Posters for the 2006 Confinement and the Hadron Spectrum conference

Ultrasoft quark damping in high-temperature QCD

-Abstract:

We determine the quark damping rates in the context of next-to-leading order hard-thermal-loop summed perturbation of high-temperature QCD where weak coupling is assumed. The quarks are ultrasoft. Three types of divergent behavior are encountered: infrared, light-cone and at specific points determined by the gluon energies. The infrared divergence persists and is logarithmic whereas the two others are circumvented.

Pursuing the J=0 fixed pole in Deeply Virtual Compton Scattering

Presenter: Felipe J. Llanes Estrada

-Affiliation: Univ. Complutense de Madrid

-Abstract:

We revisit the J=0 fixed pole of DVCS in the modern context of Generalized Parton Distributions. In particular we recall its potential to reveal the $1/x$ form factor, connected by analytical continuation with the $1/x$ moment of parton distribution functions. We show that current Kuti-Weisskopf type parametrizations yield large systematic errors in this moment making a DVCS-based extraction at an upgraded Jlab or at a potential e-RHIC desirable.

Epsilon regime universality and improved staggered quarks

-Abstract:

We study the low-lying modes of staggered Dirac operators in SU(2) and SU(3) and show that improvement changes the distribution from lattice-like to continuum-like at lattice spacing representative of current dynamical lattice simulations.

Epsilon regime universality classes (including random matrix theory) predict different distributions for the low-lying eigenvalues of the continuum and staggered Dirac operators, reflecting the different chiral symmetry groups. At "super-fine" lattice spacings around 0.07fm, we show that improved staggered eigenvalues reflect the continuum distributions, whilst unimproved agree with the discrete predictions.

We discuss the implication of these results for taste-breaking and the fourth root trick.

Center vortices and the Atiyah-Singer index theorem

Confinement from Gauge Invariance in D=2+1 Dimensions

-Abstract:

We find, in D=2+1 dimensions, that by simply imposing non-abelian gauge invariance on the temporal gauge ground state wavefunctional of an abelian gauge theory, a confining state is obtained.

Resonance Formation in the mass region 1400 - 1500 MeV in the reaction gamma gamma -> K^0_s K^+- pi^-+

-Abstract:

The K^0_s K^+- pi^-+ final state in two-photon collisions is studied with the L3 detector at LEP, at centre-of-mass energies from 183 to 209 GeV with an integrated luminosity of 664.6 pb^-1. The eta(1475) and f1(1420) mesons are observed and are separated by measuring the formation rates as a function of the photon virtuality Q^2. The eta(1475) is dominant at Q^2 < 0.01 GeV^2, its two-photon width is found to be 0.23 +- 0.05(stat) +- 0.05(sys) keV. The f1(1420) is dominant at higher Q^2, it decays totally through K^*(892)K. Its gamma gamma - coupling parameter is 3.2 +- 0.6(stat) +- 0.7(sys) keV and its form factor is defined by the parameter Lambda_1 = 926 +- 72 +- 32.

Measurement of the photon structure function F_2^gamma with the L3 detector at LEP

-Abstract:

The e e -> e e hadrons reaction, where one of the two electrons is detected in a low polar-angle calorimeter, is analysed in order to measure the hadronic photon structure function F_2^gamma. The full high-energy and high-luminosity data set, collected with the L3 detector at centre-of-mass energies 189GeV < root(s) < 209GeV, corresponding to an integrated luminosity of 608/pb is used. The Q^2 range 11 GeV^2 < Q^2 < 34 GeV^2 and the x range 0.006 < x < 0.556 are considered. The data are compared with recent parton density functions.

Quark-hadron duality and hadron properties from correlators of pseudoscalar and axial currents

-Abstract:

We discuss OPE and quark-hadron duality for 2- and 3-point correlators of the axial (A) and pseudoscalar (P) currents of the light quarks. In the chiral limit these correlators are often dominated by nonperturbative power corrections leading to subtleties of quark-hadron duality relations and of the extraction of properties of light pseudoscalars. For the 2-point correlators, we show the sum rule for to be sensitive to the excited light pseudoscalar. For the 3-point correlators, we demonstrate the way the correct behaviour of the pion form factor at large momentum transfers in agreement with perturbative QCD emerges from condensate terms in the OPE for the and correlators. The local-duality sum rule for is shown to lead to the pion form factor with the required properties for all values of the momentum transfer.

Generalized instantaneous Bethe-Salpeter equation and exact quark propagators

-Affiliation: Austrian Academy of Sciences

-Abstract:

Assuming the wave-function renormalization and mass functions in the exact fermion propagators to depend only on the spatial components of the involved momenta allows to derive an instantaneous Bethe-Salpeter formalism which generalizes Salpeter's equation. This construction is applied to light mesons, using the full quark propagators numerically obtained as solution of the Dyson-Schwinger equation in the so-called "renormalization-group-improved rainbow-ladder truncation scheme".

