QCD Correlation Research Articles

Field strength correlators and dual effective dynamics in QCD

We establish a relation between the two-point field strength correlator in QCD and the dual field propagator of an effective dual Abelian Higgs model describing the infrared behavior of QCD. We find an analytic approximation to the dual field propagator without sources and in the presence of quark sources. In the latter situation we also obtain an expression for the static $q\overline{q}$ potential. Our derivation sheds some light on the dominance and phenomenological relevance of the two-point field strength correlator.

Gauge-invariant field strength correlators in full QCD

We study, by numerical simulations on a lattice, the behaviour of the gauge-invariant correlation functions of the gauge field strengths in the QCD vacuum with four flavours of dynamical staggered fermions.

Field strength correlators in QCD with dynamical fermions

We determine, by numerical simulations on a lattice, the gauge-invariant two-point correlation functions of the gauge field strengths in the QCD vacuum with four flavours of dynamical staggered fermions.

Topology, fermionic zero modes and flavor singlet correlators in finite temperature QCD

We extend our earlier results concerning the breaking of the U A (1) symmetry in finite temperature QCD. In particular, we use topological argments to investigate the chiral limit.

NONPERTURBATIVE FIELD CORRELATOR AND STRING REPRESENTATION FOR THE 't HOOFT LOOP AVERAGE IN THE ABELIAN HIGGS MODEL

Making use of the duality transformation, we derive in the Londons' limit of the Abelian Higgs model string representation for the 't Hooft loop average defined on the string worldsheet, which yields the values of two coefficient functions parametrizing the bilocal correlator of the dual field strength tensors. The asymptotic behaviors of these functions agree with the ones obtained within the method of vacuum correlators in QCD in the lowest order of perturbation theory. We demonstrate that the bilocal approximation to the method of vacuum correlators is an exact result in the Londons' limit, i.e. all the higher cumulants in this limit vanish. We also show that at large distances, apart from the integration over metrics, the obtained string effective theory (which in this case reduces to the nonlinear massive axionic sigma model) coincides with the low energy limit of the dual version of 4D compact QED, the so-called universal confining string theory. We derive string tension of the Nambu–Goto term and the coupling constant of the rigidity term for the obtained string effective theory and demonstrate that the latter is always negative, which means the stability of strings, while the positiveness of the former is confirmed by the present lattice data. These data enable us to find the Higgs boson charge and the vacuum expectation value of the Higgs field, which well-described QCD. We also study dynamics of the weight factor of the obtained string representation for the 't Hooft average in the loop space. In conclusion, we obtain string representation for the partition function of the correlators of an arbitrary number of Higgs currents, by virtue of which we rederive the structure of the bilocal correlator of the dual field strength tensors, which yields the surface term in the string effective action.

Field strength correlators in full QCD

We study, by numerical simulations on a lattice, the behaviour of the gauge-invariant two-point correlation functions of the gauge field strengths in the QCD vacuum with dynamical fermions.

Heavy quark pair correlations in QCD

The azimutal correlations of heavy quarks produced in the high energy $pp$ ($p\bar{p}$) collisions are calculated in the framework of QCD without the usual assumptions of the parton model. The virtual nature of the interacting gluons as well as their transverse motion and different polarizations are taken into account. We give some predictions for the azimutal correlations of charm and beauty hadrons produced at Tevatron-collider and LHC.

Field strength correlators in QCD at zero and non-zero temperature

We study, by numerical simulations on a lattice, the behaviour of the gauge--invariant field strength correlators in QCD both at zero temperature, down to a distance of 0.1 fm, and at finite temperature, across the deconfinement phase transition.

Instantons and meson correlation functions in QCD

Various QCD correlators are calculated in the instanton liquid model in zeromode approximation and $1/N_c$ expansion. Previous works are extended by including dynamical quark loops. In contrast to the original "perturbative" $1/N_c$ expansion not all quark loops are suppressed. In the flavor singlet meson correlators a chain of quark bubbles survives the $N_c\to\infty$ limit causing a massive $\eta^\prime$ in the pseudoscalar correlator while keeping massless pions in the triplet correlator. The correlators are plotted and meson masses and couplings are obtained from a spectral fit. They are compared to the values obtained from numerical studies of the instanton liquid and to experimental results.

Gauge-invariant field strength correlations in QCD at zero and non-zero temperature

We determine, by numerical simulations on a lattice, the gauge-invariant two-point correlation functions of the gauge field strengths in the QCD vacuum at zero temperature, down to a distance of 0.1 fm. We also study the behaviour of the gauge-invariant field correlators in the theory at finite temperature, across the deconfinement phase transition.

