Recursive calculations for processes with n gluons

A method is presented in which multigluon processes are calculated recursively. The technique is explicitly developed for processes where only gluons are produced and processes where in addition to the gluons also a quark-antiquark pair with or without a vector boson or e⁺e⁻ pair are present. The recursion relations are used to derive rigorously amplitudes for certain configurations, where most of the gluons have the same helicities. This proves a number of conjectures in the literature. Also expressions for amplitudes with collinear or soft gluons are derived.     

The diffractive component of particle production in the dual multistring fragmentation model

The single diffractive component is introduced in the dual Monte Carlo chain decay model of soft particle production. The diffractively excited multiparticle states in this model arise from the fragmentation of two chains formed out of the valence quarks and antiquarks (or diquarks) of the diffractively excited hadron and a sea quark-antiquark pair of the Pomeron, considered to be a gluonic object. In this way the excited clusters behave in a way quite similar to multiparticle states formed in nondiffractive meson-hadron collisions. The calculated multiparticle states agree quite well with recent data from the UA4-SPS collider collaboration and with recent data on strange particle production in diffractive photon-proton collisions.     

On the corrections of the wave function in weakly bound quarkonium

A non-relativistic quark-antiquark system with perturbative gluonic interactions (quarkonium) is considered, which allows a systematic expansion in the strong coupling constant α_s. In a non-abelian gauge theory, non-trivial corrections of the wave function already occur to O(α_s). We emphasize the existence of a renormalization, which is “natural” for such a system leaving only little freedom in the choice of the renormalization point Λ. The general corrections to O(α_s) including coulombic binding are presented. An explicit application to the lowest-order gluonic corrections of the leptonic decay of quarkonium is made. In this process the new term is sometimes much larger than the gluonic correction at the photon vertex and it varies greatly between different coulombic (S-wave) bound states.     

Regge asymptotics of scattering amplitudes in the logarithmic approximation of QCD

The method of separation is applied to the calculation of scattering amplitudes in the Regge region. The method allows to represent the nonladder contributions in a simple form. The result for the amplitude with quark-antiquark exchange and positive signature is discussed.     

Three-Jet Production of Hadrons in Higgs-Boson Decay Н → q q ¯ $$ \overline{q} $$ g

Russian Physics Journal - Within the framework of the standard model (SM), the decay of the Higgs boson into a quark-antiquark pair with gluon emission is studied. An analytical expression is...     

Mixed spin-singlet and spin-triplet cooper pairing caused by inhomogeneous magnetism

With an attractive electron-electron interaction only for spin-singlet Cooper pairing and in the presence of inhomogeneous magnetism, spin-singlet and spin-triplet pair amplitudes both occur when only a spin-singlet pair potential occurs. Pair amplitudes in $\text{k}$-space and $\text{r}$-space and the spin susceptibility show that superconductivity in the presence of inhomogeneous magnetism cannot be either purely spin-singlet or purely spin-triplet pairing.     

Probing gluonic spin-orbit correlations in photon pair production

We consider photon pair production in hadronic collisions at large mass and small transverse momentum of the pair, assuming that factorization in terms of transverse-momentum dependent parton distributions applies. The unpolarized cross section is found to have azimuthal angular dependencies that are generated by a gluonic version of the Boer-Mulders function. In addition, the single transversely polarized cross section is sensitive to the gluon Sivers function. We present simple numerical estimates for the Boer-Mulders and Sivers effects in diphoton production at RHIC and find that the process would offer unique opportunities for exploring transverse-momentum dependent gluon distributions.     

Heavy quark interactions in finite temperature QCD

We study the free energy of a heavy quark-antiquark pair in a thermal medium. We construct a simple ansatz for the free energy for two quark flavors motivated by the Debye-Hückel theory of screening.Arrival of the final proofs: 4 July 2005PACS: 11.15.Ha, 12.38.Mh, 25.75.Nq     

The screening of colour charge in the numerical hopping-parameter expansion

The screening of the quark-antiquark potential by dynamical quark-antiquark pairs is numerically investigated in SU(2) colour gauge theory with Wilson fermions. The expected qualitative behaviour is born out by a high-order hopping-parameter expansion. The screening length is about 0.8 fm and the dissociation energy of a heavy quark-antiquark pair is near 600–800 MeV.     

Partonic Structure of the Pomeron in the Modified GLR Equation

The gluon recombination effect in the pomeron is studied by using the modified Gribov-Levin-Ryskin evolution equation. We find that the measured parton distributions in the pomeron can be generated dynamically from a purely gluonic input on assuming a small size for the pomeron.     

The importance of pair current contributions arising from Δ(1236) configurations

The importance of purely nucleonic pair current diagrams is estimated compared to those which are connected with Δ(1236) isobars. By a simple examination of the different spin and isospin structures we found that there may be a 15% correction which should not be neglected in further quantitative calculations of magnetic properties.     

Application of QCD-sum rules to the resonance Λ(1405)

We investigate the resonance Λ(1405) in the framework of QCD-sum rules. It is found that in addition to local operators consisting of three quarks also those consisting of three quarks and a quark-antiquark pair both in a color singlet and flavor octet are important.     

