arXiv subjects

Mannque Rho

Publications and source records attributed to Mannque Rho.

At least 199 records · Page 11Linked to original sources

arXiv1995

Chiral Lagrangian Approach to Exchange Vector Currents in Nuclei

Exchange vector currents are calculated up to one-loop order (corresponding to next-to-next-to-leading order) in chiral perturbation theory. As an illustration of the power of the approach, we apply the formalism to the classic nuclear process $n+p\rightarrow d +γ$ at thermal energy. The exchange current correction comes out to be $(4.5 \pm 0.3)$ \% in amplitude giving a predicted cross section $σ= (334\pm 3)\ {\mbox mb}$ in excellent agreement with the experimental value $(334.2\pm 0.5)\ {\mbox mb}$. Together with the axial charge transitions computed previously, this result provides a strong support for the power of chiral Lagrangians in nuclear physics. As a by-product of our results, we suggest an open problem in the application of chiral Lagrangian approach to nuclear processes that has to do with giving a physical meaning to the short-range correlations that play an important role in nuclei.

nucl-th↗

arXiv1995

Chiral Restoration in Hot and/or Dense Matter

Chiral restoration phase transition in hot and/or dense hadronic matter is discussed in terms of the BR scaling based on chiral symmetry and scale anomaly of QCD. The precise connection between the scalar field that figures in the trace anomaly and the sigma field that figures in the linear $σ$ model is established. It is suggested that in hot and/or dense medium, the nonlinear $σ$ model linearizes with the help of a dilaton to a linear $σ$ model with medium-renormalized constants. The relevance of Georgi's vector symmetry and/or Weinberg's ``mended symmetry" in chiral restoration is pointed out. Some striking consequences for relativistic heavy-ion collisions and dense matter in compact stars following stellar collapse are discussed.

hep-ph↗

arXiv1995

Finite-Temperature Corrections in the Dilated Chiral Quark Model

We calculate the finite-temperature corrections in the dilated chiral quark model using the effective potential formalism. Assuming that the dilaton limit is applicable at some short length scale, we interpret the results to represent the behavior of hadrons in dense {\it and} hot matter. We obtain the scaling law, $\frac{f_π(T)}{f_π} = \frac{m_Q (T)}{m_Q} \simeq \frac{m_σ(T)}{m_σ}$ while we argue, using PCAC, that pion mass does not scale within the temperature range involved in our Lagrangian. It is found that the hadron masses and the pion decay constant drop faster with temperature in the dilated chiral quark model than in the conventional linear sigma model that does not take into account the QCD scale anomaly. We attribute the difference in scaling in heat bath to the effect of baryonic medium on thermal properties of the hadrons. Our finding would imply that the AGS experiments (dense {\it and} hot matter) and the RHIC experiments (hot and dilute matter) will ``see" different hadron properties in the hadronization phase.

hep-ph↗

arXiv1995

Kaon Condensation in Dense Stellar Matter

This article combines two talks given by the authors and is based on works done in collaboration with G.E. Brown and D.-P. Min on kaon condensation in dense baryonic medium treated in chiral perturbation theory using heavy-baryon formalism. It contains, in addition to what was recently published, astrophysical backgrounds for kaon condensation discussed by Brown and Bethe, a discussion on a renormalization-group analysis to meson condensation worked out together with H.K. Lee and S.-J. Sin, and the recent results of K. M. Westerberg in the bound-state approach to the Skyrme model. Negatively charged kaons are predicted to condense at a critical density $2\lsim ρ/ρ_0\lsim 4$, in the range to allow the intriguing new phenomena predicted by Brown and Bethe to take place in compact star matter.

hep-ph↗

arXiv1995

CHIRAL SYMMETRY RESTORATION AS THE GEORGI VECTOR LIMIT

I discuss recent work done with Gerry Brown on chiral phase transition at high temperature and/or density described in terms of Georgi's vector limit. The notion of ``mended symmetry" is suggested to play an important role in understanding the properties of hadrons in dense and/or hot matter before reaching the phase transition. It is shown that while the QCD vacuum in baryon-free space is resistant to ``melting" up to the critical temperature, baryon-rich medium can induce the vacuum to become softer in temperature: the hadron masses drop faster in temperature when baryon matter is present.

