In a flat Friedmann-Lemaître-Robertson-Walker (FLRW) geometry, we consider the expansion of the universe powered by the gravitationally induced 'adiabatic' matter creation. To demonstrate how matter creation works well with the expanding universe, we have considered a general creation rate and analyzed this rate in the framework of dynamical analysis. The dynamical analysis hints the presence of a non-singular universe (without the big bang singularity) with two successive accelerated phases, one at the very early phase of the universe (i.e. inflation), and the other one describes the current accelerating universe, where this early, late accelerated phases are associated with an unstable fixed point (i.e. repeller) and a stable fixed (attractor) points, respectively. We have described this phenomena by analytic solutions of the Hubble function and the scale factor of the FLRW universe. Using Jacobi Last multiplier method, we have found a Lagrangian for this matter creation rate describing this scenario of the universe. To match with our early physics results, we introduce an equivalent dynamics driven by a single scalar field and discussed the associated observable parameters compared them with the latest PLANCK data sets. Finally, introducing the teleparallel modified gravity, we have established an equivalent gravitational theory in the framework of matter creation.PACS numbers: 95.35.+d, 95.36.+x, 98.80.Es.

If we live on the weak brane with zero effective cosmological constant in a warped 5D bulk spacetime, gravitational waves and brane fluctuations can be generated by a part of the 5D Weyl tensor and carries information of the gravitational field outside the brane. We consider on a cylindrical symmetric warped FLRW background a U(1) selfgravitating scalar field coupled to a gauge field without bulk matter. It turns out that brane fluctuations can be formed dynamically, due to the modified energy-momentum tensor components of the scalar-gauge field ("cosmic string"). As a result, we find that the late-time behavior could be significantly deviate from the standard evolution of the universe. The effect is triggered by the time-dependent warpfactor with two branches of the form) ( with τ, c i constants) and the modified brane equations comparable with a dark energy effect. This is a brane-world mechanism, not present in standard 4D FLRW, where the large disturbances are rapidly damped as the expansion proceed. Because gravity can propagate in the bulk, the cosmic string can build up a huge angle deficit (or mass per unit length) by the warpfactor and can induce massive KK-modes felt on the brane. Disturbances in the spatial components of the stress-energy tensor cause cylindrical symmetric waves, amplified due to the presence of the bulk space and warpfactor. They could survive the natural damping due to the expansion of the universe. It turns out that one of the metric components becomes singular at the moment the warp factor develops a extremum. This behavior could have influence on the possibility of a transition from acceleration to deceleration or vice versa. PACS numbers: 06.20.Jr, 95.30.Dr, 95.30.Sf, 98.62.Ra, 98.80.-k, 98.80.Es, 98.80.Jk IntroductionIt is conjectured that the expansion of our universe is accelerating. Recent observations provide strong evidence of this acceleration. The explanation of this remarkable phenomenon is rather difficult: one needs a dark energy field with an effectively negative pressure, p < − 1 3 ρ. From several independent observational data, one finds Ω Λ ≈ 0.7 and Ω M ≈ 0.3, where Ω M and Ω Λ stand for the energy densities of matter and dark energy respectively with respect to the critical ones [1,2,3,4,5]. We should live now in the cosmological constant dominated era (and approximately flat, Ω 0 = Ω M0 + Ω Λ0 ≈ 1), while at earlier times there was a radiation and matter dominated era.There are some fundamental questions. First, will the acceleration last forever. Secondly, why there is the huge discrepancy between ρ Λ ≃ 10 −123 in Planck units and vacuum energy density ρ V ≃ 10 −3 which is 10 120 times greater than the value we need to accelerate the expansion of the universe. Thirdly, the value must be incredibly fine-tuned, Ω Λ ∼ Ω M . So it would be a logical step to try to explain the late-time acceleration without the need for dark energy [6]. It is also conjectured that one needs an inflaton field in the very early stage of our universe, to solve the flatness and horizon ...

The time evolution of a self-gravitating U(1) cosmic string on a warped five-dimensional (5D) axially symmetric spacetime is numerically investigated. Although cosmic strings are theoretically predicted in four-dimensional (4D) general relativistic models, there is still no observational evidence of their existence. From recent observations of the cosmic microwave background (CMB), it is concluded that these cosmic strings cannot provide a satisfactory explanation for the bulk of density perturbations. They even could not survive inflation. It is conjectured that only in a 5D warped braneworld model there will be observable imprint of these so-called cosmic superstrings on the induced effective 4D brane metric for values of the symmetry breaking scale larger than the grand unified theory (GUT) values. The warp factor makes these strings consistent with the predicted mass per unit length on the brane. However, in a time-dependent setting, it seems that there is a wavelike energy–momentum transfer to infinity on the brane, a high-energy braneworld behavior. This in contrast to earlier results in approximation models. Evidence of this information from the bulk geometry could be found in the gravitational cosmic background radiation via gravitational wave energy–momentum affecting the brane evolution. Fluctuations of the brane when there is a U(1) gauge field present, are comparable with the proposed brane tension fluctuations, or branons, whose relic abundance can be a dark matter candidate. We briefly made a connection with the critical behavior at the threshold of black hole formation found by Choptuik several decades ago in self-gravitating time-dependent scalar field models. The critical distinction between dispersion of the scalar waves and singular behavior fade away when a time-dependent warp factor is present.