The $$B\rightarrow \bar{K}\pi \ell \ell $$ distribution at low hadronic recoil

The general class of Bianchi cosmological models with dark energy in the form of modified Chaplygin gas with variable Λ and G and bulk viscosity have been considered. We discuss three types of average scale factor by using a special law for deceleration parameter which is linear in time with negative slope. The exact solutions to the corresponding field equations are obtained. We obtain the solution of bulk viscosity (ξ), cosmological constant (Λ), gravitational parameter (G) and deceleration parameter (q) for different equations of state. The model describes an accelerating Universe for large value of time t, wherein the effective negative pressure induced by Chaplygin gas and bulk viscous pressure are driving the acceleration.     

Generalized holographic dark energy model

In this paper, the model of the holographic Chaplygin gas has been extended to two general cases: first the case of a modified variable Chaplygin gas and second the case of the viscous generalized Chaplygin gas. The dynamics of the model is expressed by the use of scalar fields and scalar potentials.     

Observational constraints on modified Chaplygin gas in Horava–Lifshitz gravity with dark radiation

Cosmological models with modified Chaplygin gas (MCG) in the framework of Horava–Lifshitz (HL) theory of gravity, both with and without detailed balance, are obtained. The equation of state (EOS) for a MCG contains three unknown parameters namely, A, α, B. The allowed values of some of these parameters of the EOS are determined using the recent astrophysical and cosmological observational data. Using observational data from H(z)-z, baryon acoustic oscillation (BAO) peak parameter and cosmic microwave background (CMB) shift parameter we study cosmologies in detailed-balance and beyond detailed-balance scenario. In this paper we take up the beyond detailed-balance scenario in totality and contribution of dark radiation in detailed-balance scenario on the parameters of the EOS. We explore the effect of dark radiation on the whole range of the effective neutrino parameter (ΔN _ν ) to constrain matter contributing parameter B in both the detailed-balance and the beyond detailed-balance scenarios. It has been observed that greater the dark radiation less the matter contribution in the MCG in both the scenario considered here. In order to check the validity of beyond detailed-balance scenario we plot supernovae magnitudes (μ) with red-shift of Union2 data and then the variation of state parameter with redshift is studied. It is noted that beyond detailed-balance scenario is suitable for cosmological model in HL gravity with MCG.     

Cosmic-coincidence problem and variable constants of physics

The standard model of cosmology is investigated using a time-dependent cosmological constant Λ and Newton gravitational constant G. The total energy content is described by the modified Chaplygin gas equation of state. It is found that the time-dependent constants coupled with the modified Chaplygin gas interpolate between the earlier matter to the later dark-energy dominated phase of the universe. We also achieve a convergence of the parameter ω→−1, almost at the present time. Thus our model fairly alleviates the cosmic-coincidence problem, which demands ω=−1 at the present time.     

FRW Cosmological Model with Modified Chaplygin Gas and Dynamical System

The Friedmann-Robertson-Walker (FRW) model with dynamical Dark Energy (DE) in the form of modified Chaplygin gas (MCG) has been investigated. The evolution equations are reduced to an autonomous system on the two dimensional phase plane and it can be interpreted as the motion of the particle in an one dimensional potential. Also the dynamical system analysis has been extended to examine the critical points at infinity with will exist provided the equation of state parameter $\omega<-\frac{1}{3}$ . Finally, theoretical points are asymptotically stable or unstable.     

Time-Dependent Density of Viscous Modified Chaplygin Gas with Arbitrary α

In this paper we study modified Chaplygin gas which has viscosity for the case of arbitrary α instead of α=0.5. We obtain behavior of the energy density of modified Chaplygin gas with respect to the constant and time-dependent bulk viscosity. We find also, numerically, effect of α on the energy density.     

