Cosmic acceleration from effective forces?

We revise the dynamics of interacting vector-like dark energy, a theoretical framework proposed to explain the accelerated expansion of the universe. By investigating the interaction between vector-like dark energy and dark matter, we analyze its effects on the cosmic expansion history and the thermodynamics of the accelerating universe. Our results demonstrate that the presence of interaction significantly influences the evolution of vector-like dark energy, leading to disti...

We consider the possibility that the dark sector of our Universe contains a negative cosmological constant dubbed $\lambda$. For such models to be viable, the dark sector should contain an additional component responsible for the late-time accelerated expansion rate ($X$). We explore the departure of the expansion history of these models from the concordance $\Lambda$ Cold Dark Matter model. For a large class of our models the accelerated expansion is transient with a nontriv...

In this paper we study new cosmological models involving new forms of non-gravitational interaction between cold dark matter and dark energy. The main purpose is to demonstrate the applicability of the forms of interaction to the problem in modern cosmology known as accelerated expansion of the large scale universe. It is well known, that a non-gravitational interaction can improve theoretical prediction, but a fundamental theory allowing to derive the form of the interaction...

The accelerated expansion of the universe has been established through observations of supernovae, the growth of structure, and the cosmic microwave background. The most popular explanation is Einsteins cosmological constant, or dynamic variations hereof. A recent paper demonstrated that if dark matter particles are endowed with a repulsive force proportional to the internal velocity dispersion of galaxies, then the corresponding acceleration of the universe may follow that o...

Is Dark Energy justified as an alternative to the cosmological constant $\Lambda$ in order to explain the acceleration of the cosmic expansion ? It turns out that a straightforward dimensional analysis of Einstein equation provides us with clear evidences that the geometrical nature of $\Lambda$ is the only viable source to this phenomenon, in addition of the application of Ockham's razor principle. This contribution is primarily a review of the main stream in the interpretat...

The problem of explaining the acceleration of the expansion of the universe and the observational and theoretical difficulties associated with dark matter and dark energy are discussed. The possibility that GR does not correctly describe the large-scale structure of the universe is considered and an alternative gravity theory is proposed as a possible resolution to the problems.

Using a general classification of dark enegy models in four classes, we discuss the complementarity of cosmological observations to tackle down the physics beyond the acceleration of our universe. We discuss the tests distinguishing the four classes and then focus on the dynamics of the perturbations in the Newtonian regime. We also exhibit explicitely models that have identical predictions for a subset of observations.

The universe content is considered as a non-perfect fluid with bulk viscosity and can be described by a general equation of state (endowed some deviation from the conventionally assumed cosmic perfect fluid model). An explicitly bulk viscosity dark energy model is proposed to confront consistently with the current observational data sets by statistical analysis and is shown consistent with (not deviated away much from) the concordant $\Lambda$ Cold Dark Matter (CDM) model by ...

In this paper it has been shown that the neutrino bulk viscous stresses can give rise to the late time acceleration of the universe. It is found that a number of spatially flat FRW models with a negative deceleration parameter can be constructed using neutrino viscosity and one of them mimics a $\Lambda$CDM model. This does not require any exotic dark energy component or any modification of gravity.

This paper deals with the cancellation mechanism, which identifies the energy density of space-time expansion in an empty universe with the zero-point energy density and avoids the scale discrepancy with the observed energy density (cosmological constant problem). Using an intrinsic degree of freedom which describes the coupling of a variable cosmological term $\Lambda$ with non-relativistic matter and radiation, the following consequences are demonstrated by coupling only a ...