Showing papers in "Il Nuovo Cimento B in 1997"

A time-dependent "cosmological constant" phenomenology.

Abstract: A cosmological-constant term in the energy density of the universe turns out to be taken in serious consideration in today research Many experimental data on the structure of the present universe are in agreement with models in which the cosmological-constant term contribution in the density parameter V (given by the ratio of the mean mass density to the critical density of the corresponding Einstein-de Sitter model r c43H 2 O8pG) is relevant with respect to the matter term This happens in the number count of galaxies as well as in the spectrum of the Cosmic Microwave Background Radiation (CMBR) [1-3] On the one hand, there is the well-known problem concerning the theoretical and experimental limits on the values that the cosmological costant should assume, connected, respectively, with the vacuum expectation value of the energy density and the present observational limits, in the sense that they differ by 120 orders of magnitude [4, 5] On the other hand, despite these discrepancies, the presence of a cosmological-constant term is requested to avoid

Gravitation Gauge Group

Abstract: — The suggested theory involves a drastic revision of the role of local internal symmetries in the physical concept of curved geometry. Under the reflection of fields and their dynamics from Minkowski to Riemannian space a standard gauge principle of local internal symmetries has been generalized. A gravitation gauge group is proposed, which is generated by hidden local internal symmetries. In all circumstances, it seemed to be of the greatest importance for the understanding of the physical nature of gravity. The most promising aspect in our approach so far is the fact that the energy-momentum conservation laws of gravitational interacting fields are formulated quite naturally by exploiting all the advantages of auxiliary shadow fields on flat shadow space. The mechanism developed here enables one to infer Einstein’s equation of gravitation, but only with a strong difference from Einstein’s theory at the vital point of well-defined energy-momentum tensor of gravitational field and conservation laws. The gravitational interaction as well as the general distortion of the manifold G(2 .2 .3) with hidden group U loc (1 ) has been considered.

Green functions for classical euclidean maxwell theory

Abstract: Recent work on the quantization of Maxwell theory has used a non-covariant class of gauge-averaging functionals which include explicitly the effects of the extrinsic-curvature tensor of the boundary, or covariant gauges which, unlike the Lorentz case, are invariant under conformal rescalings of the background four-metric. This paper studies in detail the admissibility of such gauges at the classical level. It is proved that Euclidean Green functions of a second- or fourth-order operator exist which ensure the fulfillment of such gauges at the classical level, i.e. on a portion of flat Euclidean four-space bounded by three-dimensional surfaces. The admissibility of the axial and Coulomb gauges is also proved.

An investigation of singular lagrangians as field systems

Abstract: — The link between the treatment of singular Lagrangians as field systems and the general approach is studied. It is shown that singular Lagrangians as field systems are always in exact agreement with the general approach. Two examples and the singular Lagrangian with zero-rank Hessian matrix are studied. The equations of motion in the field systems are equivalent to the equations which contain acceleration, and the constraints are equivalent to the equations which do not contain acceleration in the general-approach treatment. PACS 11.10 – Field theory.

Black-hole creation in quantum cosmology

Abstract: — It is proven that the probability of a black hole created from the de Sitter space-time background, at the WKB level, is the exponential of one quarter of the sum of the black hole and cosmological horizon areas, or the total entropy of the universe. This is true not only for the spherically symmetric cases of the Schwarzschild or Reissner-Nordstrom black holes, but also for the rotating case of the Kerr black hole and the rotating charged case of the Newman black hole. The de Sitter metric is the most probable evolution at the Planckian era of the universe.

Liquids xenon and argon, dark matter detectors with background rejection.

Abstract: — The potential of liquids xenon and argon as dark matter targets is discussed emphasising the former. Significant discrimination of very small signals against betaOgamma backgrounds can be achieved in several ways; firstly via the collection of scintillation light alone in conjunction with a likelihood technique to fully exploit the digitised photon arrival times; secondly via the collection of both light and ionisation charge, either in a simple ionisation chamber or in the proportional scintillation mode. Published alpha and beta data are used to assess the discrimination.

Multimomentum maps on null hypersurfaces

Abstract: Summary. — This paper studies the application of multimomentum maps to the constraint analysis of general relativity on null hypersurfaces. It is shown that, unlike the case of spacelike hypersurfaces, some constraints which are second class in the Hamiltonian formalism turn out to contribute to the multimomentum map. To recover the whole set of secondary constraints found in the Hamiltonian formalism, it is necessary to combine the multimomentum map with those particular EulerLagrange equations which are not of evolutionary type. The analysis is performed on the outgoing null cone only.

Dirac equation in spatially homogeneous cosmological models (

Abstract: Dirac equation is an outstanding achievement whose consequences the physicists are very far to exhaust due to the complexity of the calculations involved The establishment of this equation was the starting point for many research problems, one of which is the study of spin-1/2 particles in the presence of gravitational fields Brill and Wheeler [1] studied the interaction of neutrinos with the gravitational field of a spherically symmetrical body They developed the mathematical formalism to study spinors in curved space-time and opened the road for many researchers The quantum mechanics of particles in curved space-times has been analysed in many articles and some important results are the creation of particles due to the expansion of space-time [2] and the Hawking radiation of a black hole [3] These developments go in the direction of a unified theory of quantum and gravitational fields In this context, the knowledge of exact solutions of the Dirac equation in curved space-time is demanded The most studied cosmological backgrounds are the Robertson-Walker ones, due to their simplicity and their accuracy in the fitting of the astronomical data of the recent eras of cosmological evolution We can refer to Parker [4], Isham and Nelson [5], Ford [6], Andretsch and Schafer [7], Kovalyov and Legare [8], Barut and Duru [9] and Villalba and Percoco [10] Recently, a great effort has been done to solve the massless Dirac equation by applying the method of separation of variables to a general diagonal metric [11, 12]

Null detection of the excess rotation measure in the Virgo supercluster of galaxies (

Abstract: — The intracluster magnetic field of the Virgo supercluster of galaxies is investigated using an available data set of reliable Faraday rotation measures of extragalactic radio sources Unlike the result reported by Vallee (Astron J, 99 (1990) 459), no excess RM were detected in the Virgo Taking relevant physical values of the Virgo into account, this null detection, however, cannot rule out the possibility that the strength of Virgo’s intracluster magnetic field be as strong as comparable to that of Coma (1 mG) More RM data are substantiated for better understanding of the nature of Virgo’s magnetic field

Universal dark matter and expansion age from an electromagnetical cosmology

Abstract: Summary. — From our simple electromagnetical cosmology which is consistent with recent observational results, it is suggested that the dark matter mainly consists of roughly equal proportions of nucleons and neutrinos, and that for long-distance scales an apparent paradoxical small expansion age applies as observed. PACS 98.80 ‐ Cosmology. PACS 04.50 ‐ Gravity in more than four dimensions, Kaluza-Klein theory, unified field theories; alternative theories of gravity.