Co-Existence of Modified Chaplygin Gas and Other Dark Energies in the Framework of Fractal Universe

In this work, we consider a non-flat universe in the framework of fractal cosmology. We have investigated the co-existence of different kinds of dark energy models such as tachyonic field, DBI-essence, hessence, k-essence, dilaton, quintessence with the modified Chaplygin gas (MCG) in fractal universe and obtained the statefinder parameters. The natures of the scalar fields and the concerned potentials have been analyzed by the correspondence scenario in the fractal universe.     

Viscous Generalized Chaplygin Gas with Arbitrary α

In this paper we study generalized Chaplygin gas which has viscosity for the case of arbitrary α. We obtained modified time-dependent energy density due to bulk viscosity and generalized Chaplygin gas. We have obtained the energy density in terms of α, and also we plotted it with respect to time by different α.     

Comparing the VGCG model as the unification of dark sectors with observations

Current observations indicate that 95% of the energy density in the universe is the unknown dark component.The dark component is considered composed of two fluids:dark matter and dark energy.Or it is a mixture of these two dark components,i.e.,one can consider it an exotic unknown dark fluid.With this consideration,the variable generalized Chaplygin gas(VGCG)model is studied with not dividing the unknown fluid into dark matter and dark energy parts in this paper.By using the Markov Chain Monte Carlo method,the VGCG model as the unification of dark sectors is constrained,and the constraint results on the VGCG model parameters are,n=0.00057+0.0001+0.0009-0.0006-0.0006,α=0.0015+0.0003+0.0017-0.0015-0.0015and B s=0.778+0.016+0.030-0.016-0.035,obtained by the cosmic microwave background data from the 7-year WMAP full data points,the baryon acoustic oscillation data from Sloan Digital Sky Survey(SDSS)and 2-degree Field Galaxy Redshift(2dFGRS)survey,and the Union2 type Ia supernova data with systematic errors.At last,according to the evolution of deceleration parameter it is shown that an expanded universe from deceleration to acceleration can be obtained in VGCG cosmology.     

Dark Energy Models in Plane Symmetric Space-Time with Time Varying Λ Term

This paper deals with the Einstein’s field equations for the space-time described by an inhomogeneous plane symmetric metric in presence of dark energy with time varying cosmological term Λ. The dark energy is given by either the quintessence or Chaplygin gas. It is shown that the models are isotropic and the deceleration parameter of the models is constant.     

A modified Chaplygin gas model with interaction

A modified Chaplygin gas (MCG) model of unifying dark energy and dark matter is considered in this paper, in which dark energy interacts with dark matter. Concretely, the evolution of such a unified dark sectors model is studied and the statefinder diagnostic to the MCG model is performed in our model. By analysis, it is shown that the effective equation of state (EoS) parameter of dark energy can cross the so-called phantom divide ω = −1, the behavior of MCG will be like ΛCDM in the future and therefore our Universe will not end up with Big Rip in the future. Furthermore, we plot the evolution trajectories of the MCG model in the statefinder parameter r–s plane and illustrate the discrimination between this scenario and the generalized Chaplygin gas (GCG) model.     

Observational Constraints on the Chaplygin Gas with Inverse Power Law Potential in Braneworld Inflation

We study Chaplygin gas as a candidate for inflation in the context of braneworld inflationary model. We investigate this model in the framework of the Randall–Sundrum type II, considering a original and generalized Chaplygin gas. We use inverse power law potential to examine the behavior of some inflationary spectrum parameters such as the spectral index n_s, the ratio r and the running of the scalar spectral index dn_s/dlnk, our results are in agreement with recent observational data for a particular choice of e-folding number N and parameters space of the model.     

