Linking infrared and ultraviolet parameters of pion-like states in strongly coupled gauge theories

It has been shown previously that in a relativistic constituent-quark model, predictions for the electromagnetic form factor of the \(\pi \) meson match not only experimental data but also, in the limit of large momentum transfers, the asymptotics derived from Quantum Chromodynamics (QCD). This is remarkable since no parameters are introduced to provide for this infrared-ultraviolet link. Here, we follow this approach, going beyond QCD. We obtain numerical relations between the gauge coupling constant, the decay constant and the charge radius of the pion-like meson in general strongly-coupled theories. These relations are compared to published lattice results for SU(2) gauge theory with two fermion flavours, and a good agreement is demonstrated. Further applications of the approach, to be explored elsewhere, include composite Higgs and dark-matter models.     

Study of Color Transparency in Electroproduction of Vector Mesons Off Nuclei

Within a light-cone Quantum Chromodynamics formalism based on the Green function technique incorporating color transparency, coherence length effects and gluon shadowing we study electroproduction of vector mesons off nuclei. We found rather large color transparency effects in the range of Q ²(10-20) GeV². They are stronger at low than at high energies and can be easily identified by HERMES or at JLab. We provide predictions for incoherent and coherent vector meson production for future measurements.     

Large-p_T inclusive \pi^0 cross sections and next-to-leading-order QCD predictions

We review the phenomenology of production at large transverse momentum in proton-induced collisions. Uncertainties in the next-to-leading-order predictions of Quantum Chromodynamics are discussed. The comparison with data reveals that the disagreement between theory and experiment lies essentially in an overall normalization factor. The situation for production is contrasted with that of prompt-photon production in hadronic collisions. Received: 7 October 1999 / Published online: 17 February 2000     

Analytical expressions for pulse profile of neutron stars in plasma environments

The European Physical Journal C - We construct the five loop anomalous dimensions of the basic fields in Quantum Chromodynamics in a linear covariant gauge in the modified Regularization Invariant...     

量子色动力学演化方程中的高扭度效应

结合HERA有关核子结构函数与其斜率的实验数据,讨论了在量子色动力学演化方程中存在高扭度重组效应的可能性. 关键词： 结构函数 高扭度效应 演化方程     

Neutrino production of charm

Cross Sections for the production of charm and bottom in neutrino (antineutrino) reactions are calculated in asymptotically free Quantum Chromodynamics. Total and differential cross sections are given for Cabibbo suppressed valence and Cabibbo favoured strange quark ocean production. The next order Quantum Chromodynamic correction to the charm production cross section is calculated. Arguments and estimates for the distribution of final state charmed hadrons are considered.     

On the partial-wave analysis of mesonic resonances decaying to multiparticle final states produced by polarized photons

Meson spectroscopy is going through a revival with the advent of high statistics experiments and new advances in the theoretical predictions. The Constituent Quark Model (CQM) is finally being expanded considering more basic principles of field theory and using discrete calculations of Quantum Chromodynamics (lattice QCD). These new calculations are approaching predictive power for the spectrum of hadronic resonances and decay modes. It will be the task of the new experiments to extract the meson spectrum from the data and compare with those predictions. The goal of this report is to describe one particular technique for extracting resonance information from multiparticle final states. The technique described here, partial wave analysis based on the helicity formalism, has been used at Brookhaven National Laboratory (BNL) using pion beams, and Jefferson Laboratory (JLab) using photon beams. In particular this report broadens this technique to include production experiments using linearly polarized real photons or quasi-real photons. This article is of a didactical nature. We describe the process of analysis, detailing assumptions and formalisms, and is directed towards people interested in starting partial wave analysis.     

Chiral Estimate of QCD Pseudocritical Line

JETP Letters - Relatively low crossover temperature suggests that chiral symmetry restoration in Quantum Chromodynamics may well be described within the low-energy effective theory. The shape of...     

QCD development in the early universe

Physics of Atomic Nuclei - The high-energy limit of Quantum Chromodynamics is generated by the contraction of its gauge groups. Contraction parameters are taken identical with those of the...     

Hadronic jets associated with a photon trigger

We consider, within Quantum Chromodynamics, the fragmentation function of a quark into a hadron and a photon. A simple analytic expression is given which is adequate for practical applications. A measurable quantity is proposed, which is independent of the hadronization process and tests the underlying dynamics.     

Bethe-Salpeter equations forq $$\bar q$$ andqqq systems in the instantaneous approximation

We consider a model for elastic scattering and inelastic diffractive production at high energy, which is inspired by Quantum Chromodynamics. The pomeron arises in our model from gluon exchange between quark constituents. The color-neutrality of each hadron implies strong cancellations among the gluon exchanges. Hence our model is “subtractive”, in contrast to the old “additive” quark model. The subtractive model provides a natural explanation for the large cross section which is observed for diffractive dissociation. We show that multiple gluon exchange contributes significantly, alongside two gluon exchange, in building the pomeron.     

微扰量子色动力学理论

量子色动力学(QCD)是强作用理论最好的候补者。本文从理论和唯象观点方面介绍了微扰量子色动力学理论的几个主要研究课题、基本成果和存在问题。     

Isospin violation, light quark masses, and all that

Isospin violation is driven through the light quark mass difference and electromagnetic effects. I review recent progress in extracting the light quark mass difference and tests of the chiral dynamics of Quantum Chromodynamics in various reactions involving light as well as heavy quarks.     

QCD on the lattice and light hadron spectroscopy

Results in lattice Quantum Chromodynamics with fermions are reviewed. Estimates for the hadron spectrum on large lattices without and with light fermion polarization loops are discussed, and the results for different fermion regularizations are compared. The effects of the loops are found to be significant in lattice units, but to a greater part they can be reabsorbed in a redefinition of the overall scale. New estimates for the light quark masses with Wilson fermions are also presented. They differ substantially from previous estimates obtained by other methods in the continuum, and are much smaller. Finally it is argued that staggered fermions can lead to some anomalous results, which arise because of the doubling problem.     

Estimating higher order perturbative coefficients using Borel transform

A new method of estimating higher order perturbative coefficients is discussed. It exploits the rapid, asymptotic growth of perturbative coefficients and the information on the singularities in the complex Borel plane. A comparison with other methods is made in several Quantum Chromodynamics (QCD) expansions.     

Interacting hadron resonance gas meets lattice QCD

We present, in the framework of the interacting hadron resonance gas, an evaluation of thermodynamical quantities. The interaction is modelled via a correction for the finite size of the hadrons. We investigate the sensitivity of the model calculations on the radius of the hadrons, which is a parameter of the model. Our calculations for thermodynamical quantities as energy and entropy densities and pressure are confronted with predictions using the lattice Quantum Chromodynamics (QCD) formalism.     

Hadrons Ltd.: A Limited Corporation?

We report on some recent progress in hadron spectroscopy. We centre on unquenched results from Lattice and from the Quark Model Static Approach to Quantum Chromodynamics. We also review quenched Quark Model results for the non-static part of the hadron spectrum and emphasize the role that effective hadron?Chadron components may be playing to explain spectral anomalies. Glueballs and multiquarks proposals are briefly examined.     

Inclusive study of neutrino and antineutrino interactions with nuclei at energiesE_v^{( - )} \leqq 30 GeV

Neutrino and antineutrino charged current reactions are studied inclusively at energies below 30 GeV using the freon filled bubble chamber SKAT at the Serpukhov accelerator. Data are given for the nucleon structure functions and the differential spectradσ/dy. The results are compared with predictions of the Quark-Parton Model and Quantum Chromodynamics.