hep-ph↗

arXiv1995

Effective Field Theories for Hadrons and Nuclei

Hadron structure and nuclear structure are discussed from the common ground of effective chiral Lagrangians modeling QCD at low energy. The topics treated are the chiral bag model in large $N_c$ QCD, its connection to heavy-baryon chiral perturbation theory (HB\chpt),\ the role of nonabelian Berry gauge connections for baryon excitations and the application of HB\chpt \ to the thermal $n+p\rightarrow d +γ$ process and to the axial-charge transitions in heavy nuclei.

hep-ph↗

arXiv1994

Radiative Neutron-Proton Capture in Effective Chiral Lagrangians

We calculate the cross-section for the thermal $n+p\rightarrow d+γ$ process in chiral perturbation theory to next-to-next-to-leading order using heavy-fermion formalism. The exchange current correction is found to be $(4.5\pm 0.3)~\%$ in amplitude and the chiral perturbation at one-loop order gives the cross section $σ_{th}^{np}=(334\pm 2)\ {\mbox mb}$ which is in agreement with the experimental value $(334.2\pm 0.5)\ {\mbox mb}$. Together with the axial charge transitions, this provides a strong support for the power of chiral Lagrangians for nuclear physics.

nucl-th↗

arXiv1994

Heavy-Quark Symmetry and Skyrmions

We review recent development on combining heavy-quark symmetry and chiral symmetry in the skyrmion structure of the baryons containing one or more heavy quarks, c (charmed) and b (bottom). We describe two approaches: One going from the chiral symmetry regime of light quarks to the heavy-quark symmetry regime which will be referred to as ``bottom-up" approach and the other going down from the heavy-quark limit to the realistic finite-mass regime which will be referred to as ``top-down." A possible hidden connection between the two symmetry limits is suggested. This review is based largely on the work done -- some unpublished -- by the authors since several years.

hep-ph↗

arXiv1994

Renormalization-Group Flow Analysis of Meson Condensations in Dense Matter

We present a renormalization-group (RG) flow argument for s-wave kaon condensation in dense nuclear-star matter predicted in chiral perturbation theory. It is shown that it is the {\it relevant} mass term together with {\it any} attractive interaction for the kaon in medium that triggers the instability. We show that a saddle point of multi-dimensional RG flow can imply a phase transition. Pion condensation is also analyzed along the same line of reasoning.

hep-ph↗

arXiv1994

Kaon Condensation in Dense Stellar Matter

This talk is based on work done in collaboration with G.E. Brown and D.-P. Min on kaon condensation in dense baryonic medium treated in chiral perturbation theory using heavy-baryon formalism. It contains, in addition to what was recently published, some new results based on the analysis on kaonic atoms by Friedman, Gal and Batty and a discussion on a renormalization-group analysis to meson condensation made together with H.K. Lee and Sin. Negatively charged kaons are predicted to condense at the critical density $2\lsim ρ/ρ_0\lsim 4$, in the range to allow all the intriguing new phenomena predicted by Brown and Bethe to take place in compact star matter.

hep-ph↗

arXiv1994

Chiral Symmetry in Nuclear Physics

The role of chiral symmetry in nuclear physics is summarized. The topics treated are the chiral bag model for nucleon structure resulting from large $N_c$ QCD, the pion cloud in chiral perturbation theory for low-energy electroweak nuclear response functions, ``swelled hadrons" in nuclear matter, chiral symmetry restoration in terms of the Georgi vector limit and pseudo-Goldstone meson condensation in nuclear medium.

nucl-th↗

arXiv1994

Chiral Symmetry Restoration and the Georgi Vector Limit

The chiral phase transition at high temperature and/or density is interpreted in terms of Georgi's vector limit. We discuss three cases as possible support for this scenario: Quark-number susceptibility, cool kaons in heavy-ion process and an instanton-molecule picture for chiral restoration. Both the notion of ``mended symmetry" and the Georgi vector limit are suggested to be relevant in nuclear physics of dense matter.

hep-ph↗

arXiv1994

An Effective Chiral Lagrangian Approach to Kaon-Nuclear Interactions: Kaonic atom and kaon condensation

