8523168
Fixed-Point Analysis of the Low-Energy Constants in the Pion-Nucleon Chiral Lagrangian
In the framework of heavy-baryon chiral perturbation theory, we investigate the fixed point structure of renormalization group equations (RGE) for the ratios of the renormalized low energy constants (LECs) that feature in the pion-nucleon chiral Lagrangian. The ratios of the LECs deduced from our RGE analysis are found to be in semi-quantitative agreement with those obtained from direct fit to the experimental data. The naturalness of this agreement is discussed using a simple dimensional analysis combined with Wilsonian RGEs.
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.
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.
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.
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}.
14454392
Does Lorentz Boost Destroy Coherence
It is shown that the time-energy uncertainty relation can be combined into the position-momentum uncertainty relation covariantly in the quark model of hadrons. This leads to a Lorentz-invariant form of the uncertainty relations. This model explains that the quark model and the parton model are two different manifestations of the same covariant model. In particular, this covariant model explains why the coherent amplitudes in the quark model become incoherent, after a Lorentz boost, in the parton model. It is shown that this lack of coherence is consistent with the present form of quantum mechanics.
123462298
Overlap of shape resonance and Cooper-minimum structure in photoionization
Examples of a Cooper minimum inside the range of a shape-resonance maximum of a photoionization cross section have been found in numerical calculations within a single-electron model in a relativistic Hartree-Fock-Slater potential. In these model calculations for the photoionization of tin and uranium we find relatively broad shape resonances in all the $d$ and $f$ subshells. In addition a Cooper minimum occurs in the outer subshells of these high-angular-momentum states within the region of the shape-resonance maximum. We examine the matrix elements for these subshells and the resulting cross sections and angular distributions.
119495662
Direct radiative recombination of electrons with atomic ions: Cross sections and rate coefficients
Simple expressions are obtained which permit systematic estimates of the rate coefficients for direct radiative recombination (DRR) of fast electrons with atomic ions of various ionic species. The analysis utilizes a set of cross sections obtained through numerical calculations combined with the use of an interpolation scheme to smoothly connect reduced cross sections (apart from normalizations) of the bremsstrahlung tip region and the low-lying DRR region. It is shown that these numerical cross sections can be reproduced by the predictions of a modified semiclassical Kramers formula with an appropriate effective charge Z/sub eff/, which is larger than the effective charge which reproduces the energy levels of the states into which capture occurs. In accord with this modified Kramers formula, the numerically obtained total cross sections are shown to scale with Z/sub eff//sup 2//K for each isoelectronic sequence, and with a parameter (n/sub 0/)/sub eff/ which characterizes each isoelectronic sequence. Using these scaling properties, simple analytic expressions are obtained for recombination rate coefficients, for the rate of electron kinetic-energy loss, and for the rate of radiated power loss, assuming a classical Maxwell-Boltzmann thermal distribution of continuum electrons.
668406
Quantization of electromagnetic fields in a circular cylindrical cavity
We present a quantization procedure for the electromagnetic field in a circular cylindrical cavity with perfectly conducting walls, which is based on the decomposition of the field. A new decomposition procedure is proposed; all vector mode functions satisfying the boundary conditions are obtained with the help of this decomposition. After expanding the quantized field in terms of the vector mode functions, it is possible to derive the Hamiltonian for this quantized system.
122981620
Illustrative examples of the symplectic group
Simple illustrative examples are given for understanding the symplectic group. Transformation properties of the Sp(2) group are discussed in terms of the two‐dimensional geometry of circles and ellipses, two‐by‐two matrices, and in terms of a group‐theoretical language similar to that of the Pauli spin matrices. The isomorphism between the Sp(2) and SO(2,1) groups is discussed in detail. It is noted that this isomorphism is similar to that between the SU(2) and rotation groups. Simple illustrative physcial examples are given also for using the symplectic group in nuclear physics, statistical mechanics, and in high‐energy physics.