2,662 research outputs found

### Formfactor of the relativistic scalar bound state calculated in Minkowski space

We have calculated the electromagnetic elastic form factor of a two body
scalar bound state. The Bethe-Salpeter equation is solved directly in the
Minkowski space using the Perturbation Theory Integral Representation. At soft
coupling regime the obtained results are compared with those following from a
quasipotential spectator (Gross) approximation.Comment: 2 figure

### Analytical solution for the correlator with Gribov propagators

Propagators approximated by a meromorphic functions with complex conjugated
poles are widely used to model infrared behavior of QCD Green's functions. In
this paper, analytical solutions for two point correlator made out of functions
with complex conjugated poles or branch points have been obtained in the
Minkowski space for the first time. As a special case the Gribov propagator has
been considered as well. The result is different from the naive analytical
continuation of the correlator primarily defined in the Euclidean space. It is
free of ultraviolet divergences, and instead of Lehmann it rather satisfies
Gribov integral representation.Comment: 13pp, 2figs. Integral representation for Gribov correlator derived
and added, new results in new figure added. Sections reordere

### The quark spectral functions and the Hadron Vacuum Polarization from application of DSEs in Minkowski space

The hadronic vacuum polarization function $\Pi_h$ for two light flavors is
computed on the entire domain of spacelike and timelike momenta using a
framework of Dyson-Schwinger equations. The analytical continuation of the
function $\Pi_h$ is based on the utilization of the Gauge Technique with the
entry of QCD Green's functions determined from generalized quark spectral
functions. For the first time, the light quark spectral functions are extracted
from the solution of the gap equation for the quark propagator. The scale is
set up by the phenomena of dynamical chiral symmetry breaking, which is a
striking feature of low energy QCD.Comment: New Appendix was added wherein the new method of extraction of the
quark spectral function is explained in detail

### Solution of Dynamical Spontaneous Chiral Symmetry Breaking in Minkowski Space, Linearized approximation

Chiral symmetry breaking and mass generation is studied in a vectorial,
confining asymptotic free gauge theory. Using the Schwinger-Dyson equation in
improved ladder approximation, we calculate the fermion propagator in the whole
Minkowski space. The estimate for $f_{\pi}$ and the dependence of physical mass
on a coupling strength is provided. We focus on the extraction of spectral
function of fermion propagator in the strongly coupled regime. Our calculations
indicate that up to the crossover between walking and QCD-like running
dynamics, the real pole of the propagator is not excluded and very likely it is
actually developed at zero temperature theory.Comment: 14 pages, 6 figure

### Muon pair production with hadronic vacuum polarization re-evaluated using new precise data

The interference effect between leptonic radiative corrections and hadronic
polarization functions is calculated via optical theorem for $\mu-$pair
productions. Fine selected new data for the production cross section
$\sigma_h(e^+e^-\rightarrow hadrons$) are used for calculation of hadronic
vacuum polarization, which enter the dressed photon propagator in muon pair
production. The result is compared with KLOE experiment for $\mu^{-}\mu^{+}$
production at $\phi$ meson energy, as well as the running fine structure
coupling is compared with recent KLOE2 experiment for radiative return
$\mu^{-}\mu^{+}$ production at $\omega/\rho$ meson energy.Comment: 11 figures, 15 page

### On the decoupling solution for pinch technique gluon propagator

Within a simple Ansatz for renormalized gluon propagator and using gauge
invariant pinch-technique for Schwinger-Dyson equation, the limits on the
effective gluon mass is derived. We calculated scheme invariant running
coupling, which in order to be well defined, gives the lower limit on the gluon
mass. We conclude mass should be larger as $m>0.4\Lambda$ in order to avoid
Landau ghost. The upper limit is estimated from assumed quark mass generation
which requires gauge coupling must be large enough to trigger chiral symmetry
breaking. It allows only small range of $m$, which lead to a reasonably large
infrared coupling. Already for $m\simeq \Lambda$ we get no chiral symmetry
breaking at all. Further, we observe that sometimes assumed or postulated
Khallen-Lehmann representation for running coupling is not achieved for any
value of $m$.Comment: 6p, error corrected, new upper boundary on the effective gluon mass
estimated from CHS

### Solving the Bethe-Salpeter equation for fermion-antifermion pseudoscalar bound state in Minkowski space

The new method of solution of the Bethe-Salpeter equation for quark-antiquark
pseudoscalar bound state is proposed. With the help of integral representation
the results are directly obtained in Minkowski space. Dressing of Greens
functions is naturally considered providing thus the correct inclusion of the
running coupling constant and the quark propagators as well as. The first
numerical results are presented for a simplified ladder approximation.Comment: 19 pages, 1 figur

### Gauge Technique approximation to the $\pi \gamma$ production and the pion transition form factor

The pion transition form factor $G(q^2)$ is computed on the entire domain of
spacelike and timelike
momenta using a quantum field theory continuum approach. In analytical
continuation of the function $G(Q^2)$ we utilized the Gauge Technique with the
quark propagator
determined from Minkowski space solution of QCD Dyson-Schwinger equations.
The scale is set up by the phenomena of dynamical chiral symmetry breaking,
which is a striking feature of low energy QCD.Comment: Typos and grammar corrected. New refs. adde

### Lattice data inspired but Minkowski space calculated QCD fundamental propagator

We study the Dyson-Schwinger equation for the quark propagator in Minkowski
space. In order to have analytical behaviour at the timelike axis of momenta
under control, we use the Stieltjes and the Hilbert transformation for the
interaction kernels and discuss the solution from the perspective of these
transformations. In addition, a lattice fit for the gluon propagator and
approximation for quark-gluon vertex are employed, and within the model the
quark propagator is obtained through the solution of Dyson-Schwinger equation
in Minkowski space. The resulting propagators in all studied cases do not show
up particle like pole and production thresholds. Instead of, the quark
propagator satisfies Hilbert transformation and the associated dynamical mass
function becomes complex without a presence of particle like branch point.Comment: Explanatory section redone, split an enlarged into two new Sections,
new simplify results added for LA, typos corrected the 26 pp, 6 fig

### Electromagnetic production of pions and quark dynamical mass in Minkowski space

Mechanism for generation of vector meson resonances is studied in the
framework of QCD Dyson-Schwinger equations, which are defined and actually
solved in Minkowski space. It is suggested that the timelike pion form factor
is generated by the interference of the background quark loops together with
the resonant structure predominantly created in the photon-quark-antiquark
vertex. It is suggested that QCD Green's functions involving quark fields are
oscillating for timelike arguments, which makes the interference effect among
various QCD Green's functions quite strong and important for the correct
description of production processes. A further peculiarities of dynamical
chiral symmetry breaking and confinement phenomena as viewed in Minkowski space
are discussed.Comment: too simple for correct description of the pion formfacto

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