Narrow Results

In this paper we consider a non-minimally coupled scalar field, and show that its equation of state parameter can cross over -1, ω→-1, and bouncing condition. Also we obtain the stability conditions and consider reconstructing for our model.

In this paper we consider FRW cosmology in modified gravity which contains arbitrary functions f(ϕ). It is shown that the bouncing solution appears in the model whereas the equation of state (EoS) parameter crosses the phantom divider. The reconstruction of the model is also investigated with the aim to reconstruct the arbitrary functions and variables of the model.

In this paper, we examine the potential strong coupling problem at early times in a bouncing cosmological model with “strong gravity in the past” (Jordan frame), which is conformally related to inflation (Einstein frame). From naive-dimensional analysis in the Jordan frame, one would conclude that the quantum strong coupling energy scale can be lower than the classical energy scale. However, from the Einstein frame prospective, this should not be the case. We illustrate this point by calculation in the Jordan frame which shows cancellations of the dangerous contributions in the tree level amplitude.

We study in this paper chameleon cosmology applied to Friedmann–Robertson–Walker space, which gives rise to the equation of state (EoS) parameter larger than -1 in the past and less than -1 today, satisfying current observations. We also study cosmological constraints on the model using the time evolution of the cosmological redshift of distant sources, which directly probes the expansion history of the universe. Due to the evolution of the universe's expansion rate, the model-independent cosmological redshift drift (CRD) test is expected to experience a small, systematic drift as a function of time. The model is supported by the observational data obtained from the test.

In this paper, we investigate the effect modified dispersion relation (MDR) on the entropy-area relation of FRW universe, leading to the modification of Friedmann equations. In this regard, we show that limitations imposed by MDR leads to certain modifications of bouncing universe thermodynamics.

This paper is devoted to study FRW universe in the context of Chern–Simons corrected $f(R)$ gravity. In particular, the work provides the investigation of cosmological dynamics within modified gravity by assuming a suitable Hubble parameter that might result in a realistic bouncing universe. For this purpose, we consider a suitable Hubble parameter and examine the bouncing cosmology by assuming a well-known $f(R)$ gravity model. Further, we explore the behavior of energy density and pressure profiles by employing the chosen Hubble parameter. We obtain positive and increasing trends of energy density during the bouncing phase while the negative behavior of pressure in our work could potentially be associated with cosmic expansion. We have also studied the energy conditions and in our case NEC is not violated perhaps due to the reason that the equation of state parameter is not crossing the phantom divide. However, the SEC is violated justifying a successful bounce. Moreover, the validation of DEC and TEC suggests that the chosen model is well behaved in nature. The Hubble parameter passing through the bouncing point shows an increasing trend, indicating an expansion phase after the bounce. The equation of state parameter is negative after the bouncing spot, particularly around $\omega \approx -1$. This behavior justifies the current cosmic expansion. The deceleration parameter exhibits a negative behavior implies that the cosmological model demonstrates cosmic expansion. Thus all the results validate the existence of a bouncing universe with the chosen model in Chern–Simons corrected $f(R)$ gravity.

In this paper, we investigate the bouncing universe in a modified gravity model $f(Q,T)$. The bouncing universe theory posits that the universe goes through periodic expansions and contractions, with a “bounce” occurring at the end of each contraction that leads to a new expansion. This theory suggests that our universe didn’t emerge on its own out of nothing, but is instead the latest in a series of universes that have been expanding and contracting for eternity. It has gained renewed interest in recent years as a potential alternative to the Big Bang theory, which suggests that our universe began with a massive expansion from a singularity. According to the above explanations, first, we review of $f(Q,T)$ gravity model, then the bouncing universe scenario according to the $f(Q,T)$ gravity model in some special functions is analyzed in detail. We find that in which condition of parameters space, bouncing occurs.

We study locally rotationally symmetric (LRS) Bianchi type-I cosmological model in the presence of general theory of relativity. The source for energy–momentum tensor is assumed a perfect fluid. The field equations have been solved by using special form of the average scale factor $a(t)={[{(t-t_0)}^2+\frac{t_0}{1-\beta }]}^{\frac{1}{1-\beta }}$, where $t_0$ is initial cosmic time and $\beta <1$ is constant, proposed by Cai et al. [J. High Energy Phys.710, 071 (2007)]. The physical properties and bouncing behavior of the model are discussed through graphical representation. The violation of strong energy condition (SEC) further supports the behavior of accelerated expansion of the Universe. The stability analysis of the model is discussed through geometrical representation.

In this work, we have studied how incorporating viscous fluids leads to exact bounce cosmological solutions in general relativity (GR) framework. Specifically, we propose a novel parameterization of bulk viscosity coefficient of the form $\zeta ={\zeta }_0{(t-t_0)}^{-2n}H$, where ${\zeta }_0$, with $n$ being some positive constants and $t_0$ being the bounce epoch. We investigate how this form of bulk viscosity may assist in explaining the early universe’s behavior, with a particular focus on non-singular bounce scenario by studying the various energy conditions and other related cosmological observables and how the model parameters affect the evolution of the Universe. We demonstrate that the null energy conditions (NEC) and strong energy conditions (SEC) violation occurs at the bounce point while dominant energy conditions (DEC) is satisfied. Finally, we carried out a stability check based on linear order perturbation to the Hubble parameter. We found that the perturbation vanishes asymptotically at later times, which indicates a stable behavior of the bounce scenario.