Hawking-de Sitter Thermalization of Quasi-Minkowskian Massless Scalaron Production,Energy Density Content and Back-Reaction

Projecting the closed form expression of the de Sitter scalar field operator onto the Minkowskian positive frequency massless modes, we compute the corresponding Bogolubov coefficient which is associated to the (massless) quasiparticle creation during the stationary quasi-de Sitter stage of the Universe. Thereafter, we derive the expression of the thermalized energy density which reveals an interesting mixture of de Sitter false vacuum and dark-radiation, exotic dust and black body radiation. Setting the temperature to the value of the Hawking one for the de Sitter spacetime, we finally analyze the (straightforward) back-reaction of the newly created “matter” on the scale function. It basically points out three stages of highly continuous evolution represented by an initially short radiation-like era, a somewhat long-lasting connecting phase made of coherent massless oscillations, in its beginnings, ended up by the dark-radiation (i.e. curvature-like term) contribution and, finally, a much slower exponential expansion than the initial de Sitter one.     

Wess–Zumino Currents on S3 × R Spacetime

Based on the group theory powerful techniques, as a rigorous tool for treating fields on S ³ × R spacetime, which is the manifold of SU(2), we put the supersymmetric Wess–Zumino model on the S ³ × R background. After deriving the system of Klein–Gordon–Dirac-type equations, for the scalar and Majorana fields, we get in the corresponding current, besides the supercurrent, an additional term due to the coupling of spin to gravity. Finally, considerations on the solutions of the fields equations are made, pointing out significant differences from the Minkowskian case.     

Natural brane-confinement from massive Z 2-spontaneously broken Kaluza-Klein excitations in the bulk

For a real scalar field minimally coupled to bulk gravity, in five dimensions, we analytically solve the Gordon equation, near one of the degenerated vacua of an effective potential with a spontaneously broken Z ₂-symmetry. Dealing with the back-reaction from the excited massive modes on the whole scale function, we are pointing out that the lighter excitations of the scalar in the bulk turn more and more the warp function into the one of a partition on the confined brane.      

Fermions on spacetimes of spatially closed hypersurfaces

Using a convenient compact time-like coordinate f  [0, 1], characterizing the whole big bang–big crunch spacetime history cyclicly evolving with a 2π conformal period, we write down the Dirac-type equation in a FRW matter-dominated Universe. It turns out that, by accepting the idea of existence of an alternative time gauge, as for example in the projected Universe, one is able to derive closed form solutions, for physically meaningful cases.     

Coherent Planar Symmetric Spacetimes Generated by Progressive Waves of Nambu–Goldstone Bosons

Within a SO(3,1) ?gauge invariant pseudo-orthonormal (Cartan) formalism, in the present paper, we are going to deal with the Einstein–Nambu–Goldstone system of equations, for a manifold with at least G₄ up to G₆ group of motion and a massless source-field excited along the z ?direction. This is also equivalent with the pure radiation energy–momentum tensor coming from circularly polarized waves generated by a rotating magnetic field. The corresponding essential equation which establishes the connection between the spacetime geometry and the matter-field is solved in some physically interesting cases.     

Fermions in a Kerr-Newman space-time

The aim of this paper is to put the U(1) -gauge theory of fermions in the spacetime described by a Kerr-Newman metric. The field equations have rather complicated expressions essentially different from the Minkowskian spacetime.     

LARGE-SCALE PATHOLOGY OF UNIVERSES WITH VII0×VIII ISOMETRIES

The goal of this paper is to show somewhat unexpected globally pathologic properties in universes described by a class of static planary symmetric exact solutions with G ₆-group of motion. In order to achieve this aim, the Killing vectors, the null geodesics and the Penrose diagrams corresponding to different expressions of g ₄₄=–e ^2f(z), with f(z) solutions of Einstein's equations, have been employed. Finally, woking in a particular gauge, we focus on the behaviour of the radiating electromagnetic modes and derive the observable components of E and B and the expressions of the essential component of the Umov-Poynting vector.     

A Maxwell Field Equations Class of Exact Solutions on Matter-Dominated Spatially Closed Friedman-Robertson-Walker Universe

Working in a spatially closed Friedman-Robertson-Walker universe with cosmological dust, we investigate a particular source-free Maxwell field generated by a rotationally-symmetric potential A with one of the components in the direction of and the other along . Using the (, , )-Euler coordinates on S ³ and a compact timelike coordinate f, we obtain a class of parametric solutions that allows us to write down the essential components of the Maxwell tensor as well as the induction and the electric field intensity pointing out, besides the non-propagating fundamental electric field, a burst of electromagnetic radiation.