Narrow Results

In this paper, we study the effect of the dynamical screening of the four-quark interaction on the chiral phase transition and the baryon number fluctuations at finite temperature and magnetic field in an effective model inspired by QCD in the Coulomb gauge. The screening leads to a medium-dependent coupling that generates inverse magnetic catalysis at finite magnetic field. We observe the decreasing temperature of the chiral crossover, in agreement with lattice QCD predictions, and find a critical point for large magnetic fields. We also observe a strong enhancement of the baryon number fluctuations in the vicinity of the crossover.

The standard PTMG method, invented and tested for the inversion of the fermion matrix (Dirac-operator) in the case of U(1) and SU(2) lattice gauge theories with staggered fermions, has now been generalized to SU(3). A crucial ingredient of the new algorithm is the way SU(3) link elements are averaged in the generation of the coarse grid link elements. Numerical results are presented for the two-dimensional case. For 128 × 128 lattices and physically relevant values of the coupling constant β and of the quark mass m_q, the new algorithm is an order of magnitude faster in CPU time than its leading competitor, the Conjugate-Gradient algorithm.

A relativistic Coulomb-like resummation factor in quantum chromodynamics is suggested, based on the solution of the quasipotential equation.

The recently obtained solutions of Dirac equation in the confining SU(3)-Yang–Mills field in Minkowski spacetime are applied to describe the energy spectra of quarkonia (charmonium and bottomonium). The nonrelativistic limit is considered for the relativistic effects to be estimated in a self-consistent way and it is shown that the given effects are extremely important for both the energy spectra and the confinement mechanism.

The high parton density regime of the quantum chromodynamics (QCD), where the physics of parton saturation is expected to be dominant, is briefly discussed. Some phenomenological aspects of saturation are described, mainly focusing on possible signatures of the nonlinear QCD dynamics in the heavy quark production in electron–proton/nucleus collisions. Implications of these effects in the heavy quark production in ultraperipheral heavy-ion collisions are also presented.

In 2001 the CDF experiment began a data-taking run at the highest centre-of-mass energies in the world. Expectations were high that this data would lead to an increased understanding of top physics and possible discovery of the Higgs boson and non-Standard Model particles. In this review we describe the aims and scope of this data-taking run, some of the upgrades carried out on CDF and our current experimental status. We briefly discuss the breadth of the CDF physics programme, before describing selected topics in quantum chromodynamics, heavy quark, electroweak and exotic physics. Latest results and projected ultimate experimental reach will be shown.

We review the present status of the QCD corrected cross-sections and kinematic distributions for the production of a Higgs boson in association with bottom quarks at the Fermilab Tevatron and CERN Large Hadron Collider. Results are presented for the Minimal Supersymmetric Standard Model where, for large tan β, these production modes can be greatly enhanced compared to the Standard Model case. The next-to-leading order QCD results are much less sensitive to the renormalization and factorization scales than the lowest order results, but have a significant dependence on the choice of the renormalization scheme for the bottom quark Yukawa coupling. We also investigate the uncertainties coming from the Parton Distribution Functions and find that these uncertainties can be comparable to the uncertainties from the remaining scale dependence of the next-to-leading order results. We present results separately for the different final states depending on the number of bottom quarks identified.

A model based on the analytic approach to QCD, involving a summation of threshold singularities and taking into account the nonperturbative character of the light quark masses, is applied to find hadronic contributions to different physical quantities. It is shown that the suggested model allows us to describe well such objects as the hadronic contribution to the anomalous magnetic moment of the muon, the ratio of hadronic to leptonic τ-decay widths in the vector channel, the Adler D-function, the smeared R_Δ-function, and the hadronic contribution to the evolution of the fine structure constant.

The target mass effects in polarized DIS have been studied. It was demonstrated that taking into account the first-order target mass corrections to g₁ a very good approximation of the exact formula is achieved. It was also shown that their magnitude in the pre-asymptotic DIS region is small except for x > 0.65, where their large effect is partially suppressed by the large values of Q² due to the cut W² > 4 GeV². The difference between the size of the target mass and higher twist corrections is illustrated.

We consider one-loop effective action of SU(3) QCD with a most general constant chromomagnetic (chromoelectric) background which has two independent Abelian field components. The effective potential with a pure magnetic background has a local minimum only when two Abelian components and of color magnetic field are orthogonal to each other. The nontrivial structure of the effective action has important implication in estimating quark–gluon production rate and p_T-distribution in quark–gluon plasma. In general the production rate depends on three independent Casimir invariants, in particular, it depends on the relative orientation between chromoelectric fields.

A review is presented of recent results in QCD from the H1 and ZEUS experiments at HERA, emphasizing the use of higher order calculations to describe the data.

On the basis of the confinement mechanism earlier proposed by author, the electric form factor of η-meson is nonperturbatively calculated. The latter is then applied to describe electromagnetic decay η→2γ which entails estimates for parameters of the confining SU(3)-gluonic field in η-meson. The corresponding estimates of the gluon concentrations, electric and magnetic color field strengths are also adduced for the mentioned field.

A complete expression for the p_T-distribution of the gluon production rate in the homogeneous chromoelectric field has been obtained. Our result contains a new additional term proportional to the singular function . We demonstrate that the presence of this term is consistent with the dual symmetry of QCD effective action and allows to reproduce the known result for the total imaginary part of the effective action after integration over transverse momentum.

We discuss some problems concerning the application of perturbative QCD to high energy processes. In particular for hard processes, we analyze higher order and higher twist corrections. It is argued that these effects are of great importance for understanding the behaviour of pion electromagnetic form factor at moderately large momentum transfers. For soft processes, we show that summing the contributions of the lowest twist operators leads to a Regge-like amplitude.

The Fierz transformations (Ft) for SU(2) and SU(3) operators in eighth-order fermion interactions are derived. These terms appear in expansions in terms of fermion currents of the following form: I₁ I₂ I₃ I₄ and also the composite , where Γ⁽ⁱ⁾ are either the SU(2) Pauli matrices or SU(3) Gell-Mann matrices. The calculation is carried out using the exchange projector operators.

Recent QCD sum rule determinations of the light quark masses are reviewed. In the case of the strange quark mass, possible uncertainties are discussed in the framework of finite energy sum rules.

Charm production data from HERA may be used to determine the charm quark mass and jet production data from HERA may be used to determine α_s(M_Z). Recent results are summarised.

At sufficiently large separation between a quark and an antiquark the quantum chromodynamics (QCD) string breaks into parts due to creation of light quark–antiquark pairs. We show that a background magnetic field affects the breaking of the QCD string oriented in the transverse directions with respect to the axis of the magnetic field. Using semiclassical approach we argue that above certain, the background magnetic field eB ≈0.3 GeV² breaking of the transverse string should become energetically unfavorable.

We apply analytic perturbation theory (APT) to the QCD analysis of the xF₃(x, Q²) structure function considering a combined set of deep inelastic scattering data presented by several collaborations, and extract values of the scale parameter Λ_QCD, the parameters of the form of the xF₃ structure function, and the x-shape of the higher twist (HT) contribution. We study the difference between the results obtained within the standard perturbative and analytic approaches in comparison with the experimental errors and state that the greatest difference occurs for large x.