65 research outputs found
Composite antisymmetric-tensor Nambu-Goldstone bosons in a four-fermion interaction model and the Higgs mechanism
Starting from the Fierz transform of the two-flavour 't Hooft interaction (a
four-fermion Lagrangian with antisymmetric Lorentz tensor interaction terms
augmented by an NJL type Lorentz scalar inetraction responsible for dynamical
symmetry breaking and quark mass generation), we show that: (1) antisymmetric
tensor Nambu-Goldstone bosons appear provided that the scalar and tensor
couplings stand in the proportion of two to one, which ratio appears naturally
in the Fierz transform of the two-flavour 't Hooft interaction; (2) non-Abelian
vector gauge bosons coupled to this system acquire a non-zero mass.
Axial-vector fields do not mix with antisymmetric tensor fields, so there is no
mass shift there.Comment: 13 pages, RevTex, 2 EPS figure
Discriminating between effective theories of U_{A}(1) symmetry breaking
We address the question if one can empirically distinguish between the two
proposed solutions to the `` problem'': the 't Hooft, and the
Veneziano-Witten symmetry breaking effective interactions. Two
hadronic observables are offered as discriminants: (1) The scalar ()
meson spectrum; (2) Weinberg's second spectral sum rule. Their present
experimental status is discussed.Comment: 6 pages, 1 eps file, Yonsei "Hadrons and Nuclei" conference
proceeding
A Lagrangian for the Chiral (1/2,0) + (0,1/2) Quartet Nucleon Resonances
We study the nucleon and three N* resonances' properties in an effective
linear realization chiral SU_L(2) x SU_R(2) and U_A(1) symmetric Lagrangian. We
place the nucleon fields into the so-called "naive" (1/2,0) + (0, 1/2) and
"mirror" (0, 1/2) + (1/2,0) (fundamental) representations of SU_L(2) x SU_R(2),
two of each -distinguished by their U_A(1) chiral properties, as defined by an
explicit construction of the nucleon interpolating fields in terms of three
quark (Dirac) fields. We construct the most general one-meson-baryon chiral
interaction Lagrangian assuming various parities of these four nucleon fields.
We show that the observed masses of the four lowest lying nucleon states can be
well reproduced with the effective Lagrangian, after spontaneous symmetry
breakdown, without explicit breaking of U_A(1) symmetry. This does not mean
that explicit U_A(1) symmetry breaking does not occur in baryons, but rather
that it does not have a unique mass prediction signature that exists e.g. in
the case of spinless mesons. We also consider briefly the axial couplings with
chiral representation mixing.Comment: Published in International Journal of Modern Physics
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
Pseudoscalar Mesons in the SU(3) Linear Sigma Model with Gaussian Functional Approximation
We study the SU(3) linear sigma model for the pseudoscalar mesons in the
Gaussian Functional Approximation (GFA). We use the SU(3) linear sigma model
Lagrangian with nonet scalar and pseudo-scalar mesons including symmetry
breaking terms. In the GFA, we take the Gaussian Ansatz for the ground state
wave function and apply the variational method to minimize the ground state
energy. We derive the gap equations for the dressed meson masses, which are
actually just variational parameters in the GFA method. We use the
Bethe-Salpeter equation for meson-meson scattering which provides the masses of
the physical nonet mesons. We construct the projection operators for the flavor
SU(3) in order to work out the scattering T-matrix in an efficient way. In this
paper, we discuss the properties of the Nambu-Goldstone bosons in various
limits of the chiral symmetry.Comment: 28 pages, comments and suggestions welcom
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