QCD String Research Articles

Semisuperfluid strings in high density QCD

We show that topological superfluid strings/vortices with flux tubes exist in the color-flavor locked (CFL) phase of color superconductors. Using a Ginzburg-Landau free energy we find the configurations of these strings. These strings can form during the transition from the normal phase to the CFL phase at the core of very dense stars. We discuss an interesting scenario for a network of strings and its evolution at the core of dense stars.

Baryon Vertices in AdS Black Hole Backgrounds

We numerically computed the energy of QCD string junctions in non-supersymmetric SU(N) gauge theories as the energy of brane configurations in the background of AdS black hole solutions, and extracted the contribution of baryon vertices. We obtain a negative vertex energy for the three- and four-dimensional Yang-Mills theories and a vanishing vertex energy for the five-dimensional theory.

Thermal time scales in a color glass condensate

In a model of relativistic heavy ion collisions wherein the unconfined quark-gluon plasma is condensed into glass, we derive the Vogel-Fulcher-Tammann cooling law. This law is well known to hold true in condensed matter glasses. The high energy plasma is initially created in a very hot negative temperature state and cools down to the Hagedorn glass temperature at an ever decreasing rate. The cooling rate is largely determined by the QCD string tension derived from hadronic Regge trajectories. The ultimately slow relaxation time is a defining characteristic of a color glass condensate.

QCD string and the Lorentz nature of confinement

We address the question of the Lorentz nature of the effective long-range interquark interaction generated by the QCD string with quarks at the ends. Studying the Dyson-Schwinger equation for a heavy-light quark-antiquark system, we demonstrate explicitly how a Lorentz-scalar interaction appears in the Diraclike equation for the light quark, as a consequence of chiral symmetry breaking. We argue that the effective interquark interaction in the Hamiltonian of the QCD string with quarks at the ends stems from this effective scalar interaction.

PROBING THE 5TH DIMENSION WITH THE QCD STRING

A salient feature of String/Gauge duality is an extra 5th dimension. Here we study the effect of confining deformations of AdS5 and compute the spectrum of a string stretched between infinitely massive quarks and compare it with the quantum states of the QCD flux as determined by Kuti, Juge and Morningstar in lattice simulations. In the long flux tube limit the AdS string probes the metric near the IR cutoff of the 5th dimension with a spectrum approximated by a Nambu-Goto string in 4-d flat space, whereas at short distance the string moves to the UV region with a discrete spectrum for pure AdS5. We also review earlier results on glueballs states and the cross-over between hard and soft diffractive scattering that support this picture.

Vortices on the worldsheet of the QCD string

We investigate the properties of the QCD string in the Euclidean SU ( N ) pure gauge theory when the space–time dimensions transverse to it are periodic. From the point of view of an effective string theory, the string tension σ and the low-energy constants c k of the theory are arbitrary functions of the sizes of the transverse dimensions L ⊥ . Since the gauge theory is linearly confining in D = 2 , 3 and 4 dimensions, we propose an effective string action for the flux-tube energy levels at any choice of L ⊥ , given σ ( L ⊥ ) and c k ( L ⊥ ) . The Lüscher term only depends on the number of massless bosonic degrees of freedom and the effective theory can account for its evolution as a function of L ⊥ . As the size of one transverse dimension is varied, we predict a Kosterlitz–Thouless transition of the worldsheet field theory at σ ( L ⊥ ) L ⊥ 2 ≃ 1 / 8 π driven by vortices, after which the periodic component of the worldsheet displacement vector develops a mass gap and the effective central charge drops by one unit. The universal properties of the transition are emphasised.

