arXiv subjects

Mannque Rho

Publications and source records attributed to Mannque Rho.

At least 181 records · Page 10Linked to original sources

arXiv1998

The Proton Spin in the Chiral Bag Model : Casimir Contribution and Cheshire Cat Principle

The flavor singlet axial charge has been a source of study in the last years due to its relation to the so called {\it Proton Spin Problem}. The relevant flavor singlet axial current is anomalous, i.e., its divergence contains a piece which is the celebrated $U_A(1)$ anomaly. This anomaly is intimately associated with the $η^\prime$ meson, which gets its mass from it. When the gauge degrees of freedom of QCD are confined within a volume as is presently understood, the $U_A(1)$ anomaly is known to induce color anomaly leading to "leakage" of the color out of the confined volume (or bag). For consistency of the theory, this anomaly should be canceled by a boundary term. This ``color boundary term" inherits part or most of the dynamics of the volume (i.e., QCD). In this paper, we exploit this mapping of the volume to the surafce via the color boundary condition to perform a complete analysis of the flavor singlet axial charge in the chiral bag model using the Cheshire Cat Principle. This enables us to obtain the hitherto missing piece in the axial charge associated with the gluon Casimir energies. The result is that the flavor singlet axial charge is small independent of the confinement (bag) size ranging from the skyrmion picture to the MIT bag picture, thereby confirming the (albeit approximate) Cheshire Cat phenomenon.

hep-ph↗

arXiv1998

Scaling Of Chiral Lagrangians And Landau Fermi Liquid Theory For Dense Hadronic Matter

We discuss the Fermi-liquid properties of hadronic matter derived from a chiral Lagrangian field theory in which Brown-Rho (BR) scaling is incorporated. We identify the BR scaling as a contribution to Landau's Fermi liquid fixed-point quasiparticle parameter from "heavy" isoscalar meson degrees of freedom that are integrated out from a low-energy effective Lagrangian. We show that for the vector (convection) current, the result obtained in the chiral Lagrangian approach agrees precisely with that obtained in the semi-phenomenological Landau-Migdal approach. This precise agreement allows one to determine the Landau parameter that enters in the effective nucleon mass in terms of the constant that characterizes BR scaling. When applied to the weak axial current, however, these two approaches differ in a subtle way. While the difference is small numerically, the chiral Lagrangian approach implements current algebra and low-energy theorems associated with the axial response that the Landau method misses and hence is expected to be more predictive.

nucl-th↗

arXiv1998

Effective Field Theory for Low-Energy Two-Nucleon Systems

We illustrate how effective field theories work in nuclear physics by using an effective Lagrangian in which all other degrees of freedom than the nucleonic one have been integrated out to calculate the low-energy properties of two-nucleon systems, viz, the deuteron properties, the np 1S0 scattering amplitude and the M1 transition amplitude entering into the radiative np capture process. Exploiting a finite cut-off regularization procedure, we find all the two-nucleon low-energy properties to be accurately described with little cut-off dependence, in consistency with the general philosophy of effective field theories.

hep-ph↗

arXiv1998

Effective Field Theories For Nuclei And Dense Matter

A recent development on the working of effective field theories in nuclei and in dense hadronic matter is discussed. We consider two extreme regimes: One, dilute regime for which fluctuations are made on top of the matter-free vacuum; two, dense systems for which fluctuations are treated on top of the "vacuum" defined at a given density, with masses and coupling constants varying as function of matter density ("Brown-Rho scaling"). Based on an intricate -- as yet mostly conjectural -- connection between the in-medium structure of chiral Lagrangian field theory which is a beautiful effective theory of QCD and that of Landau Fermi liquid theory which is an equally beautiful and highly successful effective theory of many-body systems, it is suggested that a chiral Lagrangian with Brown-Rho scaling in the mean field is equivalent to Fermi-liquid fixed point theory. I make this connection using electroweak and strong responses of nuclear matter up to nuclear matter density and then extrapolating to higher densities encountered in heavy-ion collisions and compact stars.

nucl-th↗

arXiv1998

The Solar Proton Burning Process Revisited In Chiral Perturbation Theory

The proton burning process p + p -> d + e(+) + ν(e), important for the stellar evolution of main-sequence stars of mass equal to or less than that of the Sun, is computed in effective field theory using chiral perturbation expansion to the next-to-next-to leading chiral order. This represents a model-independent calculation consistent with low-energy effective theory of QCD comparable in accuracy to the radiative np capture at thermal energy previously calculated by first using very accurate two-nucleon wavefunctions backed up by an effective field theory technique with a finite cut-off. The result obtained thereby is found to support within theoretical uncertainties the previous calculation of the same process by Bahcall and his co-workers.

