82 research outputs found
eta and eta' mesons and dimension 2 gluon condensate <A^2>
The study of light pseudoscalar quark-antiquark bound states in the
Dyson-Schwinger approach with the effective QCD coupling enhanced by the
interplay of the dimension 2 gluon condensate and dimension 4 gluon
condensate , is extended to the eta-eta' complex. We include the effects
of the gluon axial anomaly into the Dyson-Schwinger approach to mesons. The
calculated masses, mixing and two-photon decay widths of eta and eta' mesons
are in agreement with experiment. Also, in a model-independent way, we give the
modification of the Gell-Mann--Okubo and Schwinger nonet relations due to the
interplay of the gluon anomaly and SU(3) flavor symmetry breaking.Comment: 15 pages, 2 tables, 1 eps figure, revtex
Search for solar hadronic axions produced by a bremsstrahlung-like process
We have searched for hadronic axions which may be produced in the Sun by a
bremsstrahlung-like process, and observed in the HPGe detector by an
axioelectric effect. A conservative upper limit on the hadronic axion mass m_a
< 334 eV at 95% C.L. is obtained. Our experimental approach is based on the
axion-electron coupling and it does not include the axion-nucleon coupling,
which suffers from the large uncertainties related to the estimation of the
flavor-singlet axial-vector matrix element.Comment: 9 pages, 3 figures; version to appear in PL
Axial anomaly and the interplay of quark loops with pseudoscalar and vector mesons in the gamma* --> pi+ pi0 pi- process
Motivated by the ongoing measurements of the Primakoff process pi- gamma* -->
pi- pi0 by COMPASS collaboration at CERN, the transition form factor for the
canonical anomalous process gamma* --> pi+ pi0 pi- is calculated in a
constituent quark loop model. The simplest contribution to this process is the
quark "box" amplitude. In the present paper we also explicitly include the
vector meson degrees of freedom, i.e., the rho and the omega, thus giving rise
to additional, resonant contributions. We find that in order to satisfy the
axial anomaly result, a further subtraction in the resonant part is needed. The
results are then compared with the vector meson dominance model as well as the
Dyson--Schwinger calculations, the chiral perturbation theory result, and the
available data.Comment: 21 pages, 8 eps figures, revtex4, a factor of 2 in resonant
contribution corrected, three figures revised and one added, discussion
enlarged and references adde
Pseudoscalar Meson Nonet at Zero and Finite Temperature
Theoretical understanding of experimental results from relativistic heavy-ion
collisions requires a microscopic approach to the behavior of QCD n-point
functions at finite temperatures, as given by the hierarchy of Dyson-Schwinger
equations, properly generalized within the Matsubara formalism. The convergence
of sums over Matsubara modes is studied. The technical complexity of
finite-temperature calculations mandates modeling. We present a model where the
QCD interaction in the infrared, nonperturbative domain, is modeled by a
separable form. Results for the mass spectrum of light quark flavors (u, d, s)
and for the pseudoscalar bound-state amplitudes at finite temperature are
presented.Comment: 14 pages, 11 figures, accepted for publication in Physics of
Particles and Nuclei Letters, based on invited lectures at "Dense Matter In
Heavy Ion Collisions and Astrophysics", 21.08-01.09 2006, Dubna, Russi
Search for hadronic axions using axioelectric effect
We made a search for hadronic axions which could be emitted from the Sun in
M1 transitions between the first 14.4 keV thermally excited and the ground
state in Fe-57, and absorbed in the HPGe detector by axioelectric effect. An
upper limit on hadronic axion mass of 400 eV is obtained at the 95% confidence
level.Comment: 4 pages, 1 eps figure, revtex; typos corrected, paragraph adde
Dynamical SU(3) linear sigma model and the mixing of eta'-eta and sigma-f_0 mesons
The SU(3) linear sigma model is dynamically generated in loop-order using the
nonstrange-strange basis. Only self-consistent logarithmic divergent graphs are
needed, with quadratic divergent graphs replaced by SU(3) mass-shell equal
splitting laws. The latter lead to an eta'-eta mixing angle of 41.84 deg which
is consistent with phenomenology. Finally this above SU(3) linear sigma model
in turn predicts strong decay rates which are all compatible with data.Comment: 14 pages, 1 figure, elsart; version to appear in J. Phys. G, appendix
added, some typos correcte
Infrared enhanced analytic coupling and chiral symmetry breaking in QCD
We study the impact on chiral symmetry breaking of a recently developed model
for the QCD analytic invariant charge. This charge contains no adjustable
parameters, other than the QCD mass scale , and embodies asymptotic
freedom and infrared enhancement into a single expression. Its incorporation
into the standard form of the quark gap equation gives rise to solutions for
the dynamically generated mass that display a singular confining behaviour at
the origin. Using the Pagels-Stokar method we relate the obtained solutions to
the pion decay constant , and estimate the scale parameter ,
in the presence of four active quarks, to be about 880 MeV.Comment: 14 pages, 3 figures; to appear in J. Phys.
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