We study the cosmological evolutions of equation state for dark energy $w_{\mathrm{DE}}$ in exponential and logarithmic as well their combination $f(T)$ theories. show that crossing phantom divide line $w_{\mathrm{DE}} = -1$ can be realized combined theory even though it cannot or theory. In particular, is from > to < -1$, opposite manner $f(R)$ gravity models. also demonstrate this feature favored by recent observational data.

We review inflationary cosmology in modified gravity such as $R^2$ with its extensions order to generalize the Starobinsky inflation model. In particular, we explore realized by three kinds of effects: modification gravity, quantum anomaly, and term loop cosmology. It is explicitly demonstrated that these models, spectral index scalar modes density perturbations tensor-to-scalar ratio can be consistent Planck results. Bounce $F(R)$ also explained.

We demonstrate that there appear finite-time future singularities in $f(T)$ gravity with $T$ being the torsion scalar. reconstruct a model of realizing singularities. In addition, it is explicitly shown power-low type correction term $T^\beta$ ($\beta>1$) such as $T^2$ can remove gravity. Moreover, we study models inflation early universe, $\Lambda$CDM model, Little Rip cosmology and Pseudo-Rip cosmology. It demonstrated disintegration bound structures for cosmologies occurs same way...

Employing the modified entropy-area relation suggested by Tsallis and Cirto \cite{non3}, holographic hypothesis, a new dark energy (HDE) model is proposed. Considering flat Friedmann-Robertson-Walker (FRW) universe in which there no interaction between cosmos sectors, cosmic implications of proposed HDE are investigated. Interestingly enough, we find that identification IR-cutoff with Hubble radius, can lead to late time accelerated Universe even absence two sectors Universe. This contrast...

We reconstruct $F(R)$ gravity models with exponential and power-law forms of the scale factor in which bounce cosmology can be realized. explore stability reconstructed analyzing perturbations from background solutions. Furthermore, we study an model a sum exponentials form factor, where early universe as well late-time cosmic acceleration realized unified manner. As result, build second order polynomial type terms $R$ show that it could stable. Moreover, when is expressed by form, derive...

We investigate irregularity factors for a self-gravitating spherical star evolving in the presence of imperfect fluid. explore gravitational field equations and dynamical with systematic construction $f(R,T)$ gravity, where $T$ is trace energy-momentum tensor. Furthermore, we analyze two well-known differential (which occupy principal importance exploration causes energy density inhomogeneities) help Weyl tensor conservation laws. The are examined particular cases dust, isotropic anisotropic...

In order to apply holography and entropy relations the whole universe, which is a gravitational thus nonextensive system, for consistency one should use generalized definition universe horizon entropy, namely Tsallis entropy. We formulate holographic dark energy, generalization of standard energy quantified by new dimensionless parameter δ, possessing latter as particular sub-case. provide simple differential equation density parameter, well an analytical expression its equation-of-state...

Abstract In our investigation, we pioneer the development of geometrically deformed strange stars within framework teleparallel gravity theory through gravitational decoupling via complete geometric deformation (CGD) technique. The significant finding is precise solution for star (SS) models achieved vanishing complexity factor scenario. Further, introduce concept space-time caused by dark matter (DM) content in DM haloes, leading to perturbations metric potentials $$g_{tt}$$ <mml:math...

We investigate the future evolution of dark energy universe in modified gravities, including F(R) gravity, and string-inspired scalar Gauss–Bonnet ones, ideal fluid with an inhomogeneous equation state (EoS). The Friedmann–Robertson–Walker dynamics for all these theories may be presented a universal form by using effective EoS without specifying its explicit form. construct several examples gravity which produces accelerating cosmologies ending at finite-time singularities four known types...

We study inflation and late-time acceleration in the expansion of universe non-minimal electromagnetism, which electromagnetic field couples to scalar curvature function. It is shown that power-law can be realized due gravitational coupling field, large-scale magnetic fields generated breaking conformal invariance through its coupling. Furthermore, it demonstrated both a modified Maxwell-F(R) gravity consistent with solar-system tests cosmological bounds free instabilities. At small typical...

The generation of large-scale magnetic fields is studied in dilaton electromagnetism inflationary cosmology, taking into account the dilaton's evolution throughout inflation and reheating until it stabilized with possible entropy production. It shown that an observationally interesting strength at present time could be generated if conformal invariance Maxwell theory broken through coupling between electromagnetic such a way resultant quantum fluctuations field have nearly scale-invariant...

