The hidden flat like universe II

In a recent work, a particular class of f (T ) gravity, where T is the teleparallel torsion scalar, has been derived. This class has been identified by flat-like universe (FLU) assumptions [1]. The model is consistent with the early cosmic inflation epoch. A quintessence potential has been constructed from the FLU f (T )-gravity. We show that the first order potential of the induced quintessence is a quasi inverse power law inflation with an additional constant providing an end of the inflation with no need to an extra mechanism. At e-folds N * = 55 before the end of the inflation, this type of potential can perform both E and B modes of the cosmic microwave background (CMB) polarization pattern.

The European Physical Journal C, 2015

We study a single fluid component in a flat like universe (FLU) governed by f (T ) gravity theories, where T is the teleparallel torsion scalar. The FLU model, regardless the value of the spatial curvature k, identifies a special class of f (T ) gravity theories. Remarkably, the FLU f (T ) gravity does not reduce to teleparallel gravity theory. In large Hubble spacetime the theory is consistent with the inflationary universe scenario and respects the conservation principle. The equation of state (EoS) evolves similarly in all models k = 0, ±1. We study the case when the torsion tensor is made of a scalar field, which enables to derive a quintessence potential from the obtained f (T ) gravity theory. The potential produces Starobinsky-like model naturally without using a conformal transformation, with higher orders continuously interpolate between Starobinsky and quadratic inflation models. The slow-roll analysis shows double solutions so that for a single value of the scalar tilt (spectral index) n s the theory can predict double tensor-to-scalar ratios r of E-mode and B-mode polarizations.

We study a single-fluid component in a flat like universe (FLU) governed by f (T ) gravity theories, where T is the teleparallel torsion scalar. The FLU model, regardless of the value of the spatial curvature k, identifies a special class of f (T ) gravity theories. Remarkably, FLU f (T ) gravity does not reduce to teleparallel gravity theory. In large Hubble spacetime the theory is consistent with the inflationary universe scenario and respects the conservation principle. The equation of state evolves similarly in all models k = 0, ±1. We study the case when the torsion tensor consists of a scalar field, which enables to derive a quintessence potential from the obtained f (T ) gravity theory. The potential produces Starobinsky-like model naturally without using a conformal transformation, with higher orders continuously interpolate between Starobinsky and quadratic inflation models. The slow-roll analysis shows double solutions, so that for a single value of the scalar tilt (spectral index) n s the theory can predict double tensor-to-scalar ratios r of E-mode and B-mode polarizations.

In the present work we derive an exact solution of an isotropic and homogeneous Universe governed by f (T ) gravity. We show how the torsion contribution to the FRW cosmology can provide a unique origin for both early and late acceleration phases of the Universe. The three models (k = 0, ±1) show a built-in inflationary behavior at some early Universe time; they restore suitable conditions for the hot Big bang nucleosynthesis to begin. Unlike the standard cosmology, we show that even if the Universe initially started with positive or negative sectional curvatures, the curvature density parameter enforces evolution to a flat Universe. The solution constrains the torsion scalar T to be a constant function at all time t, for the three models. This eliminates the need for dark energy (DE). Moreover, when the continuity equation is assumed for the torsion fluid, we show that the flat and closed Universe models violate the conservation principle, while the open one does not. The evolution of the effective equation of state (EoS) of the torsion fluid implies a peculiar trace from a quintessence-like DE to a phantom-like one crossing a matter and radiation EoS in between; then it asymptotically approaches a de Sitter fate.

The European Physical Journal C, 2014

In the present work we derive an exact solution of an isotropic and homogeneous Universe governed by f (T ) gravity. We show how the torsion contribution to the FRW cosmology can provide a unique origin for both early and late acceleration phases of the Universe. The three models (k = 0, ±1) show a built-in inflationary behavior at some early Universe time; they restore suitable conditions for the hot Big bang nucleosynthesis to begin. Unlike the standard cosmology, we show that even if the Universe initially started with positive or negative sectional curvatures, the curvature density parameter enforces evolution to a flat Universe. The solution constrains the torsion scalar T to be a constant function at all time t, for the three models. This eliminates the need for dark energy (DE). Moreover, when the continuity equation is assumed for the torsion fluid, we show that the flat and closed Universe models violate the conservation principle, while the open one does not. The evolution of the effective equation of state (EoS) of the torsion fluid implies a peculiar trace from a quintessence-like DE to a phantom-like one crossing a matter and radiation EoS in between; then it asymptotically approaches a de Sitter fate.

Arxiv preprint astro-ph/0302148, 2003

2021

We study early universe with a particular form of F(T) Telleparallel gravity theory, in which inflation is driven by a scalar field. To ensure slow rollover, two different potentials are chosen in a manner, such that they remain almost flat for large initial value of the scalar field. Inflationary parameters show wonderful fit with the presently available Planck's data set. The energy scale of inflation is sub-Planckian and graceful exit from inflation is also administered. The chosen form of F(T) administers late-time cosmic acceleration too. In the process, unification of the early inflation with late-time acceleration is ensured. Unfortunately, a decelerated radiation dominated era is only possible with a different form of (quartic) potential, which being devoid of a flat section does not admit slow rollover.

We derived a uniquely exact f (T) formula of the lowest possible energy of an isotropic and homogeneous universe. We show that vanishing of the energy-momentum tensor T µν of matter does not imply vanishing of the teleparallel torsion scalar T , in contrast to general relativity, where Ricci scalar vanishes. The theory provides an exponential scale factor independent of the choice of the sectional curvature. In addition, the obtained f (T) of the open universe model shows a decaying form to the small present value of cosmological constant which contributes directly to solve the fine-tuning problem of the cosmological constant. The Equation of State (EoS) of the torsion fluid has been studied. We study the case when the torsion potential is made of a scalar field and its consequences on the inflationary description.

2003

We started the evolution of a flat universe from a nonsingular state called prematter which is governed by an inflationary equation of state P=(g -1)r , where g represents the initial vacuum dominance of the universe. The evolution of the universe-except in the prematter era-is affected neither by the initial vacuum dominance nor by the initial expansion rate of the

Physical Review D, 1981

The standard model of hot big bang cosmology requires initial conditions which are problematic in two ways: (1) the early universe is assumed to be highly homogeneous, in spite of the fact that separated regions were causally disconnected (horizon problem); and (2) the initial value of the Hubble constant must be fine tuned to extraordinary accuracy to produce a universe as flat (i.e., near critical mass density) as'the one we see today (flatness problem). These problems would disappear if, in its early history, the universe supercooled to temperatures 28 or more orders of magnitude below the critical temperature for some phase transition. A huge expansion factor would then result from a period of exponential growth, and the entropy of the universe would be multiplied by a huge factor when the latent heat is released. Such a scenario is completely natural in the context of grand unified models of elementary particle interactions. In such models, the supercooling is also relevant to the problem of monopole suppression. Unfortunately, the scenario seems to lead to some unacceptable consequences, so modifications must be sought.