The structure of vacuum in hadrons and quarks mass-spectrum

-Affiliation: Rostov-on-Don State Pedagogical University

-Abstract:

In the framework of Standard Model, the possibility of spontaneous breaking of translational space symmetry is considered, caused by interaction of quark with the field of intermediate z-bosons. It was shown that in the case of strong interaction inhomogeneous space distribution (the cloud) of Z-boson condensate can be formed, with the quark localized within it. It was demonstrated, that mass of the quark in the localized state can be thousands time lower than that of the inoculating one, which, in turn, can have the order of 10 GEv. The origin of P- and CP-noninvariance problem in this model is solved automatically.

Fall-apart decays of polyquark mesons

-Abstract:

We analyse fall-apart decays of a(980) and X(3872), assuming these mesons are tetraquark hadrons. Two extreme options - confined diquark-diquark states and molecular states - are considered. For a0(980), the observed width can be obtained assuming that this meson is a diquark-diquark composite with a relatively large size of around 1-1.5 fm. The pure K \bar K molecular-type state, however, can be excluded. For the X(3872), a sufficiently small width can be obtained if it is a dominantly isospin-0 diquark-diquark composite with a very large size of >2.5 fm. The pure molecular option appears possible if the binding energy is tiny, E_b<0.2 MeV, corresponding to a huge size.

Are light hadronic coherent-like states possible?

-Affiliations: ITEP Moscow; Inst. Superior Tecnico, Portugal

-Abstract:

We investigate a possibility of building quasistable coherent-like states of pions using, as a testground, a chiral potential quark model.

How confinement is lost when Abelian monopoles or center vortices are removed

-Affilation: ITEP Moscow

-Abstract:

We study the properties of configurations from which center vortices on one hand or Abelian monopoles on the other hand have been removed. We confirm the loss of confinement and investigate in what respect the modified ensembles differ from the confining ones from the point of view of the complementary confinement scenario.

Coulombic contribution and fat center vortex model

-Affiliation: University of Tehran

-Abstract:

A fat center vortex model is one of the phenomenological models which is fairly successful to interpret the linear potential between static sources. However, the Coulombic part of the potential has not been investigated by the model yet. In an attempt to get the Coulombic contribution, we are studying different vortex profiles and vortex sizes.

Nucleon and N-Delta(1232) Transition Electromagnetic Form Factors

-Authors: Franz Gross(1), G. Ramalho(2) and M.T. Pe\~na(2,3)

-Presenter: G. Ramalho

-Affiliation: (1) College of William and Mary, Williamsburg, USA, and TJNAF, USA (2) CFTP-IST, Lisbon, Portugal (3) Department of Physics-IST, Lisbon, Portugal

-Abstract:

Using the manifestly covariant spectator theory, and modeling the nucleon as a system of three constituent quarks with their own electromagnetic structure, we show that all four nucleon electromagnetic form factors can be very well described by a manifestly covariant nucleon wave function with zero orbital angular momentum. We also show results obtained for the N-Delta(1232) transition form factors calculated with the same nucleon wave function, and a wave function for the Delta(1232) including S and D orbital waves for the relative motion of the quark-diquark pair.

The Nucleon Parton Distribution for Finite Density

-Abstract:

We present the evolution of the nucleon structure function with barion density in the phenomenological model for the parton distribution in nuclei, where the nuclear Fermi motion fully accounts for the collective motion of partons in nuclear medium. The sea parton distributions are described by additional virtual pions in hadron in such a way as to reproduce the nuclear lepton pair production data and saturate the energy-momentum sum rule. The influence of Fermi motion changes the nucleon rest energy and consequently the transverse momentum square of partons inside bound nucleons. Finally we estimate in the Sigma model the critical density where the fluctuations of pion field lead to the chiral symmetry restoration.

Fitting the lattice gluon propagator and the question of positivity violation

-Affiliation: University of Coimbra

-Abstract: The compatibility of several functional forms used to fit the Dyson-Schwinger gluon propagator with the gluon propagator computed from large asymmetric lattices is investigated. Furthermore, we report on the violation of positivity of the Landau gauge lattice gluon propagator.

Susceptibilities near critical points and signs of effective restoration of chiral and axial symmetries

-Authors: C. A. de Sousa, P. Costa, M. C. Ruivo

-Presenter: C. A. de Sousa

-Abstract:

One of the important feature of the Quantum Chromodynamics (QCD) lagrangian is related to its symmetries and the different ways they can be realized in nature. It is well known that QCD has an approximate U(3) chiral symmetry with its subsymmetry UA(1) being explicitly broken by the axial anomaly. In this context, the explicit and spontaneous breaking of chiral symmetry, as well as the UA(1) anomaly, play a special role, allowing for several well known nontrivial assumptions of low energy QCD.

The aim of the present work is to study, in the framework of the SU(3) Nambu-Jona-Lasinio model, the possible restoration of chiral and axial symmetries at different scenarios: finite temperature and zero chemical potential with constant and temperature dependent anomaly coupling constant, and finite temperature and chemical potential with constant anomaly coupling strength. In this last scenario two cases will be considered: Case I for realistic values of quarks masses, and Case II for semi-realistic values.

The order parameter as well as the order parameter susceptibilities for the chiral transition are analyzed. The results are compared with the lattice calculations. We observe clear peaks in the susceptibilities even when the transitions are crossover.

Medium effects on mesonic modes are analyzed as well as the convergence of chiral partners. This complements the information concerning phase transitions and provides the criterion to define effective restoration of chiral and axial symmetries.