128 research outputs found
A Pilot Study on effects of vaccination on immunity of broiler chickens
A pilot study was carried out with the aim of highlighting the effects of NDV vaccine on the immune responses of broiler chickens challenged with NDV. Twenty (20) broilers of day-old were used for the study. They were grouped into five of four per group. During the study they were fed with standard feeds and clean water ad libitum. Both vaccinated and unvaccinated groups were challenged with 0.2 saline suspension of 106 ELD50 intradermal inoculation of NDV challenged strain. The vaccinated groups showed neither clinical signs nor symptoms of NDV infections while unvaccinated group showed 100% mortality after 48hr. This result indicate that vaccines is still very important in the prevention, management and control of poultry diseases as maternal immunity passed on to the young chicks at precocial stage could not be relied on to fight against infectious disease in broiler chickens. Therefore, the use of locally produced vaccines should be encouraged among farmers for the prevention, control and management of outbreaks of viral infections in our community. Key: Challenged, Poultry birds- broilers, Newcastle disease virus, Vaccinatio
Pinch Technique for Schwinger-Dyson equations
In the context of scalar QED we derive the pinch technique self-energies and
vertices directly from the Schwinger-Dyson equations. After reviewing the
perturbative construction, we discuss in detail the general methodology and the
basic field-theoretic ingredients necessary for the completion of this task.
The construction requires the simultaneous treatment of the equations governing
the scalar self-energy and the fundamental interaction vertices. The resulting
non-trivial rearrangement of terms generates dynamically the Schwinger-Dyson
equations for the corresponding Green's functions of the background field
method. The proof relies on the extensive use of the all-order Ward-identities
satisfied by the full vertices of the theory and by the
one-particle-irreducible kernels appearing in the usual skeleton expansion. The
Ward identities for these latter quantities are derived formally, and several
subtleties related to the structure of the multiparticle kernels are addressed.
The general strategy for the generalization of the method in a non-Abelian
context is briefly outlined, and some of the technical difficulties are
discussed.Comment: 43 pages, 11 figures; title and abstract slightly modified, several
clarifying discussions added; final version to match the one accpted for
publication in JHE
Displacement Operator Formalism for Renormalization and Gauge Dependence to All Orders
We present a new method for determining the renormalization of Green
functions to all orders in perturbation theory, which we call the displacement
operator formalism, or the D-formalism, in short. This formalism exploits the
fact that the renormalized Green functions may be calculated by displacing by
an infinite amount the renormalized fields and parameters of the theory with
respect to the unrenormalized ones. With the help of this formalism, we are
able to obtain the precise form of the deformations induced to the Nielsen
identities after renormalization, and thus derive the exact dependence of the
renormalized Green functions on the renormalized gauge-fixing parameter to all
orders. As a particular non-trivial example, we calculate the gauge-dependence
of at two loops in the framework of an Abelian Higgs model, using a
gauge-fixing scheme that preserves the Higgs-boson low-energy theorem for
off-shell Green functions. Various possible applications and future directions
are briefly discussed.Comment: 41 pages, 8 figure
Direct observation of incommensurate magnetism in Hubbard chains
The interplay between magnetism and doping is at the origin of exotic
strongly correlated electronic phases and can lead to novel forms of magnetic
ordering. One example is the emergence of incommensurate spin-density waves
with a wave vector that does not match the reciprocal lattice. In one dimension
this effect is a hallmark of Luttinger liquid theory, which also describes the
low energy physics of the Hubbard model. Here we use a quantum simulator based
on ultracold fermions in an optical lattice to directly observe such
incommensurate spin correlations in doped and spin-imbalanced Hubbard chains
using fully spin and density resolved quantum gas microscopy. Doping is found
to induce a linear change of the spin-density wave vector in excellent
agreement with Luttinger theory predictions. For non-zero polarization we
observe a decrease of the wave vector with magnetization as expected from the
Heisenberg model in a magnetic field. We trace the microscopic origin of these
incommensurate correlations to holes, doublons and excess spins which act as
delocalized domain walls for the antiferromagnetic order. Finally, when
inducing interchain coupling we observe fundamentally different spin
correlations around doublons indicating the formation of a magnetic polaron
Gluon mass generation in the PT-BFM scheme
In this article we study the general structure and special properties of the
Schwinger-Dyson equation for the gluon propagator constructed with the pinch
technique, together with the question of how to obtain infrared finite
solutions, associated with the generation of an effective gluon mass.
