8,270 research outputs found
The Epstein-Glaser causal approach to the Light-Front QED. I: Free theory
In this work we present the study of light-front field theories in the realm
of axiomatic theory. It is known that when one uses the light-cone gauge
pathological poles arises, demanding a prescription to be
employed in order to tame these ill-defined poles and to have correct Feynman
integrals due to the lack of Wick rotation in such theories. In order to shed a
new light on this long standing problem we present here a discussion based on
the use rigorous mathematical machinery of distributions combined with physical
concepts, such as causality, to show how to deal with these singular
propagators in a general fashion without making use of any prescription. The
first step of our development will consist in showing how analytic
representation for propagators arises by requiring general physical properties
in the framework of Wightman's formalism. From that we shall determine the
equal-time (anti)commutation relations in the light-front form for the scalar,
fermionic fields and for the dynamical components of the electromagnetic field.
In conclusion, we introduce the Epstein-Glaser causal method in order to have a
mathematical rigorous treatment of the free propagators of the theory, allowing
us to discuss the general treatment for propagators of the type . Moreover, we show that at given conditions our results reproduce known
prescriptions in the literature.Comment: 34 pages, v2 matching the published versio
Causal approach for the electron-positron scattering in Generalized Quantum Electrodynamics
In this paper we study the generalized electrodynamics contribution for the
electron-positron scattering process, , the
Bhabha scattering. Within the framework of the standard model, for energies
larger when compared to the electron mass, we calculate the cross section
expression for the scattering process. This quantity is usually calculated in
the framework of the Maxwell electrodynamics and, by phenomenological reasons,
corrected by a cut-off parameter. On the other hand, by considering the
generalized electrodynamics instead of Maxwell's, we can show that the effects
played by the Podolsky mass is actually a natural cut-off parameter for this
scattering process. Furthermore, by means of experimental data of Bhabha
scattering we will estimate its lower bound value. Nevertheless, in order to
have a mathematically well defined description of our study we shall present
our discussion in the framework of the Epstein-Glaser causal theory.Comment: 24 pages, V2 to match published versio
Analysis of Deterioration in a Plasma Focus Device
Indexación: Scopus.The Plasma Focus (PF) is a kind of dense transient plasmas in with high-pulsed voltage. To produce devices for eld application it is necessary to obtain PF equipment able to operate for a long period of time. Thus, a reliability analysis is indispensable. In this work a reliability analysis program for plasma focus devices is presented. The program considers a criticality analysis using Failure Modes and Effects Criticality Analysis (FMECA) to identify the most important failure modes of the system. Said failure modes are studied operating the Plasma Focus for many cycles, obtaining from them the characteristic curves of V(t) and İ(t). Feature Extraction (FE) techniques are applied to obtain a list of parameters that correlate to the degrading process. Furthermore, Machine Learning tools are used to learn from the obtained data, linking the changes in these parameters during its life cycle to the decay of the system in hope for future implementation of a predictive maintenance system and a reference for data analysis and prediction in PFs. The study was applied to a portable plasma focus device operated at 2 joules of stored energy. © Published under licence by IOP Publishing Ltd.The work is supported by IAEA CRP contract 20370 and by grant ACT-1115, CONICYT, Chile.https://iopscience.iop.org/article/10.1088/1742-6596/1043/1/01204
The Nuclear Yukawa Model on a Lattice
We present the results of the quantum field theory approach to nuclear Yukawa
model obtained by standard lattice techniques. We have considered the simplest
case of two identical fermions interacting via a scalar meson exchange.
Calculations have been performed using Wilson fermions in the quenched
approximation. We found the existence of a critical coupling constant above
which the model cannot be numerically solved. The range of the accessible
coupling constants is below the threshold value for producing two-body bound
states. Two-body scattering lengths have been obtained and compared to the non
relativistic results.Comment: 15 page
Analysis of nucleotide diversity of NAT2 coding region reveals homogeneity across Native American populations and high intra-population diversity.
N-acetyltransferase 2 (NAT2), an important enzyme in clinical pharmacology, metabolizes antibiotics such as isoniazid and sulfamethoxazole, and catalyzes the transformation of aromatic and heterocyclic amines from the environment and diet into carcinogenic intermediates. Polymorphisms in NAT2 account for variability in the acetylator phenotype and the pharmacokinetics of metabolized drugs. Native Americans, settled in rural areas and large cities of Latin America, are under-represented in pharmacogenetics studies; therefore, we sequenced the coding region of NAT2 in 456 chromosomes from 13 populations from the Americas, and two from Siberia, detecting nine substitutions and 11 haplotypes. Variants *4 (37%), *5B (23%) and *7B (24%) showed high frequencies. Average frequencies of fast, intermediate and slow acetylators across Native Americans were 18, 56 and 25%, respectively. NAT2 intra-population genetic diversity for Native Americans is higher than East Asians and similar to the rest of the world, and NAT2 variants are homogeneously distributed across native populations of the continent
Density functional electronic spectrum of the cluster and possible local Jahn-Teller distorsions in the La-Ba-Cu-O superconductor
We present a density functional theory (DFT) calculation in the generalized
gradient approximation to study the possibility for the existence of
Jahn-Teller (JT) or pseudo Jahn-Teller (PJT) type local distortions in the
La-Ba-Cu-O superconducting system. We performed the calculation and
correspondingly group theory classification of the electronic ground state of
the CuO elongated octahedra cluster, immersed in a background
simulating the superconductor. Part of the motivation to do this study is that
the origin of the apical deformation of the CuO cluster is not
due to a pure JT effect, having therefore a non {\it a priori} condition to
remove the degeneracy of the electronic ground state of the parent regular
octahedron. We present a comparative analysis of the symmetry classified
electron spectrum with previously reported results using unrestricted
Hartree-Fock calculations (UHF). Both the DFT and UHF calculations produced a
non degenerate electronic ground state, not having therefore the necessary
condition for a pure JT effect. However, the appearance of a degenerate E
state near to the highest occupied molecular orbital in the DFT calculation,
suggests the possibility for a PJT effect responsible for a local distortion of
the oxidized CuO cluster.Comment: 12 pages, 3 figures, submitted to International Journal of Modern
Physics B (IJMPB
The Knudsen temperature jump and the Navier-Stokes hydrodynamics of granular gases driven by thermal walls
Thermal wall is a convenient idealization of a rapidly vibrating plate used
for vibrofluidization of granular materials. The objective of this work is to
incorporate the Knudsen temperature jump at thermal wall in the Navier-Stokes
hydrodynamic modeling of dilute granular gases of monodisperse particles that
collide nearly elastically. The Knudsen temperature jump manifests itself as an
additional term, proportional to the temperature gradient, in the boundary
condition for the temperature. Up to a numerical pre-factor of order unity,
this term is known from kinetic theory of elastic gases. We determine the
previously unknown numerical pre-factor by measuring, in a series of molecular
dynamics (MD) simulations, steady-state temperature profiles of a gas of
elastically colliding hard disks, confined between two thermal walls kept at
different temperatures, and comparing the results with the predictions of a
hydrodynamic calculation employing the modified boundary condition. The
modified boundary condition is then applied, without any adjustable parameters,
to a hydrodynamic calculation of the temperature profile of a gas of inelastic
hard disks driven by a thermal wall. We find the hydrodynamic prediction to be
in very good agreement with MD simulations of the same system. The results of
this work pave the way to a more accurate hydrodynamic modeling of driven
granular gases.Comment: 7 pages, 3 figure
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