Role of Large Gluonic Excitation Energy for Narrow Width of Penta-Quark Baryons in QCD String Theory

We study the narrow decay width of low-lying penta-quark baryons in the QCD string theoryin terms of gluonic excitations. In the QCD string theory, the penta-quark baryon decays via a gluonic-excited state of a baryon and meson system, where a pair of Y-shaped junction and anti-junction is created. Since lattice QCD shows that the lowest gluonic-excitation energy takes a large value of about 1 GeV, the decay of the penta-quark baryon near the threshold is considered as a quantum tunneling process via a highly-excited state (a gluonic-excited state) in the QCD string theory. This mechanism strongly suppresses the decay and leads to an extremely narrow decay width of the penta-quark system.

Pentaquarks: Facts and puzzles

On the occasion of the celebration of the 70th birthday of Prof. Yu.A. Simonov, we contribute a brief review of the status of exotic baryons, which are most likely pentaquark states. We summarize the experimental status of exotic baryons, discuss the baryon antidecuplet to which exotic baryons possibly belong, and review theoretical expectations for the masses and widths of recently discovered Θ and Ξ3/2 baryons which have come from studies of QCD sum rules, lattice QCD, and quark models. We also pay special attention to the dynamical calculation of pentaquark masses in a framework of the QCD string approach originally elaborated by Simonov for baryons and using the Jaffe-Wilczek \([ud]^2 \bar q\) approximation for the pentaquark states.

Non-Abelian Meissner effect in Yang-Mills theories at weak coupling

We present a weak-coupling Yang--Mills model supporting non-Abelian magnetic flux tubes and non-Abelian confined magnetic monopoles. In the dual description the magnetic flux tubes are prototypes of the QCD strings. Dualizing the confined magnetic monopoles we get gluelumps which convert a "QCD string" in the excited state to that in the ground state. Introducing a mass parameter m we discover a phase transition between the Abelian and non-Abelian confinement at a critical value m=m_* of order of Lambda. Underlying dynamics are governed by a Z_N symmetry inherent to the model under consideration. At m>m_* the Z_N symmetry is spontaneously broken, resulting in N degenerate Z_N (Abelian) strings. At m<m_* the Z_N symmetry is restored, the degeneracy is lifted, and the strings become non-Abelian. We calculate tensions of the non-Abelian strings, as well as the decay rates of the metastable strings, at N >> 1.

Spectrum of Heavy–Light Mesons in the QCD String Picture

We describe in detail predictions of the QCD string approach for the masses of the heavy—light D, Ds, B, and Bs mesons, including orbitally and radially excited states. We discuss the role of the proper dynamics of the QCD string in the formation of the spectrum of the heavy—light mesons, with quark self-energy corrections calculated self-consistently in the same picture. We give our predictions in terms of the current quark masses; the string tension—the only dimensional parameter describing the interquark interaction; and the strong coupling constant, which differs for the fine and the hyperfine interactions. The results are compared with the predictions of other models and with the experimental and lattice results.

Current correlators in QCD: Operator product expansion versus large distance dynamics

We analyse the structure of current-current correlators in coordinate space in large $N_c$ limit when the corresponding spectral density takes the form of an infinite sum over hadron poles. The latter are computed in the QCD string model with quarks at the ends, including the lowest states, for all channels. The corresponding correlators demonstrate reasonable qualitative agreement with the lattice data without any additional fits. Different issues concerning the structure of the short distance OPE are discussed.

Dilatonic repulsons and confinement via the AdS/CFT correspondence

We study a class of dilatonic deformations of asymptotically AdS_5 X S^5 geometry analytically and numerically. The spacetime is non-supersymmetric and suffers from a naked singularity. We propose that the causality bound may serve as a criterion for such a geometry with a naked singularity to still make sense in the AdS/CFT correspondence. We show that the static string, the one corresponding to a large Wilson loop in the dual gauge theory, reveals confinement in a certain range of parameters of our solutions, where the singularity exhibits the repulsion that can well cloak the singularity from the static string probe. In particular, we find the exact expression for the tension of the QCD strings. We also discuss a possible interpretation of our solution in terms of unstable branes and their tachyon matter.

