271 research outputs found
Chiral condensate at finite density using chiral Ward identity
In order to study partial restoration of the chiral symmetry at finite
density, we investigate the density corrections of the chiral condensate up to
next-leading order of density expansion using the chiral Ward identity and an
in-medium chiral perturbation theory. In our study, we assume that all the
in-vacuum quantities for the pion, the nucleon and the pi N interaction are
determined and focus on density expansion of the in-medium physical quantities.
We perform diagrammatic analysis of the correlation functions which provide the
in-medium chiral condensate. This density expansion scheme shows that medium
effects to the chiral condensate beyond the linear density come from density
corrections to the pi N sigma term as a result of the interactions between pion
and nucleon in nuclear matter. We also discuss that higher density
contributions beyond order of rho^2 cannot be fixed only by the in-vacuum pi N
dynamics but we need NN two-body dynamics in vacuum to fix divergence appearing
in the calculation of the rho^2 dependence of the chiral condensate with the pi
N dynamics.Comment: 13 pages, 9 figure
A new N* resonance as a hadronic molecular state
We report our recent work on a hadronic molecule state of the KbarKN system
with I=1/2 and J^P=1/2^+. We assume that the Lambda(1405) resonance and the
scalar mesons, f_{0}(980), a_{0}(980), are reproduced as quasi-bound states of
KbarN and KbarK, respectively. Performing non-relativistic three-body
calculations with a variational method for this system, we find a quasibound
state of the KbarKN system around 1910 MeV below the three-body breakup
threshold. This state corresponds to a new baryon resonance of N* with
J^P=1/2^+. We find also that this resonance has the cluster structure of the
two-body bound states keeping their properties as in the isolated two-particle
systems. We also briefly discuss another hadronic molecular state composed by
two Kbar and one N, which corresponds to a Xi^* resonance.Comment: Talk given at Workshop on the Physics of Excited Nucleon --
NSTAR2009, Beijing April 19 - 22, 200
Strange magnetic moment of the nucleon and SU(3) breaking: group theoretical approach
An extended group-theoretical approach to magnetic moments of the octet
baryons is proposed with the aim of extracting the strange magnetic moment of
the nucleon. Special attention is given to flavor SU(3) breaking. In this
approach, isoscalar and isovector magnetic moments are treated separately in
view of their different behavior under SU(3) breaking. We conclude that the
anomalous magnetic moment associated with the flavor singlet current is small.
Together with the small isoscalar anomalous magnetic moment of the nucleon,
this implies suppression of the strange magnetic moment of the proton which is
found to be small and positive, mu^(s) = (0.16 \pm 0.03) mu_N in units of the
nuclear magneton.Comment: 6 pages, no figure, 6 tables, use REVTeX
Negative Parity Baryons in the QCD Sum Rule
Masses and couplings of the negative parity excited baryons are studied in
the QCD sum rule. Separation of the negative-parity spectrum is proposed and is
applied to the flavor octet and singlet baryons. We find that the quark
condensate is responsible for the mass splitting of the ground and the
negative-parity excited states. This is expected from the chiral symmetry and
supports the idea that the negative-parity baryon forms a parity doublet with
the ground state. The meson-baryon coupling constants are also computed for the
excited states in the QCD sum rule. It is found that the \pi NN^* coupling
vanishes in the chiral limit.Comment: 13pp, LaTeX, 1 EPS figure, uses epsf.sty, Talk given by M.O. at
CEBAF/INT workshop "N* physics", Seattle, September (1996), to appear in the
proceeding
Chiral symmetry aspects of positive and negative parity baryons
Chiral symmetry aspects for baryon properties are studied. After a brief
discussion on general framework, we introduce two distinctive chiral group
representations for baryons: the naive and mirror assignments. Using linear
sigma models, nucleon properties are studied in both representations. Finally,
we propose an experiment to distinguish the two assignments in the reactions of
pion and eta productions.Comment: PTPTeX 12 pages, Proceedings for the YITP-RCNP workshop Chiral
Restoration in Nuclear Medium, Kyoto, October 200
Determination of the axial coupling constant in the linear representations of chiral symmetry
If a baryon field belongs to a certain linear representation of chiral
symmetry of , the axial coupling constant can be
determined algebraically from the commutation relations derived from the
superconvergence property of pion-nucleon scattering amplitudes. This
establishes an algebraic explanation for the values of of such as the
non-relativistic quark model, large- limit and the mirror assignment for
two chiral partner nucleons. For the mirror assignment, the axial charges of
the positive and negative parity nucleons have opposite signs. Experiments of
eta and pion productions are proposed in which the sign difference of the axial
charges can be observed.Comment: 7 pages, proceedings for EMI int. conf. at RCNP, Dec. 200
Structure of the sigma meson and the softening
We study the structure of the sigma meson, the lowest-lying resonance of the
pi pi scattering in the scalar-isoscalar channel, through the softening
phenomena associated with the partial restoration of chiral symmetry. We build
dynamical chiral models to describe the pi pi scattering amplitude, in which
the sigma meson is described either as the chiral partner of the pion or as the
dynamically generated resonance through the pi pi attraction. It is shown that
the internal structure is reflected in the softening phenomena; the softening
pattern of the dynamically generated sigma meson is qualitatively different
from the behavior of the chiral partner of the pion. On the other hand, in the
symmetry restoration limit, the dynamically generated sigma meson behaves
similarly to the chiral partner.Comment: 10 pages, 2 figures, 1 table, talk give at HNP09, November 16-19,
2009, RCNP, Osaka Universit
Electric Mean Squared Radii of Lambda(1405) in Chiral Dynamics
The electric mean squared radii _E of Lambda(1405) are calculated in the
chiral unitary model. We describe the Lambda(1405) as a dynamically generated
resonance fully in the octet meson and octet baryon scattering. We also
consider ``Lambda(1405)'' as a bound state of KbarN. For the later
``Lambda(1405),'' we obtain negative and larger absolute value of electric mean
squared radius than that of ordinary baryons, which implies that Lambda(1405)
have structure of widely spread K^- around p.Comment: 4 pages, 1 figure, use ws-mpla.cls. Talk given at Workshop on Chiral
Symmetry in Hadron and Nuclear Physics: Chiral07, Osaka, Japan, 13-16 Nov
200
- âŠ