4,311 research outputs found
Schwinger's Principle and Gauge Fixing in the Free Electromagnetic Field
A manifestly covariant treatment of the free quantum eletromagnetic field, in
a linear covariant gauge, is implemented employing the Schwinger's Variational
Principle and the B-field formalism. It is also discussed the abelian Proca's
model as an example of a system without constraints.Comment: 8 pages. Format PTPtex. No figur
Pimenta longa nova alternativa econĂ´mica para o pequeno agricultor.
Nos últimos anos, tem-se buscado na Amazônia novas alternativas para a exploração agroindustrial dos recursos vegetais de valor comercial. Neste sentido, a espécie Piper hispidinervium, vulgarmente conhecida como pimenta longa, encontrada em condições silvestres somente no Estado do Acre, vem despertando grande interesse de empresas nacionais e internacionais, processadoras de óleos essenciais. Desde 1992, a Embrapa Acre vem pesquisando a pimenta longa com o objetivo de transformá-la em uma alternativa de atividade produtiva para a agricultura familiar na Amazônia, com um sistema de cultivo que agregue valor através do processamento primário no campo.bitstream/item/135621/1/3676.pd
First Order Actions: a New View
We analyse systems described by first order actions using the Hamilton-Jacobi
(HJ) formalism for singular systems. In this study we verify that generalized
brackets appear in a natural way in HJ approach, showing us the existence of a
symplectic structure in the phase spaces of this formalism
Bopp-Podolsky black holes and the no-hair theorem
Bopp-Podolsky electrodynamics is generalized to curved space-times. The
equations of motion are written for the case of static spherically symmetric
black holes and their exterior solutions are analyzed using Bekenstein's
method. It is shown the solutions split-up into two parts, namely a
non-homogeneous (asymptotically massless) regime and a homogeneous
(asymptotically massive) sector which is null outside the event horizon. In
addition, in the simplest approach to Bopp-Podolsky black holes, the
non-homogeneous solutions are found to be Maxwell's solutions leading to a
Reissner-Nordstr\"om black hole. It is also demonstrated that the only exterior
solution consistent with the weak and null energy conditions is the Maxwell's
one. Thus, in light of energy conditions, it is concluded that only Maxwell
modes propagate outside the horizon and, therefore, the no-hair theorem is
satisfied in the case of Bopp-Podolsky fields in spherically symmetric
space-times.Comment: 9 pages, updated to match published versio
On Equivalence of Duffin-Kemmer-Petiau and Klein-Gordon Equations
A strict proof of equivalence between Duffin-Kemmer-Petiau (DKP) and
Klein-Gordon (KG) theories is presented for physical S-matrix elements in the
case of charged scalar particles interacting in minimal way with an external or
quantized electromagnetic field. First, Hamiltonian canonical approach to DKP
theory is developed in both component and matrix form. The theory is then
quantized through the construction of the generating functional for Green
functions (GF) and the physical matrix elements of S-matrix are proved to be
relativistic invariants. The equivalence between both theories is then proved
using the connection between GF and the elements of S-matrix, including the
case of only many photons states, and for more general conditions - so called
reduction formulas of Lehmann, Symanzik, Zimmermann.Comment: 23 pages, no figures, requires macro tcilate
Podolsky Electromagnetism at Finite Temperature: Implications on Stefan-Boltzmann Law
In this work we study Podolsky electromagnetism in thermodynamic equilibrium.
We show that a Podolsky mass-dependent modification to the Stefan-Boltzmann law
is induced and we use experimental data to limit the possible values for this
free parameter.Comment: 13 pages, submitted to Physical Review
Hamilton-Jacobi formalism for Linearized Gravity
In this work we study the theory of linearized gravity via the
Hamilton-Jacobi formalism. We make a brief review of this theory and its
Lagrangian description, as well as a review of the Hamilton-Jacobi approach for
singular systems. Then we apply this formalism to analyze the constraint
structure of the linearized gravity in instant and front-form dynamics.Comment: To be published in Classical and Quantum Gravit
Cosmic String in Scalar-Tensor Gravity
The gravitational properties of a local cosmic string in the framework of
scalar-tensor gravity are examined. We find the metric in the weak-field
approximation and we show that, contrary to the General Relativity case, the
cosmic string in scalar-tensor gravitation exerces a force on non-relativistic,
neutral test particle. This force is proportional to the derivative of the
conformal factor and it is always attractive. Moreover, this
force could have played an important role at the Early Universe, although
nowadays it can be neglegible. It is also shown that the angular separation
remains unaltered for scalar-tensor cosmic strings.Comment: 15 pages, LATEX, no figure
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