Singularity structure of massless QCD at finite temperature

A complete relativistic calculation to first order in the strong coupling constantα _s is presented for deep inelastic scattering of leptons off a heat bath of quarks and gluons. The singularity structure is studied and the cancellation of all collinear and infrared divergences is proven. It is shown that it is necessary to include all processes of a given order (i.e. not only the gluon emission and absorption as usually stated). We show that for non-equilibriumn _F andn _B distributions the collinear singularities do not cancel.     

Collective excitations of nuclear matter

It has been shown that in a renormalizable gauge-invariant field-theory model, besides the usual factorizable contribution to the parity-violating vector-meson-exchange potential there is a nonseparable contribution which is equally important. Both contributions have been calculated in the model based on the Bethe-Salpeter equation which describes vector mesons as bound quark-antiquark states. Complete expressions for parity-violating nuclear potentials have been given for the Cabibbo and the Weinberg-Salam models, including the asymptotically-free field-theory version of the latter, which employs coloured quarks and vector gluons.     

胶子非弹性散射过程对夸克胶子等离子体中双轻子产生的影响

双轻子是研究夸克物质的形成和性质的重要探针.本文基于化学平衡化的黏滞性夸克胶子等离子体演化模型,计算了相对论重离子碰撞能量下金-金对心碰撞形成的夸克胶子等离子体中的双轻子产额.在黏滞性计算中加入了胶子非弹性散射过程对黏滞系数的贡献.相较仅考虑夸克和胶子弹性散射的情况,双轻子的产额有较明显的降低.这表明在黏滞系数中加入胶子非弹性散射的贡献使得系统的演化过程加快,演化时间变短.     

Diffractive production of dijets at HERA

We investigate the production of a quark-antiquark pair in diffractive photon-proton scattering, approximating soft pomeron exchange by the exchange of two nonperturbative gluons. In deep inelastic scattering at HERA, events with two jets and the scattered proton in the final state are predicted to be observable, with an important contribution from charm production. For photoproduction of light quark jets with high transverse momentum we find that both exchanged gluons must have a large invariant mass, so that the cross section is very small, whereas for charm quarks it is quite appreciable. From our calculation we also extract the quark structure function of the pomeron for the scaling variablez no too close to 0 or 1, finding a strong flavour dependence and a behaviour somewhat harder thanz(1?z) for light quarks.     

Toy model of the repulsive core of the nucleon-nucleon potential

We study the simplest quark model assuming that the sea of gluons and quark-antiquark pairs can be treated as a part of a static force and proceeding to calculate the hadronic states by solving the Schrödinger equation for a static confining interaction. We refer to this model, starting from a system of six interacting constituent quarks, and examine how the picture of two structureless nucleons can change when the effects caused by the substructure of the nucleons are taken into account.     

Peripheral processes 2 → 3 and 2 → 4 in QED and QCD in $$p(\bar p)p$$ high-energy collisions

Differential cross sections of processes with high-energy p(-p)p collisions—creation of a scalar, a pseudoscalar and a lepton pair—are considered in the Weizsacker-Williams approximation in QED in the QCD framework, processes with conversion of the initial proton (antiproton) to fermionic jets accompanied with one gluon jet and the state of two gluons and a quark-antiquark pair (without a rapidity gap) are considered in the framework of the effective Regge action of Lipatov’s theory. The process of creation of a Higgs boson accompanied with two fermionic jets is considered. The azimuthal correlation in the process of two gluon jets separated by a rapidity gap is investigated. The gluon Reggeization effects are taken into account. Some distributions are illustrated by numerical calculations.     

Supersymmetry and weak,electromagnetic and strong interactions

We study a possible way to construct supersymmetric theories which could be considered as realistic, excepted that the problem of mass generation for electron, muon and quarks remains. There is a new class of leptons which includes charged ones, and a “photonic neutrino”. Spin $\text{1}\text{2}$-gluons and heavy spin 0- quarks are associated with ordinary vector gluons and quarks.     

Colour gluons and scaling in a unified gauge model

Deep inelastic weak and electromagnetic processes are considered within the parton framework taking the partons to be integrally charged quarks and coloured gluons. Despite the participation of the spin-one gluons in these processes, scaling is shown to be maintained by treating the problem in a unified gauge model based on the groupSU (3)_colour⊗SU _L (2)⊗U(1). This is a consequence of the vector-dominance type of couplings between the gluons and the weak or electromagnetic vector bosons which are induced by the spontaneous breakdown of gauge symmetry. As a further consequence it is found that in the asymptotic region far above the gluon masses the colour octet parts of the weak and electromagnetic currents of the quarks are damped so that, in particular, the integrally charged quarks behave as fractionally charged quarks in this region.     

Quark-antiquark effects in baryons

The formalism for a new generation of unquenched quark models for baryons is presented. The effects of quark-antiquark pairs are taken into account in an explicit form via a microscopic, QCD-inspired, quark-antiquark creation mechanism. As an application, the quark-antiquark contribution to the spin of the proton is discussed.     

