arXiv subjects

Mannque Rho

Publications and source records attributed to Mannque Rho.

At least 163 records · Page 9Linked to original sources

arXiv2000

Physics of Dense and Superdense Matter

I discuss a few aspects of dense hadronic matter and superdense QCD matter that are considered to be relevant to the physics of compact astrophysical systems. The connection between a "bottom-up approach" and a "top-down approach" is made with the help of an effective field theory strategy. Topics treated are meson condensation going up from low density and color superconductivity going down from asymptotic density with the approach to the chiral phase transition made in terms of Brown-Rho scaling.

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arXiv2000

Effective Field Theories, Landau-Migdal Fermi-Liquid Theory and Effective Chiral Lagrangians for Nuclear Matter

We reinterpret Landau-Migdal Fermi-liquid theory of nuclear matter as an effective chiral field theory with a Fermi surface. The effective field theory is formulated in terms of a chiral Lagrangian with its {\it mass and coupling parameters} scaling a la Brown-Rho and with the Landau-Migdal parameters identified as the fixed points of the field theory. We show how this mapping works out for response functions to the EM vector current and then using the same reasoning, make prediction on nuclear axial current, in particular on the enhanced axial-charge transitions in heavy nuclei. We speculate on how to extrapolate the resulting theory which appears to be sound both theoretically and empirically up to normal nuclear matter density $ρ_0$, to hitherto unexplored higher density regime relevant to relativistic heavy-ion processes and to cold compact (neutron) stars.

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arXiv2000

Pi0 -> Gamma Gamma in Dense QCD

QCD superconductors in the color-flavor-locked (CFL) phase support light excitations (generalized pions) in the form of particle-particle or hole-hole excitations. We analyze the generalized process $\tildeπ^0\to\tildeγ\tildeγ$ in the weak coupling limit and show that it is related to the recently suggested Wess-Zumino-Witten (WZW) term. In dense QCD, the radiative decay of the generalized pion is constrained by geometry and vanishes at large density.

hep-ph↗

arXiv2000

Effective Field Theory For Nuclei: Confronting Fundamental Questions in Astrophysics

Fundamental issues involving nuclei in the celebrated solar neutrino problem are discussed in terms of an effective field theory adapted to nuclear few-body systems, with a focus on the proton fusion process and the hep process. Our strategy in addressing these questions is to combine chiral perturbation theory -- an effective field theory of QCD -- with an accurate nuclear physics approach to arrive at a more effective effective field theory that reveals and exploits a subtle role of the chiral-symmetry scale in short-distance effects encoded in short-range nuclear correlations. Our key argument is drawn from the close analogy of the principal weak matrix element figuring in the hep process to the suppressed matrix elements in the polarized neutron-proton capture at threshold currently being measured in the laboratories.

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arXiv2000

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 $\la\barψψ\ra$, $\laψψ\ra$ and $\laψ^\daggerψ\ra$. We find that in the regime $μ<μ_c$, where $μ_c$ is found to be around $0.4 m_F$ with $m_F$ being the renormalizaton point of chiral condensate, we have a chiral symmetry-breaking phase with almost zero fermion number density and in the case of $μ>μ_c$ the system sits in the mixed phase characterized by $\la ψ^\daggerψ\ra\neq 0$ and $\la ψψ\ra\neq 0$ as long as the renormalization point, $M_0$, corresponding to a superconducting gap is not zero, $M_0\neq 0$.

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arXiv2000

A Schematic Model for $ρ$-$a_1$ Mixing at Finite Density and In-Medium Effective Lagrangian

Based on schematic two-level models extended to $a_1$-meson degrees of freedom, we investigate possible mechanisms of chiral restoration in the vector/axialvector 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 $π\leftrightarrow [Δ(1232)N^{-1}]\equiv\hatπ$, $ρ\leftrightarrow [N^* (1520)N^{-1}]\equiv\hatρ$, etc.. In a mean-field type treatment the in-medium gauge coupling $\hat g$, the (axial-) vector meson masses and $\hat f_π$ 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 axialvector correlators to the pion decay constant. Using in-medium $ρ$/$a_1$ spectral functions (computed in the two-level model) also leads to a substantial reduction of the pion decay constant with increasing density.

