QCD vacuum

From that time the validity of such parameters was confirmed by theoretical variational calculations (D. Diakonov et.al., 1984) and recent lattice simulations of the QCD vacuum (see (T. De Grand et.al., 1998 M.C. Chu et.al., 1994 T. DeGrand, 2001 P. Faccioli et.al., 2003 J. Negele, 1999)). The following figure represent results of lattice calculations (J. Negele, 1999). 

The presence of instantons in QCD vacuum very strongly affects light quark properties, owing consequent generation of quark-quark interactions. These effects lead to the formation of the massive constituent interacting quarks. This implies spontaneous breaking of chiral symmetry (SBCS), which leads to the collective massless excitations of... 

We present in brief the results of the calculations of quark condensate, GG —> 2 photons correlator and QCD vacuum magnetic susceptibility. 

Recently QCD vacuum magnetic susceptibility was calculated and is defined as ... 

Keywords QCD, instanton, vacuum, quark, action, chiral symmetry. 

There is also a topological term which is essential in order to satisfy the t Hooft anomaly conditions [32-34] at the effective Lagrangian level. It is important to note that respecting the t Hooft anomaly conditions is more than an academic exercise. In fact, it requires that the form of the Wess-Zumino term is the same in vacuum and at non-zero chemical potential. Its real importance lies in the fact that it forbids a number of otherwise allowed phases which cannot be ruled out given our rudimentary treatment of the non-perturbative physics. As an example, consider a phase with massless protons and neutrons in three-color QCD with three flavors. In this case chiral symmetry does not break. This is a reasonable realization of QCD for any chemical potential. However, it does not satisfy the t Hooft anomaly conditions and hence cannot be considered. Were it not for the t Hooft anomaly conditions, such a phase could compete with the CFL phase. 

We have seen that the quark mass dependence of ferromagnetism should be important, while we have treated it as an input parameter. When we consider the realization of chiral symmetry in QCD, the quark mass should be dynamically generated as a result of the vacuum superconductivity qq pairs are condensed in the vacuum. We consider here SU(2)l x SU(2)r symmetry. Then Lagrangian should be globally invariant under the operation of any group element with constant parameters, except the symmetry-breaking term... 

Polarization contributions due to the loops of pions and other hadrons cannot be calculated with the help of the QCD perturbation theory. It is easy to estimate hadron vacuum polarization using some low energy model like vector dominance [25]. In a more accurate approach one uses experimental... 

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