Rip Scenario Research Articles

Impossibility of rips and cosmological singularities in a universe merging with baby universes

Understanding the late-time acceleration of the universe and its subtleties is one of the biggest mysteries in cosmology. A lot of different approaches have been put forward to deal with this, ranging from the conventional cosmological constant to various models of dark energy and beyond. Recently one very interesting approach to explaining the late time acceleration has been put forward, where the expansion of the universe is driven by mergers with other “baby” universes and has been shown to be quite viable as well from the point of view of recent observational data. So in this work we examine the possibility of various rip scenarios and other future cosmological singularities in such “multiversal” scenario, probing such singularities for the first time in a multi universe scenario. We examine two models of such a baby universe merging cosmology, and show that remarkably no rip scenario or future cosmological singularity is possible in such models.

Big Rip in Swiss-cheese brane-worlds with cosmic transit

We study the Big Rip scenario in Swiss-cheese brane-worlds. The results obtained have been found to be independent of the value of the cosmological constant Λ whether it is positive, negative, or zero. Negative tension branes are not allowed in the current model. There is a sign flipping in cosmic pressure corresponding to the sign flipping in the deceleration parameter from positive to negative. The evolution of the equation of state parameter shows the presence of three phases: the matter-dominant decelerating era, the accelerated-Quitessence phase, and the phantom phase. The evolution of the potential and kinetic term also shows a change of sign. The energy conditions and cosmographic parameters have also been investigated.

Big Rip Scenario in Brans-Dicke Theory

In this work, we present a Big Rip scenario within the framework of the generalized Brans-Dicke (GBD) theory. In the GBD theory, we consider an evolving BD parameter along with a self-interacting potential. An anisotropic background is considered to have a more general view of the cosmic expansion. The GBD theory with a cosmological constant is presented as an effective cosmic fluid within general relativity which favours a phantom field dominated phase. The model parameters are constrained so that the model provides reasonable estimates of the Hubble parameter and other recent observational aspects at the present epoch. The dynamical aspects of the BD parameter and the BD scalar field have been analysed. It is found that the present model witnesses a finite time doomsday at a time of tBR≃16.14Gyr, and for this scenario, the model requires a large negative value of the Brans-Dicke parameter.

General dynamical properties of cosmological models with nonminimal kinetic coupling

We consider cosmological dynamics in the theory of gravity with the scalar field possessing the nonminimal kinetic coupling to curvature given as η Gμνϕ,μϕ,ν, where η is an arbitrary coupling parameter, and the scalar potential V(ϕ) which assumed to be as general as possible. With an appropriate dimensionless parametrization we represent the field equations as an autonomous dynamical system which contains ultimately only one arbitrary function χ (x)= 8 π | η | V(x/√8 π) with x=√8 πϕ. Then, assuming the rather general properties of χ(x), we analyze stationary points and their stability, as well as all possible asymptotical regimes of the dynamical system. It has been shown that for a broad class of χ(x) there exist attractors representing three accelerated regimes of the Universe evolution, including de Sitter expansion (or late-time inflation), the Little Rip scenario, and the Big Rip scenario. As the specific examples, we consider a power-law potential V(ϕ)=M4(ϕ/ϕ0)σ, Higgs-like potential V(ϕ)=λ/4(ϕ2−ϕ02)2, and exponential potential V(ϕ)=M4 e−ϕ/ϕ0.

Cosmology with nonminimal kinetic coupling and a Higgs-like potential

We consider cosmological dynamics in the theory of gravity with the scalar field possessing the nonminimal kinetic coupling to curvature given as κGμνϕ,μϕ,ν, and the Higgs-like potential . Using the dynamical system method, we analyze stationary points, their stability, and all possible asymptotical regimes of the model under consideration. We show that the Higgs field with the kinetic coupling provides an existence of accelerated regimes of the Universe evolution. There are three possible cosmological scenarios with acceleration: (i) The late-time de Sitter epoch when the Hubble parameter tends to the constant value, as t → ∞, while the scalar field tends to zero, 0ϕ(t)→ , so that the Higgs potential reaches its local maximum . (ii) The Big Rip when H(t)∼(t*−t)−1 → ∞ and ϕ(t)∼(t*−t)−2 → ∞ as t → t*. (iii) The Little Rip when H(t)∼ t1/2 → ∞ and ϕ(t)∼ t1/4 → ∞ as t → ∞. Also, we derive modified slow-roll conditions for the Higgs field and demonstrate that they lead to the Little Rip scenario.

Inhomogeneous Viscous Fluids in a Friedmann-Robertson-Walker (FRW) Universe

We give a brief review of some aspects of inhomogeneous viscous fluids in a flat Friedmann-Robertson-Walker Universe. In general, it is pointed out that several fluid models may bring the future Universe evolution to become singular, with the appearance of the so-called Big Rip scenario. We investigate the effects of fluids coupled with dark matter in a de Sitter Universe, by considering several cases. Due to this coupling, the coincidence problem may be solved, and if the de Sitter solution is stable, the model is also protected against the Big Rip singularity.

