Nonperturbative expansion in QCD

The purpose of this article is to construct the nonperturbative expansion in quantum chromodynamics using a new small parameter and apply it to the investigation of the connection between nonperturbative and perturbative regimes of the effective coupling constant. We calculate the nonperturbative renormalization group β-function and discuss the properties of the series convergence using the two-loop approximation in this method. Based on the information from meson spectroscopy we derive the effective coupling constant in the perturbative region.     

非微扰色动力学的新途径

本文首先对于所谓光前ＱＣＤ作一概述,然后阐述Ｋ．Ｇ．Ｗｉｌｓｏｎ等人最近提出和发展的非微扰ＱＣＤ理论方案的基本内容． We explain the ideas of the light - front QCD and describe an outline of Wilson S approach to nonperturbative QCD.     

Nonperturbative dynamics in the color-magnetic QCD vacuum

In the deconfinement phase of QCD, quarks and gluons interact with the dense stochastic color-magnetic vacuum. We consider the dynamics of quarks in this deconfinement phase using the field correlators method and derive an effective nonperturbative interquark potential, in addition to the usual perturbative short-range interaction. We find the resulting angular-momentum-dependent interaction to be attractive enough to maintain bound states and, for light quarks (and gluons), to cause emission of quark and gluon pairs. Possible consequences for the strong-interacting quark-gluon plasma are briefly discussed. The text was submitted by the authors in English.     

Nonperturbative QCD vacuum and colour superconductivity

We discuss the possibility of existence of colour superconducting state in real QCD vacuum with nonzero _sGG. We argue, that nonperturbative gluonic fields might play a crucial role in colour superconductivity scenario.     

Nonperturbative phenomena in QCD at finite temperature

The main objective of the present study is to analyze various nonperturbative phenomena in QCD both at low, T < T _c , and at high, T > T _c , temperatures. New methods are developed that make it possible, on one hand, to describe data obtained by numerically simulating QCD on a lattice and, on the other hand, to study new physical phenomena in QCD at finite temperature.     

Nonperturbative nonrenormalization theorem for supersymmetric QCD

We show that no radiative masses are acquired by the Goldstone pion supermultiplet in supersymmetric QCD. Thus, in contrast to ordinary QCD, the mass difference m_π²+−m_π²0 remains zero even after electromagnetism is turned on. Bound state Goldstone supermultiplets obey a nonrenormalization theorem analogous to that obeyed by elementary chiral superfields.     

Nonperturbative QCD near the light cone

We give an overview of current theoretical approaches to nonperturbative QCD. We especially discuss QCD near the light cone.     

Nonperturbative QCD thermodynamics in the external magnetic field

The thermodynamics of quarks and gluons strongly depends on the vacuum colormagnetic field, which grows with the temperature T, so that spatial string tension \(\sigma _s =\mathrm{const}~ g^4 (T) T^2\). We investigate below what happens when one imposes in addition constant magnetic field and discover remarkable structure of the resulting thermodynamic potential.     

The QCD spectrum: Mixing,strong decays,and the role of sea quarks

The light hadron spectrum as computed in nonperturbative QCD is reviewed and compared to lattice data and experiment. The mixing of mesons, hybrids, and glueballs is calculated in the field correlator method. The strong decay mechanisms are found in the method and compared to the known phenomenological models. The role of sea quarks (unquenched approximation) is studied analytically, using radially excited mesons as an example, and compared to experiment.     

Zweig-forbidden radiative orthoquarkonium decays in perturbative QCD

We calculate helicity amplitudes and decay rates for Zweig-forbidden radiative decays of a ${}^3\text{S}{}_1\text{(}\text{Q}\text{Q}\text{)}$ bound state into ${}^1\text{S}{}_0\text{(}\text{q}\text{q}\text{)}\text{and}{}^3\text{P}{}_{\mathrm{J}}\text{(}\text{q}\text{q}\text{)}$ states in lowest-order QCD. We employ a new technique of scalarizing loop integrals by using covariant helicity projectors. Thereby we are able to integrate analytically all occuring loop integrals.When applied to $\text{J}\text{ψ}$ decays our results are in reasonable agreement with present experimental results. ψ′ decays will provide a further test of the model. Transitions from bottonium to charmonium are most interesting since there all dynamical assumptions are well satisfied. Unfortunately the transitions rates are very small.     

The radiativeK* meson decays in QCD

ThegK ^o* K ^o _γ andgK ^+* K ⁺ _γ coupling constants and the radiative decay widths are calculated in the context of QCD sum rules. It is found that the discrepancy between the experimental data and theoretical results still exists.