arXiv subjects

V. Gogohia

Publications and source records attributed to V. Gogohia.

28 records · Page 2Linked to original sources

arXiv2000

How to calculate the quantum part of the truly nonperturbative Yang-Mills vacuum energy density in the axial gauge QCD

Using the effective potential approach for composite operators, we have formulated a general method how to calculate the truly nonperturbative vacuum energy density in the axial gauge QCD quantum models of its ground state. It is defined as integrated out the truly nonperturbative part of the full gluon propagator over the deep infrared region (soft momentum region). The nontrivial minimization procedure makes it possible to determine the value of the soft cutoff in terms of the corresponding nonperturbative scale parameter which is inevitably presented in any nonperturbative model for the full gluon propagator. If the chosen Ansatz for the full gluon propagator is a realistic one, then our method uniquely determines the truly vacuum energy density, which is always finite, automatically negative and it has no imaginary part (stable vacuum). We illustrate it by considering the Abelian Higgs model of dual QCD ground state. We have explicitly shown that the vacuum of this model without string contributions is unstable against quantum corrections.

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arXiv1999

Triviality of the quark propagator in the ladder approximation in QCD

The validity of the ladder approximation (LA) in QCD and QED in the context of the corresponding Schwinger-Dyson (SD) equations and Slavnov-Taylor (ST) and Ward-Takahashi (WT) identities is investigated. In contrast to QED, in QCD bacause of color degrees of freedom the summation of the ladder diagrams within the Bethe-Salpeter (BS) integral equation for the quark-gluon vertex at zero momentum transfer on account of the corresponding ST identity does provide an an addition constraint on the quark SD equation itself. Moreover, the solution of the constraint equation requires the full quark propagator should be almost trivial (free-type) one, i. e. there is nontrivial quark propagator in the LA in QCD. This triviality results in the fact that the standard LA ignores the self-interaction between gluons caused by color charges (non-Abelian character of QCD).

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arXiv1998

Dynamical structure of the chiral QCD vacuum in the zero modes enhancement quantum model

Using the effective potential approach for composite operators we have formulated the quantum model of the QCD vacuum. It is based on the existence and importance of the nonperturbative $q^{-4}$-type dynamical, topologically nontrivial excitations of the gluon field configuration. The QCD vacuum is found stable since the vacuum energy density has no imaginary part. Moreover, a possible ground (stationary) state of the nonperturbative Yang-Mills (quenched QCD) vacuum is discovered. The vacuum energy density at stationary state depends on a scale at which nonperturbative effects become important. The quark part of the vacuum energy density depends in addition on the constant of integration of the corresponding Schwinger-Dyson equation. The value of the above mentioned scale is determined from the bounds for the pion decay constant in the chiral limit. Our value for the chiral QCD vacuum energy density is one order of magnitude bigger than the instanton based models can provide while a fair agreement with recent phenomenological and lattice results for the chiral condensate is obtained.

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arXiv1998

Chiral topology in the zero modes enhancement quantum model of the QCD vacuum

Using effective potential approach for composite operators we have formulated quantum model of the QCD vacuum. It is based on the existence and importance of the nonperturbative $q^{-4}$, topologically nontrivial excitations of the gluon field configurations there. As a result of this the QCD vacuum is found stable and it has a stationary state. The value of the scale reponsible for the nonperturbative dynamics is taken from the bounds for the pion decay constant in the chiral limit. We have obtained good numerical agreement with the phenomenological values of the topological susceptibility, the mass of $η'$ meson, the gluon condensate. An excellent agreement with the phenomenological values of the above mentioned quantities is achived by simply summing up our contributions and instanton-induced contributions due to Negele et al to the vacuum energy density.

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arXiv1997

Calculation of the Vacuum Energy Density and Gluon Condensate within Zero Modes Enhancement Model of the QCD Vacuum

The nonperturbative vacuum structure which emerges from the zero modes enhancement (ZME) model of the true QCD vacuum, appears to be well suited to describe quark confinement, dynamical chiral symmetry breaking (DCSB), current-effective (dynamical)-constituent, as well as constituent-valence quark transformations, the Okubo-Zweig-Iizuka (OZI) rule, dimensional transmutation, etc. It is based on the solution to the Schwinger-Dyson (SD) equation for the quark propagator in the infrared (IR) domain. The importance of the instanton-type fluctuations in the true QCD vacuum for the ZME model is also discussed. This allows to calculate new, more realistic values for the vacuum energy density (apart from the sign, by definition, the bag constant) and the gluon condensate. Our numerical results for the gluon condensate for different numbers of quark flavor $N_f$ are 2-3 times lager than it is estimated in the QCD sum rules approach. This is in good agreement with recent phenomenological estimates of this quantity.

