International Journal of Modern Physics D

In continuing our series on metric–affine gravity (see Gronwald, Int. J. Mod. Phys.D6, 263 (1997) for Part I), we review the exact solutions of this theory.

Vector potentials and their associated fields are embodied in the left and right spin connections and their spin curvatures. These measure the path-dependence of the transport of spin frames, or the "vorticity of the spinfluid," produced by local sources. Electroweak interactions emerge from PT-antisymmetric u(1) × su(2) phase perturbations of the spin frames which do not show up in the spacetime tetrad. Gravitation emerges from PT-symmetric spin perturbations, whose path dependence shows up as spacetime curvature. We also predict a new "nonsymmetric" component of electrogravitation on particles with nontrivial electroweak form factors.

The Hamiltonian constraint formalism is used to obtain the first explicit complete analysis of nontrivial viable dynamic modes for the Poincaré gauge theory of gravity. Two modes with propagating spin-zero torsion are analyzed. The explicit form of the Hamiltonian is presented. All constraints are obtained and classified. The Lagrange multipliers are derived. It is shown that a massive spin-0^- mode has normal dynamical propagation but the associated massless 0^- is pure gauge. The spin-0⁺ mode investigated here is also viable in general. Both modes exhibit a simple type of "constraint bifurcation" for certain special field/parameter values.

We study the possible existence of charged black holes in the Bergmann–Wagoner class of scalar-tensor theories (STT) of gravity in four dimensions. The existence of black holes is shown for anomalous versions of these theories, with a negative kinetic term in the Lagrangian. The Hawking temperature T_H of these holes is zero, while the horizon area is (in most cases) infinite. As a special case, the Brans–Dicke theory is studied in more detail, and two kinds of infinite-area black holes are revealed, with finite and infinite proper time needed for an infalling particle to reach the horizon; among them, analyticity properties select a discrete subfamily of solutions, parametrized by two integers, which admit an extension beyond the horizon. The causal structure and stability of these solutions with respect to small radial perturbations is discussed. As a by-product, the stability properties of all spherically symmetric electrovacuum STT solutions are outlined.

Identification of gravitationally lensed Gamma Ray Bursts (GRBs) in the BATSE 4B catalog can be used to constrain the average redshift <z> of the GRBs. In this paper we investigate the effect of evolving lenses on the <z> of GRBs in different cosmological models of the universe. The cosmological parameters Ω and Λ have an effect on the <z> of GRBs. The other factor which can change the <z> is the evolution of galaxies. We consider three evolutionary model of galaxies. In particular, we find that the upper limit on <z> of GRBs is higher in evolving model of galaxies as compared to non-evolving models of galaxies.

The technique known as group averaging provides powerful machinery for the study of constrained systems. However, it is likely to be well-defined only in a limited set of cases. Here, we investigate the possibility of using a "renormalized" group averaging in certain models. The results of our study may indicate a general connection between superselection sectors and the rate of divergence of the group averaging integral.

Polarizations of electromagnetic waves from distant galaxies are known to be correlated with the source orientations. These quantities have been used to search for signals of cosmological birefringence. We review and classify transformation properties of the polarization and source orientation observables. The classifications give a firm foundation to certain practices which have sprung up informally in the literature. Transformations under parity play a central role, showing that parity violation in emission or in the subsequent propagation is an observable phenomenon. We also discuss statistical measures, correlations and distributions which transform properly and which can be used for systematic data analysis.

The spherically symmetric thin shells of the barotropic fluids with the linear equation of state are considered within the frameworks of general relativity. We study several aspects of the shells as completely relativistic models of stars, first of all the neutron stars and white dwarfs, and circumstellar shells. The exact equations of motion of the shells are obtained. Also we calculate the parameters of the equilibrium configurations, including the radii of static shells. Finally, we study the stability of the equilibrium shells against radial perturbations.