Nuclear modifications of fragmentation functions and rescaling models

We discuss nuclear modification of fragmentation functions in the context of the so-called ``rescaling models''. These models implement partial deconfinement inside nuclei by modifying the fragmentation functions perturbatively. We apply these models to the analysis of nuclear hadron production in deep inelastic scattering processes at the HERMES and EMC experiments.Comment: 6 pages, 3 figures, uses espcrc1.sty. Talk presented at "QCD-N'02", Ferrara (ITA), April 3rd-6th, 200

Boundary between Hadron and Quark/Gluon Structure of Nuclei

We show that the boundary between quark-dominated and hadron-dominated regions of nuclear structure may be blurred by multi-nucleon quark clusters arising from color percolation. Recent experiments supporting partial percolation in cold nuclei and full percolation in hot/dense nuclear matter include: deep inelastic lepton-nucleus scattering, relativistic heavy-ion collisions and the binding energy in $^5 He_{\Lambda}$.Comment: 10 pages, 4 figures; added references; improved figures; fixed a typo (wrong sign in Eqn 6); Fixed typos in Equation 2; updated reference

Higher Twist Effects in Deep Inelastic Scattering on Nuclei

Particle production in deep inelastic scattering on nuclei is reduced due to absorption of the produced particles in the nucleus. The photon ejects a quark from a bound nucleon which propagates through the nucleus forming a prehadron before turning into a hadron. We calculate the higher twist effect in hadronization which dominates the $z \to 1$ region of fragmentation.Comment: Based on a talk given by H.J. Pirner at the Fifth International Conference on Perspectives in Hadronic Physics, Trieste, May 200

Vacuum Expectation Value of a Wegner-Wilson Loop near the Light Cone

Vacuum expectation values for one Wegner-Wilson loop representing a moving quark-antiquark pair are calculated in four-dimensional Euclidean and Minkowski space-time. The calculation uses gluon field strength correlators with perturbative gluon exchange and non-perturbative correlations from the stochastic vacuum model. The expectation value of a Wegner-Wilson loop forming a hyperbolic angle in Minkowski space-time is connected by an analytical continuation to the expectation value of the Wegner-Wilson loop in Euclidean four-space. The obtained result shows how confinement enters into the light-cone Hamiltonian for valence quarks independently of the chosen model.Comment: 12 pages, 2 figures, sections 2 and 3 shortened, more details added in section

Linking the Quark Meson Model with QCD at High Temperature

We model the transition of a system of quarks and gluons at high energies to a system of quarks and mesons at low energies in a consistent renormalization group approach. Flow equations interpolate between the physics of the high-temperature degrees of freedom and the low-temperature dynamics at a scale of 1 GeV. We also discuss the dependence of the equation of state on baryon density and compare our results with recent lattice gauge simulations.Comment: 11 pages, 4 figures additional discussion of the second order phase transitio

Low x Scattering as a Critical Phenomenon

We discuss deep inelastic scattering at low $x$ as a critical phenomenon in 2+1 space-time dimensions. QCD (SU2) near the light cone becomes a critical theory in the limit of $\lim x \to 0$ with a correlation mass $m(x) \propto x^{\nu/2}$. We conjecture that the perturbative dipole wave function of the virtual photon in the region $1/Q<x_{\bot}<1/m$ obeys correlation scaling $\Psi \propto (x_{\bot})^{-(1+n)}$ before exponentially decaying for distances larger than the inverse correlation mass. This behavior combined with an $x$ -independent dipole proton cross section gives a longitudinal structure function which shows the dominant features of the experimental data. For SU3 QCD a similar second order phase transition is possible in the presence of quark zero modes on the light cone.Comment: 15 pages, latex, 2 eps figure

Critical Correlations of Wilson Lines in SU(3) and the High Energy γ∗p\gamma^*p Cross Section

We discuss deep inelastic scattering at high energies as a critical phenomenon in 2+1 space - time dimensions. In the limit of Bjorken $x \to 0$, $QCD$ SU(3) with quark fields becomes a critical theory with a diverging correlation length $\xi(x) \propto x^{-\frac{1}{2 \lambda_2}}$ where the exponent $\lambda_2=2.52$ is obtained from the center group Z(3) of SU(3). We conjecture that the dipole wave function of the virtual photon for transverse sizes $1/Q<x_{\bot}<\xi$ obeys correlation scaling $\Psi \propto (x_{\bot})^{-(1+n)}$ before exponentially decaying for distances larger than the correlation length. Using this behavior combined with different $x$ -independent dipole proton cross sections we calculate the proton structure function and compare with the experimental data. We take the good agreement with the measured proton structure function F$_2(x,Q^2)$ as an indication that at high energies dimensional reduction to an effective three dimensional theory with a critical point occurs.Comment: 21 pages, 3 figure

The Spectrum of the Dirac Operator in the Linear Sigma Model with Quarks

We derive the spectrum of the Dirac operator for the linear sigma-model with quarks in the large N_c approximation using renormalization group flow equations. For small eigenvalues, the Banks-Casher relation and the vanishing linear term are recovered. We calculate the coefficient of the next to leading term and investigate the spectrum beyond the low energy regime.Comment: 15 pages, 6 figures, to appear in Phys. Rev.