Lepto-quark matter

In certain extensions of the standard model with additionalU(1) gauge symmetries, the anomalies between the quarks and leptons no longer cancel. It is shown that the anomalies can be cancelled by invoking representations oflepto-quark fermions. Lepto-quarks represent new fermionic matter that carries quark as well as lepton numbers. An extension of the standard model with three and four families of conventional quarks and leptons is presented in which freedom from anomalies is secured through the presence of lepto-quark matter representations. The gauge symmetry of the model isSU(2) _L XU(1) _q XU(1) _l whereU(1) _q andU(1) _l refer to distinct hypercharge sources for the quarks and the leptons.     

On lepton pair production in proton-antiproton collisions at intermediate energies

The lepton pair production via the quark-antiquark annihilation subprocess in collisions of beam antiproton with the proton target at E _beam = 14 GeV is studied on the basis of the event sample simulated by PYTHIA6 generator. Different kinematical variables which may be useful for the design of the muon system and the electromagnetic calorimeter of the detector of PANDA experiment at FAIR, as well as for the study of proton structure functions in the available x-Q ² kinematical region, are considered. It is also argued that the measurement of the total transverse momentum of a lepton-antilepton system may provide important information about the intrinsic transverse momentum 〈k _T 〉 that appears due to the Fermi motion of quarks inside the nucleon. Another interesting possibility is the measurement of the production rate of two or three lepton pairs in one event that can give the information about the rate of multiple quarks interactions and the proton space structure. The problems due to the presence of fake leptons that appear from meson decays, as well as due to the contribution of background QCD processes and minimum bias events, are also discussed. The set of cuts which allows one to separate the events with the signal lepton pairs from different kind of background events is proposed. The article is published in the original.     

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.     

Charged spin-1 gluons,parton model and the Archimedes effect

In a gauge theory of (SU(2)×U(1))_flavour×SU(3)_colour with un-confined integer-charged quarks and massive integer-charged gluons both quarks and gluons contribute to electro- and neutrino-production. The gluon parton contribution to the lepto-production of colour is considered. Supported in part by NSF Grant No. GP43662X, and in part by UGC Research Assistantship, U.K.; Supported in part by a Senior Visiting Fellowship awarded by the Science Research Council, U.K., and by NSF Grant No. GP43662X;     

Signals of excited quarks and leptons

e⁺e^? annihilation to two photons (including beam polarization) and quark-antiquark annihilation to gluons are discussed as possible tools to investigate the existence (and handedness) of excited electrons and quarks. Properties of these particles can also be explored in eγ and ep colliders; production cross sections and the impact of these particles on structure functions are derived.     

Nonperturbative dynamics in the chromomagnetic QCD vacuum above the deconfinement temperature

We investigate the residual chromomagnetic nonperturbative interaction between colour sources which survives above the deconfinement temperature. This interaction is demonstrated to be attractive enough to support bound states of quarks (and gluons). Although, for heavy quarks, such bound states appear to be very shallow and thus to dissociate easily, for light quarks (and gluons), the interaction is found to be strong enough to lead to quark (gluon) pair creation in the vacuum and thus to a complete rebuild of the vacuum state. The text was submitted by the authors in English.     

A logical explanation for quarks

We construct a quantum logic which generates the usual quark states. It follows from this model that quarks can combine only in quark-antiquark pairs and quark (and antiquark) triples. The ground meson and baryon states are also generated and gluons are discussed.     

Measurement of the charge asymmetry in the decays KoL → π±e±ν and KoL → π±μ±ν

Assuming Regge behaviour at small x together with the generalized vector dominance model we give an estimate of the quark-antiquark pairs (core quarks) contribution in deep inelastic lepton-hadron scattering processes. At x = 0.02 the core quark contribution is about 50% and 75% for x = 0.002.     

Selection rules in a unified gauge model of leptons and hadrons

Decay modes and lifetimes of quarks, vector mesons and protons are determined for the unified model of leptons and hadrons recently proposed by Pati and Salam. It is found that while both the quarks and gauge mesons decay too rapidly to be observed, protons will be comfortably stable against decay into leptons, consistent with earlier estimates and existing experimental evidence. It is of special interest that while quarks may not be directly observable, their presence may be verified owing to the uniqueness of their preferred decay into quite a large number of pions. We also discuss an anomalous lepton-hadron scattering process whose occurrence would imply the presence of exotic SU(4) gluons carrying both baryon and lepton number.     

Heavy quark production in parton model and in QCD

The cross sections of heavy quark production inpp collision and for their photo- and electroproduction are calculated in the framework of QCD. The virtual nature of the interacting gluons as well as their transverse motion and different polarizations are taken into account. The obtained cross sections exhibit more rapid growth with the initial energy than the parton model predictions and thep _T distributions of produced heavy quarks are more smooth.     

Monte Carlo study of three-dimensional QCD at finite temperature

Three-dimensional QCD at finite temperature is analyzed using Monte Carlo calculations. It is shown that confinement at low temperature is lost through a second-order phase transition. At high temperature, static quarks are liberated and screened and it is argued that timelike (A₀) gluons are liberated. Just above the critical temperature electric correlation functions seem to be dominated by a resonance of two timelike gluons, whose existence is suggested by perturbation theory. The influence of an external magnetic field close to the critical point is considered.