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.
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.
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.
1457184
The Vector and Axial-Vector Susceptibilities and Effective Degrees of Freedom in the Vector Manifestation
The question as to what the relevant degrees of freedom are at the thermal chiral phase transition is addressed in terms of the “vector manifestation (VM)” of chiral symmetry à la Harada and Yamawaki. We find that both the vector susceptibility χV and the axial-vector susceptibility χA at the chiral transition could receive contributions from other degrees of freedom than pions in the chiral limit. The possible candidates are zero-mass vector mesons and quasiquarks. In the presence of these degrees of freedom, hidden local symmetry (HLS) theory with vector manifestation predicts that χV equals χA in consistency with chiral invariance and that both the time component f t π and the space component f s π of the pion decay constant vanish at the chiral phase transition. With the VM, the pion velocity vπ proportional to f s π/f t π at T = Tc is predicted to be equal to 1. These results are obtained in the leading order in power counting but we expect them to hold more generally in the chiral limit thanks to the VM point. and Department of Physics and Astronomy, University of South Carolina, Columbia, SC 29208 and School of Physics, Korea Institute for Advanced Study, Seoul 130-012, Korea.
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.
15573253
O(3,3)-like Symmetries of Coupled Harmonic Oscillators
In classical mechanics, the system of two coupled harmonic oscillators is shown to possess the symmetry of the Lorentz group O(3,3) or SL(4,r) in the four‐dimensional phase space. In quantum mechanics, the symmetry is reduced to that of O(3,2) or Sp(4), which is a subgroup of O(3,3) or SL(4,r), respectively. It is shown that among the six Sp(4)‐like subgroups, only one possesses the symmetry which can be translated into the group of unitary transformations in quantum mechanics.
67811641
ENERGY SPREAD ISSUE IN LASER UNDULATOR BASED XFELs
At the Center for the Exploration of Energy and Matter (CEEM) in Indiana University, we have been developing a new XFEL concept, which is based on inverse Compton scattering and a laser undulator instead of the conventional magnetic undulator. In this paper, we report an estimation of the energy spread growth in the electron storage ring due to the inverse Compton scattering itself and their impacts on the FEL lasing in the laser undulator based XFEL concept.
119889363
Symmetries of two‐mode squeezed states
It is known that the symmetry of two‐mode squeezed states is governed by the group Sp(4) which is locally isomorphic to the O(3,2) de Sitter group. It is shown that this complicated ten‐parameter group can be regarded as a product of two three‐parameter Sp(2) groups. It is shown also that two coupled harmonic oscillators serve as a physical basis for the symmetry decomposition. It is shown further that the concept of entropy is needed when one of the two modes is not observed. The entropy is zero when the system is uncoupled. The system reaches thermal equilibrium when the entropy becomes maximal.
120447860
Covariant Harmonic Oscillators and the Quark Model
An attempt is made to give a physical interpretation to the phenomenological wave function of Yukawa, which gives a correct nucleon form factor in the symmetric quark model. This wave function is first compared with the Bethe-Salpeter wave function. It is shown that they have similar Lorentz-contraction properties in the high-momentum limit. A hyperplane harmonic oscillator is then introduced. It is shown that the Yukawa wave function, which is defined over the entire four-dimensional Euclidean space, can be interpreted in terms of the three-dimensional hyperplane oscillators. It is shown further that this wave function satisfies a Lorentz-invariant differential equation from which excited harmonic-oscillator states can be constructed, and from which a gauge-invariant electromagnetic interaction can be generated.
119414218
Covariant Harmonic Oscillators and Diffractive Excitations
We use convariant harmonic-oscillator wave functions to describe quark- model hadrons in Glauber's model of diffractive scattering. It is shown that the Glauber model can be constructed in the center-of-mass system in terms of fully covariant quantities. For elastic scattering, the covariant model gives the same result as that using nonrelativistic harmonic-oscillator wave functions. For the transition from the n = 0 to n = 2 states, which includes the diffractive excitations to the N (1470) and N (1690) resonances, the relativistic effect is simply a multiplication of the nonrelativistic amplitude by the factor (1- $alpha$$sup 2$), $alpha$ being the velocity difference between the incoming nucleon and the final-state resonance. We discuss the effects of these results on the existing nonrelativistic calculations.