13 research outputs found

### 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

### Critical Correlations of Wilson Lines in SU(3) and the High Energy $\gamma^*p$ 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.