1,613 research outputs found
Renormalized Poincar\'e algebra for effective particles in quantum field theory
Using an expansion in powers of an infinitesimally small coupling constant
, all generators of the Poincar\'e group in local scalar quantum field
theory with interaction term are expressed in terms of annihilation
and creation operators and that result from a
boost-invariant renormalization group procedure for effective particles. The
group parameter is equal to the momentum-space width of form factors
that appear in vertices of the effective-particle Hamiltonians, . It
is verified for terms order 1, , and , that the calculated generators
satisfy required commutation relations for arbitrary values of .
One-particle eigenstates of are shown to properly transform under
all Poincar\'e transformations. The transformations are obtained by
exponentiating the calculated algebra. From a phenomenological point of view,
this study is a prerequisite to construction of observables such as spin and
angular momentum of hadrons in quantum chromodynamics.Comment: 17 pages, 5 figure
Improving Lattice Quark Actions
We explore the first stage of the Symanzik improvement program for lattice
Dirac fermions, namely the construction of doubler-free, highly improved
classical actions on isotropic as well as anisotropic lattices (where the
temporal lattice spacing, a_t, is smaller than the spatial one). Using field
transformations to eliminate doublers, we derive the previously presented
isotropic D234 action with O(a^3) errors, as well as anisotropic D234 actions
with O(a^4) or O(a_t^3, a^4) errors. Besides allowing the simulation of heavy
quarks within a relativistic framework, anisotropic lattices alleviate
potential problems due to unphysical branches of the quark dispersion relation
(which are generic to improved actions), facilitate studies of lattice
thermodynamics, and allow accurate mass determinations for particles with bad
signal/noise properties, like glueballs and P-state mesons. We also show how
field transformations can be used to completely eliminate unphysical branches
of the dispersion relation. Finally, we briefly discuss future steps in the
improvement program.Comment: Tiny changes to agree with version to appear in Nucl. Phys. B (33
pages, LaTeX, 13 eps files
Lattice QCD on Small Computers
We demonstrate that lattice QCD calculations can be made -- times
faster by using very coarse lattices. To obtain accurate results, we replace
the standard lattice actions by perturbatively-improved actions with
tadpole-improved correction terms that remove the leading errors due to the
lattice. To illustrate the power of this approach, we calculate the
static-quark potential, and the charmonium spectrum and wavefunctions using a
desktop computer. We obtain accurate results that are independent of the
lattice spacing and agree well with experiment.Comment: 15 pages, 3 figs incl as LaTex pictures Minor additions to tables and
tex
Scale Setting in QCD and the Momentum Flow in Feynman Diagrams
We present a formalism to evaluate QCD diagrams with a single virtual gluon
using a running coupling constant at the vertices. This method, which
corresponds to an all-order resummation of certain terms in a perturbative
series, provides a description of the momentum flow through the gluon
propagator. It can be viewed as a generalization of the scale-setting
prescription of Brodsky, Lepage and Mackenzie to all orders in perturbation
theory. In particular, the approach can be used to investigate why in some
cases the ``typical'' momenta in a loop diagram are different from the
``natural'' scale of the process. It offers an intuitive understanding of the
appearance of infrared renormalons in perturbation theory and their connection
to the rate of convergence of a perturbative series. Moreover, it allows one to
separate short- and long-distance contributions by introducing a hard
factorization scale. Several applications to one- and two-scale problems are
discussed in detail.Comment: eqs.(51) and (83) corrected, minor typographic changes mad
Lack of Mutual Respect in Relationship The Endangered Partner
Violence in a relationship and in a family setting has been
an issue of concern to various interest groups and professional organizations.
Of particular interest in this article is violence against women
in a relationship. While there is an abundance of knowledge on violence
against women in general, intimate or partner femicide seems to have
received less attention. Unfortunately, the incidence of violence against
women, and intimate femicide in particular, has been an issue of concern
in the African setting.
This article examines the trends of intimate femicide in an African setting
in general, and in Botswana in particular. The increase in intimate
femicide is an issue of concern, which calls for collective effort to address.
