Narrow Results

We analyze the universe as a thermodynamic system, homogeneously filled up by exotic matters popularly named as dark energies. Different dark energy models are chosen. We start with the equation of continuity and derive the time and scale factor relations for different EoSs of different dark energy models. To do the time-scale factor relation analysis, nature of dependences on different dark energy modeling parameters have been studied. For this, the help of different plots are used. In general, different dark energies show different properties while occurrences of future singularities are considered. Those properties can be supported by the graphical analysis of their cosmic time-scale factor studies.

We consider a homogeneous and isotropic Universe, described by the minisuperspace Lagrangian with the scale factor as a generalized coordinate. We show that the energy of a closed Universe is zero. We apply the uncertainty principle to this Lagrangian and propose that the quantum uncertainty of the scale factor causes the primordial fluctuations of the matter density. We use the dynamics of the early Universe in the Einstein–Cartan theory of gravity with spin and torsion, which eliminates the big-bang singularity and replaces it with a nonsingular bounce. Quantum particle production in highly curved spacetime generates a finite period of cosmic inflation that is consistent with the Planck satellite data. From the inflated primordial fluctuations we determine the magnitude of the temperature fluctuations in the cosmic microwave background, as a function of the numbers of the thermal degrees of freedom of elementary particles and the particle production coefficient which is the only unknown parameter.

To justify the 20-year old distant Ia Supernova observations which revealed to us that our universe is experiencing a late-time cosmic acceleration, propositions of existence of exotic fluids inside our universe are made. These fluids are assumed to occupy homogeneously the whole space of the universe and to exert negative pressure from inside such that the late-time accelerated expansion is caused. Among the different suggested models of such exotic matters/energy popularly coined as dark matter/dark energy (DE), a well-known and popular process is “introduction of redshift parametrization” of the equation of state (EoS) parameter of these fluids. We, very particularly, take the parametrization proposed by Barboza and Alcaniz (BA) along with the cosmological constant. We use 39 data points for Hubble’s parameter calculated for different redshifts and try to constrain the DE EoS parameters for BA modeling. We then constrain the DE parametrization parameters in the background of Einstein’s general relativity, loop quantum gravity and Horava–Lifshitz gravity one after another. We find the $1\sigma$, $2\sigma$ and $3\sigma$ confidence contours for all these cases and compare them with each other. We try to speculate which gravity is constraining the parameters most and which one is letting the parameters to stay within a larger domain. We tally our results of 557 points Union2 Sample and again compare them for different gravity theories.

The main motivation of our study is to explore Rényi holographic dark energy, Sharma–Mittal holographic dark energy, Rényi new agegraphic dark energy, and Sharma–Mittal new agegraphic dark energy in the context of generalized Rastall gravity with the two-fluid system, dark energy, and dark matter. In this regard, we have considered the scale factors into two distinct categories, one of which corresponds to the future singularity, whereas the other represents initial singularity. By employing future event horizon as infrared (IR)-cutoff, different cosmological quantities like deceleration parameter, equation of state (EoS) parameter are evaluated, and their ramifications have been described graphically. Analyzing the squared speed of sound, we have seen classically stable and unstable behavior for each of the considered models. Finally, we study ${\omega }_D$–${\omega }_D^{\prime }$ plane and find the thawing/freezing regions.

In this paper, we develop a Hamiltonian formulation for the universe and show that it conforms with the accelerated expansion of the universe. We obtain some novel relations from this formulation which, though phenomenological, might be auspicious regarding a better perception of our universe.

In this work, we have studied various cosmological parameters in the presence of viscous new Tsallis holographic dark energies for interacting scenarios in the framework of Chern–Simons modified gravity. The bulk viscosity has been considered with the bulk viscous pressure chosen in the form $\mathrm{\Pi }=-3H\left(\right.{\xi }_0+{\xi }_{1}H+{\xi }_2(Ḣ+H^2)\left)\right.$. Hubble parameter $H$ has been obtained from the above choice of scale factor and in this viscous scenario, the effective pressure has been obtained in Chern–Simons framework whose field equation, cosmological consequences have been investigated. It has been observed that for the interaction scenario in the presence of bulk viscosity the EoS parameter is staying above $-1$, which indicates quintessence behavior. Hence, for the universe filled with a bulk viscous fluid can have the possibility of avoidance of big-rip, although the earlier transition from quintessence to phantom is not avoidable.

