED PARTICLE MODEL
FIELD THEORIES
FUNCTIONS
MATHEMATICAL MODELS
PARTICLE MODELS
PARTICLE PROPERTIES
POSTULATED PARTICLES
QUANTUM FIELD THEORY
QUARK MODEL
645400* - High Energy Physics- Field Theory