Full QCD Theory Research Articles

Width of the flux tube in SU(3) pure gauge theory

In this paper, we present results obtained from the flux tubes between a quark and an antiquark in SU(3) pure gauge lattice field theory. We fit the transverse distribution of the energy density and the parallel components of the chromoelectric and chromomagnetic fields with several functions and used the coefficients obtained from the fit for computation of the width of the flux tube. Subsequently, we looked into in the dependence of the width of the flux tube on the distance between the static quark-antiquark sources and temperatures. Finally, we compared our results with those from other similar studies. We observed that the numerical value of the width of the flux tube computed from the pure gauge theory is larger than that from the full QCD theory, and the width of the flux tube widened until Tc, and then decreased above the critical temperature.

Hidden analytic relations for two-loop Higgs amplitudes in QCD

We compute the Higgs plus two-quark and one-gluon amplitudes () and Higgs plus three-gluon amplitudes () in the Higgs effective theory with a general class of operators. By changing the quadratic Casimir C F to C A , the maximally transcendental parts of the amplitudes turn out to be equivalent to that of the amplitudes, which also coincide with the counterparts in SYM. This generalizes the so-called maximal transcendentality principle to the Higgs amplitudes with external quark states, thus the full QCD theory. We further verify that the correspondence applies also to two-loop form factors of more general operators, in both QCD and scalar-YM theory. Another interesting relation is also observed between the planar amplitudes and the minimal density form factors in SYM.

NNLO QCD corrections to \u03b3 + \u03b7c(\u03b7b) exclusive production in electron-positron collision

Based on the NRQCD factorization formalism, we calculate the next-to-next-to-leading order QCD corrections to the heavy quarkonium ηc(ηb) production associated with a photon at electron-positron colliders. By matching the amplitudes calculated in full QCD theory to a series of operators in NRQCD, the short-distance coefficients up to NNLO QCD radiative corrections are determined. It turns out that the full set of master integrals that we obtained could be analytically expressed in terms of Goncharov Polylogarithms, integrals over polylogarithms and complete elliptic integrals, which mostly do not exist in the literature and could be employed in the analyses of other physical processes. In phenomenology, numerical calculations of NNLO K-factors and cross sections of e+e− → γ + ηc(ηb) processes in BESIII and B-factory experiments are performed, which may stand as a test of the NRQCD higher order calculation while confronting to the data.

Summary on [formula omitted] and precise [formula omitted] from heavy-light QCD spectral sum rules

We summarize recent results obtained in [S. Narison, arXiv:1209.2023 (2012).] on the running m¯c,b(m¯c,b) in the MS¯ scheme and fD(s),B(s) using QCD spectral sum rules (QSSR) known to N2LO PT series, including all dimension-six NP condensate contributions in the full QCD theory, an estimate of the N3LO terms based on the geomteric growth of the PT series and using the most recent values of the QCD input parameters given in Table 1. The study of the effects of the subtraction scale μ on “different QSSR data” and the use (for the first time) of the Renormalization Group Invariant (RGI) scale independent quark masses in the analysis are emphasized. The estimates [rigourous model-independent upper bounds within the SVZ framework] reported in Table 2: fD/fπ=1.56(5)[⩽1.68(1)], fB/fπ=1.58(5)[⩽1.80(3)] and fDs/fK=1.58(4)[⩽1.63(1)], fBs/fK=1.50(3)[⩽1.61(3.5)], improve previous QSSR estimates. The remarkable agreements with some of the experimental data on fD,Ds and with lattice simulations within dynamical quarks confirm both the success of the QSSR semi-approximate approach based on the OPE in terms of the quark and gluon condensates and of the Minimal Duality Ansatz (MDA) for parametrizing the hadronic spectral function which we have tested from the complete data of the J/ψ and ϒ systems. The running quark masses m¯c(mc)=1286(66)MeV and m¯b(mb)=4236(69)MeV from MD,B are in good agreement though less accurate than the ones from recent J/ψ and ϒ sum rules.