astro-ph↗

arXiv1997

Chiral Symmetry, Landau Fermi Liquid And Dense Hadronic Matter

I describe how effective chiral Lagrangian field theories work for nuclei and nuclear matter by going from the deuteron to dense hadronic matter via BR scaling and Landau Fermi-liquid fixed point parameters, with possible applications to relativistic heavy-ion processes and compact ``nuclear stars.''

hep-ph↗

arXiv1997

Thermodynamic Properties of Effective Chiral Lagrangians with BR Scaling

We show that effective chiral Lagrangians endowed with Brown-Rho scaling can be mapped to Landau Fermi-liquid fixed point theory in a way consistent with general constraints following from thermodynamics. This provides a unified scheme to treat, starting from normal nuclear matter, hadronic matter under extreme conditions that is encountered in relativistic heavy-ion collisions and in the interior of compact stars.

hep-ph↗

arXiv1997

Chiral Symmetry and Meson-Exchange Currents

The meson-exchange current in nuclei, a long-standing problem in nuclear physics, is described in modern theory of strong interactions, namely, QCD expressed in terms of effective chiral Lagrangian field theory. Some old results are given a modern interpretation and some new results are predicted. Among the topics treated are an accurate calculation of the radiative np capture process at thermal energy, the enhanced axial charge transition in heavy nuclei, Brown-Rho (BR) scaling in dense medium induced by vacuum changes, dropping meson masses and "mended symmetry" in relativistic heavy-ion processes and the link between the physics of dilute and dense hadronic systems through a mapping of effective chiral Lagrangians to Landau Fermi-liquid theory.

nucl-th↗

arXiv1997

A New State Of Hadronic Matter At High Density

We propose in this article that if the chemical potential exceeds a critical value in dense hadronic medium, a first-order phase transition to a new state of matter with Lorentz symmetry spontaneously broken (in addition to the explicit breaking) takes place. As a consequence, light vector mesons get excited as ``almost'' Goldstone bosons. Since the light vector mesons dominantly couple to photons, the presence of these new vector mesons could lead to an enhancement in the dilepton production from dense medium at an invariant mass lower than the free-space vector-meson mass. We provide a low-energy quark model which demonstrates that the above scenario is a generic case for quark theories with a strong interaction in the vector channel. We discuss possible relevance of this phase to the phenomenon of the enhanced dilepton production at low invariant masses in relativistic heavy-ion collisions.

hep-ph↗

arXiv1997

Fluctuations In ``BR-Scaled'' Chiral Lagrangians

We develop arguments for "mapping" the effective chiral Lagrangian whose parameters are given by "BR scaling" to a Landau Fermi-liquid fixed-point theory for nuclear matter in describing fluctuations in various flavor (e.g., strangeness) directions. We use for this purpose the effective Lagrangian used by Furnstahl, Tang and Serot that incorporates the trace anomaly of QCD in terms of a light-quark (quarkonium) degree of freedom with the heavy (gluonium) degree of freedom integrated out. The large anomalous dimension $d_{an}\approx 5/3$ for the scalar field found by Furnstahl et al to be needed for a correct description of nuclear matter is interpreted as an indication for a strong-coupling regime and the ground state given by the BR-scaled parameters is suggested as the background around which fluctuations can be rendered weak so that mean-field approximation is reliable. We construct a simple model with BR scaled parameters that provides a satisfactory description of the properties of matter at normal nuclear matter density. Given this, fluctuations around the BR scaled background are dominated by tree diagrams. Our reasoning relies heavily on recent developments in the study of nucleon and kaon properties in normal and dense nuclear matter, e.g., nucleon and kaon flows in heavy-ion processes, kaonic atoms, and kaon condensation in dense compact-star matter.

hep-ph↗

arXiv1997

Color Anomaly and Flavor-Singlet Axial Charge of the Proton in the Chiral Bag: The Cheshire Cat Revisited

Quantum effects inside the chiral bag induce a color anomaly which requires a compensating surface term to prevent breakdown of color gauge invariance. We show that the presence of this surface term first discovered several years ago allows one to derive in a gauge-invariant way a chiral-bag version of the Shore-Veneziano two-component formula for the flavor-singlet axial charge of the proton. This has relevance to what is referred to as the ``proton spin problem" on the one hand and to the Cheshire-Cat phenomenon in hadron structure on the other. We show that when calculated to the leading order in the color gauge coupling and for a specific color electric monopole configuration in the bag, one can obtain a striking Cheshire-Cat phenomenon with a negligibly small singlet axial charge.

