Narrow Results

We study the f(R) theory of gravity in an anisotropic metric and its effect on the baryon number-to-entropy ratio. The mechanism of gravitational baryogenesis based on the CPT-violating gravitational interaction between derivative of the Ricci scalar curvature and the baryon-number current is investigated in the context of the f(R) gravity. The gravitational baryogenesis in the Bianchi type I (BI) Universe is examined. We survey the effect of anisotropy of the Universe on the baryon asymmetry from the point of view of the f(R) theories of gravity and its effect on $n_b/s$ for radiation dominant regime.

Anisotropic cosmological models are constructed in f(R, T) gravity theory to investigate the dynamics of universe concerning the late time cosmic acceleration. Using a more general and simple approach, the effect of the coupling constant and anisotropy on the cosmic dynamics have been investigated. In this study, it is found that cosmic anisotropy substantially affects cosmic dynamics.

We study the possibly existing anisotropy in the accelerating expansion Universe with various supernovae data, the baryon acoustic oscillation and the observational Hubble data. We present combined results from these probes, deriving constraints on the equation of state (EoS), $w$, of dark energy (DE) and its energy density in the Universe. We fit the cosmological parameters simultaneously employing the maximum likelihood analysis. By combining data and considering anisotropy effects, we find that the EoS of DE are $w(0.01\le z\le 1.75)=-0.998\pm 0.056$, $w(0<z<1)=-1.086\pm 0.065$, $w(0.15<z<1.1)=-1.096\pm 0.123$ and $w(0.01<z<2.3)=-1.0426\pm 0.054$ within $1{\sigma }^{\prime }$ confidence level. Finally, introducing an anisotropy appears to improve the fit to observations with respect to that provided by an isotropic $w$CDM model.

In this work, we consider the Universe is being filled with matter composed of a chameleon-type dark energy scalar field. Employing a particular form of potential, we discuss the field's role in the accelerating phase of the Universe for an anisotropic model using the logamediate and intermediate forms of scale factors. The natures of statefinder and slow-roll parameters are discussed diagrammatically.

This work is devoted to study the roles of Dirac–Born–Infeld (DBI)-essence, scalar field, phantom field, normal tachyonic field and phantom tachyonic field models driving the present expansion of the universe with acceleration in anisotropic background. To understand the different phase of the Bianchi I universe, the statefinder parameters and deceleration parameter are investigated diagrammatically. The radiation era to $\mathrm{\Lambda }$CDM model has been generated. The anisotropic parameters are analyzed during the evolution of the universe. It has been shown that DBI-essence, scalar field, phantom field, normal tachyonic field and phantom tachyonic field play an active role of dark energy which causes the acceleration of the anisotropic universe.

It was shown recently that a very simple nonlocal de Sitter gravity model contains exact vacuum cosmological solution which mimics dark energy and dark matter in flat space. Some other interesting solutions have been also found. In this paper, we proceed with finding several new exact cosmological solutions which belong to Bianchi I space. These solutions are simple generalizations of solutions previously found in the FLRW case of the same nonlocal de Sitter gravity model. Obtained results are discussed.

In this work, we have considered a noncanonical complex scalar field named hessence to play the role of quintom in anisotropic universe (particularly in the Bianchi I model) as a new approach to look into the unknown mysterious world of dark energy. We have solved the field equations by considering the power-law form of scale factors and found the potential function in terms of ϕ with some restrictions. We also show here that hessence can avoid the Q-ball formation in anisotropic universe.

In this paper, the dynamical behavior of the anisotropic universe has been investigated in $f(R,T)$ theory of gravity. The functional $f(R,T)$ has been rescaled in the form $f(R,T)=\mu R+\mu T$, where $R$ is the Ricci scalar and $T$ is the trace of energy momentum tensor. Three cosmological models are constructed using the power law expansion in Bianchi type $V{I}_h$ ($BV{I}_h$) universe for three different values of $h=-1,0,1$, where the matter field is considered to be of bulk viscous fluid. It is observed that the anisotropic $BV{I}_h$ model in the modified theory of gravity is in agreement with a quintessence phase for the value of $h=-1$ and $0$. We could not obtain a viable cosmological model in accordance with the present day observations for $h=1$. The bulk viscous coefficient in both the cases are found to be positive and remain constant at late time. The physical behaviors of the models along with the energy conditions are also studied.

