144,619 research outputs found

### Symmetries of hadrons after unbreaking the chiral symmetry

We study hadron correlators upon artificial restoration of the spontaneously
broken chiral symmetry. In a dynamical lattice simulation we remove the lowest
lying eigenmodes of the Dirac operator from the valence quark propagators and
study evolution of the hadron masses obtained. All mesons and baryons in our
study, except for a pion, survive unbreaking the chiral symmetry and their
exponential decay signals become essentially better. From the analysis of the
observed spectroscopic patterns we conclude that confinement still persists
while the chiral symmetry is restored. All hadrons fall into different chiral
multiplets. The broken U(1)_A symmetry does not get restored upon unbreaking
the chiral symmetry. We also observe signals of some higher symmetry that
includes chiral symmetry as a subgroup. Finally, from comparison of the \Delta
- N splitting before and after unbreaking of the chiral symmetry we conclude
that both the color-magnetic and the flavor-spin quark-quark interactions are
of equal importance.Comment: 12 pages, 14 figures; final versio

### Effective restoration of the U_A(1) symmetry with temperature and density

We investigate the full U(3)$\otimes$U(3) chiral symmetry restoration, at
finite temperature and density, on the basis of a quark model which
incorporates the most relevant properties of QCD in this context: explicit and
spontaneous breaking of chiral symmetry and axial U$_A$(1) symmetry breaking. A
specific lattice-inspired behavior of the topological susceptibility, combined
with the convergence of chiral partners, signals the onset of an effective
chiral symmetry restoration. The results suggest that the axial part of the
symmetry is restored before the possible restoration of the full
U(3)$\otimes$U(3) chiral symmetry can occur. This conclusion is valid in the
context of both finite temperature and density.Comment: 5 pages, 2 figures; PRD versio

### Chiral Symmetry

The exact classical solution of the equation of the motion for the
Nambu-Goldstone fermion of the nonlinear representation of supersymmetry and
its physical significance are discussed, which gives a new insight into the
chiral symmetry of the standard model for the low energy particle physics.Comment: 7 pages, some arguments revised, conclusions unchange

### Can Chiral Symmetry Explain the Small Pentaquark Width?

It is shown that the decay amplitude for the Jaffe-Wilczek type pentaquarks
is not suppressed by chiral symmetry. On the other hand, pentaquarks of
positive or negative parity built up of an antiquark and two chirally different
diquarks in an $S$-state are stable in the limit of a strictly unbroken chiral
symmetry. These states can decay only via the spontaneous breaking of chiral
symmetry. However, this breaking is strong because of the sizeable magnitude of
the quark condensate. Thus, chiral symmetry cannot be the cause of a tiny decay
amplitude, even for pentaquarks which are stable in the strict chiral symmetry
limit.Comment: Talk given at the 10th International Baryons Conference at Ecole
Polytechnique (Palaiseau, France) 25 - 29 October 200

### Chiral symmetry restoration in excited hadrons, quantum fluctuations, and quasiclassics

In this paper, we discuss the transition to the semiclassical regime in
excited hadrons, and consequently, the restoration of chiral symmetry for these
states. We use a generalised Nambu-Jona-Lasinio model with the interaction
between quarks in the form of the instantaneous Lorentz-vector confining
potential. This model is known to provide spontaneous breaking of chiral
symmetry in the vacuum via the standard selfenergy loops for valence quarks. It
has been shown recently that the effective single-quark potential is of the
Lorentz-scalar nature, for the low-lying hadrons, while, for the high-lying
states, it becomes a pure Lorentz vector and hence the model exhibits the
restoration of chiral symmetry. We demonstrate explicitly the quantum nature of
chiral symmetry breaking, the absence of chiral symmetry breaking in the
classical limit as well as the transition to the semiclassical regime for
excited states, where the effect of chiral symmetry breaking becomes only a
small correction to the classical contributions.Comment: RevTeX4, 20 pages, 4 Postscript figures, uses epsfig.sty, typos
correcte

### The structure of N(1535) in the aspect of chiral symmetry

The structure of N(1535) is discussed in dynamical and symmetry aspects based
on chiral symmetry. We find that the N(1535) in chiral unitary model has
implicitly some components other than meson-baryon one. We also discuss the
N(1535) in the chiral doublet picture.Comment: 4 pages, no figure, talk given at Workshop on Chiral Symmetry in
Hadron and Nuclear Physics: Chiral07, Osaka, Japan, 13-16 Nov 200

### Dyson-Schwinger Equation and Quantum Phase Transitions in Massless QCD

We study the stability of the highest symmetric solution (Wigner-solution) of
Dyson-Schwinger equations in chiral limit and at zero temperature. Our results
confirm that if the chemical potential is not very large, the QCD vacuum is in
the chiral symmetry breaking phase and the quantum phase-transition of the
chiral symmetry restoration is in first order. Meanwhile it seems that there is
not competition between chiral symmetry breaking phase and color
superconductivity phase since the color superconductivity phase appears only if
the chemical potential is very large. Moreover, we propose that chiral symmetry
breaking arises from the positive feedback with respect to the mass
perturbation.Comment: 12 pages, 6 figure

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