We discuss conformal issues of pure and extended teleparallel gravity. In particular, we present formulations transformation in Furthermore, propose scalar gauge field theories gravity study torsion explicitly demonstrate that a power-law acceleration (including the $\ensuremath{\Lambda}\mathrm{CDM}$ universe) as well de Sitter expansion Universe can be realized with field, lead to model. It is also shown solution exist

We study inflationary cosmology and the late-time accelerated expansion of universe in nonminimal Yang-Mills (YM) theory, which YM field couples to a function scalar curvature. It is shown that power-law inflation can be realized due field-gravitational coupling may caused by quantum corrections. Moreover, it demonstrated both modified YM-$F(R)$ gravity consistent with solar-system tests. Furthermore, this result also vector-$F(R)$ gravity. In addition, we consider duality electromagnetic...

We explore thermodynamics of the apparent horizon in f(T) gravity with both equilibrium and non-equilibrium descriptions. find same dual equilibrium/non-equilibrium formulation for as f(R) gravity. In particular, we show that second law can be satisfied universe temperature outside inside horizon.

We explore bounce cosmology in F(G) gravity with the Gauss–Bonnet invariant G. reconstruct theory to realize bouncing behavior early universe and examine stability conditions for its cosmological solutions. It is demonstrated that an exponential as well a power-law scale factor naturally occurs modified gravity. also derive model produce ekpyrotic scenario. Furthermore, we construct composed of sum two functions show not only early-time but late-time cosmic acceleration can occur...

We investigate the descriptions for observables of inflationary models, in particular, spectral index curvature perturbations, tensor-to-scalar ratio, and running index, framework perfect fluid models $F(R)$ gravity theories through reconstruction methods. Furthermore, inflation are compared with recent cosmological observations such as Planck satellite BICEP2 experiment. It is demonstrated explicit examples that may lead to universe consistent data. also shown several especially, a...

We explore the evolutionary behaviors of compact objects in a modified gravitational theory with help structure scalars. Particularly, we consider spherical geometry coupled heat- and radiation-emitting shearing viscous matter configurations. construct scalars by splitting Riemann tensor orthogonally $f(R,T)$ gravity without constant $R$ $T$ constraints, where is Ricci scalar trace energy-momentum tensor. investigate influence modification on physical meaning functions for radiating It...

We reconstruct an explicit model of modified gravity in which a crossing the phantom divide can be realized. It is shown that (finite-time) Big Rip singularity appears (i.e., so-called Jordan-frame), whereas corresponding scalar field theory obtained through conformal transformation Einstein frame) becomes infinite-time one. Furthermore, we investigate relations between theories with realizing and gravitational by using inverse transformation. demonstrated describing nonphantom phase...

We explore the possibility of further gravitational wave modes in $F(T)$ gravity, where $T$ is torsion scalar teleparallelism. It explicitly demonstrated that gravity are equivalent to those General Relativity. This result achieved by calculating Minkowskian limit for a class analytic function $F(T)$. consequence also confirmed preservative analysis around flat background weak field with scalar-tensor representation gravity.

We demonstrate how holonomy corrections in loop quantum cosmology (LQC) prevent the Big Rip singularity by introducing a quadratic modification terms of energy density ρ Friedmann equation Friedmann-Lemaître-Robertson-Walker (FLRW) space-time consistent and useful way. In addition, we investigate whether other kind singularities like Type II,III IV survive or are avoided LQC when universe is filled barotropic fluid with state P = −ρ−f(ρ), where pressure f(ρ) function ρ. It shown that Little...

We explore the effects of considering various infrared (IR) cutoffs, including particle horizon, Ricci horizon and Granda-Oliveros (GO) on properties Tsallis holographic dark energy (THDE) model, proposed inspired by generalized entropy formalism \cite{THDE}. Interestingly enough, we find that for as IR cutoff, obtained THDE model can describe accelerated universe. This is in contrast to usual HDE which cannot lead an universe, if one consider cutoff. also investigate cosmological...

We explore trace-anomaly driven inflation in modified gravity. It is explicitly shown that $T^2$ teleparallel gravity, the de Sitter can occur, although quasi happens $R^2$ Furthermore, we investigate influence of trace anomaly on inflation. found $f(T)$ end because it becomes unstable due to anomaly, whereas also higher derivative be realized and will over thanks for smaller parameter regions comparison with those teleparallelism. The instability gravity (both taking account anomaly)...