Phase space classification of Kaluza-Klein cosmologies

This work provides an analysis of all possible solutions to the Einstein equations for a class of spatially homogeneous vacuum cosmological models with (Robertson-Walker) × (n-sphere) and (Robertson-Walker) × (n-sphere)×(torus) symmetries. Using qualitative theory of dynamical systems we show that classical evolution of the models can lead to contraction of the extra dimensions.     

Kaluza-Klein theory from the viewpoint of gauge theory of gravity

We consider Kaluza-Klein theory based on the fiber bundle. We obtain the modified Kaluza-Klein metric as an invariant line element of a bundle. Its reduced action includes a higher derivative action in gravitation as well as a term linear inR.     

Particle mass spectrum and strong gravity

Regarding the strong gravity as a source of hadronic interactions, the masses of several stable particles and resonances, including the newly found -resonances, are derived from a simple, semiclassical dimensional analysis. Particles are constructed successively from each others in a bootstrap-like manner. A particle property dusk is introduced, which in the cases of stable baryons is identified with strangeness. The theoretical background of the construction procedure is discussed.     

Kaluza-Klein theory and Dirac equation in higher dimensional Riemann-Cartan space

The higher dimensional Kaluza-Klein theory in Riemann-Cartan space is discussed. To clarify its implications, we investigate the simplest five-dimensional case of the theory in detail. The Einstein-like, Maxwell, and Dirac equations in four-dimensional space-time are obtained by reducing the corresponding five-dimensional field equations. The effect of spin-spin interaction induced by torsion is revealed by analyzing the Dirac equation in this case.     

Is strong gravity an aspect of strong interaction?

A more general treatment is given of the field equations of the model for strong gravity proposed by the author in 1976. It seems possible to treat strong gravity and strong interaction by the same formalism, suggesting that strong gravity is just an aspect of strong interaction. The essential idea in these models is that a hadron is a de Sitter microsphere of radius of about 1 fm and the requisite gauge field is a fourth-rank tensor in the de Sitter space of the hadron. A three-dimensional formulation of the model is presented and further possibilities outlined.     

Hawking radiation and strong gravity black holes

We show that the strong gravity theory of Salam et al. places severe restrictions on black hole evaporation. Two major implications are that: mini black holes (down to masses ～ 10^?16 kg) would be stable in the present epoch; and that some suggested mini black hole mechanisms to explain certain astrophysical phenomena would not work. The first result implies that f-gravity appears to make black holes much safer by removing the possibility of extremely violent black hole explosions suggested by Hawking.     

Gauge theories of weak and strong gravity

A review of some recent papers on gauge theories of weak and strong gravity is presented. For weak gravity, SL(2, C) gauge theory along with tetrad formulation is described which yields massless spin-2 gauge fields (quanta gravitons). Next a unified SL(2n,C) model is discussed along with Higgs fields. Its internal symmetry is SU(n). The free field solutions after symmetry breaking yield massless spin-1 (photons) and spin-2 (gravitons) gauge fields and also massive spin-1 and spin-2 bosons. The massive spin-2 gauge fields are responsible for short range superstrong gravity. Higgs-fermion interaction can lead to baryon and lepton number non-conservation. The relationship of strong gravity with other forces is also briefly considered.     

An alternative method of reduction to four-dimensional space in Kaluza-Klein theory

A method for constructing gauge field theories with spontaneous symmetry breaking is suggested, and applied to the theory of Kaluza-Klein type. It is shown that the method naturally leads to the appearance of fields and a lagrangian, providing spontaneous breaking of the gauge invariance. The method also allows one to interpret in a novel way the nature of the extra dimensions of space.     

Testing Newtonian gravity in space

We propose to measure the universal constant of gravity G in space by means of a small scale planetary system in geosynchronous orbit; test particle satellites of different nuclear composition and with different distances from the central mass would allow one to check possible variations with material and distance. With current technology G can be measured with a relative accuracy of 10⁻⁵ or better depending on the capability of controlling some perturbations which act at the level of 10⁻⁶ (i.e. ≈ 10⁻¹¹ cm s⁻²; however, particular dynamical configurations mutuated from celestial mechanics should allow detection of differential effects with composition and distance (if any) to at least 10⁻⁶. Distance variations will be detected only if acting on a distance scale of 10 m.     

