Probing the Time Variation of a Fine Structure Constant Using Galaxy Clusters and the Quintessence Model

We explore a possible time variation of the fine structure constant (α ≡ e 2/ℏ c) using the Sunyaev–Zel’dovich effect measurements of galaxy clusters along with their X-ray observations. Specifically, the ratio of the integrated Comptonization parameter Y SZ D A 2 and its X-ray counterpart Y X is used as an observable to constrain the bounds on the variation of α. Considering the violation of the cosmic distance duality relation, this ratio depends on the fine structure constant of ∼ α 3. We use the quintessence model to provide the origin of α time variation. In order to give a robust test on α variation, two galaxy cluster samples, the 61 clusters provided by the Planck collaboration and the 58 clusters detected by the South Pole Telescope (SPT), are collected for analysis. Their X-ray observations are given by the XMM-Newton survey. Our results give ζ = − 0.203 − 0.099 + 0.101 for the Planck sample and ζ = − 0.043 − 0.148 + 0.165 for the SPT sample, indicating that α is constant with redshift within 3σ and 1σ for the two samples, respectively.

On the occurrence of finite-time singularities in Swampland-related quintessence dark energy models

In this work, we focus on the phase space singularities of interactive quintessence model in the presence of matter fluid. This model is related to swampland studies, that the outcomes affect all these swampland-related models with the same dynamical system. We shall form the dynamical system corresponding to the cosmological system, which is eventually autonomous, and by using the dominant balances technique we shall investigate the occurrence or not of finite-time singularities. Our results indicate that the dynamical system of the model may develop finite-time singularities, but these are not general singularities, like in the case that the matter fluids were absent, in which case singularities occurred for general initial conditions. Hence, the presence of matter fluids affects the dynamical system of the cosmological system, making the singularities to depend on the initial conditions, instead of occurring for general initial conditions.

Quintessence Model Calculations for Bulkviscous Fluid and Low Value Predictions of Thecoefficient of Bulk Viscosity in General as Well as Modified Gravity With the Form F(R,T)=R+F(T) and F(T)=λT.

In this paper we have defined the effect of bulk viscosity on Quintessence model and scaler field potential as well as on classical field. We have shown the same effect for modified gravity with f(R,T)= R+f(T). In the derivation we have predicted the possibility of time dependent evolution of gravitational constant G and anisotropy.

Reconstruction of quintessence field for the THDE with swampland correspondence in f(R,T) gravity

In the present work, we construct the Tsallis holographic quintessence model of dark energy in [Formula: see text] gravity with Hubble horizon as infrared (IR) cut-off. In a flat Friedmann–Robertson–Walker (FRW) background, the correspondence among the energy density of the quintessence model with the Tsallis holographic density permits the reconstruction of the dynamics and the potentials for the quintessence field. The suggested Hubble horizon IR cut-off for the Tsallis holographic dark energy (THDE) density acts for two specific cases: (i) THDE 1 and (ii) THDE 2. We have reconstructed the Tsallis holographic quintessence model in the region [Formula: see text] for the equation of state (EoS) parameter for both the cases. we investigate the behavior of several well-known statefinder quantities, like the deceleration parameter, the jerk and the parameter [Formula: see text]. In addition, the quintessence phase of the THDE models is analyzed with swampland conjecture to describe the accelerated expansion of the Universe.

Interacting ghost dark energy in complex quintessence theory

We employ a ghost model of interacting dark energy to obtain the equation of state $$\omega $$ ω for ghost energy density in an FRW universe in complex quintessence theory. We reconstruct the potential and study the dynamics of the scalar field that describes complex quintessence cosmology. We perform $$\omega -\omega '$$ ω - ω ′ analysis and stability analysis for both non-interacting and interacting cases and find that the same basic conclusion as for the real model, where $$\omega ' = d\omega / d ln a$$ ω ′ = d ω / d l n a . Taking account of the effect of the complex part and assuming the real part of the quintessence field to be a slow-rolling field, we conclude that the non-interacting model cannot describe the real universe since this will lead to fractional energy density $$\Omega _D > 1$$ Ω D > 1 , where $$\Omega _D$$ Ω D can be defined as the ratio of $$\rho _D$$ ρ D to $$\rho _{cr}$$ ρ cr . However, for the interacting case, if we take present $$\Omega _D =0.73$$ Ω D = 0.73 , then we can determine that $$b^2 = 0.0849$$ b 2 = 0.0849 , where $$b^2$$ b 2 is the interaction coupling parameter between matter and dark energy. In the real quintessence model, $$\Omega _D$$ Ω D and $$b^2$$ b 2 are independent parameters, whereas in the complex quintessence model, we conclude that there is a relationship between these two parameters.

Dynamics of quintessence in generalized uncertainty principle

We investigate the quintessence scalar field model modified by the generalized uncertainty principle in the background of a spatially flat homogeneous and isotropic universe. By performing a dynamical system analysis we examine the nature of the critical points and their stability for two potentials, one is the exponential potential and the other is a general potential. In the case of an exponential potential, we find some new critical points for this modified quintessence scenario that describe the de Sitter universes, and these critical points do not appear in the standard quintessence model with an exponential potential. This is one of the main results of this work. Now for the general potential our analysis shows that the physical properties of the critical points remain exactly the same as for the exponential potential which means that within this modified quintessence scenario all kind of potentials have same behaviour. This kind of result is completely new in cosmology because with the change of the potential, differences are usually expected in all respect.

Non-linear phenomenology of disformally coupled quintessence

ABSTRACT The quintessence model is one of the simplest and better known alternatives to Einstein’s theory for gravity. The properties of the solutions have been studied in great detail in the background, linear and non-linear contexts in cosmology. Here we discuss new phenomenology that is induced by adding disformal terms to the interactions. Among other results, we show analytically and using cosmological simulations ran with the code isis that the model possesses a mechanism through which it is possible to obtain repulsive fifth forces, which are opposite to gravity. Although the equations are very complex, we also find that most of the new phenomenology can be explained by studying background quantities. We used our simulation data to test approximate relations that exist between the metric and scalar field perturbations as well as between the fifth force and gravity. Excellent agreement was found between exact and approximated solutions, which opens the way for running disformal gravity cosmological simulations using simply a Newtonian solver. These results could not only help us to find new ways of testing gravity, but also provide new motivations for building alternative models.