This article also examines trends offemicide in Botswana, and the
antecedents and the precipitating factors. Some studies have implicated
societal and cultural dynamics as playing significant roles in intimate
femicide in the African setting. It is believed that the patriarchal nature
of most African settings and the ideology of male supremacy have relegated
women to a subordinate role. Consequently, respect for women
in any relationship with men is lopsided in favor of men and has led to
abuse of women, including intimate femicide. Other militating factors in
intimate femicide ,are examined and the implications for counseling to
assist the endangered female partner are discussed
Thermal Field Theory and Generalized Light Front Coordinates
The dependence of thermal field theory on the surface of quantization and on
the velocity of the heat bath is investigated by working in general coordinates
that are arbitrary linear combinations of the Minkowski coordinates. In the
general coordinates the metric tensor is non-diagonal. The
Kubo, Martin, Schwinger condition requires periodicity in thermal correlation
functions when the temporal variable changes by an amount
. Light front quantization fails since
, however various related quantizations are possible.Comment: 10 page
Nutrient availability of different batches of wheat distillers dried grains with solubles with and without exogenous enzymes for broiler chickens
Wheat distillers' dried grains with solubles (DDGS) are being used increasingly in the poultry feed industry but their nutritional value is variable. The aim of this experiment was to examine the effect of batch to batch variation of wheat DDGS produced by the same manufacturer on the growth performance, dietary N corrected apparent metabolizable energy (AMEn), energy conversion ratio (ECR), total tract dry matter retention (DMR), nitrogen retention (NR) and fat digestibility (FD) coefficients when fed to broilers in complete diets with and without enzyme supplementation. Six UK wheat DDGS samples, produced by a single manufacturer, were used in a broiler experiment. Six diets containing 150 g/kg of each selected wheat DDGS sample were mixed. Each diet was then split into two batches and one of them was supplemented with commercial enzyme preparation, providing 1220 units xylanase and 152 units of β-glucanase/kg diet, resulting in 12 experimental diets. Each diet was fed ad libitum to five pens of two male Ross 308 broilers from 7 to 21 d old. Enzyme supplementation improved dietary AMEn, DMR, NR (P < 0.001) and FD (P < 0.05) compared to non-supplemented diets. There was DDGS sample by enzyme interaction (P < 0.05) on daily weight gain and ECR. The results suggest that the variability in AMEn of DDGS samples produced from a single manufacturer is greater than expected compared to the variability of whole wheat samples but substantially lower than expected from wheat DDGS samples from different EU manufacturers. This experiment has shown that the variation in feeding value of wheat DDGS may be explained by the variability in polysaccharide contents
Characterization of an alpha-L-fucosidase from the periodontal pathogen Tannerella forsythia
The periodontal pathogen Tannerella forsythia expresses several glycosidases which are linked to specific growth requirements and are involved in the invasion of host tissues. α-l-Fucosyl residues are exposed on various host glycoconjugates and, thus, the α-l-fucosidases predicted in the T. forsythia ATCC 43037 genome could potentially serve roles in host-pathogen interactions. We describe the molecular cloning and characterization of the putative fucosidase TfFuc1 (encoded by the bfo_2737 = Tffuc1 gene), previously reported to be present in an outer membrane preparation. In terms of sequence, this 51-kDa protein is a member of the glycosyl hydrolase family GH29. Using an artificial substrate, p-nitrophenyl-α-fucose (KM 670 μM), the enzyme was determined to have a pH optimum of 9.0 and to be competitively inhibited by fucose and deoxyfuconojirimycin. TfFuc1 was shown here to be a unique α(1,2)-fucosidase that also possesses α(1,6) specificity on small unbranched substrates. It is active on mucin after sialidase-catalyzed removal of terminal sialic acid residues and also removes fucose from blood group H. Following knock-out of the Tffuc1 gene and analyzing biofilm formation and cell invasion/adhesion of the mutant in comparison to the wild-type, it is most likely that the enzyme does not act extracellularly. Biochemically interesting as the first fucosidase in T. forsythia to be characterized, the biological role of TfFuc1 may well be in the metabolism of short oligosaccharides in the periplasm, thereby indirectly contributing to the virulence of this organism. TfFuc1 is the first glycosyl hydrolase in the GH29 family reported to be a specific α(1,2)-fucosidase
Boost-Invariant Running Couplings in Effective Hamiltonians
We apply a boost-invariant similarity renormalization group procedure to a
light-front Hamiltonian of a scalar field phi of bare mass mu and interaction
term g phi^3 in 6 dimensions using 3rd order perturbative expansion in powers
of the coupling constant g. The initial Hamiltonian is regulated using momentum
dependent factors that approach 1 when a cutoff parameter Delta tends to
infinity. The similarity flow of corresponding effective Hamiltonians is
integrated analytically and two counterterms depending on Delta are obtained in
the initial Hamiltonian: a change in mu and a change of g. In addition, the
interaction vertex requires a Delta-independent counterterm that contains a
boost invariant function of momenta of particles participating in the
interaction. The resulting effective Hamiltonians contain a running coupling
constant that exhibits asymptotic freedom. The evolution of the coupling with
changing width of effective Hamiltonians agrees with results obtained using
Feynman diagrams and dimensional regularization when one identifies the
renormalization scale with the width. The effective light-front Schroedinger
equation is equally valid in a whole class of moving frames of reference
including the infinite momentum frame. Therefore, the calculation described
here provides an interesting pattern one can attempt to follow in the case of
Hamiltonians applicable in particle physics.Comment: 24 pages, LaTeX, included discussion of finite x-dependent
counterterm
Nonperturbative Description of Deep Inelastic Structure Functions in Light-Front QCD
We explore the deep inelastic structure functions of hadrons
nonperturbatively in an inverse power expansion of the light-front energy of
the probe in the framework of light-front QCD. We arrive at the general
expressions for various structure functions as the Fourier transform of matrix
elements of different components of bilocal vector and axial vector currents on
the light-front in a straightforward manner. The complexities of the structure
functions are mainly carried by the multi-parton wave functions of the hadrons,
while, the bilocal currents have a dynamically dependent yet simple structure
on the light-front in this description. We also present a novel analysis of the
power corrections based on light-front power counting which resolves some
ambiguities of the conventional twist analysis in deep inelastic processes.
Further, the factorization theorem and the scale evolution of the structure
functions are presented in this formalism by using old-fashioned light-front
time-ordered perturbation theory with multi-parton wave functions.
Nonperturbative QCD dynamics underlying the structure functions can be explored
in the same framework. Once the nonperturbative multi-parton wave functions are
known from low-energy light-front QCD, a complete description of deep inelastic
structure functions can be realized.Comment: Revtex, 30 pages and no figur
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