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arXiv1997

An investigation of the phase transition in the extended bag model

By proposing an Ansatz for the pressure (measured in terms of the bag constant) of the hadronic gas in equilibrium, we have formulated a rather simple method which allows one to analytically investigate the bulk thermodynamic propertities in the vicinity of the phase transition. This makes it also possible to take into account the nonperturbative vacuum effects from both sides of the equilibrium condition. As an example of our approach, we have calculated the crossover (critical or transition) temperature $T_c$ and the critical chemical potential $μ_c$ (as functions of the bag constant) from the noninteracting quark-gluon plasma state equation. Our results for $T_c(N_f=0)=241.5 MeV$ and $T_c(N_f=2)=160.6 MeV$ are in good agreement with recent lattice data. The extensive densities such as the entropy density, specific heat, etc. are calculated as well. A general scheme how to calculate the latent heat, the critical density, etc. within the extended bad model is also described and it is applied to the two models of the hadronic gas phase.

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arXiv1997

The Isentropic Equilibrium Deconfining Phase Transition in the Extended Bag Model

By using an Ansatz for the pressure (measured in terms of the bag constant) of the hadronic gas in equilibrium, we have formulated a new bag-type model for the phase transition, i. e. the extended bag model. This allows one to take into account the nonperturbative vacuum effects from both sides of the equilibrium condition. We have explicitly shown that our model automatically provides an isentropic equilibrium deconfining phase transition from the quark-gluon plasma phase to the hadronic gas phase with a temperature and chemical potential dependent bag pressure at the phase boundary. This makes it possible to regulate the total entropy and baryon number in both phases, i. e. the flow of the specific entropy per baryon across the phase boundary. We have also determined the functional form of the temperature and chemical potential dependence of the bag pressure outside the phase boundary.

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arXiv1996

A Nonperturbative Calculation of Basic Chiral QCD Parameters within Dynamical Equations Approach to QCD at Low Energies

Basic chiral QCD parameters (the pion decay constant, the quark and gluon condensates, the dynamically generated quark mass, etc) as well as the vacuum energy density have been calculated from first principles within a recently proposed dynamical equations approach to QCD at low energies. The zero modes enhancement (ZME) model of quark confinement and dynamical chiral symmetry breaking (DCSB) based on the solution to the Schwinger-Dyson (SD) equation for the quark propagator in the infrared (IR) domain was used for this purpose. There are only two independent quantities by means of which calculations should be done within our approach. Our unique input data was chosen to be the pion decay constant in the chiral limit given by the chiral perturbation theory at the hadronic level (CHPTh). Phenomenological estimates of these quantities, as well as the vacuum energy density, are in good agreement with our numerical results. The nonperturbative vacuum structure which emerges from the ZME model, appears to be well suited to describe quark confinement, DCSB, current-effective (dynamical)-constituent, as well as constituent-valence quark transformations, the Okubo-Zweig-Iizuka (OZI) rule, dimensional transmutation, etc. The importance of the instanton-type fluctuations in the true QCD vacuum for the ZME model is also emphasized. This allows to predict new, more realistic values for the vacuum energy density (apart from the sign, by definition, the bag constant) and the gluon condensate.

hep-ph↗

arXiv1996

A Nonperturbative Calculation of Basic Chiral QCD Parameters Within Zero Modes Enhancement Model of the QCD Vacuum. II

Basic chiral QCD parameters (the pion decay constant, the quark and gluon condensates, the dynamically generated quark mass, etc) as well as the vacuum energy density (up to the sign, by definition, the bag constant) have been calculated from first principles within a recently proposed zero modes enhancement (ZME) model of the true QCD vacuum. Our unique input data was chosen to be the pion decay constant in the chiral limit as given by the chiral perturbation theory at the hadronic level (CHPTh). In order to analyze our numerical results we set a scale by two different ways. In both cases we obtain almost the same numerical results for all chiral QCD parameters. Phenomenological estimates of these quantites as well as vacuum energy density are in good agreement with our numerical results. Complementing them by the numerical value of the instanton contribution to the vacuum energy density, we predict new, more realistic values for the vacuum energy density, the bag constant and the gluon condensate.

hep-ph↗

arXiv1995

A Nonperturbative Calculation of Basic Chiral QCD Parameters Within Zero Modes Enhancement Model of the QCD Vacuum. I

A new zero modes enhancement (ZME) model of the true QCD vacuum is breifly described. It makes possible to analytically investigate and calculate numerically low-energy QCD structure from first principles. Expressions of basic chiral QCD parameters (the pion decay constant, the quark and gluon condensates, the dynamically generated quark mass, etc) as well as the vacuum energy density (up to the sign, by definition, the bag constant), suitable for numerical calculations, have been derived. Solution to the Schwinger-Dyson (SD) equation for the quark propagator in the infrared (IR) domain on the basis of the ZME effect in QCD was used for this purpose. There are only two independent quantities (free parameters) by means of which calculations must be done within our approach. The first one is the integration constant of the above mentioned quark SD equation of motion. The second one is a scale at which nonperturbative effects begin to play a dominant role.

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