Hamiltonian Flow Equations for a Dirac Particle in an External Potential

We derive and solve the Hamiltonian flow equations for a Dirac particle in an external static potential. The method shows a general procedure for the set up of continuous unitary transformations to reduce the Hamiltonian to a quasidiagonal form.Comment: 6 page

Wilson Loop-Loop Correlators in AdS/QCD

We calculate the expectation value of one circular Wilson loop and the correlator of two concentric circular Wilson loops in AdS/QCD using the modified AdS_5-metric given in Ref.[1]. The confinement properties of this metric in AdS/QCD are analyzed and compared with QCD and Nambu-Goto theory in four dimensions.Comment: 22 pages, 14 figure

Unifying Nucleon and Quark Dynamics at Finite Baryon Number Density

We present a model of baryonic matter which contains free constituent quarks in addition to bound constituent quarks in nucleons. In addition to the common linear sigma-model we include the exchange of vector-mesons. The percentage of free quarks increases with baryon density but the nucleons resist a restoration of chiral symmetry.Comment: 8 pages LaTeX, 3 postscript figures, submitted to Phys. Lett.

Thermodynamics of AdS/QCD within the 5D dilaton-gravity model

We calculate the pressure, entropy density, trace anomaly and speed of sound of the gluon plasma using the dilaton potential of Ref. arXiv:0911.0627[hep-ph] in the dilaton-gravity theory of AdS/QCD. The finite temperature observables are calculated from the Black Hole solutions of the Einstein equations, and using the Bekenstein-Hawking equality of the entropy with the area of the horizon. Renormalization is well defined, because the T=0 theory has asymptotic freedom. Comparison with lattice simulations is made.Comment: 4 pages, 4 figures. To appear in the proceedings of 15th International Conference in Quantum Chromodynamics (QCD 10), Montpellier, France, 28 Jun - 3 Jul 201

Phenomenology of AdS/QCD and Its Gravity Dual

We construct the dilaton potential in the gravity dual theory of AdS/QCD for the warp factor of Refs.{1,2}. Using this AdS_5-metric with properties similar to QCD, we find that the gravity dual leads to a meaningful gauge coupling in the region between the charmonium and bottonium mass, but differs slightly from QCD in the extreme UV. When we fix the ultraviolet behavior in accord with the beta-function, we can obtain good agreement with the overall heavy quark-antiquark potential. Although the leading order proportional to -\alpha^{4/3}/r differs from perturbative QCD, the full potential agrees quite well with the short distance QCD potential in NNLO.Comment: 42 pages, 13 figures, 1 tabl

The Ratio of Gluon Distributions in Sn and C

We calculate the ratio of gluon densities, G^Sn(x)/G^C(x), for 0.01<x<0.1, from the new high statistics data on F_2^Sn/F_2^C taken by the NM Collaboration. For small x, the shadowing in the gluon distribution is about equal to the shadowing of quark distribution. The antishadowing in the gluon distribution, however, is roughly 10%. We also compare with the ratio difference, R=sigma_L/sigma_T, from Sn and C.Comment: LaTeX, 9 page

Finite size vertex corrections to the three-gluon decay widths of J/ψJ/\psi and Υ\Upsilon and a redetermination of αs(μ)\alpha_s(\mu) at μ=mc\mu=m_c and mbm_b

We calculate the corrections to the three-gluon decay widths $\Gamma_{3g}$ of $c\bar c$ and $b \bar b$ quarkonia due to the finite extension of the $Q\bar Q\to 3g$ vertex function. The widths computed with zero range vertex are reduced by a factor $\gamma$ where $\gamma=0.31$ for the $J/\psi$ and $\gamma=0.69$ for the $\Upsilon$. These large corrections necessitate a redetermination of the values $\alpha_s(\mu)$ extracted from $\Gamma_{3g}$. We find $\alpha_s(m_c)=0.28\pm.01$ and $\alpha_s(m_b)=0.20\pm.01$.Comment: 11 pages, HD-TVP-93-0

Renormalization Group Flow Equation at Finite Density

For the linear sigma model with quarks we derive renormalization group flow equations for finite temperature and finite baryon density using the heat kernel cutoff. At zero temperature we evolve the effective potential to the Fermi momentum and compare the solutions of the full evolution equation with those in the mean field approximation. We find a first order phase transition either from a massive constituent quark phase to a mixed phase, where both massive and massless quarks are present, or from a metastable constituent quark phase at low density to a stable massless quark phase at high density. In the latter solution, the formation of droplets of massless quarks is realized even at low density.Comment: 30 pages, 9 figures; typos corrected, section 3 revised, one reference added, two references updated, submitted to Phys. Rev.

An Approach towards a Constituent Quark Model on the Light Cone

We use the vacuum expectation value of a Wegner-Wilson loop representing a fast moving quark-antiquark pair to derive the light cone Hamiltonian for a $q\bar q$ meson. We solve the corresponding Schr\"odinger equation for various trial wave functions. The result shows how confinement determines the meson mass and wave function for valence quarks on the light cone. We also parametrize the effect of the spin-dependent splitting for a light meson and charmonium. The correct chiral-symmetry breaking pattern for the pion mass is obtained due to the self-energy of the quark.Comment: 17 pages and 5 figure

Scaling properties of high p_T inclusive hadron production

We analyze the scaling properties of inclusive hadron production in proton-proton and in heavy ion collisions from fixed target to collider energies. At large transverse momentum p_T, the invariant cross section exhibits a power-like behavior Ed^3\sigma/d^3p\propto p_T^{-n} at fixed transverse x, x_T=2p_T/\sqrt{s}, and fixed center-of-mass scattering angle \theta_{cm}. Knowledge of the exponent n allows one to draw conclusions about the production mechanisms of hadrons, which are poorly known, even at high p_T. We find that high-p_T hadrons are produced by different mechanisms at fixed-target and collider energies. For pions, higher-twist subprocesses where the pion is produced directly dominate at fixed target energy, while leading-twist partonic scattering plus fragmentation is the most important mechanism at collider energies. High-p_T baryons on the other hand appear to be produced by higher-twist mechanisms at all available energies. The higher-twist mechanism of direct proton production can be verified experimentally by testing whether high p_T protons are produced as single hadrons without accompanying secondaries. In addition, we find that medium-induced gluon radiation in heavy ion collisions can violate scaling.Comment: 14 pages, 3 figure