Remarks on Duffin-Kemmer-Petiau theory and gauge invariance

Two problems relative to the electromagnetic coupling of Duffin-Kemmer-Petiau (DKP) theory are discussed: the presence of an anomalous term in the Hamiltonian form of the theory and the apparent difference between the Interaction terms in DKP and Klein-Gordon (KG) Lagrangians. For this, we first discuss the behavior of DKP field and its physical components under gauge transformations. From this analysis, we can show that these problems simply do not exist if one correctly analyses the physical components of DKP field.Comment: 19 pages, no figure

2D Ising-Heisenberg model with quartic interaction

We propose a two-dimensional spin-1/2 Ising-Heisenberg model with quartic interaction. In this sense the phase diagram for the model at zero temperature is studied, obtaining four different configurations for the unitary cell. It should be observed that using the rotation and spin inversion symmetry we have only three spin configurations that are relevant. In addition, the model under consideration will be straightforwardly mapped to the exactly solved eight-vertex model and the conditions for obtaining an exact solution will be investigated. The analysis was performed for two different conditions, namely, where the free fermion condition (FFC) and \ the symmetrical eight-vertex condition (SEVC) are satisfied.Предлагается двумерная модель Ising-Heisenberg со спином 1/2 и с четверным взаимодействием. Анализируется фазовая диаграмма для модели при нулевой температуре, и получены четыре различных конфигурации для унитарной ячейки. Отмечается, что при учете симметрии вращения и инверсии спина имеются только три конфигурации спина, имеющие смысл. Кроме того, рассматриваемая модель прямо отображается на точно решаемую модель с восемью вершинами, и условия получения точного решения исследованы. Анализ был сделан для двух различных условий, а именно, для случая свободных фермионов (FFC) и случая восьми симметричных вершин (SEVC).Пропонується двовимірна модель Іsіng-Heіsenberg зі спіном 1/2 і із четверною взаємодією. Аналізується фазова діаграма для моделі при нульовій температурі, й отримані чотири різних конфігурації для унітарної комірки. Відзначається, що при обліку симетрії обертання й інверсії спіна є тільки три конфігурації спіна, які мають сенс. Крім того, розглянута модель прямо відображається на точно розв'язувану модель із вісьма вершинами. Умови одержання точного рішення досліджені. Аналіз був зроблений для двох різних умов, а саме, для случаю вільних ферміонів (FFC) і случаю восьми симетричних вершин (SEVC

The causal approach to scalar QED via Duffin-Kemmer-Petiau equation

In this work we consider the scalar QED via Duffin-Kemmer-Petiau equation in the framework of Bogoliubov-Epstein-Glaser causal perturbation theory. We calculate the lowest order distributions for Compton scattering, vacuum polarization, the self energy and, by using a Ward identity, the vertex correction. The causal method provides a mathematically well defined and noneffective theory which determines, in a natural way, the propagator and the vertex of the usual effective theory

Electromagnetic field at Finite Temperature: A first order approach

In this work we study the electromagnetic field at Finite Temperature via the massless DKP formalism. The constraint analysis is performed and the partition function for the theory is constructed and computed. When it is specialized to the spin 1 sector we obtain the well-known result for the thermodynamic equilibrium of the electromagnetic field.Comment: 6 pages, Latex2e, title changed and minimal modification

Generalized Transformation for Decorated Spin Models

The paper discusses the transformation of decorated Ising models into an effective \textit{undecorated} spin models, using the most general Hamiltonian for interacting Ising models including a long range and high order interactions. The inverse of a Vandermonde matrix with equidistant nodes $[-s,s]$ is used to obtain an analytical expression of the transformation. This kind of transformation is very useful to obtain the partition function of decorated systems. The method presented by Fisher is also extended, in order to obtain the correlation functions of the decorated Ising models transforming into an effective undecorated Ising models. We apply this transformation to a particular mixed spin-(1/2,1) and (1/2,2) square lattice with only nearest site interaction. This model could be transformed into an effective uniform spin-$S$ square lattice with nearest and next-nearest interaction, furthermore the effective Hamiltonian also include combinations of three-body and four-body interactions, particularly we considered spin 1 and 2.Comment: 16 pages, 4 figure

Bose-Einstein Condensation and Free DKP field

The thermodynamical partition function of the Duffin-Kemmer-Petiau theory is evaluated using the imaginary-time formalism of quantum field theory at finite temperature and path integral methods. The DKP partition function displays two features: (i) full equivalence with the partition function for charged scalar particles and charged massive spin 1 particles; and (ii) the zero mode sector which is essential to reproduce the well-known relativistic Bose-Einstein condensation for both theories.Comment: 12 pages, 2 eps figures. To be published in Physics Letter

Lattice distortions in a sawtooth chain with Heisenberg and Ising bonds

An exactly solvable model of the sawtooth chain with Ising and Heisenberg bonds and with coupling to lattice distortion for Heisenberg bonds is considered in the magnetic field. Using the direct transfer-matrix formalism an exact description of the thermodynamic functions is obtained. The ground state phase diagrams for all regions of parameters values containing phases corresponding to the magnetization plateaus at $M=0,1/4$ and 1/2 have been obtained. Exact formulas for bond distortions for various ground states are presented. A novel mechanism of magnetization plateau stabilization corresponding to $M=1/4$ state is reported.Comment: 16 pages, 12 figure

Study of elementary reactions with the hades dielectron spectrometer

Results obtained with the HADES dielectron spectrometer at GSI are discussed, with emphasis on dilepton production in elementary reactions.Díaz Medina, José, [email protected] ; Gil Ortiz, Alejandro, [email protected]

Study of dielectron production in C+C collisions at 1 AGeV

The emission of e+e- pairs from C+C collisions at an incident energy of 1 GeV per nucleon has been investigated. The measured production probabilities, spanning from the pi0-Dalitz to the rho/omega! invariant-mass region, display a strong excess above the cocktail of standard hadronic sources. The bombarding-energy dependence of this excess is found to scale like pion production, rather than like eta production. The data are in good agreement with results obtained in the former DLS experiment.Comment: submitted to Physics Letters