A fresh look into [formula omitted] and precise [formula omitted] from heavy–light QCD spectral sum rules

Using recent values of the QCD (non-)perturbative parameters given in Table 1 and an estimate of the N3LO QCD perturbative contributions based on the geometric growth of the PT series, we re-use QCD spectral sum rules (QSSR) known to N2LO PT series and including all dimension-six NP condensate contributions in the full QCD theory, for improving the existing estimates of m¯c,b and fD(s),B(s) from the open charm and beauty systems. We especially study the effects of the subtraction point on “different QSSR data” and use (for the first time) the Renormalization Group Invariant (RGI) scale-independent quark masses in the analysis. The estimates [rigourous model-independent upper bounds within the SVZ framework] reported in Table 8: fD/fπ=1.56(5)[⩽1.68(1)], fB/fπ=1.58(5)[⩽1.80(3)] and fDs/fK=1.58(4)[⩽1.63(1)], fBs/fK=1.50(3)[⩽1.61(3.5)], which improve previous QSSR estimates, are in perfect agreement (in values and precisions) with some of the experimental data on fD,Ds and on recent lattice simulations within dynamical quarks. These remarkable agreements confirm both the success of the QSSR semi-approximate approach based on the OPE in terms of the quark and gluon condensates and of the Minimal Duality Ansatz (MDA) for parametrizing the hadronic spectral function which we have tested from the complete data of the J/ψ and ϒ systems. The values of the running quark masses m¯c(mc)=1286(66) MeV and m¯b(mb)=4236(69) MeV from MD,B are in good agreement though less accurate than the ones from recent J/ψ and ϒ sum rules.

Interplay between chiral and deconfinement phase transitions

By using the dressed Polyakov loop or dual chiral condensate as an equivalent order parameter of the deconfinement phase transition, we investigate the relation between the chiral and deconfinement phase transitions at finite temperature and density in the framework of three-flavor Nambu-Jona-Lasinio (NJL) model. It is found that in the chiral limit, the critical temperature for chiral phase transition coincides with that of the dressed Polyakov loop in the whole (T,µ) plane. In the case of explicit chiral symmetry breaking, it is found that the phase transitions are flavor dependent. For each flavor, the transition temperature for chiral restoration is smaller than that of the dressed Polyakov loop in the low baryon density region where the transition is a crossover, and, the two critical temperatures coincide in the high baryon density region where the phase transition is of first order. Therefore, there are two critical end points, i.e, and at finite density. We also explain the feature of = in the case of 1st and 2nd order phase transitions, and < in the case of crossover, and expect this feature is general and can be extended to full QCD theory.

Chiral condensate and dressed Polyakov loop in the Nambu–Jona-Lasinio model

We investigate the chiral condensate and the dressed Polyakov loop or dual chiral condensate at finite temperature and density in the two-flavor Nambu--Jona-Lasinio model. The dressed Polyakov loop is regarded as an equivalent order parameter of deconfinement phase transition in a confining theory. We find the behavior of a dressed Polyakov loop in the absence of any confinement mechanism quite interesting. With only quark degrees of freedom present, it still shows an order parameter like behavior. It is found that in the chiral limit, the critical temperature for chiral phase transition coincides with that of the dressed Polyakov loop in the whole $(T,\ensuremath{\mu})$ plane. In the case of explicit chiral symmetry breaking, it is found that the transition temperature for chiral restoration ${T}_{c}^{\ensuremath{\chi}}$ is smaller than that of the dressed Polyakov loop ${T}_{c}^{\mathcal{D}}$ in the low baryon density region where the transition is a crossover. With the increase of the current quark mass the difference between the two transition temperatures is found to be increasing. However, the two critical temperatures coincide in the high baryon density region where the phase transition is of first order. We give an explanation on the feature of ${T}_{c}^{\ensuremath{\chi}}={T}_{c}^{\mathcal{D}}$ in the case of 1st and 2nd order phase transitions, and ${T}_{c}^{\ensuremath{\chi}}&lt;{T}_{c}^{\mathcal{D}}$ in the case of crossover, and expect this feature is general and can be extended to full QCD theory. Our result might indicate that in the case of crossover, there exists a small region where chiral symmetry is restored, but the color degrees of freedom are still confined.

A COMPLETE HEAVY QUARK EFFECTIVE LAGRANGIAN FROM QCD

We show how to construct a heavy quark effective Lagrangian which contains both ‘particle fields’ and ‘antiparticle fields’. This differs from the previous constructed heavy quark effective Lagrangian which includes only one of these fields. The Lorentz invariant of the full QCD theory trivially implies that of this effective Lagrangian without the need of summing over the velocity. This effective Lagrangian is reparametrization invariant for an arbitrary velocity. In particular our form of effective Lagrangian permits an expansion in powers of the heavy quark momenta characterizing its off-shellness divided by its mass.