Accretion in strong field gravity with eXTP

In this paper we describe the potential of the enhanced X-ray Timing and Polarimetry(eXTP) mission for studies related to accretion flows in the strong field gravity regime around both stellar-mass and supermassive black-holes. eXTP has the unique capability of using advanced "spectral-timing-polarimetry" techniques to analyze the rapid variations with three orthogonal diagnostics of the flow and its geometry, yielding unprecedented insight into the inner accreting regions, the effects of strong field gravity on the material within them and the powerful outflows which are driven by the accretion process.     

The propagation kernel for strong coupling gravity

The strong coupling limit of Einstein gravity in d+1$d+1$ dimensions gives rise to a quantum theory where after factorization of the conformal factor mode SL(d,R)/SO(d)$\mathrm{SL}(d,\mathbb{R})/\mathrm{SO}(d)$ nonlinear sigma-models are spatially coupled by the diffeomorphism constraint. A functional integral representation for the theory?s propagation kernel is derived in completions of the proper time gauge which manifestly invokes only physical gauge invariant degrees of freedom. In the weak field limit it reduces to the propagation kernel of massless and transversal-traceless free fields. For strong fields a covariant normal coordinate expansion is developed which covers the configuration manifold globally. Its leading order approximant resembles a semiclassical propagation kernel but without the need to solve the classical constraints. The results have implications for the ground state structure of quantum gravity.     

Tests of relativistic gravity in space

We review the foundations of Einstein’s general theory of relativity, discuss recent progress in the tests of relativistic gravity, and present motivations for new generation of high-accuracy gravitational experiments. We discuss the advances in our understanding of fundamental physics anticipated in the near future and evaluate discovery potential of the recently proposed gravitational experiments.     

A Hamiltonian approach to the strong gravity limit

The Hamiltonian for general relativity is examined in the strong gravity (SG) limitG . In this limit a perfect fluid moves irrotationally along geodesics. An appropriate SG limit for the scalar field is developed such that the energy density has a limit. The solutions in this limit, which were previously known, are shown to come out simply and directly. A classification of the trace-free part of the momentum is given in the Appendix.     

Development of an atom-interferometer gravity gradiometer for gravity measurement from space

Recent progress in cold atom interferometry has lead to a new method of sensitive inertial sensing. Significant performance enhancement of cold atom interferometer-based sensors is anticipated when operated in the microgravity environment in space. Based on cold atom interferometer techniques, we are developing a quantum gravity gradiometer for satellite-based global gravity field mapping. As a first step, we have built a laboratory-based gradiometer employing component technologies suitable for a future flight instrument. This paper describes the implementation of the laboratory instrument and its initial results. PACS 03.75.Dg; 39.20.+q; 32.80.Pj; 04.80.-y     

Kaluza-Klein cosmologies

In generalized Kaluza-Klein theories the scale set by the size of the extra space-dimensions is close to the grand unification scale of supersymmetric GUT's with minimal number of Higgs supermultiplets. In view of this observation, we explore cosmologies in which the “effective” dimensionality of space depends on time. Such cosmologies are studied in higher-dimensional Jordan-Brans-Dicke theories, and in 10- and 11-dimensional supergravity. The preferential expansion of three space-like dimensions is noted in the latter theory. Cosmology in pure higher-dimensional Einstein theory, where there is no preferential expansion of three space-like dimensions, has been discussed by Chodos and Detweiler.     

SuperW n gravity on compactified moduli space

We study the divergent behavior ofW gravity theories. As a tool, we use the Grothendieck-Riemann-Roch theorem on the compactified moduli space. We show thatW _n gravity has severe divergences caused by negative masses. However, for superextension ofW _n gravity the divergences by negative masses are miraculously cured by the counterpart contribution of superpartners.