2251108
Competition Between Induced Symmetry Breaking, Cooper Pairing and Chiral Condensate at Finite Density
We study the competition between induced symmetry breaking (ISB), 
Cooper pairing (superconductivity) and chiral condensation at finite non-asymptotic density. Using a quantum mechanical model studied recently by Ilieva and Thirring, we analyze the expectation value of the fermion number density $\la a^*a\ra$ in the presence of chemical potential and discuss relevance of the ISB phenomenon in the model. By Bogoliubov transformation, we obtain the ground state energy and find that a phase with both superconducting and mean field gap is a true ground state. We also study the effective potentials of a two-dimensional field theory model for competitions between $\la\bar\psi\psi\ra$, $\la\psi\psi\ra$ and $\la\psi^\dagger\psi\ra$. We find that in the regime $\mu \mu_c$ the system sits in the mixed phase characterized by 
$\la \psi^\dagger\psi\ra\neq 0$ and $\la \psi\psi\ra\neq 0$ as long as the renormalization point, $M_0$, corresponding to a superconducting gap is not zero, $M_0\neq 0$.
18963275
Heavy quarkonium in a holographic QCD model
Encouraged by recent developments in AdS/QCD models for the light quark system, we study heavy quarkonium in the framework of the AdS/QCD models. We calculate the masses of cc vector meson states using the AdS/QCD models at zero and at finite temperature. Among the models adopted in this work, we find that the soft-wall model describes the low-lying heavy quark meson states at zero temperature relatively well. At finite temperature, we observe that once the bound state is above T{sub c}, its mass will increase with temperature until it dissociates at a temperature of around 494 MeV. It is shown that the dissociation temperature is fixed by the infrared cutoff of the models. The present model serves as a unified nonperturbative model to investigate the properties of bound quarkonium states above T{sub c}.
7806265
Meson exchange effect on color superconductivity
We investigate the effects of pion and gluon exchanges on the formation of two-flavor color superconductivity at moderate density, � < 1GeV . The chiral quark model proposed by Manohar and Georgi containing pions as well as gluons is employed to show that the pion exchange reduces substantially the value of the superconducting gap gotten with the gluon exchange only. It turns out that the pion exchanges produce a repulsion between quark-quark pair in a spin and isospin singlet state. We suggest that the phase consisiting of pions, gluons and quarks is one of the candidates of in-medium QCD phase at moderate density.
119341368
A Schematic model for rho - a(1) mixing at finite density and in-medium effective Lagrangian
Based on schematic two-level models extended to a{sub 1}-meson degrees of freedom, we investigate possible mechanisms of chiral restoration in the vector-axial-vector channels in cold nuclear matter. In the first part of this article we employ the massive Yang-Mills framework to construct an effective chiral Lagrangian based on low-energy mesonic modes at finite density. The latter are identified through nuclear collective excitations of ''meson''-sobar type such as {pi}{r_reversible}[{delta}(1232)N{sup -1}]{identical_to}{pi}, {rho}{r_reversible}[N{sup *}(1520)N{sup -1}]{identical_to}{rho}, etc. In a mean-field type treatment the in-medium gauge coupling g, the (axial-)vector meson masses and f{sub {pi}} are found to decrease with density indicating the approach towards chiral restoration in the language of in-medium effective fields. In the second part of our analysis we evaluate the (first) in-medium Weinberg sum rule which relates vector and axial-vector correlators to the pion decay constant. Using in-medium {rho}/a{sub 1} spectral functions (computed in the two-level model) also leads to a substantial reduction of the pion decay constant with increasing density. (c) 2000 The American Physical Society.
14062402
Consequences of the partial restoration of chiral symmetry in AdS/QCD
Chiral symmetry is an essential concept in understanding QCD at low energy. We treat the chiral condensate, which measures the spontaneous breaking of chiral symmetry, as a free parameter to investigate the effect of partially restored chiral symmetry on the physical quantities in the frame work of an AdS/QCD model. We observe an interesting scaling behavior among the nucleon mass, pion decay constant and chiral condensate. We propose a phenomenological way to introduce the temperature dependence of a physical quantity in the AdS/QCD model with the thermal AdS metric.
