International Journal of Modern Physics D

Gauge field theories may quite generally be defined as describing the coupling of a matter-field to an interaction-field, and they are suitably represented in the mathematical framework of fiber bundles. Their underlying principle is the so-called gauge principle, which is based on the idea of deriving the coupling structure of the fields by satisfying a postulate of local gauge covariance. The gauge principle is generally considered to be sufficient to define the full structure of gauge-field theories. This paper contains a critique of this usual point of view: firstly, by emphazising an intrinsic gauge theoretic conventionalism which crucially restricts the conceptual role of the gauge principle and, secondly, by introducing a new generalized equivalence principle — the identity of inertial and field charge (as generalizations of inertial and gravitational mass) — in order to give a conceptual justification for combining the equations of motion of the matter-fields and the field equations of the interaction-fields.

Geodesics are studied in the spacetime described by the γ metric. Their behaviour is compared with the spherically symmetric situation, bringing out the sensitivity of the trajectories to deviations from spherical symmetry.

We show that the evolution of the quintessence energy density Ω_Q is model independent in an accelerating universe. The accelerating behavior has lasted at most 0.5 e-folds of expansion assuming a present day value of Ω_Q=2/3. The generic evolution differs from the exact solution by a percentage given by r=2γ_Q, with γ_Q=(ρ_Q+p_Q)/ρ_Q. For a small γ_Q the evolution remains a good approximation for a long period. Nucleosynthesis bounds on Ω_Q suggest that the model independent solution is valid for at least 12 e-folds of expansion which includes then the scale of radiation and matter equality. We can, therefore, establish model independent conditions on the cosmological parameters at some factor scale a_i≪a₀. Finally, we discuss the relevance of this result to the cosmological coincidence problem.

Linearly polarized cylindrical waves in four-dimensional vacuum gravity are mathematically equivalent to rotationally symmetric gravity coupled to a Maxwell (or Klein–Gordon) field in three dimensions. The quantization of this latter system was performed by Ashtekar and Pierri in a recent work. Employing that quantization, we obtain here a complete quantum theory which describes the four-dimensional geometry of the Einstein–Rosen waves. In particular, we construct regularized operators to represent the metric. It is shown that the results achieved by Ashtekar about the existence of important quantum gravity effects in the Einstein–Maxwell system at large distances from the symmetry axis continue to be valid from a four-dimensional point of view. The only significant difference is that, in order to admit an approximate classical description in the asymptotic region, states that are coherent in the Maxwell field need not contain a large number of photons anymore. We also analyze the metric fluctuations on the symmetry axis and argue that they are generally relevant for all of the coherent states.

If the universe has a nontrivial shape (topology) the sky may show multiple correlated images of cosmic objects. These correlations can be couched in terms of distance correlations. We propose a statistical quantity which can be used to reveal the topological signature of any Robertson–Walker (RW) spacetime with nontrivial topology. We also show through computer-aided simulations how one can extract the topological signatures of flat, elliptic, and hyperbolic RW universes with nontrivial topology.

We discuss the two-dimensional dilaton gravity with a scalar field as the source matter. The coupling between the gravity and the scalar, massless, field is presented in an unusual form. We work out two examples of these couplings, and solutions with black-hole behaviour are discussed and compared with those found in the literature.

Measurements of the distances to SNe Ia have produced strong evidence that the expansion of the Universe is really accelarating, implying the existence of a nearly uniform component of dark energy with the simplest explanation as a cosmological constant. In this paper a small changing cosmological term is proposed, which is a function of a slow-rolling scalar field, by which the de Sitter primordial black holes' properties, for both charged and uncharged cases, are carefully examined and the relationship between the black hole formation and the energy transfer of the inflaton is eluciated. The criterion for primordial black hole formation is given.

In gravitational thermodynamics, the origin of a black hole's entropy is the topology of its instanton or constrained instanton. We prove that the entropy of an arbitrary nonrotating black hole is one quarter the sum of the products of the Euler characteristics of its horizons with their respective areas. The Gauss–Bonnet-like form of the action is not only crucial for the evaluation, but also for the existence of the entropy. This result covers all previous results on the entropy of a nonrotating black hole with a regular instanton. The argument can be readily extended into the lower or higher dimensional model. The problem of quantum creation of such a black hole is completely resolved.

Astrophysical jets are observed to come out with relativistic speed and are extremely collimated. Here we study the effect of momentum deposition by hot photons from the torus like, puffed up inner region of the accretion disc on radial outflows. We calculate the radiative momentum deposition force on the outflows and find that there is a focusing effect. The size of the radiating torus completely determines the location where the radiative force is maximum. We solve the steady state equations of motion of the radial outflow, in Schwarzschild geometry to show that the acceleration achieved is appreciable, when it is compared with Bondi-type outflow. We also show that, the photon momentum deposition force results in bringing the sonic point closer to the black hole thereby resulting in a more energetic outflows as compared to purely thermally driven outflow. Particularly interesting is that in many cases, where bound matters are freed and driven off as outflows after sufficient momentum is deposited.

We investigate the evolution of the electroweak phase transition, using a one-Higgs effective potential that can be regarded as an approximation for the Minimal Supersymmetric Standard Model. The phase transition occurs in a small interval around a temperature T_t below the critical one. We calculate this temperature as a function of the parameters of the potential and of a damping coefficient related to the viscosity of the plasma. The parameters that are relevant for baryogenesis, such as the velocity and thickness of the walls of bubbles and the value of the Higgs field inside them, change significantly in the range of temperatures where the first-order phase transition can occur. However, we find that in the likely interval for T_t there is no significant variation of these parameters. Furthermore, the temperature T_t is in general not far below the temperature at which bubbles begin to nucleate.

Primordial nucleosynthesis is regarded as a success story of the standard big bang (SBB) cosmology. In this article nucleosynthesis is explored in models in which the cosmological scale factor R(t) increases linearly with time. This relationship of R(t) and t continues from the period when nucleosynthesis begins until the present time. It turns out that weak interactions remain in thermal equilibrium upto temperatures which are two orders of magnitude lower than the corresponding (weak interaction decoupling) temperatures in SBB. Inverse beta decay of the proton can ensure adequate production of helium while producing primordial metallicity much higher than that produced in SBB. Attractive features of such models are the absence of the horizon, flatness and age problems as well consistency with classical cosmological tests.

We present the solutions for the metric outside a monopole resulting from the breaking of a global 0(3) symmetry within the framework of Lyra geometry. We have shown that monopole exerts gravitational force on matter around it.