Energy conservation constraints on multiplicity correlations in QCD jets

We compute analytically the effects of energy conservation on the self-similar structure of parton correlations in QCD jets. The calculations are performed both in the constant and running coupling cases. It is shown that the corrections are phenomenologically sizeable. On a theoretical ground, energy conservation constraints preserve the scaling properties of correlations in QCD jets beyond the leading log approximation.

Energy conservation constraints on multiplicity correlations in QCD jets

We compute analytically the effects of energy conservation on the self-similar structure of parton correlations in QCD jets. The calculations are performed both in the constant and running coupling cases. It is shown that the corrections are phenomenologically sizeable. On a theoretical ground, energy conservation constraints preserve the scaling properties of correlations in QCD jets beyond the leading log approximation.

ABELIAN PROJECTION AND STUDIES OF GAUGE-VARIANT QUANTITIES IN THE LATTICE QCD WITHOUT GAUGE FIXING

We suggest a new (dynamical) Abelian projection of the lattice QCD. It contains no gauge condition imposed on gauge fields so that Gribov copying is avoided. Configurations of gauge fields that turn into monopoles in the Abelian projection can be classified in a gauge-invariant way. In the continuum limit, the theory respects the Lorentz invariance. A similar dynamical reduction of the gauge symmetry is proposed for studies of gauge-variant correlators (like a gluon propagator) in the lattice QCD. Though the procedure is harder for numerical simulations, it is free of gauge-fixing artifacts, like the Gribov horizon and copies.

Reply to "Comment on 'Current correlators in QCD at finite temperature' "

We insist that, contrary to the statement by Dominguez and Loewe in the preceding Comment, only the hadron basis provides a tractable framework for calculations in QCD at low temperatures, while the quark-gluon-based perturbative treatment is not applicable in this case.

Comment on "Current correlators in QCD at finite temperature"

We address some criticisms by Eletsky and Ioffe on the extension of QCD sum rules to finite temperature. We argue that this extension is possible, provided the Operator Product Expansion and QCD-hadron duality remain valid at non-zero temperature. We discuss evidence in support of this from QCD, and from the exactly solvable two- dimensional sigma model O(N) in the large N limit, and the Schwinger model.

Instanton-anti-instanton pair-induced asymptotics of perturbation theory in QCD.

The instanton--antiinstanton pair induced asymptotics of perturbation theory expansion for QCD correlators is considered. It is argued that though the true asymptotics is dominated by renormalon, the instanton-induced contribution may dominate in the intermediate asymptotics $n= 5\div 15$. Obtained asymptotic formulae are valid for $N_f \le N_c$. For $N_f =N_c$ the finite nonperturbative expression for instanton--antiinstanton contribution was also found. At $q^2<0$ the imaginary part of correlators in the case $N_f =N_c$ is suppressed like $1/\log (q/\Lambda)$, but the present accuracy of instanton calculations allows to fix it unambiguously. The series of corrections to the instanton induced asymptotics of the order of $\sim (\log(n)/n)^k$ is found.

Nucleon properties from unconventional interpolating fields.

Interpolating fields, used to excite hadrons from the QCD vacuum in nonperturbative field-theoretic investigations of hadron properties, are explored with an emphasis on unconventional nucleon interpolators. The QCD continuum model for excited state contributions to QCD correlation functions is a central element in extracting the physics contained in these alternate correlation functions. The analysis confirms the independence of nucleon properties obtained from different interpolating fields. However, this independence comes about in a trivial manner. These results provide a resolution to the long standing debate over the optimal nucleon interpolating field to be used in QCD Sum Rule analyses.

Next-to-leading-order temperature corrections to correlators in QCD.

Corrections of order $T^4$ to vector and axial current correlators in QCD at a finite temperature $T<T_c$ are obtained using dispersion relations for the amplitudes of deep inelastic scattering on pions. Their relation with the operator product expansion is presented. An interpretation of the results in terms of $T$-dependent meson masses is given: masses of $\rho$ and $a_1$ start to move with temperature in order $T^4$.

Baryonic and gluonic correlators in hot QCD

We extend our earlier work on static color singlet correlators in high- T QCD (DeTar correlators) to baryonic and gluonic sources, and estimate the corresponding screening masses using the dimensionally reduced theory. We discuss spin and polarization dependence of meson and baryon masses in the T → ∞ limit, and possible nonperturbative effects at non-asymptotic temperatures.

QCD correlation functions and instantons

QCD point-to-point correlation functions at distances .2-1 fm are very different for different channels, and they tell us a lot about inter-quark interactions. Recent studies based on experimental data, ‘instanton liquid’ approach and lattice measurements are reviewed. Agreement between all of them show that instanton-induced forces dominate the light quark physics, and new findings by Negele et al, that hadrons survive ‘cooling’, make this statement obvious. We also argue that chiral symmetry restoration is due to breaking of the ‘instanton liquid’ into polarized ‘instanton molecules’.