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arXiv2000

Generalized Mesons in Dense QCD

QCD superconductors in the color-flavor-locked (CFL) phase support excitations (generalized mesons) that can be described as pairs of particles or holes (rather than particle-hole) around a gapped Fermi surface. In weak coupling and to leading logarithm accuracy the scalar and pseudoscalar excitations are massless and the vector and axial-vector excitations are massive and degenerate. The massless scalar excitations are combined with the longitudinal gluons leading to the Meissner effect in the CFL phase. The mass of the composite vector excitations is close to twice the gap in weak coupling, but goes asymptotically to zero with increasing coupling thereby realizing Georgi's vector limit in cold and dense matter. We discuss the possible mixing of the composite scalar and vector excitations with the gluons, their possible coupling to the modified photons and their decay into light pseudoscalars in the CFL phase. The issue of hidden gauge-symmetry in the QCD superconductor is critically examined. The physical implications of our results on soft dilepton and neutrino emission in cold and dense matter are briefly discussed.

hep-ph↗

arXiv1999

Generalized Pions in Dense QCD

QCD superconductors in the color-flavor-locked (CFL) phase sustain light Goldstone modes (that will be referred to as generalized pions) that can be described as pairs of particle and/or hole excitations around a gapped Fermi surface. In weak coupling and to leading logarithm accuracy, their form factor, mass and decay constant can be evaluated exactly. These modes are found to satisfy an axial-Ward-identity, constraining the mass of the Goldstone modes in the CFL phase.

hep-ph↗

arXiv1999

Dense QCD : Overhauser or BCS Pairing ?

We discuss the Overhauser effect (particle-hole pairing) versus the BCS effect (particle-particle or hole-hole pairing) in QCD at large quark density. In weak coupling and to leading logarithm accuracy, the pairing energies can be estimated exactly. For a small number of colors, the BCS effect overtakes the Overhauser effect, while for a large number of colors the opposite takes place, in agreement with a recent renormalization group argument. In strong coupling with large pairing energies, the Overhauser effect may be dominant for any number of colors, suggesting that QCD may crystallize into an insulator at a few times nuclear matter density, a situation reminiscent of dense Skyrmions. The Overhauser effect is dominant in QCD in 1+1 dimensions, although susceptible to quantum effects. It is sensitive to temperature in all dimensions.

hep-ph↗

arXiv1999

Selected Topics in Astro-Hadron Physics: Going from a Proton to Nuclei to Neutron Stars

The effort currently in vogue in some small circle of physicists to go from a proton to nuclei to compact stars involves various aspects of particle and nuclear physics that require input from laboratory experiments, transcending narrow specialization in diverse sub-fields. Several topics on this matter are discussed in this note. The notion of Cheshire Cat Principle is introduced for nucleons, nuclei and dense hadronic matter and is confronted with experimental data on the proton, two-nucleon systems and heavy-ion experiments, with a leaping extrapolation to the structure of neutron stars. The matter discussed here illustrates that a close contact with experiments, indispensable in the present case, is essential for significant progress in {\it any} field of physics. I suggest that this is a field that has a tremendous potential for breakthrough in the Asia Pacific countries, particularly in Korea, where some of the seminal works in this area have been done by young theorists, both pre- and post-graduate.

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arXiv1999

Elastic Parton-Parton Scattering from AdS/CFT

Using the AdS/CFT correspondence and the eikonal approximation, we evaluate the elastic parton-parton scattering amplitude at large $N$ and strong coupling $g^2N$ in N=4 SYM. We obtain a scattering amplitude with a Regge behavior that unitarizes at large $\sqrt{s}$.

hep-th↗

arXiv1999

Qualitons At High Density

In the color-flavor-locked (CFL) phase of the QCD superconductor we show that baryons behave as qualitons (called "superqualitons") with quantum numbers $B=(1 {\rm mod} 2)/3$, S=1/2 and Y=B. An intriguing possibility implied by this identification is that light baryonic modes in the form of superqualitons could be excited below the (color) superconducting gap in the CFL phase, a novel phenomenon foreign to normal superconductors.

hep-ph↗

arXiv1999

Effective Field Theory For Nuclei, Dense Matter And The Cheshire Cat

In this talk I discuss three related topics based on some of the recent developments in hadron and nuclear physics: one, effective field theory approach to two-nucleon systems; two, an explanation of the flavor singlet axial charge in the proton (i.e., "proton spin problem") in terms of a Cheshire Cat phenomenon; and three, the quark-hadron duality in hadronic matter at high density and "qualitons" at high density ("superqualitons"). The principal common theme in these discussions will be the emergence of the generic feature of the Cheshire Cat Principle.

