362 research outputs found
A locally anisotropic geometrical model of space-time based on CMBR
We study a locally anisotropic model of General Relativity in the framework
of a more general geometrical structure than the Riemannian one. In this model
the observable anisotropy of the CMBR (WMAP) is represented by a tensor of
anisotropy and it is included in the metric structure of space-time. As well,
some interesting special cases of spaces are considered.Comment: 5 pages, 0 figures, 7th International Astronomy Conference of the
Hellenic Astronomical Society, curvature and connection sections decreased,
minor explanation added, fixed some typo
Modified Einstein and Finsler Like Theories on Tangent Lorentz Bundles
We study modifications of general relativity, GR, with nonlinear dispersion
relations which can be geometrized on tangent Lorentz bundles. Such modified
gravity theories, MGTs, can be modeled by gravitational Lagrange density
functionals with generalized/ modified scalar
curvature , trace of matter field tensors and modified
Finsler like generating function . In particular, there are defined
extensions of GR with extra dimensional "velocity/ momentum" coordinates. For
four dimensional models, we prove that it is possible to decouple and integrate
in very general forms the gravitational fields for
-modified gravity using nonholonomic 2+2 splitting
and nonholonomic Finsler like variables . We study the modified motion and
Newtonian limits of massive test particles on nonlinear geodesics approximated
with effective extra forces orthogonal to the four--velocity. We compute the
constraints on the magnitude of extra-accelerations and analyze perihelion
effects and possible cosmological implications of such theories. We also derive
the extended Raychaudhuri equation in the framework of a tangent Lorentz
bundle. Finally, we speculate on effective modelling of modified theories by
generic off-diagonal configurations in Einstein and/or MGTs and Finsler
gravity. We provide some examples for modified stationary (black) ellipsoid
configurations and locally anisotropic solitonic backgrounds.Comment: latex2e, 20 pages; version accepted to IJMPD; changed title and
modifications following requests of refere
The Vicious Cycle of the Foreign Military Debt
This paper aims at estimating first the effects of defense spending on the main determinants of growth, and second the extent to and the channels through which the military debt of Greece influences the overall debt burden of the country, and consequently the critical determinants of economic growth and development. Increased imports of sophisticated weapons and military equipment can be financed at the cost of investment (guns v. ploughshares), or/and at the cost of human capital formation (guns v. butter and chalk), or at the cost of increasing the foreign debt of the country. It is this last case which is investigated in this paper. Our empirical results indicate that whatever the necessity and the benefits of the security aspect of defense, its economic costs are quite substantial. The military as a claimant of resources has a negative and non trivial effect on physical capital accumulation, and human capital formation. Moreover, financing increased military imports through borrowing from abroad has a negative and significant effect on the determinants of growth and development.Key Words: Defense Burden, Foreign Military Debt, Growth Rate, Investment, Education.
Friedmann Robertson-Walker model in generalised metric space-time with weak anisotropy
A generalized model of space-time is given, taking into consideration the
anisotropic structure of fields which are depended on the position and the
direction (velocity).In this framework a generalized FRW-metric the
Raychaudhouri and Friedmann equations are studied.A long range vector field of
cosmological origin is considered in relation to the physical geometry of
space-time in which Cartan connection has a fundamental role.The generalised
Friedmann equations are produced including anisotropic terms.The variation of
anisotropy is expressed in terms of the Cartan torsion tensor of the
Finslerian space-time.A possible estimation of the anisotropic parameter
can be achieved with the aid of the de-Sitter model of the empty flat universe
with weak anisotropy. Finally a physical generalisation for the model of
inflation is also studied.Comment: 21 pages- to appear in GR
Weak Gravitational Field in Finsler-Randers Space and Raychaudhuri Equation
The linearized form of the metric of a Finsler - Randers space is studied in
relation to the equations of motion, the deviation of geodesics and the
generalized Raychaudhuri equation are given for a weak gravitational field.
This equation is also derived in the framework of a tangent bundle. By using
Cartan or Berwald-like connections we get some types "gravito -
electromagnetic" curvature. In addition we investigate the conditions under
which a definite Lagrangian in a Randers space leads to Einstein field
equations under the presence of electromagnetic field. Finally, some
applications of the weak field in a generalized Finsler spacetime for
gravitational waves are given.Comment: 22 pages, matches version published in GER
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