38 research outputs found
Dynamical effects of QCD in systems
We study the coupling of a tetraquark system to an exchanged meson-meson
channel, using a pure gluonic theory based four-quark potential {\em matrix}
model which is known to fit well a large number of data points for lattice
simulations of different geometries of a four-quark system. We find that if
this minimal-area-based potential matrix replaces the earlier used simple
Gaussian form for the gluon field overlap factor in its off-diagonal terms,
the resulting -matrix and phase shifts develop an angle dependence whose
partial wave analysis reveals wave and higher angular momentum components
in it. In addition to the obvious implications of this result for the
meson-meson scattering, this new feature indicates the possibility of orbital
excitations influencing properties of meson-meson molecules through a
polarization potential. We have used a formalism of the resonating group
method, treated kinetic energy and overlap matrices on model of the potential
matrix, but decoupled the resulting complicated integral equations through the
Born approximation. In this exploratory study we have used a quadratic
confinement and not included the spin-dependence; we also used the
approximation of equal constituent quark masses.Comment: 18 pages, 9 figure
Dynamical implications of gluonic excitations in meson-meson systems
We study meson-meson interactions using an extended basis
that allows calculating coupling of an ordinary meson-meson system to a
hybrid-hybrid one. We use a potential model matrix in this extended basis which
at quark level is known to provide a good fit to numerical simulations of a
system in pure gluonic theory for static quarks in a selection
of geometries. We use a combination of resonating group method formalism and
Born approximation to include the quark motion using wave functions of a
potential within a cluster. This potential is taken to be quadratic
for ground states and has an additional smeared (Gaussian) for
the matrix elements between hybrid mesons. For the parameters of this
potential, we use values chosen to 1) minimize the error resulting from our use
of a quadratic potential and 2) best fit the lattice data for differences of
and configurations of the gluonic field between a quark
and an antiquark. At the quark (static) level, including the gluonic
excitations was noted to partially replace the need for introducing many-body
terms in a multi-quark potential. We study how successful such a replacement is
at the (dynamical) hadronic level of relevance to actual hard experiments. Thus
we study effects of both gluonic excitations and many-body terms on mesonic
transition amplitudes and the energy shifts resulting from the second order
perturbation theory (i.e. from the respective hadron loops). The study suggests
introducing both energy and orbital excitations in wave functions of scalar
mesons that are modelled as meson-meson molecules or are supposed to have a
meson-meson component in their wave functions.Comment: 26 pages, 10 figure
Effect of the Quark-Gluon Vertex on Dynamical Chiral Symmetry Breaking
In this work we investigate how the details of the quark-gluon interaction
vertex affect the quantitative description of chiral symmetry breaking and
dynamical mass generation through the gap equation. We employ the Maris-Tandy
(MT) and Qin-Chang (QC) models for the gluon propagator and the effective
strong running coupling. The gap equation is solved by employing several vertex
Anstze which have been constructed in order to implement some
of the key aspects of a gauge field theory such as gauge invariance and
multiplicative renormalizability. We find that within a small variation of MT
and QC model parameters, all truncations point towards the same quantitative
pattern of chiral symmetry breaking, the running quark mass function, ensuring
the robustness of this approach.Comment: 12 page