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arXiv1999

Quark Condensation, Induced Symmetry Breaking and Color Superconductivity at High Density

The phase structure of hadronic matter at high density relevant to the physics of compact stars and relativistic heavy-ion collisions is studied in a low-energy effective quark theory. The relevant phases that figure are (1) chiral condensation, (2) diquark color condensation (color superconductivity) and (3) induced Lorentz-symmetry breaking (ISB). For reasonable strengths for four-Fermi interactions implied by one-gluon exchange quark interactions as well as instanton-mediated interactions, we find that the ISB phase sets in at a moderate density while the quark condensate vanishes, followed by color superconductivity associated with scalar diquark condensation appearing only at an asymptotic density. Lack of confinement in the model makes the result of this analysis only qualitative but the hierarchy of the transitions we find seems to be quite robust.

hep-ph↗

arXiv1999

On Making Predictions With Effective Field Theories In Nuclear Physics

Based on the effective field theory previously formulated by us to accurately postdict all low-energy two-nucleon properties as well as predict certain electroweak transitions in heavy nuclei, we make parameter-free predictions for the polarized np capture process \vec{n}+\vec{p} --> d +γpresently being measured at the Institut Laue-Langevin in Grenoble. Other participants of this meeting are invited to make their own predictions using their preferred approaches and join the bet for the best prediction to confront the forthcoming experiment.

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arXiv1999

A Schematic Model For Density-Dependent Vector Meson Masses

A schematic two-level model consisting of a "collective" bosonic state and an "elementary" meson is constructed that provides interpolation from a hadronic description (a la Rapp/Wambach) to B/R scaling for the description of properties of vector mesons in dense medium. The development is based on a close analogy to the degenerate schematic model of Brown for giant resonances in nuclei.

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arXiv1998

Chiral Symmetry In Nuclear Physics

How chiral symmetry -- which is a basic ingredient of quantum chromodynamics (QCD) for light-quark hadrons -- enters and plays an eminent role in nuclear physics is discussed. This is done in two steps. In the first step, I introduce the notion of the Cheshire Cat Principle which describes how a strong-interaction phenomenon can be described in various different languages. In the second step, I treat two cases of widely different density regimes. The first case deals with formulating nuclear physics of {\it dilute} nuclear systems with a focus on both bound and scattering processes in two-nucleon systems in terms of effective field theories (EFT), e.g., in the framework of chiral perturbation theory. The second case requires formulating effective field theories for {\it dense} hadronic matter such as heavy nuclei and nuclear matter under normal as well as extreme conditions expected to be encountered in compact stars and in heavy-ion collisions at relativistic energy. The first case is rigorously formulated but the second relies on several assumptions that appear to be reasonable but need ultimately to be justified. The Cheshire Cat Principle is proposed to play an essential role in lending support to the latter development.

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arXiv1998

The Power Of Effective Field Theories In Nuclei: The Deuteron, NN Scattering and Electroweak Processes

We show how effectively effective quantum field theories work in nuclear physics. Using the physically transparent cut-off regularization, we study the simplest nuclear systems of two nucleons for both bound and scattering states at a momentum scale much less than the pion mass. We consider all the static properties of the deuteron, the two-nucleon scattering phase-shifts, the n + p --> d + γprocess at thermal energy and the solar proton fusion process p + p --> d + e(+) + ν(e), and we demonstrate that these are all described with great accuracy in the expansion to the next-to-leading order. We explore how a "new" degree of freedom enters in an effective theory by turning on and off the role of the pion in the Lagrangian.

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