159 research outputs found
Two-Dimensional QCD in the Wu-Mandelstam-Leibbrandt Prescription
We find the exact non-perturbative expression for a simple Wilson loop of
arbitrary shape for U(N) and SU(N) Euclidean or Minkowskian two-dimensional
Yang-Mills theory regulated by the Wu-Mandelstam-Leibbrandt gauge prescription.
The result differs from the standard pure exponential area-law of YM_2, but
still exhibits confinement as well as invariance under area-preserving
diffeomorphisms and generalized axial gauge transformations. We show that the
large N limit is NOT a good approximation to the model at finite N and conclude
that Wu's N=infinity Bethe-Salpeter equation for QCD_2 should have no bound
state solutions. The main significance of our results derives from the
importance of the Wu-Mandelstam-Leibbrandt prescription in higher-dimensional
perturbative gauge theory.Comment: 7 pages, LaTeX, REVTE
Standard ion transfer potential at the water|butyronitrile interface
Butyronitrile is an organic solvent stable enough to be used in photochemical reactions at liquid/liquid interfaces. However, it provides a rather short polarisation window making the analysis of ion transfer across the water|butyronitrile interface challenging. Here, steady-state cyclic voltammetry, at microhole-supported micro-interfaces, was used to measure Gibbs energies of transfer. A linear relationship between the standard Gibbs energies of ion partition for the water|butyronitrile interface and the water|1,2-dichloroethane and water|nitrobencene interfaces was found, making easy to extrapolate the Gibbs energy of other ions from this empiric correlation.Fil: Riva, Julieta Soledad. Swiss Federal Institute Of Technology Epfl; Suiza. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas; Argentina. Universidad Nacional de CĂłrdoba. Facultad de Matemática, AstronomĂa y FĂsica; ArgentinaFil: Bassetto, V. C.. Swiss Federal Institute Of Technology Epfl; SuizaFil: Girault, Hubert. Swiss Federal Institute Of Technology Epfl; SuizaFil: Olaya, A. J.. Swiss Federal Institute Of Technology Epfl, Lausanne
Correlators of Wilson loops and local operators from multi-matrix models and strings in AdS
We study correlation functions of Wilson loops and local operators in a
subsector of N=4 SYM which preserves two supercharges. Localization arguments
allow to map the problem to a calculation in bosonic two-dimensional Yang-Mills
theory. In turn, this can be reduced to computing correlators in certain
Gaussian multi-matrix models. We focus on the correlation function of a Wilson
loop and two local operators, and solve the corresponding three-matrix model
exactly in the planar limit. We compare the strong coupling behavior to string
theory in AdS_5xS^5, finding precise agreement. We pay particular attention to
the case in which the local operators have large R-charge J \sim sqrt{lambda}
at strong coupling.Comment: 50 pages, 9 figures. v2: minor changes, references adde
OPE coefficient functions in terms of composite operators only. Singlet case
A method for calculating coefficient functions of the operator product
expansion, which was previously derived for the non-singlet case, is
generalized for the singlet coefficient functions. The resulting formula
defines coefficient functions entirely in terms of corresponding singlet
composite operators without applying to elementary (quark and gluon) fields.
Both "diagonal" and "non-diagonal" gluon coefficient functions in the product
expansion of two electromagnetic currents are calculated in QCD. Their
renormalization properties are studied.Comment: 33 pages, 15 figures, minor corrections are mad
Similarity Renormalization, Hamiltonian Flow Equations, and Dyson's Intermediate Representation
A general framework is presented for the renormalization of Hamiltonians via
a similarity transformation. Divergences in the similarity flow equations may
be handled with dimensional regularization in this approach, and the resulting
effective Hamiltonian is finite since states well-separated in energy are
uncoupled. Specific schemes developed several years ago by Glazek and Wilson
and contemporaneously by Wegner correspond to particular choices within this
framework, and the relative merits of such choices are discussed from this
vantage point. It is shown that a scheme for the transformation of Hamiltonians
introduced by Dyson in the early 1950's also corresponds to a particular choice
within the similarity renormalization framework, and it is argued that Dyson's
scheme is preferable to the others for ease of computation. As an example, it
is shown how a logarithmically confining potential arises simply at second
order in light-front QCD within Dyson's scheme, a result found previously for
other similarity renormalization schemes. Steps toward higher order and
nonperturbative calculations are outlined. In particular, a set of equations
analogous to Dyson-Schwinger equations is developed.Comment: REVTex, 32 pages, 7 figures (corrected references
Use of molecular markers can help to understand the genetic diversity of Babesia bovis.