Chiral symmetry breaking and dual gluon mass in the confining region of QCD

The dual Meissner effect description of QCD in the confining region provides 1q4 behaviour for the gluon propagator and involves the dual gluon mass m as a parameter. This is used in the Schwinger–Dyson equation for the quarks in the infrared region to exhibit chiral symmetry breaking for light quarks. Using the light quark condensate as input, the dual gluon mass is determined and its importance in showing the asymptotic free behaviour of the extrinsic curvature coupling in the rigid QCD string is discussed.

QCD‐like gauge dynamics from gravity duals

AbstractWe describe attempts to study QCD‐like gauge dynamics using a deformed version of the AdS/CFT Correspondence. The Yang Mills* geometry is dual to a gauge theory that is non‐supersymmetric Yang Mills in the infra‐red but reverts to N = 4 super Yang Mills in the ultra‐violet. The geometry describes a discrete, calculable glueball spectrum with a mass gap. Wilson loops in the geometry display QCD string breaking.

Universal light quark mass dependence and heavy-light meson spectroscopy

Clean predictions are presented for all the spin-averaged heavy-light meson spectroscopies. A new symmetry is identified wherein the energy eigenstates have a universal dependence on both the light and heavy quark masses. This universality is used in an efficient analysis of these mesons within the QCD string or flux tube picture. We give unique predictions for all the D, ${D}_{s},$ B, and ${B}_{s}$ type mesons in terms of just four measured quantities.

Resolution of the pion puzzle: The QCD string in Nambu-Goldstone mesons

Pions and kaons have double nature: the chiral dynamics of Nambu-Goldstone bosons together with the usual string dynamics common to all mesons. To uncover the interplay of both dynamics the effective chiral Lagrangian is derived from the QCD Lagrangian using the Field Correlator Method and the pion self-energy (mass) operator is written explicitly. The latter contains an infinite number of poles, but normalized to zero at zero momentum because of spontaneous chiral symmetry breaking. As a result one obtains the Gell-Mann-Oakes-Renner relation for the ground state pion and (slightly shifted by chiral dynamics) the usual spectrum of radially excited pions starting with $\pi(1300)$.

QCD strings with spinning quarks

We construct a consistent action for a massive spinning quark on the end of a QCD string that leads to pure Thomas precession of the quark's spin. The string action is modified by the addition of Grassmann degrees of freedom to the string such that the equations of motion for the quark spin follow from boundary conditions, just as do those for the quark's position.

Effects of Perturbative Exchanges in a QCD String Model

The QCD string model for baryons derived by Yu. A. Simonov and used for the calculation of baryon magnetic moments in a previous paper is extended to include also perturbative gluon and meson exchanges. The mass spectrum of the baryon multiplet is studied. For the meson interaction, either pseudoscalar or pseudovector coupling is used. Predictions are compared with the experimental data. Besides these exchanges, the influence of excited quark orbitals on the baryon ground state are considered by performing a multichannel calculation. The nucleon-Δ splitting increases due to the mixing of higher quark states, while the baryon magnetic momenta decrease. The multichannel calculation with perturbative exchanges is shown to yield reasonable magnetic moments, while the mass spectrum is close to experiment.

Vakuum, konfainment i struktury KKhD v metode vakuumnykh korrelyatorov

Vakuum, konfainment i struktury KKhD v metode vakuumnykh korrelyatorov

CONFINING POTENTIAL IN A COLOR DIELECTRIC MEDIUM WITH PARALLEL DOMAIN WALLS

We study quark confinement in a system of two parallel domain walls interpolating different color dielectric media. We use the phenomenological approach in which the confinement of quarks appears considering the QCD vacuum as a color dielectric medium. We explore this phenomenon in QCD2, where the confinement of the color flux between the domain walls manifests, in a scenario where two 0-branes (representing external quark and antiquark) are connected by a QCD string. We obtain solutions of the equations of motion via first-order differential equations. We find a new color confining potential that increases monotonically with the distance between the domain walls.