hep-ph↗

arXiv1996

QCD Vacuum Changes in Nuclei

In this talk, I discuss how the changes in the QCD vacuum induced by increasing nuclear matter density affect nuclear properties under normal as well as extreme conditions. The quark condensate which is the order parameter for the mode in which chiral symmetry is manifested is expected to change as matter density or temperature is changed. The topics discussed are ``BR scaling," its connection to the structure of nuclei in Landau's Fermi liquid theory and a variety of consequences on such nuclear properties as effective nucleon mass, nuclear gyromagnetic ratios, $g_A^\star$, axial-charge transitions in nuclei and on the fluctuations of nuclear matter into the strange-flavor direction as observed in heavy-ion collisions. I will also present a simple explanation of the recent dilepton data in the CERN-CERES heavy-ion experiments involving densities greater than that of nuclear matter and of the Indiana results on the longitudinally polarized proton scattering from heavy nuclei, evidencing dropping vector-meson masses in medium which can be interpreted as signaling an aspect of chiral symmetry restoration in dense medium. The test of BR scaling provides a bridge between the physics of extreme conditions (e.g. relativistic heavy-ion collisions) and the physics of normal conditions which has conventional descriptions, thereby setting the stage for formulating many-body theory for nuclear matter starting from an effective chiral Lagrangian.

nucl-th↗

arXiv1996

Connection between Effective Chiral Lagrangians and Landau-Migdal Fermi Liquid Theory of Nuclear Matter

I discuss in this lecture how to make a connection between effective chiral Lagrangians -- low-energy effective theory of QCD -- and Landau Fermi liquid theory extended by Migdal to nuclear matter. The practical purpose of such a connection is to provide a link between certain observables in relativistic heavy-ion processes and those in low-energy spectroscopy, giving a new insight into how chiral dynamics manifests itself in nuclear systems.

nucl-th↗

arXiv1996

From Chiral Lagrangians to Landau Fermi Liquid Theory of Nuclear Matter

A simple relation between the effective parameters of chiral Lagrangians in medium as predicted by BR scaling and Landau Fermi liquid parameters is derived. This provides a link between an effective theory of QCD at mean-field level and many-body theory of nuclear matter. It connects in particular the scaling vector-meson mass probed by dileptons produced in heavy-ion collisions (e.g., CERES of CERN-SPS) to the scaling nucleon-mass relevant for low-energy spectroscopic properties, e.g., the nuclear gyromagnetic ratios $δg_l$ and the effective axial-vector constant $g_A^\star$.

nucl-th↗

arXiv1995

The Changes in Properties of Hadrons in Nuclei and Nuclear Matter

The changes of hadron properties in dense and/or hot matter are discussed in terms of effective chiral Lagrangians with the parameters of the theory scaled in a simple way. The phenomenologically successful Walecka model is identified as a mean field chiral Lagrangian with the scaled parameters. Kaon condensation and chiral restoration transitions can be described within the same mean field framework.

nucl-th↗

arXiv1995

From Chiral Mean Field to Walecka Mean Field and Kaon Condensation

A unified treatment of normal nuclear matter described by Walecka's mean field theory and kaon condensed matter described by chiral perturbation theory is proposed in terms of mean fields of an effective chiral Lagrangian. The BR scaling is found to play a key role in making the link between the ground state properties of nuclear matter and the fluctuation into the strangeness-flavor direction. A simple prediction for kaon condensation is presented.

nucl-th↗

arXiv1995

The Role of Lambda(1405) in Kaon-Proton Interactions

S-wave $K^-p$ scattering into various channels near threshold are analyzed in heavy-baryon chiral perturbation theory with $Λ(1405)$ introduced as an independent field. This is the approach that predicted the critical density $2<=ρ_c/ρ_0 <=3$ for negatively charged kaon condensation. We show that chiral perturbation expansion treating the $Λ(1405)$ as elementary is consistent with {\it all} threshold data including a double-charge-exchange process suppressed at leading order of chiral expansion in the absence of the $Λ(1405)$. We also discuss S-wave $K^+ p$ scattering phase shifts at low energy.

hep-ph↗

arXiv1995

Quark Confinement in a Constituent Quark Model

On the level of an effective quark theory, we define confinement by the absence of quark anti-quark thresholds in correlation functions. We then propose a confining Nambu-Jona-Lasinio-type model. The confinement is implemented in analogy to Anderson localization in condensed matter systems. We study the model's phase structure as well as its behavior under extreme conditions, i.e.\ high temperature and/or high density.

hep-ph↗