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.     

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.     

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.      

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.     

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.     

Coherently perturbed Milne Universe

The present paper deals with the formulation of Einstein–Gordon equations for Friedmann–Robertson–Walker (FRW) geometries, in feedback reaction with the quartically self-interacting physical field, arisen from the “inner parity” spontaneous breaking. The Hamiltonian density non-positive extrema would classically forbid both spatially closed and flat homogeneous and isotropic worlds, if these allow the physical field to (repeatedly) go through and to settle down in a ground state. It turns out that the fixed point exact solutions of the spontaneous Z₂-symmetry breaking Einstein–Gordon equations are describing either anti-de Sitter or Milne Universes. The latter is consistent with the recent gravity lensing and supernova data, which have confirmed the hypothesis of an Universe dominated by dark energy, whose nature is completely unknown at present. Finally, by taking the electroweak symmetry scale to be the Z₂-invariance breaking one, we speculate on the cosmological implications of the Higgs–anti-de Sitter bubbles.