Exploiting the known all-order correspondence between the pinch technique and
the background field method, we demonstrate that, contrary to the standard
formulation, the non-perturbative gluon self-energy is transverse
order-by-order in the dressed loop expansion, and separately for gluonic and
ghost contributions. We next present a comprehensive review of several subtle
issues relevant to the search of infrared finite solutions, paying particular
attention to the role of the seagull graph in enforcing transversality, the
necessity of introducing massless poles in the three-gluon vertex, and the
incorporation of the correct renormalization group properties. In addition, we
present a method for regulating the seagull-type contributions based on
dimensional regularization; its applicability depends crucially on the
asymptotic behavior of the solutions in the deep ultraviolet, and in particular
on the anomalous dimension of the dynamically generated gluon mass. A
linearized version of the truncated Schwinger-Dyson equation is derived, using
a vertex that satisfies the required Ward identity and contains massless poles
belonging to different Lorentz structures. The resulting integral equation is
then solved numerically, the infrared and ultraviolet properties of the
obtained solutions are examined in detail, and the allowed range for the
effective gluon mass is determined. Various open questions and possible
connections with different approaches in the literature are discussed.Comment: 54 pages, 24 figure
Gauge-Independent Off-Shell Fermion Self-Energies at Two Loops: The Cases of QED and QCD
We use the pinch technique formalism to construct the gauge-independent
off-shell two-loop fermion self-energy, both for Abelian (QED) and non-Abelian
(QCD) gauge theories. The new key observation is that all contributions
originating from the longitudinal parts of gauge boson propagators, by virtue
of the elementary tree-level Ward identities they trigger, give rise to
effective vertices, which do not exist in the original Lagrangian; all such
vertices cancel diagrammatically inside physical quantities, such as current
correlation functions or S-matrix elements. We present two different, but
complementary derivations: First, we explicitly track down the aforementioned
cancellations inside two-loop diagrams, resorting to nothing more than basic
algebraic manipulations. Second, we present an absorptive derivation,
exploiting the unitarity of the S-matrix, and the Ward identities imposed on
tree-level and one-loop physical amplitudes by gauge invariance, in the case of
QED, or by the underlying Becchi-Rouet-Stora symmetry, in the case of QCD. The
propagator-like sub-amplitude defined by means of this latter construction
corresponds precisely to the imaginary parts of the effective self-energy
obtained in the former case; the real part may be obtained from a (twice
subtracted) dispersion relation. As in the one-loop case, the final two-loop
fermion self-energy constructed using either method coincides with the
conventional fermion self-energy computed in the Feynman gauge.Comment: 30 pages; uses axodraw (axodraw.sty included in the src); final
version to appear in Phys. Rev.
Pinch Technique and the Batalin-Vilkovisky formalism
In this paper we take the first step towards a non-diagrammatic formulation
of the Pinch Technique. In particular we proceed into a systematic
identification of the parts of the one-loop and two-loop Feynman diagrams that
are exchanged during the pinching process in terms of unphysical ghost Green's
functions; the latter appear in the standard Slavnov-Taylor identity satisfied
by the tree-level and one-loop three-gluon vertex. This identification allows
for the consistent generalization of the intrinsic pinch technique to two
loops, through the collective treatment of entire sets of diagrams, instead of
the laborious algebraic manipulation of individual graphs, and sets up the
stage for the generalization of the method to all orders. We show that the task
of comparing the effective Green's functions obtained by the Pinch Technique
with those computed in the background field method Feynman gauge is
significantly facilitated when employing the powerful quantization framework of
Batalin and Vilkovisky. This formalism allows for the derivation of a set of
useful non-linear identities, which express the Background Field Method Green's
functions in terms of the conventional (quantum) ones and auxiliary Green's
functions involving the background source and the gluonic anti-field; these
latter Green's functions are subsequently related by means of a Schwinger-Dyson
type of equation to the ghost Green's functions appearing in the aforementioned
Slavnov-Taylor identity.Comment: 45 pages, uses axodraw; typos corrected, one figure changed, final
version to appear in Phys.Rev.
Asymptotic properties of Born-improved amplitudes with gauge bosons in the final state
For processes with gauge bosons in the final state we show how to
continuously connect with a single Born-improved amplitude the resonant region,
where resummation effects are important, with the asymptotic region far away
from the resonance, where the amplitude must reduce to its tree-level form.
While doing so all known field-theoretical constraints are respected, most
notably gauge-invariance, unitarity and the equivalence theorem. The
calculations presented are based on the process , mediated by a
possibly resonant Higgs boson; this process captures all the essential
features, and can serve as a prototype for a variety of similar calculations.
By virtue of massive cancellations the resulting closed expressions for the
differential and total cross-sections are particularly compact.Comment: 23 pages, Latex, 4 Figures, uses axodra
The pinch technique at two-loops: The case of mass-less Yang-Mills theories
The generalization of the pinch technique beyond one loop is presented. It is
shown that the crucial physical principles of gauge-invariance, unitarity, and
gauge-fixing-parameter independence single out at two loops exactly the same
algorithm which has been used to define the pinch technique at one loop,
without any additional assumptions. The two-loop construction of the pinch
technique gluon self-energy, and quark-gluon vertex are carried out in detail
for the case of mass-less Yang-Mills theories, such as perturbative QCD. We
present two different but complementary derivations. First we carry out the
construction by directly rearranging two-loop diagrams. The analysis reveals
that, quite interestingly, the well-known one-loop correspondence between the
pinch technique and the background field method in the Feynman gauge persists
also at two-loops. The renormalization is discussed in detail, and is shown to
respect the aforementioned correspondence. Second, we present an absorptive
derivation, exploiting the unitarity of the -matrix and the underlying BRS
symmetry; at this stage we deal only with tree-level and one-loop physical
amplitudes. The gauge-invariant sub-amplitudes defined by means of this
absorptive construction correspond precisely to the imaginary parts of the
-point functions defined in the full two-loop derivation, thus furnishing a
highly non-trivial self-consistency check for the entire method. Various future
applications are briefly discussed.Comment: 29 pages, uses Revtex, 22 Figures in a separate ps fil
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