1,776 research outputs found
Structure of the nuclear force in a chiral quark-diquark model
We discuss the structure of the nuclear force using a lagrangian derived from
hadronization of a chiral quark and diquark model. A generalized trace log
formula including meson and nucleon fields is expanded to the order in which
relevant terms emerge. It is shown that the nuclear force is composed of long
and medium range parts of chiral meson exchanges and short range parts of
quark-diquark exchanges. The ranges of the scalar and vector interactions
coincide well with those of sigma () and omega () meson
exchanges if the size of the nucleon core of a quark-diquark bound state is
adjusted appropriately.Comment: 12 pages, 9 figure
Thermal properties and evolution of the factor for 2+1 flavors
Thermal evolution of the axial anomaly is investigated in the system of the
linear sigma model for flavors. We explore the functional form of the
effective potential and the coefficient of the `t Hooft determinant term. It is
found that the latter develops a non-trivial structure as a function of the
chiral condensate and grows everywhere with respect to the temperature. This
shows that mesonic fluctuations strengthen the axial anomaly at finite
temperature and it does not get vanished at the critical point. The phenomenon
has been found to have significance in the thermal properties of the mesonic
spectra, especially concerning the system.Comment: 9 pages, 6 figures, typos corrected, matches published versio
Two Nucleon-States in a Chiral Quark-Diquark Model
We study the ground and first excited states of nucleons in a chiral
quark-diquark model. We include two quark-diquark channels of the
scalar-isoscalar and axial-vector-isovector types for the nucleon states. The
diquark correlation violating the spin-flavor SU(4) symmetry allows to
treat the two quark-diquark channels independently. Hence the two states appear
as the superpositions of the two quark-diquark channels; one is the nucleon and
the other is a state which does not appear in the SU(4) quark models.
With a reasonable choice of model parameters, the mass of the excited state
appears at around 1.5 GeV, which we identify with the Roper resonance N(1440).Comment: 11 pages, 5 figures. Errors are corrected. Conclusions are not
affecte
Structure of the Nucleon and Roper Resonance with Diquark Correlations
We investigate the electric form factors of the nucleon and Roper resonance
using a quark-diquark model. We find that the charge radii of the nucleon and
Roper resonance are almost the same in size.Comment: To appear in the proceedings of Chiral 07, Osaka, Japan, November
13-16, 2007. 4pages, 4figure
Modern Dynamical Coupled-Channels Calculations for Extracting and Understanding the Nucleon Spectrum
We give an overview of recent progress in the spectroscopic study of nucleon
resonances within the dynamical coupled-channels analysis of meson-production
reactions. The important role of multichannel reaction dynamics in
understanding various properties of nucleon resonances is emphasized.Comment: 11 pages, 8 figures. Plenary talk at The 14th International
Conference on Meson-Nucleon Physics and the Structure of the Nucleon
(MENU2016), Kyoto, Japan, July 25-30, 201
Exotic Tetraquark ud bar[s] bar[s] of J^P=0^+ in the QCD Sum Rule
We study a QCD sum rule analysis for an exotic tetraquark ud bar[s] bar[s] of
J^P=0^+ and I = 1. We construct q q bar[q] bar[q] currents in a local product
form and find that there are five independent currents for this channel. Due to
high dimensional nature of the current, it is not easy to form a good sum rule
when using a single current. This means that we do not find any sum rule window
to extract reliable results, due to the insufficient convergence of the OPE and
to the exceptional important role of QCD continuum. Then we examine sum rules
by using currents of linear combinations of two currents among the independent
ones. We find two reasonable cases that predict a mass of the tetraquark around
1.5 GeV.Comment: 15 pages, 8 figures, revised versio
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
Nucleon axial couplings and [(1/2,0) + (0,1/2)]-[(1,1/2) + (1/2,1)] chiral multiplet mixing
Three-quark nucleon interpolating fields in QCD have well-defined SU_L(2) x
SU_R(2) and U_A(1) chiral transformation properties. Mixing of the [(1,1/2) +
(1/2,1)] chiral multiplet with one of [(1/2,0) + (0,1/2)] or [(0,1/2) +
(1/2,0)] representation can be used to fit the isovector axial coupling g_A(1)
and thus predict the isoscalar axial coupling g_A(0) of the nucleon, in
reasonable agreement with experiment. We also use a chiral meson-baryon
interaction to calculate the masses and one-pion-interaction terms of J=1/2
baryons belonging to the [(0,1/2) + (1/2,0)] and [(1,1/2) + (1/2,1)] chiral
multiplets and fit two of the diagonalized masses to the lowest-lying nucleon
resonances thus predicting the third J=1/2 resonance at 2030 MeV, not far from
the (one-star PDG) state Delta(2150).Comment: To appear in Modern Physics Letters
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