Belinfante Tensors Induced by Matter-Gravity Couplings

We show that any generally covariant coupling of matter fields to gravity gives rise to a conserved, on-shell symmetric energy-momentum tensor equivalent to the canonical energy-momentum tensor of the flat-space theory. For matter fields minimally coupled to gravity our algorithm gives the conventional Belinfante tensor. We establish that different matter-gravity couplings give metric energy-momentum tensors differing by identically conserved tensors. We prove that the metric energy-momentum tensor obtained from an arbitrary gravity theory is on-shell equivalent to the canonical energy-momentum tensor of the flat-space theory.Comment: 10 pages, LaTex; misprints corrected, references added; to appear in Physical Review

A test generation framework for quiescent real-time systems

We present an extension of Tretmans theory and algorithm for test generation for input-output transition systems to real-time systems. Our treatment is based on an operational interpretation of the notion of quiescence in the context of real-time behaviour. This gives rise to a family of implementation relations parameterized by observation durations for quiescence. We define a nondeterministic (parameterized) test generation algorithm that generates test cases that are sound with respect to the corresponding implementation relation. Also, the test generation is exhaustive in the sense that for each non-conforming implementation a test case can be generated that detects the non-conformance

Gravitomagnetism in Metric Theories: Analysis of Earth Satellites Results, and its Coupling with Spin

Employing the PPN formalism the gravitomagnetic field in different metric theories is considered in the analysis of the LAGEOS results. It will be shown that there are several models that predict exactly the same effect that general relativity comprises. In other words, these Earth satellites results can be taken as experimental evidence that the orbital angular momentum of a body does indeed generate space--time geometry, notwithstanding they do not endow general relativity with an outstanding status among metric theories. Additionally the coupling spin--gravitomagnetic field is analyzed with the introduction of the Rabi transitions that this field produces on a quantum system with spin 1/2. Afterwards, a continuous measurement of the energy of this system is introduced, and the consequences upon the corresponding probabilities of the involved gravitomagnetic field will be obtained. Finally, it will be proved that these proposals allows us, not only to confront against future experiments the usual assumption of the coupling spin--gravotimagnetism, but also to measure some PPN parameters and to obtain functional dependences among them.Comment: 10 page

Negative Energy Density States for the Dirac Field in Flat Spacetime

Negative energy densities in the Dirac field produced by state vectors that are the superposition of two single particle electron states are examined. I show that for such states the energy density of the field is not bounded from below and that the quantum inequalities derived for scalar fields are satisfied. I also show that it is not possible to produce negative energy densities in a scalar field using state vectors that are arbitrary superpositions of single particle states.Comment: 11 pages, LaTe

A Note on the Relativistic Covariance of the B−B- Cyclic Relations

It is shown that the Evans-Vigier modified electrodynamics is compatible with the Relativity Theory.Comment: ReVTeX file, 14pp., no figure

Polarization Correlations of 1S0 Proton Pairs as Tests of Bell and Wigner Inequalities

In an experiment designed to overcome the loophole of observer dependent reality and satisfying the counterfactuality condition, we measured polarization correlations of 1S0 proton pairs produced in 12C(d,2He) and 1H(d,He) reactions in one setting. The results of these measurements are used to test the Bell and Wigner inequalties against the predictions of quantum mechanics.Comment: 8 pages, 4 figure

Energy and directional signatures for plane quantized gravity waves

Solutions are constructed to the quantum constraints for planar gravity (fields dependent on z and t only) in the Ashtekar complex connection formalism. A number of operators are constructed and applied to the solutions. These include the familiar ADM energy and area operators, as well as new operators sensitive to directionality (z+ct vs. z-ct dependence). The directionality operators are quantum analogs of the classical constraints proposed for unidirectional plane waves by Bondi, Pirani, and Robinson (BPR). It is argued that the quantum BPR constraints will predict unidirectionality reliably only for solutions which are semiclassical in a certain sense. The ADM energy and area operators are likely to have imaginary eigenvalues, unless one either shifts to a real connection, or allows the connection to occur other than in a holonomy. In classical theory, the area can evolve to zero. A quantum mechanical mechanism is proposed which would prevent this collapse.Comment: 54 pages; LaTe

Extra Dirac Equations

This paper has rather a pedagogical meaning. Surprising symmetries in the $(j,0)\oplus (0,j)$ Lorentz group representation space are analyzed. The aim is to draw reader's attention to the possibility of describing the particle world on the ground of the Dirac "doubles". Several tune points of the variational principle for this kind of equations are briefly discussed.Comment: REVTeX 3.0, 14p

Currents and Superpotentials in classical gauge invariant theories I. Local results with applications to Perfect Fluids and General Relativity

E. Noether's general analysis of conservation laws has to be completed in a Lagrangian theory with local gauge invariance. Bulk charges are replaced by fluxes of superpotentials. Gauge invariant bulk charges may subsist when distinguished one-dimensional subgroups are present. As a first illustration we propose a new {\it Affine action} that reduces to General Relativity upon gauge fixing the dilatation (Weyl 1918 like) part of the connection and elimination of auxiliary fields. It allows a comparison of most gravity superpotentials and we discuss their selection by the choice of boundary conditions. A second and independent application is a geometrical reinterpretation of the convection of vorticity in barotropic nonviscous fluids. We identify the one-dimensional subgroups responsible for the bulk charges and thus propose an impulsive forcing for creating or destroying selectively helicity. This is an example of a new and general Forcing Rule.Comment: 64 pages, LaTeX. Version 2 has two more references and one misprint corrected. Accepted in Classical and Quantum Gravit

Torsion Gravity: a Reappraisal

The role played by torsion in gravitation is critically reviewed. After a description of the problems and controversies involving the physics of torsion, a comprehensive presentation of the teleparallel equivalent of general relativity is made. According to this theory, curvature and torsion are alternative ways of describing the gravitational field, and consequently related to the same degrees of freedom of gravity. However, more general gravity theories, like for example Einstein-Cartan and gauge theories for the Poincare and the affine groups, consider curvature and torsion as representing independent degrees of freedom. By using an active version of the strong equivalence principle, a possible solution to this conceptual question is reviewed. This solution favors ultimately the teleparallel point of view, and consequently the completeness of general relativity. A discussion of the consequences for gravitation is presented.Comment: RevTeX, 34 pages. Review article to be published by Int. J. Mod. Phys.