Chromomagnetic stability of the three flavor Larkin–Ovchinnikov–Fulde–Ferrell phase of QCD

We compute in the Ginzburg–Landau approximation the gluon Meissner masses for the Larkin–Ovchinnikov–Fulde–Ferrell (LOFF) phase of QCD with three flavors in the kinematical range where it is energetically favored. We find real Meissner masses and therefore chromomagnetic stability.     

Kugo–Ojima color confinement criterion and Gribov–Zwanziger horizon condition

We rewrite the Zwanziger horizon condition in terms of the Kugo–Ojima parameter for color confinement. This enables one to explain which value of the Kugo–Ojima parameter is allowed if the horizon condition is imposed. Although all the calculations are performed in the limit of vanishing Gribov parameter for simplicity, the obtained value is consistent with the result of numerical simulations. Consequently, the ghost propagator behaves like free and the gluon propagator is non-vanishing at low momenta, in harmony with recent lattice results and decoupling solution of the Schwinger–Dyson equation. The Kugo–Ojima criterion is realized only when the restriction is removed.     

Effect of neutrino trapping on the three flavor FFLO phase of QCD

We compute the effect of a non-zero lepton chemical potential on the structure of the three flavor Fulde–Ferrell–Larkin–Ovchinnikov (FFLO) phase of QCD at finite temperature. We show that, as in the BCS case, the lepton chemical potential favors two-species color superconductivity and disfavors the three species pairing. We stress that this study could be relevant for the cooling of a proto-neutron star with a FFLO core, if the temperatures are higher than the un-trapping temperature.     

Revisiting non-perturbative effects in the jet broadenings

We show that taking into account the interplay between perturbative and non-perturbative effects, the power-suppressed shift to the broadening distributions becomes B dependent, and the non-perturbative contribution to the mean values becomes proportional to . The new theoretical treatment greatly improves the consistency of the phenomenology with the notion of the universality of confinement effects in jet shapes.This work was supported in part by the EU Fourth Framework Programme ‘Training and Mobility of Researchers’, Network ‘Quantum Chromodynamics and the Deep Structure of Elementary Particles’, contract FMRX-CT98-0194 (DG 12-MIHT).     

QCD Phase Transitions and Bag Constants at Finite Chemical Potential

The global colour model at finite temperature is further extended to study the systems at finite chemical potential. The deconfinement and chiral phase transition at finite chemical potential and at temperature T = 0 K are studied simultaneously. Meanwhile the evolution of the bag constants at finite chemical potential is calculated. The dependences of results on the model parameters are discussed in detail     

Completely automated computation of the heavy-fermion corrections to the three-loop matching coefficient of the vector current

We evaluate the corrections to the matching coefficient of the vector current between Quantum Chromodynamics (QCD) and Non-Relativistic QCD (NRQCD) to three-loop order containing a closed heavy-fermion loop. The result constitutes a building block both for the bottom- and top-quark system at threshold. Strong emphasis is put on our completely automated approach of the calculation including the generation of the Feynman diagrams, the identification of the topologies, the reduction to master integrals and the automated numerical computation of the latter.     

The physics of eight flavours

We study Quantum Chromodynamics with eight flavours by use of lattice simulations and present evidence that the theory still breaks chiral symmetry in the zero temperature, continuum limit. This confirms that the lower end of the conformal window of QCD lies above Nf=8$N_f=8$.     

Field strength formulation,lattice Bianchi identities and perturbation theory for non-Abelian models

We develop an analytical approach for studying lattice gauge theories within the plaquette representation where the plaquette matrices play the role of the fundamental degrees of freedom. We start from the original Batrouni formulation and show how it can be modified in such a way that each non-Abelian Bianchi identity contains only two connectors instead of four. In addition, we include dynamical fermions in the plaquette formulation. Using this representation we construct the low-temperature perturbative expansion for U(1)$U(1)$ and SU(N)$\mathit{SU}(N)$ models and discuss its uniformity in the volume. The final aim of this study is to give a mathematical background for working with non-Abelian models in the plaquette formulation.     

Large volume behaviour of Yang-Mills propagators

We investigate finite volume effects in the propagators of Landau gauge Yang-Mills theory using Dyson-Schwinger equations on a 4-dimensional torus. In particular, we demonstrate explicitly how the solutions for the gluon and the ghost propagator tend towards their respective infinite volume forms in the corresponding limit. This solves an important open problem of previous studies where the infinite volume limit led to an apparent mismatch, especially of the infrared behaviour, between torus extrapolations and the existing infinite volume solutions obtained in 4-dimensional Euclidean space-time. However, the correct infinite volume limit is approached rather slowly. The typical scales necessary to see the onset of the leading infrared behaviour emerging already imply volumes of at least 10-15 fm in lengths. To reliably extract the infrared exponents of the infinite volume solutions requires even much larger ones. While the volumes in the Monte-Carlo simulations available at present are far too small to facilitate that, we obtain a good qualitative agreement of our torus solutions with recent lattice data in comparable volumes.     