We study effects of anisotropy (although low) on the ghost and generalized ghost dark energy (DE) models in the framework of fractal cosmology. We obtain the equation of state parameter, ${\omega }_{\mathrm{\text{DE}}}$, the deceleration parameter, and the evolution equation of the ghost and generalized ghost dark energy. We find that, in both models, ${\omega }_{\mathrm{\text{DE}}}$ cannot cross the phantom line and eventually the universe approaches a de-Sitter phase of expansion. We show that the anisotropy effects on ghost and generalized ghost dark energy (GDE) in fractal cosmology correspond to $\mathrm{\Lambda }$CDM limit on the statefinder plane. We evaluate the anisotropy effects on both the linear perturbation and the spherical collapse from the DE models and compare them with the results of the DE of the Friedmann–Robertson–Walker and $\mathrm{\Lambda }$CDM models. We also show that in ghost and generalized ghost cosmologies, the growth factor $g(a)$ rise front the values for an $\mathrm{\Lambda }$CDM universe. Finally, we constrain the model parameters by using the maximum likelihood analysis and a combined dataset of baryon acoustic oscillation (BAO) and OHD.

The impact of anisotropy on the Ricci dark energy cosmologies is investigated where it is assumed that the geometry of the universe is described by Bianchi type I (BI) metric. The main goal is to determine the astrophysical constraints on the model by using the current available data as type Ia supernovae (SNIa), the Baryon Acoustic Oscillation (BAO), and the Hubble parameter $H(z)$ data. In this regard, a maximum likelihood method is applied to constrain the cosmological parameters. Combining the data, it is found out that the allowed range for the density parameter of the model stands in $-3.6\times 10^{-3}\lesssim {\mathrm{\Omega }}_{{\sigma }_0}\lesssim -2.6\times 10^{-3}$. With the help of the Supernova Legacy Survey (SNLS) sample, we estimate the possible dipole anisotropy of the Ricci dark energy model. Then, by using a standard ${\chi }^2$ minimization method, it is realized that the transition epoch from early decelerated to current accelerated expansion occurs faster in Ricci dark energy model than $\mathrm{\Lambda }$CDM model. The results indicate that the BI model for the Ricci dark energy is consistent with the observational data.

In this paper, we have investigated an anisotropic cosmological model in $f(Q)$ gravity with string fluid in LRS Bianchi type-I universe. We have considered the arbitrary function $f(Q)=Q+\alpha \sqrt{Q}+2\mathrm{\Lambda }$, where $\alpha$ is model free parameter and $\mathrm{\Lambda }$ is the cosmological constant. We have established a relationship between matter energy density parameter ${\mathrm{\Omega }}_m$ and dark energy density parameter ${\mathrm{\Omega }}_{\mathrm{\Lambda }}$ through Hubble function using constant equation of state parameter $\omega$. We have made observational constraint on the model using ${\chi }^2$-test with observed Hubble datasets $H(z)$ and SNe Ia datasets, and obtained the best fit values of cosmological parameters. We have used these best fit values in the result and discussion. We have discussed our result with cosmographic coefficients and found a transit phase dark energy model. Also, we analyzed the Om diagnostic function for anisotropic universe and found that our model is quintessence dark energy model.

A spatially homogeneous and anisotropic Bianchi type-VI cosmological model in the framework of $f(Q,T)$ gravity has been studied by considering three different functional forms of $f(Q,T)$ i.e. $f(Q,T)=aQ+bT$, $f(Q,T)=a{Q}^k+bT$ and $f(Q,T)=-aQ-b{T}^2$. The field equation of $f(Q,T)$ gravity has been solved with the help of the Bianchi type-VI line element. The cosmological parameters of the models are evaluated, and the dynamical aspects of the model have been discussed. The result agrees with the observations of accelerated expansion of the universe.

The Barrow’s Holographic Dark Energy (BHDE) Model is proposed in an axially symmetric anisotropic spacetime which is employing Hubble horizon as an infrared cutoff (IR cutoff). The transition of the universe from a matter dominated era to a dark energy dominated era is investigated in this model. Furthermore, the Equation of State (EoS) parameter explains how the universe evolves with non-extensive term or Barrow parameter $\mathrm{\Delta }$ for both phase (i) phantom era (${\omega }_B\le -1$) and (ii) quintessence era (${\omega }_B\ge -1$). In order to reconcile the dark energy, the reconstruction of scalar field potential is considered. Some of the physical properties of the model are also described.