On-shell kaon-nucleon scattering, kaonic atom and kaon condensation are treated on the same footing by means of a chiral perturbation expansion to the next-to-next-to-leading order (``N$^2$LO"). Constraining the low-energy constants in the chiral Lagrangian by on-shell $KN$ scattering lengths and kaonic atom data, the off-shell s-wave scattering amplitude up to one-loop order corresponding to N$^2$LO and the critical density of kaon condensation up to in-medium two-loop order are computed. The effects on kaon-proton scattering of the quasi-bound $Λ(1405)$ and on kaonic atoms and kaon condensation of $Λ(1405)$-proton-hole excitations through four-Fermi interactions are studied to all orders in density within the in-medium two-loop approximation. It is found that the four-Fermi interaction terms in the chiral Lagrangian play an essential role in providing attraction for kaonic atoms, thereby inducing condensation but the critical density is remarkably insensitive to the strength of the four-Fermi interaction that figures in kaonic atoms. The prediction for the critical density is extremely robust and gives -- for ``natural" values of the four-Fermi interactions -- a rather low critical density, $ρ_c \lsim 4 ρ_0$. When the BR scaling is suitably implemented, the condensation sets in at $ρ_c\simeq 2\, ρ_0$ with loop corrections and four-Fermi interactions playing a minor role.

hep-ph↗

arXiv1994

Kaon Condensation in ``Nuclear Star" Matter

The critical density for kaon condensation in ``nuclear star" matter is computed up to two-loop order {\it in medium} (corresponding to next-to-next-to-leading order in chiral perturbation theory in free space) with a heavy-baryon effective chiral Lagrangian whose parameters are determined from $KN$ scattering and kaonic atom data. To the order considered, the kaon self-energy has highly non-linear density dependence in dense matter. We find that the four-Fermi interaction terms in the chiral Lagrangian play an important role in triggering condensation, predicting for ``natural" values of the four-Fermi interactions a rather low critical density, $ρ_c < 4 ρ_0$.

hep-ph↗

arXiv1994

Kaon-Nucleon Scattering from Chiral Lagrangians

The s-wave $K^{\pm}N$ scattering amplitude is computed up to one-loop order corresponding to next-to-next-to-leading order (or N$^2$LO in short) with a heavy-baryon effective chiral Lagrangian. Constraining the low-energy constants by on-shell scattering lengths, we obtain contributions of each chiral order up to N$^2$LO and find that the chiral corrections are ``natural" in the sense of viable effective field theories. We have also calculated off-shell $s$-wave $K^-N$ scattering amplitudes relevant to kaonic atoms and $K^-$ condensation in ``nuclear star" matter including the effect of $Λ(1405)$. The $K^-p$ amplitude is found to be quite sensitive to the intermediate $Λ(1405)$ contribution, while the $K^-n$ amplitude varies smoothly with the C.M. energy. The crossing-even one-loop corrections are found to play an important role in determining the higher-order chiral corrections.

hep-ph↗

arXiv1993

Cheshire Cat Hadrons

This article is based on a series of lectures given at ELAF 93 on the description of low-energy hadronic systems {\it in and out} of hadronic medium. The focus is put on identifying, with the help of a Cheshire Cat philosophy, the effective degrees of freedom relevant for the strong interactions from a certain number of generic symmetry properties of QCD. The matters treated are the ground-state and excited-state properties of light- and heavy-quark baryons and applications to nuclei and nuclear matter under normal as well as extreme conditions.

hep-ph↗

arXiv1993

Vanishing of Nonabelian Berry Phases in Heavy Solitonic Baryons

In this article, we show -- using a reasoning applicable to both the excitation spectrum in the chiral bag model and the hyperfine structure of diatomic molecules -- that the generic form of a non- abelian Berry potential appears in heavy-quark effective theory (HQET) and that the Berry potential vanishes for the soliton- heavy meson bound state in the heavy-quark limit. The vanishing of the Berry potential in HQET is shown to be related to the restoration of heavy-quark symmetry in infinite heavy-quark-mass limit in close analogy to diatomic molecules at infinite internuclear separation.

hep-ph↗

arXiv1993

Chiral Dynamics and Heavy-Fermion Formalism in Nuclei: I. Exchange Axial Currents

Chiral perturbation theory in heavy-fermion formalism is developed for meson-exchange currents in nuclei and applied to nuclear axial- charge transitions. Calculation is performed to the next-to-leading order in chiral expansion which involves graphs up to one loop. The result turns out to be very simple. The previously conjectured notion of "chiral filter mechanism" in the time component of the nuclear axial current and the space component of the nuclear electromagnetic current is verified to that order. As a consequence, the phenomenologically observed soft-pion dominance in the nuclear process is given a simple interpretation in terms of chiral symmetry in nuclei. In this paper, we focus on the axial current, relegating the EM current which can be treated in a similar way to a separate paper. We discuss the implication of our result on the enhanced axial-charge transitions observed in heavy nuclei and clarify the relationship between the phenomenological meson-exchange description and the chiral Lagrangian description.

hep-ph↗