Emergent cosmology, inflation and dark energy

2017

Eur. Phys. J. C

Here we generalize ideas of unified dark matterdark energy in the context of two measure theories and of dynamical space time theories. In two measure theories one uses metric independent volume elements and this allows one to construct unified dark matter-dark energy, where the cosmological constant appears as an integration constant associated with the equation of motion of the measure fields. The dynamical space-time theories generalize the two measure theories by introducing a vector field whose equation of motion guarantees the conservation of a certain Energy Momentum tensor, which may be related, but in general is not the same as the gravitational Energy Momentum tensor. We propose two formulations of this idea: (I) by demanding that this vector field be the gradient of a scalar, (II) by considering the dynamical space field appearing in another part of the action. Then the dynamical space time theory becomes a theory of Diffusive Unified dark energy and dark matter. These generalizations produce non-conserved energy momentum tensors instead of conserved energy momentum tensors which leads at the end to a formulation of interacting DE-DM dust models in the form of a diffusive type interacting Unified dark energy and dark matter scenario. We solved analytically the theories for perturbative solution and asymptotic solution, and we show that the CDM is a fixed point of these theories at large times. Also a preliminary argument as regards the good behavior of the theory at the quantum level is proposed for both theories.

“…as (7) and (25). Finally for the stress energy tensor, which comes from variation with respect to the metric we obtain…”

Section: Equation Of Motion and Solutions For Diffusive Energy Withoumentioning

confidence: 96%

Section: Introductionmentioning

confidence: 99%

Interacting diffusive unified dark energy and dark matter from scalar fields

Benisty

2017

Eur. Phys. J. C

“…Let us particularly stress that the method of non-Riemannian spacetime volumeforms is a very powerful one having profound impact in any (field theory) models with general coordinate reparametrization invariance, such as general relativity and its extensions [27]- [31], [32]- [36], [37]- [39]; strings and (higher-dimensional) membranes [40,41]; and supergravity [42,43]. Among its main features we should mention:…”

Section: Introductionmentioning

confidence: 99%

“…• Employing two independent non-Riemannian volume-forms produces effective scalar potential with two infinitely large flat regions [37,38] (one for large negative and another one for large positive values of the scalar field ϕ) with vastly different scales appropriate for a unified description of both the early and late universe' evolution. A remarkable feature is the existence of a stable initial phase of non-singular universe creation preceding the inflationary phase -stable "emergent universe" without "Big-Bang" [37].…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Metric-Independent Spacetime Volume-Forms and Dark Energy/Dark Matter Unification

Springer Proceedings in Mathematics &Amp; Statistics

Nissimov

Pacheva

2016

Self Cite

The method of non-Riemannian (metric-independent) spacetime volumeforms (alternative generally-covariant integration measure densities) is applied to construct a modified model of gravity coupled to a single scalar field providing an explicit unification of dark energy (as a dynamically generated cosmological constant) and dust fluid dark matter flowing along geodesics as an exact sum of two separate terms in the scalar field energy-momentum tensor. The fundamental reason for the dark species unification is the presence of a non-Riemannian volume-form in the scalar field action which both triggers the dynamical generation of the cosmological constant as well as gives rise to a hidden nonlinear Noether symmetry underlying the dust dark matter fluid nature. Upon adding appropriate perturbation breaking the hidden "dust" Noether symmetry we preserve the geodesic flow property of the dark matter while we suggest a way to get growing dark energy in the present universe' epoch free of evolution pathologies. Also, an intrinsic relation between the above modified gravity + single scalar field model and a special quadratic purely kinetic "k-essence" model is established as a weak-versus-strong-coupling duality.

Cosmology via Metric-Independent Volume-Form Dynamics

Springer Proceedings in Physics

Nissimov

Pacheva

2018

The method of non-Riemannian volume-forms (metric-independent covariant integration measure densities on the spacetime manifold) is applied to construct a unified model of dynamical dark energy plus dark matter as a dust fluid resulting from a hidden Noether symmetry of the pertinent scalar field Lagrangian. Canonical Hamiltonian treatment and Wheeler-DeWitt quantization of the latter model are briefly discussed.