Archimedean-type force in a cosmic dark fluid. III. Big rip, little rip, and cyclic solutions

We analyze late-time evolution of the Universe in the framework of the self-consistent model, in which the dark matter is influenced by the Archimedean-type force proportional to the four-gradient of the dark energy pressure. The dark energy is considered as a fluid with the equation of state of the relaxation type, which takes into account a retardation of the dark energy response to the Universe accelerated expansion. The dark matter is guided by the Archimedean-type force, which redistributes the total energy of the dark fluid between two its constituents, dark energy and dark matter, in the course of the Universe accelerated expansion. We focus on the constraints for the dark energy relaxation time parameter, for the dark energy equation of state parameter, and for the Archimedean-type coupling constants, which guarantee the Big Rip avoidance. In particular, we show that the Archimedean-type coupling protects the Universe from the Big Rip scenario with asymptotically infinite negative dark energy pressure, and that the Little Rip is the fate of the Universe with the Archimedean-type interaction inside the dark fluid.

Viscous little rip cosmology

Dark energy of phantom or quintessence nature with an equation of state parameter $w$ almost equal to $\ensuremath{-}1$ often leads the universe evolution to a finite-time future singularity. An elegant solution to this problem has been recently proposed [P. H. Frampton, K. J. Ludwick, and R. J. Scherrer, Phys. Rev. D 84, 063003 (2011).] under the form of the so-called little rip cosmology, which appears to be a realistic alternative to the $\ensuremath{\Lambda}\mathrm{CDM}$ model. A viscous little rip cosmology is here proposed. Whereas generically bulk viscosity tends to promote the big rip, we find that there are a number of situations where this is not the case and where the formalism nicely adjusts itself to the little rip scenario. We prove, in particular, that a viscous fluid (or, equivalently, one with an inhomogeneous [imperfect] equation of state) is perfectly able to produce a little rip cosmology as a purely viscosity effect. The possibility of its induction as a combined result of viscosity and a general (powerlike) equation of state is also investigated in detail. To finish, a physical, inertial force interpretation of the dissolution of bound structures in the little rip cosmology is presented.

Quasinormal modes of black holes absorbing dark energy

We study perturbations of black holes absorbing dark energy. Due to the accretion of dark energy, the black hole mass changes. We observe distinct perturbation behaviors for absorption of different forms of dark energy onto the black holes. This provides the possibility of extracting information whether dark energy lies above or below the cosmological constant boundary w=−1. In particular, we find in the late time tail analysis that, differently from the other dark energy models, the accretion of phantom energy exhibits a growing mode in the perturbation tail. The instability behavior found in this work is consistent with the Big Rip scenario, in which all of the bound objects are torn apart with the presence of the phantom dark energy.

Constraining a double component dark energy model using supernova type Ia data

A two-component fluid representing dark energy is studied. One of the components has a polytropic form, while the other has a barotropic form. Exact solutions are obtained and the cosmological parameters are constrained using supernova type Ia data. In general, an open universe is predicted. A big rip scenario is largely preferred, but the dispersion in the parameter space is very high. Hence, even if scenarios without future singularities can not be excluded with the allowed range of parameters, a phantom cosmology, with an open spatial section, is a general prediction of the model. For a wide range of the equation of state parameters there is an asymptotic de Sitter phase.

The Accretion of Dark Energy onto a Black Hole

The stationary, spherically symmetric accretion of dark energy onto a Schwarzschild black hole is considered in terms of relativistic hydrodynamics. The approximation of an ideal fluid is used to model the dark energy. General expressions are derived for the accretion rate of an ideal fluid with an arbitrary equation of state p = p(ρ) onto a black hole. The black hole mass was found to decrease for the accretion of phantom energy. The accretion process is studied in detail for two dark energy models that admit an analytical solution: a model with a linear equation of state, p = α(ρ − ρ0), and a Chaplygin gas. For one of the special cases of a linear equation of state, an analytical expression is derived for the accretion rate of dark energy onto a moving and rotating black hole. The masses of all black holes are shown to approach zero in cosmological models with phantom energy in which the Big Rip scenario is realized.

Partial rip scenario—a cosmology with a growing cosmological term

A cosmology with the growing cosmological term is considered. If there is no exchange of energy between vacuum and matter components, the requirement of general covariance implies the time dependence of the gravitational constant G. Irrespectively of the exact functional form of the cosmological term growth, the universe ends in a de Sitter regime with a constant asymptotic Λ, but vanishing G. Although there is no divergence of the scale factor in finite time, such as in the “Big Rip” scenario, gravitationally bound systems eventually become unbound. In the case of systems bound by non-gravitational forces, there is no unbounding effect, as the asymptotic Λ is insufficiently large to disturb these systems.