577 research outputs found
The prophylactic and therapeutic effects of a staphylococcic vaccine in bovine mastitis
LD2668 .T4 1962 O3
Verifying the Kugo-Ojima Confinement Criterion in Landau Gauge Yang-Mills Theory
Expanding the Landau gauge gluon and ghost two-point functions in a power
series we investigate their infrared behavior. The corresponding powers are
constrained through the ghost Dyson-Schwinger equation by exploiting
multiplicative renormalizability. Without recourse to any specific truncation
we demonstrate that the infrared powers of the gluon and ghost propagators are
uniquely related to each other. Constraints for these powers are derived, and
the resulting infrared enhancement of the ghost propagator signals that the
Kugo-Ojima confinement criterion is fulfilled in Landau gauge Yang-Mills
theory.Comment: 4 pages, no figures; version to be published in Physical Review
Letter
Adverse drug reactions in hospitalized children in Germany are decreasing: results of a nine year cohort-based comparison
published_or_final_versio
On the infrared freezing of perturbative QCD in the Minkowskian region
The infrared freezing of observables is known to hold at fixed orders of
perturbative QCD if the Minkowskian quantities are defined through the analytic
continuation from the Euclidean region. In a recent paper [1] it is claimed
that infrared freezing can be proved also for Borel resummed all-orders
quantities in perturbative QCD. In the present paper we obtain the Minkowskian
quantities by the analytic continuation of the all-orders Euclidean amplitudes
expressed in terms of the inverse Mellin transform of the corresponding Borel
functions [2]. Our result shows that if the principle of analytic continuation
is preserved in Borel-type resummations, the Minkowskian quantities exhibit a
divergent increase in the infrared regime, which contradicts the claim made in
[1]. We discuss the arguments given in [1] and show that the special
redefinition of Borel summation at low energies adopted there does not
reproduce the lowest order result obtained by analytic continuation.Comment: 19 pages, 1 figur
Glueballs in a Hamiltonian Light-Front Approach to Pure-Glue QCD
We calculate a renormalized Hamiltonian for pure-glue QCD and diagonalize it.
The renormalization procedure is designed to produce a Hamiltonian that will
yield physical states that rapidly converge in an expansion in free-particle
Fock-space sectors. To make this possible, we use light-front field theory to
isolate vacuum effects, and we place a smooth cutoff on the Hamiltonian to
force its free-state matrix elements to quickly decrease as the difference of
the free masses of the states increases. The cutoff violates a number of
physical principles of light-front pure-glue QCD, including Lorentz covariance
and gauge covariance. This means that the operators in the Hamiltonian are not
required to respect these physical principles. However, by requiring the
Hamiltonian to produce cutoff-independent physical quantities and by requiring
it to respect the unviolated physical principles of pure-glue QCD, we are able
to derive recursion relations that define the Hamiltonian to all orders in
perturbation theory in terms of the running coupling. We approximate all
physical states as two-gluon states, and use our recursion relations to
calculate to second order the part of the Hamiltonian that is required to
compute the spectrum. We diagonalize the Hamiltonian using basis-function
expansions for the gluons' color, spin, and momentum degrees of freedom. We
examine the sensitivity of our results to the cutoff and use them to analyze
the nonperturbative scale dependence of the coupling. We investigate the effect
of the dynamical rotational symmetry of light-front field theory on the
rotational degeneracies of the spectrum and compare the spectrum to recent
lattice results. Finally, we examine our wave functions and analyze the various
sources of error in our calculation.Comment: 75 pages, 17 figures, 1 tabl
Bulk fields with general brane kinetic terms
We analyse the effect of general brane kinetic terms for bulk scalars,
fermions and gauge bosons in theories with extra dimensions, with and without
supersymmetry. We find in particular a singular behaviour when these terms
contain derivatives orthogonal to the brane. This is brought about by
divergences arising at second and higher order in perturbation
theory. We argue that this behaviour can be smoothed down by classical
renormalization.Comment: 31 pages, v2 few typos correcte
An Algebraic Criterion for the Ultraviolet Finiteness of Quantum Field Theories
An algebraic criterion for the vanishing of the beta function for
renormalizable quantum field theories is presented. Use is made of the descent
equations following from the Wess-Zumino consistency condition. In some cases,
these equations relate the fully quantized action to a local gauge invariant
polynomial. The vanishing of the anomalous dimension of this polynomial enables
us to establish a nonrenormalization theorem for the beta function ,
stating that if the one-loop order contribution vanishes, then will
vanish to all orders of perturbation theory. As a by-product, the special case
in which is only of one-loop order, without further corrections, is
also covered. The examples of the N=2,4 supersymmetric Yang-Mills theories are
worked out in detail.Comment: 1+32 pages, LaTeX2e, typos correcte
Analytic structure of the gluon and quark propagators in Landau gauge QCD
In Landau gauge QCD the infrared behavior of the propagator of transverse
gluons can be analytically determined to be a power law from Dyson-Schwinger
equations. This propagator clearly shows positivity violation, indicating the
absence of the transverse gluons from the physical spectrum, i.e. gluon
confinement. A simple analytic structure for the gluon propagator is proposed
capturing all important features. We provide arguments that the Landau gauge
quark propagator possesses a singularity on the real timelike axis. For this
propagator we find a positive definite Schwinger function.Comment: 6 pages, 3 figures; summary of a talk given at several occasions; to
be published in the proceedings of the international conference QCD DOWN
UNDER, March 10 - 19, Adelaide, Australi
Four Fermion Field Theories and the Chern-Simons Field: A Renormalization Group Study
In (2+1) dimensions, we consider the model of a flavor, two-component
fermionic field interacting through a Chern-Simons field besides a four fermion
self-interaction which consists of a linear combination of the Gross-Neveu and
Thirring like terms. The four fermion interaction is not perturbatively
renormalizable and the model is taken as an effective field theory in the
region of low momenta. Using Zimmerman procedure for reducing coupling
constants, it is verified that, for small values of the Chern-Simons parameter,
the origin is an infrared stable fixed point but changes to ultraviolet stable
as becomes bigger than a critical . Composite operators are
also analyzed and it is shown that a specific four fermion interaction has an
improved ultraviolet behavior as increases.Comment: 9 pages, revte
- …