Universe Described by Variable Modified Chaplygin Gas with Statefinder Diagnostic in General Relativity

The universe filled with variable modified Chaplygin gas having the equation of state p=Aρ?B/ρ ^α , where 0≤α≤1, A is a positive constant and B is a positive function of the average scale factor a(t) of the universe (i.e. B=B(a)) is studied within the framework of general relativity. The new class of exact solutions of Einstein’s field equations is derived by using a time dependent deceleration parameter. The cosmic jerk parameter in our derived model is in good agreement with the recent data of astrophysical observations under appropriate condition. It is observed that the universe starts from an asymptotic Einstein static era and reaches to the ΛCDM model. So from recently developed statefinder parameters, the behavior of different stages of the universe is studied. The physical and kinematical properties of cosmological models are also discussed.     

Constraining the coupling constant between dark energy and dark matter

We have investigated constraints on the coupling between dark matter and the interacting Chaplygin gas. Our results indicate that the coupling constant c between these two entities can take arbitrary values, which can be either positive or negative, thus giving arbitrary freedom to the inter-conversion between Chaplygin gas and dark matter. Thus, our results indicate that the restriction 0<c<1 on the coupling constant occurs as a very special case. Our analysis also supports the existence of phantom energy under certain conditions on the coupling constant.     

Accelerating Universe in Brans-Dicke Theory in Presence of Chaplygin Gas

In this paper, we have considered a model for Brans-Dicke scalar field in presence of Chaplygin gas and interaction between them. We have shown that the BD parameter ω is constant or not, the Chaplygin gas provides early deceleration and late time acceleration of the universe. The graphical representation of statefinder parameters shows the total evolution of the universe starts from radiation era to phantom model.     

Constraints on the generalized Chaplygin gas model from Gamma-ray bursts

We study the generalized Chaplygin gas model (GCGM) using Gamma-ray bursts as cosmological probes. In order to avoid the so-called circularity problem we use cosmology-independent data set and Bayesian statistics to impose constraints on the model parameters. We observe that a negative value for the parameter α is favoured in a flat Universe and the estimated value of the parameter H₀ is lower than that found in literature.     

Interacting Viscous Modified Chaplygin Gas Cosmology in Presence of Cosmological Constant

Here, we consider interacting viscous modified Chaplygin gas in presence of cosmological constant. We assumed bulk viscosity as a function of density. We consider interaction between modified Chaplygin gas and baryonic matter. Then, the effects of viscosities on the cosmological parameters such as energy, density, Hubble expansion parameter, scale factor and deceleration parameter investigated. This model may be considered as a toy model of our universe.     

Fate of an accretion disc around a black hole when both the viscosity and dark energy is in effect

This paper deals with the viscous accretion flow of a modified Chaplygin gas towards a black hole as the central gravitating object. A modified Chaplygin gas is a particular type of dark energy model which mimics of radiation era to phantom era depending on the different values of its parameters. We compare the dark energy accretion with the flow of adiabatic gas. An accretion disc flowing around a black hole is an example of a transonic flow. To construct the model, we consider three components of the Navier–Stokes equation, the equation of continuity and the modified Chaplygin gas equation of state. As a transonic flow passes through the sonic point, the velocity gradient being apparently singular there, it gives rise to two flow branches: one in-falling, the accretion and the other outgoing, the wind. We show that the wind curve is stronger and the wind speed reaches that of light at a finite distance from the black hole when dark energy is considered. Besides, if we increase the viscosity, the accretion disc is shortened in radius. These two processes acting together make the system deviate much from the adiabatic accretion case. It shows a weakening process for the accretion procedure by the work of the viscous system influencing both the angular momentum transport and the repulsive force of the modified Chaplygin gas.     

A quantitative criteria for the coincidence problem

The cosmic coincidence problem is a serious challenge to dark energy model. We suggest a quantitative criteria for judging the severity of the coincidence problem. Applying this criteria to three different interacting models, including the interacting quintessence, interacting phantom, and interacting Chaplygin gas models, we find that the interacting Chaplygin gas model has a better chance to solve the coincidence problem. Quantitatively, we find that the coincidence index C for the interacting Chaplygin gas model is smaller than that for the interacting quintessence and phantom models by six orders of magnitude.