Another gravitational instability of flat space-time

Witten's demonstration of the instability of the five dimensional Kaluza-Klein ground state can be reduced to four, physical dimensions. One can then conclude that flat space-time at zero temperature with one of the spatial directions wrapped up is unstable. The decay rate is of order exp?L²/16πL²_p where L is the spatial periodicity and L_p is the Planck length. The post tunnelling evolution of the space-time is also discussed.     

Metric-torsion gravitational theories

It is shown that under certain assumptions the Einstein-Cartan field equations are not unique but may reasonably be modified to a degree. These modified Einstein-Cartan equations are proven to be unique under quite general conditions and are likely the most general equations in any metric-torsion gravitational theory whose field equations are derivable from a variational principle and such that their geometric part is independent of constants other than the speed of light and the gravitational constant.     

Gravitation in flat space-time

A previously studied Lorentz-covariant theory of gravitation is given in generally covariant form, i.e., the theory holds for arbitrary reference frames. Flat space-time is a natural condition for the conservation of energy and momentum. The energy-momentum tensor of matter and gravitation is the source of the gravitational field.     

Quantum space-time and gravitational consequences

Relativistic particle dynamics and basic physical quantities for the general theory of gravity are reconstructed from a quantum space-time point of view. An additional force caused by quantum space-time appears in the equation of particle motion, giving rise to a reformulation of the equivalence principle up to values ofO(L ²), whereL is the fundamental length. It turns out that quantum space-time leads to quantization of gravity, i.e., the metric tensorg _v () becomes operator-valued and is not commutative at different pointsx andy in usual space-time on a large scale, and its commutator depending on the vielbein field (gaugelike graviton field) is proportional toL ² multiplied by a translation-invariant wave function propagated between pointsx andy . In the given scheme, there appears to be an antigravitational effect in the motion of a particle in the gravitational force. This effect depends on the value of particle mass; when a particle is heavy its free-fall time is long compared to that for a light-weight particle. The problem of the change of time scale and the anisotropy of inertia are discussed. From experimental data from testing of the latter effect it follows thatL10^–22cm.     

Conservation theorems in curved space-time

Basic theorems on conservation laws in general space-time are given. The proofs are based on Gauss' theorem which works with ordinary divergence and not with covariant divergence. Consequences for the gravitational theory are exhibited.     

Towers of gravitational theories

In this essay we introduce a theoretical framework designed to describe black hole dynamics. The difficulties in understanding such dynamics stems from the proliferation of scales involved when one attempts to simultaneously describe all of the relevant dynamical degrees of freedom. These range from the modes that describe the black hole horizon, which are responsible for dissipative effects, to the long wavelength gravitational radiation that drains mechanical energy from macroscopic black hole bound states. We approach the problem from a Wilsonian point of view, by building a tower of theories of gravity each of which is valid at different scales. The methodology leads to multiple new results in diverse topics including phase transitions of Kaluza-Klein black holes and the interactions of spinning black hole in non-relativistic orbits. Moreover, our methods tie together speculative ideas regarding dualities for black hole horizons to real physical measurements in gravitational wave detectors.     

Gauge theories on open spin space-time manifolds

We show that the presence of nontrivial gauge interactions can correspond to passing from some integrable to nonintegrable distributions transverse to the fibers of an appropriate principalG-bundle overM. In this way we obtain a whole family of new Lagrangians, one for each nontrivial element of Hom( ₁ M, Q). For the trivial map Hom( ₁ M, Q) we obtain the known Yang-Mills equations. In this way, for example, the sectors for electromagnetic interactions can correspond to the family of inequivalent spinor structures overM.     

Dissipative fluid in conformally flat space-time

We consider a conformally flat, inhomogeneous solution of the Einstein equations for a dissipative fluid. The production of entropy is found to depend on some arbitrary functions of time. By some subsidiary conditions, such a model is shown to evolve into a homogeneous Friedmann-type universe.     

The Lewis metric and flat space-time

It is shown that the stationary solution of the Einstein equationsin vacuo, with the cylindrical symmetry obtained by Lewis, does not contain a space-time that is globally Minkowskian. It is shown that the inclusion of a certain constant of integration excludes this flat space-time metric.     

Ghost neutrino fields in flat space-time

The Weyl neutrino equation is integrated in flat space-time assuming that the energy-momentum tensor of the neutrino field vanishes. It is shown that the flux vector of the neutrino field is tangent to a twist-free and shear-free congruence of null geodesics, which is a special Robinson congruence and constitutes a geometrical representation of a null twistor. It is also shown that, conversely, given such a congruence, a ghost neutrino field can be constructed.     

Analysis of absolute space-time Lorentz theories

Two particular forms of absolute space-time theories are examined. There follows a derivation of their predictions for measurements that are within present-day detection limits.     

Stochastic quantization of linearized gravitational theories

A generalization of stochastic quantization is proposed in order to deal with higher order derivative gravitational theories. In the linear approximation the correct graviton propagator is recovered, while for the higher order derivative case, the resulting propagator has pole structure, which exhibits the impossibility of Wick rotation. The unitarity of the models is briefly discussed.     

Long-range scalar field in conformally flat space-time

Consequences of a massless scalar field in conformally flat space-time are studied. Then a wide class of solutions of the scalar field is obtained.     

Algebraic classification of gravitational fields in five-dimensional space-time

We consider the algebraic classification of five-dimensional empty space-time (Kalutsa type) with one time-like direction as a generalization of the Petrov algebraic classification of gravitational fields in four-dimensional space-time. We study two special cases: a) zero electromagnetic field and zero scalar field; b) nonzero electromagnetic field and zero scalar field. For the (1+4) separated Kalutsa five-metric we introduce the pentad metric of a tangent five-space, which is mapped together with the curvature tensor into a ten-dimensional real flat vector space. The classification is constructed in local geodesic coordinates for the above two cases. In both cases the characteristic equation can be reduced to a sixth-order equation that can be simplified when certain requirements are satisfied. Our results demonstrate the nontrivial nature of algebraic classification in five dimensions.This work was performed within the framework of the State Science and Technology Astronomy program.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 73–78, March, 1995.