Cross sections for charmonia dissociation in collisions with pions, rhos and kaons

We calculate the unpolarized cross sections for dissociation reactions of charmonia in collisions with π,ρ and K in a potential that is derived from QCD.The reactions are governed by the quark-interchange processes.The mesonic quark-antiquark relative-motion wave functions are determined by the central spinindependent terms of the potential.The numerical wave functions and cross sections are parametrized.The difference of transition amplitudes in the prior form and in the post form is explored by deriving and examining the transition amplitudes of the one-gluon-exchange spin-spin term of the potential in the two forms.We find that the post-prior discrepancy in meson-meson elastic scattering that is governed by quark-interchange processes depends on the difierence of quark or antiquark masses and of quark-antiquark spatial distributions ofthe two mesons.     

Gluonic excitation of the three-quark system in SU(3) lattice QCD

We present the first study of the gluonic excitation in the three-quark (3Q) system in SU(3) lattice QCD with beta=5.8 and 16(3) x 32 at the quenched level. For the spatially fixed 3Q system, we measure the gluonic excited-state potential, which is responsible for the properties of hybrid baryons. The lowest gluonic-excitation energy in the 3Q system is found to be about 1 GeV in the hadronic scale. This large gluonic-excitation energy is expected to bring about the success of the simple quark model without gluonic modes.     

Testing static quark-antiquark potentials with bottomonium

We investigate the question of whether experimental data on the energy levels of bottomonium can discriminate between quark-antiquark potentials which are motivated by what we know about QCD and potentials which are purely phenomenological. We restrict ourselves to bottomonium because, of all the quarkonia observed thus far, bottomonium is the least relativistic and therefore the best testing ground for the static quarkonium potential. We consider two potentials whose functional form is motivated from perturbative QCD at short quark-antiquark separations and from nonperturbative lattice QCD at large separations. We also consider three strictly phenomenological potentials. We find that the best of the three phenomenological potentials, which has never been previously used, fits the spin-averaged data at least as well as the best of the QCD-motivated potentials. We propose further measurements on bottomonium energy levels to provide additional tests.     

The Q2 evolution of flavour singlet wave functions in QCD

We calculate the Q² evolution of the quark-antiquark and gluon-gluon components of helicity-zero, flavour and colour singlet wave functions by summing diagrams to all orders in axial gauge QCD perturbation theory in the leading logarithm approximation. We find that Gegenbauer moments of these components have exactly the same scale-breaking behaviour as moments of singlet quark and gluon distribution functions in leptoproduction. The resulting singlet wave function is used to calculate the amplitudes for quark-antiquark and gluon-gluon jet production in off-shell photon-photon collisions.     

Strong coupling 1/N c expansion in the gluonic sector of lattice QCD: The next order

Continuing our previous work we determined the gluonic vacuum state up to sixth order and the lowest states with external quark-antiquark and (unscreened) gluon-gluon sources up to fourth order in the strong coupling 1/N _c expansion on the lattice. Unlike previously, we used here the colour electric flux operators on the links to define the colour electric energy. Additional remarks concerning the screening of external gluon sources and the analytic continuation toN _c =3 and zero lattice spacing are also included.     

Amplitude for N-gluon superstring scattering

We consider scattering processes involving N gluonic massless states of open superstrings with a certain Regge slope alpha'. At the semiclassical level, the string world-sheet sweeps a disk and N gluons are created or annihilated at the boundary. We present exact expressions for the corresponding amplitudes, valid to all orders in alpha', for the so-called maximally helicity violating configurations, with N = 4, 5 and N = 6. We also obtain the leading O(alpha '2) string corrections to the zero-slope N-gluon Yang-Mills amplitudes.     

On the Structure of Reggeon

Starting from the point-view that the constituent quark has its own inner structure and according to the hypothesis of the maximum non-perturbative strong interaction reaction which should be obeyed in high energy strong-soft Processes ,we proposed a structure model of the Reggeon(R). In such processes a pair of constituent quark-antiquark in colliding hadrons would individually desociate with certain probahility into a non-perturbative gluon and a spinor-like cluster firstly. The spinor-like clusters will further emit non-perturbative gluons and then annihilate each other. Corresponding to such mechanism the relevant structure of R in the field theory can be represented by summing over a set of cutting ladder diagrams, where the vertical lines are the propagators of spinor-like clusters and the rungs are non-perturbative gluons. In the multi-Regge region where the energy of the system is very large and its momentum transfer│t│is very small, under the approximation that only the leading order logarithm terms of s are preserved, the scattering amplitudes for these cutting ladder diagrams are derived and summed. Thus, a compact formula of the typical Regge pole trajectory of mesons which are composed of light quarks is obtained.     

关于Reggeon的结构

从强子组分夸克具有结构的观点出发，根据高能强作用软过程中的最大非微扰强作用反应假定,提出了关于Reggeon(IR)的结构模型.高能时对撞强子中的一对组分夸克-反夸克在最大反应下有一定的几率先分解为非微扰胶子和旋量团(反旋量团).此旋量团对将进一步演化而放射出一系列的非微扰胶子(和夸克对)并最终湮没.将这种过程与其逆向(厄米共轭)过程并合,就可得出有关的IR的场论结构图象.它是以旋量团为竖线,胶子为横线的一系列切割梯形图之和所代表.本文在系统能量大而动量转移很小的多重Regge运动学区间和只保留Ins的领头阶近似下,计算了这组切割梯形图相应的散射振幅,求出了它们的总和,得出了与轻夸克介子对应的典型Regge极点轨迹的简洁表达式,对结果进行了简单的讨论.