28478276
Vector manifestation and fate of vector mesons in dense matter
We describe in-medium properties of hadrons in dense matter near chiral restoration using a Wilsonian matching to QCD of an effective field theory with hidden local symmetry at the chiral cutoff $\Lambda$. We find that chiral symmetry is restored in vector manifestation \`a la Harada and Yamawaki at a critical matter density $n_c$. We express the critical density in terms of QCD correlators in dense matter at the matching scale. In a manner completely analogous to what happens at the critical $N_f^c$ and at the critical temperature $T^c$, the vector meson mass is found to vanish (in the chiral limit) at chiral restoration. This result provides a support for Brown-Rho scaling predicted a decade ago.
119804529
Model for relativistic bound-state perturbation theory
A model for relativistic bound-state perturbation theory is presented. For the bound-state wave function needed in the perturbation formula, the covariant-harmonic-oscillator wave function is used. As for the perturbing potential, the Feynman propagator corresponding to one-meson exchange is used. This model produces a relativistic derivation of the Breit--Fermi formula, which was recently used by De Rujula, Georgi, and Glashow in their study of hadronic masses. (AIP)
51814291
Design study on standing-wave linear accelerator
A compact standing-wave linac has been designed using S-band microwaves for medical and industrial applications. It uses a bi-periodic structure with constant impedance. It consists of a buncher section with three-cells and on-axis coupled cavities with nine-cells. The total length is 740.0 mm including the electron gun. Using SUPERFISH, HFSS and PARMELA codes, it is capable to deliver 4.5 MeV electron beams with pulsed microwaves of 4.8 MW at 2,856 MHz. In this paper, we present the detailed design studies on a compact S-band standing-wave linac.
56300970
Representations of the Poincaré group for relativistic extended hadrons
Representations of the Poincare group are constructed from the relativistic harmonic oscillator wave functions which have been effective in describing the physics of internal quark motions in the relativistic quark model. These wave functions are solutions of the Lorentz‐invariant harmonic oscillator differential equation in the ’’cylindrical’’ coordinate system moving with the hadronic velocity in which the time‐separation variable is treated separately. This result enables us to assert that the hadronic mass spectrum is generated by the internal quark level excitation, and that the hadronic spin is due to the internal orbital angular momentum. An addendum relegated to PAPS contains discussions of detailed calculational aspects of the Lorentz transformation, and of solutions of the oscillator equation which are diagonal in the Casimir operators of the homogeneous Lorentz group. It is shown there that the representation of the homogeneous Lorentz group consists of solutions of the oscillator partial diffe...
118123985
Squeezed states, time-energy uncertainty relation, and Feynman's rest of the universe
Two illustrative examples are given for Feynman's rest of the universe. The first example is the two-mode squeezed state of light where no measurement is taken for one of the modes. The second example is the relativistic quark model where no measurement is possible for the time-like separation fo quarks confined in a hadron. It is possible to illustrate these examples using the covariant oscillator formalism. It is shown that the lack of symmetry between the position-momentum and time-energy uncertainty relations leads to an increase in entropy when the system is different Lorentz frames.
14507485
Two-pearl Strings: Feynman's Oscillators
String models are designed to provide a covariant description of internal space-time structure of relativistic particles. The string is a limiting case of a series of massive beads like a pearl necklace. In the limit of infinite-number of zero-mass beads, it becomes a field-theoretic string. Another interesting limit is to keep only two pearls by eliminating all others, resulting in a harmonic oscillator. The basic strength of the oscillator model is its mathematical simplicity. This encourages us to construct two-pearl strings for a covariant picture of relativistic extended particles. We achieve this goal by transforming the oscillator model of Feynman {\it et al.} into a representation of the Poincar\'e group. We then construct representations of the O(3)-like little group for those oscillator states, which dictates their internal space-time symmetry of massive particles. This simple mathematical procedure allows us to explain what we observe in the world in terms of the fundamental space-time symmetries, and the built-in covariance of the model allows us to use the physics in the rest frame in order to explain what happens in the infinite-momentum frame. It is thus possible to calculate the parton distribution within the proton moving light-like speed in terms of the quark wave function in its rest frame.