Cattle babesiosis is a tick-borne disease responsible for significant losses for the livestock industries in tropical areas of the world. These piroplasms are under constant control of the host immune system, which lead to a strong selective pressure for arising more virulent or attenuated phenotypes. Aiming to better understand the most critical genetic modifications in Babesia bovis genome, related to virulence, an in silico analysis was performed using DNA sequences from GenBank. Fourteen genes (sbp-2, sbp-4, trap, msa-1, msa-2b, msa-2c, Bv80 (or Bb-1), 18S rRNA, acs-1, ama-1, ?-tub, cp-2, p0, rap-1a) related to parasite infection and immunogenicity and ITS region were selected for alignment and comparison of several isolates of Babesia bovis from different geographic regions around the world. Among the 15 genes selected for the study of diversity, only 7 genes (sbp-2, sbp-4, trap, msa-1, msa-2b, msa-2c, Bv80) and the ITS region presented sufficient genetic variation for the studies of phylogeny. Despite this genetic diversity observed into groups, there was not sufficient information available to associate molecular markers with virulence of isolates. However, some genetic groups no were correlated with geographic region what could indicate some typical evolutionary characteristics in the relation between parasite-host. Further studies using these genes in herds presenting diverse clinical conditions are required. The better understanding of evolutionary mechanisms of the parasite may contribute to improve prophylactic and therapeutic measures. In this way, we suggest that genes used in our study are potential markers of virulence and attenuation and have to be analyzed with the use of sequences from animals that present clinical signs of babesiosis and asymptomatic carriers
Multiple hadron production in e+e- annihilation induced by heavy primary quarks. New analysis
In this paper we present an analysis of the multiple hadron production
induced by primary heavy quarks in e+e- annihilation with the account of most
complete and corrected experimental data. In the framework of perturbative QCD,
new theoretical bounds on the asymptotically constant differences of the
multiplicities in processes with light and heavy quarks are given.Comment: 26 pages, 7 figures, to be published in Particles & Nucle
Supersymmetry and the Chiral Schwinger Model
We have constructed the N=1/2 supersymmetric general Abelian model with
asymmetric chiral couplings. This leads to a N=1/2 supersymmetrization of the
Schwinger model. We show that the supersymmetric general model is plagued with
problems of infrared divergence. Only the supersymmetric chiral Schwinger model
is free from such problems and is dynamically equivalent to the chiral
Schwinger model because of the peculiar structure of the N=1/2 multiplets.Comment: one 9 pages Latex file, one ps file with one figur
Renormalization of the mass gap
The full gluon propagator relevant for the description of the truly
non-perturbative QCD dynamics, the so-called intrinsically non-perturbative
gluon propagator has been derived in our previous work. It explicitly depends
on the regularized mass gap, which dominates its structure at small gluon
momentum. It is automatically transversal in a gauge invariant way. It is
characterized by the presence of severe infrared singularities at small gluon
momentum, so the gluons remain massless, and this does not depend on the gauge
choice. In this paper we have shown how precisely the renormalization program
for the regularized mass gap should be performed. We have also shown how
precisely severe infrared singularities should be correctly treated. This
allowed to analytically formulate the exact and gauge-invariant criteria of
gluon and quark confinement. After the renormalization program is completed,
one can derive the gluon propagator applicable for the calculation of physical
observables processes, etc., in low-energy QCD from first principles.Comment: 16 pages, no figures, no tables, some minor changes are introduce
Electroweak jet cascading in the decay of superheavy particles
We study decays of superheavy particles into leptons. We show that they
initiate cascades similar to QCD parton jets, if m_X\gsim 10^6 GeV.
Electroweak cascading is studied and the energy spectra of the produced leptons
are calculated in the framework of a broken SU(2) model of weak interactions.
As application, important for the Z-burst model for ultrahigh energy cosmic
rays, we consider decays of superheavy particles coupled on tree-level only to
neutrinos and derive stringent limit for these decays from the observed diffuse
extragalactic -ray flux.Comment: 4 pages, 1 eps figur
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