The Physics of Exclusive Reactions in QCD: Theory and Phenomenology

The modern formulation of exclusive reactions within Quantum Chromodynamics is reviewed, the emphasis being placed on the pivotal ideas and methods pertaining to perturbative and non-perturbative topics. Specific problems, related to scale locality, infrared safety, gluonic radiative corrections (Sudakov effects), and the role of hadronic size effects (intrinsic transverse momentum), are studied. These issues are more precisely analyzed in terms of the essential mechanisms of momentum transfer to a hadron while remaining intact. Different factorization schemes are considered and the conceptual lacunas are pointed out. The quite technical subject of renormalization-group evolution is given a detailed account. By combining analytical and numerical algorithms, the one-gluon exchange nucleon evolution equation is diagonalized and next-to-leading eigenfunctions are calculated in terms of Appell polynomials. The corresponding anomalous dimensions of trilinear quark operators are found to form a degenerate system whose envelope shows logarithmic large-order behavior. Selected applications of this framework are presented, focusing on the helicity-conserving elastic form factors of the pion and the nucleon. The theoretical constraints imposed by QCD sum rules on the moments of nucleon distribution amplitudes are used to determine a whole spectrum of optional solutions. They organize themselves along an “orbit” characterized by a striking scaling relation between the form-factor ratio and the projection coefficient B₄ on to the corresponding eigensolution. The main reasons for the failure of the present theoretical predictions to match the experimental data are discussed and workable explanations are sketched.     

Moments of the truncated multiplicity distributions

TIn experiment, the multiplicity distributions of inelastic processes are truncated due to finite energy, insufficient statistics or special choice of events. It is shown that the moments of such truncated multiplicity distributions possess some typical features. In particular, the oscillations of cumulant moments at high ranks and their negative values at the second rank can be considered as ones most indicative on specifics of these distributions. They allow to distinguish between distributions of different type.     

B→K Transition Form Factor with Tensor Current within the kT Factorization Approach

We apply the kT factorization approach to deal with the B→K transition form factor with tensor current in the large recoil regions. Main uncertainties for the estimation are discussed and we obtain FT^B→K （0） = 0.25±0.01±0.02, where the first error is caused by the uncertainties from the pionic wavefunctions and the second is from that of the B-meson wavefunctions. This result is consistent with the light-cone sum rule results obtained in the literature.     

Nonperturbative equation of state of quark-gluon plasma

The paper is devoted to the systematic derivation of nonperturbative thermodynamics of quark-gluon plasma, on the basis of the background perturbation theory. Vacuum background fields enter only in the form of field correlators, which are known from lattice and analytic calculations. In the lowest order in α_s the purely nonperturbative sQGP thermodynamics is expressed through single quark and gluon lines (single line approximation) which are interacting nonperturbatively with vacuum fields and with other lines. Nonperturbative EOS is obtained in terms (of the absolute value) of fundamental (adjoint) Polyakov loop L_fund(adj) and spatial string tension σ_s(T). In the lowest approximation the pressure for quarks (gluons) has a simple factorized form P_q(g) = P_SBL_fund(adj), where L_i describe the action of vacuum colorelectric fields on particle trajectory.     

Hadron structure on the lattice and in the continuum

Hadron structure physics has in recent years reached a level of precision which allows for a change of perspective. Model-based arguments are often quite unreliable. However, meanwhile they can be more and more replaced by controlled and systematic QCD approaches. The story of the strange electric form factor, which provided much of the motivation for the PAVI Conference series provides a typical example to illustrate this statement. However, high-precision theory is technically very challenging and progress is, therefore, unpleasantly slow. This fact and the present status in general is illustrated by a few typical examples.     

Nonperturbative equation of state of quark-gluon plasma: Applications

The vacuum-driven nonperturbative factors L_i for quark and gluon Green’s functions are shown to define the nonperturbative dynamics of QGP in the leading approximation. EoS obtained recently in the framework of this approach is compared in detail with known lattice data for μ = 0 including P/T⁴, ε/T⁴, . The basic role in the dynamics at T ? 3T_c is played by the factors L_i which are approximately equal to the modulus of Polyakov line for quark L_fund and gluon L_adj. The properties of L_i are derived from field correlators and compared to lattice data, in particular the Casimir scaling property follows in the Gaussian approximation valid for small vacuum correlation lengths. Resulting curves for P/T⁴, ε/T⁴, are in a reasonable agreement with lattice data, the remaining difference points out to an effective attraction among QGP constituents.     

On the energy loss of high energy quarks in a finite-size quark-gluon plasma

The induced gluon emission from a fast quark passing through a finite-size QCD plasma is studied within the light-cone path integral approach. It is shown that the leading log approximation used in previous studies fails when the gluon formation length becomes on the order of the length of the medium traversed by the quark. Calculation of the energy loss beyond the leading log approximation gives the energy loss which grows logarithmically with quark energy, contrary to the energy-independent prediction of the leading log approximation.     

Broken symmetries from minimally doubled fermions

Novel chirally symmetric fermion actions containing the minimum amount of fermion doubling have been recently proposed in the literature. We study the symmetries and renormalization of these actions and find that in each case, discrete symmetries, such as parity and time-reversal, are explicitly broken. Consequently, when the gauge interactions are included, these theories radiatively generate relevant and marginal operators. The restoration of these symmetries and the approach to the continuum limit thus require the fine-tuning of several parameters. With some assumptions, we show that this behavior is expected for actions displaying minimal fermion doubling.