This study focuses on the cosmological evolution of Barrow holographic dark energy (BHDE) in a flat FLRW-universe. We take into account a time-dependent scale factor $a(t)={[sinh(kt)]}^{\frac{1}{n}}$, where k and n are positive values, to find the solutions to field equations. This scale factor results in a smooth transition of the universe from its previous decelerating stage to its most recent accelerating stage. Using the Granda–Oliveros cut-off, we examine the chronology of the deceleration parameter, equation of state parameter, and density parameter, and we analyze the positive aspects of the BHDE model. Negative pressure values in this model suggest dark energy dominance, resulting in the universe’s acceleration. We use the statefinder parameters ($r,s$) to improve the accuracy of the results of the dark energy model that is similar to the $\mathrm{\Lambda }$-CDM model.

We consider an Anti-de Sitter universe filled by quantum conformal matter with the contribution from the usual tachyon and a perfect fluid. The model represents the combination of a trace-anomaly annihilated and a tachyon driven Anti-de Sitter universe. The influence exerted by the quantum effects and by the tachyon on the AdS space is studied. The radius corresponding to this universe is calculated and the effect of the tachyon potential is discussed, in particular, concerning the possibility to get an accelerated scale factor for the proposed model (which yields an accelerated expansion of the AdS type of universe). Fulfillment of the cosmological energy conditions in the model is also investigated.

The recognition rate of SIFT algorithm in single hand vein database has been as high as 99.5%. But with the development of Internet-plus technology, the demand for distributed systems becomes more and more significant. However, the problem of picture quality caused by cross-device makes the intraclass variations larger. For example, when gathering the dorsal hand vein images, subtle changes in relative distance and orientation among the imaging camera, the illumination LED arrays and the different location of users’ hand, as well as shielding by the external housing box from ambient light sources and so on, these will make large difference to one person’s hand images. So, including the contrast, the lightness, the shifting, the angle of rotation, the size and so on, these differences make it possible to use some traditional methods to recognize dorsal hand vein with a low recognition rate of less than 50%. Therefore, based on the traditional SIFT, this paper optimized the scale factor $\sigma$, extreme searching neighborhood structure and matching threshold $R$. It can be seen that the cross-device hand vein feature is more robust, and the recognition rate reached an average of 88.5%.

In this paper, we would like to obtain the effect of the quantum backreaction on inflationary Starobinsky cosmology in spatially flat $D$-dimensional Friedmann–Robertson–Walker universe. For this purpose, first, we obtain the vacuum expectation value of energy–momentum tensor, which is separated into two parts, UV and IR. To calculate the UV contribution, we use the WKB approximation of the mode function of the equation of motion. Since the obtained value of this contribution of the vacuum expectation value of energy–momentum tensor is divergent, we should renormalize it. Therefore, by using the dimensional regularization and introducing a counterterm action, we eliminate divergences. After that, we calculate the contributions of IR part and trace anomaly. Thus, we obtain the quantum energy density and pressure during inflation era in this model. Finally, we can find the effect of backreaction on scale factor in inflation era, which leads to the new scale factor.

In this paper, we obtain the effect of backreaction on the scale factor of the Friedmann–Lemaître–Robertson–Walker (FLRW) and de Sitter spaces. We consider a non-minimally coupled massive scalar field to the curvature scalar. For our purpose, we use the results of vacuum expectation values of energy–momentum tensor, which have been obtained previously. By substituting the quantum energy density into the Friedmann equation, we obtain the linear order perturbation of the scale factor. So, the effect of backreaction leads to the new scale factor.

Here, we have investigated the interaction of Bianchi type-I anisotropic cloud string cosmological model universe with electromagnetic field in the context of general relativity. In this paper, the energy-momentum tensor is assumed to be the sum of the rest energy density and string tension density with an electromagnetic field. To obtain exact solution of Einstein’s field equations, we take the average scale factor as an integrating function of time. Also, the dynamics and significance of various physical parameters of model are discussed.

In order to analyze Barrow holographic dark energy (BHDE) in a flat FRW universe, the time-dependent scale factor $a(t)={[sinh(\alpha t)]}^{\frac{1}{n}}$ is employed. The Hubble horizon as the IR-cutoff is taken to investigate the cosmic consequences. We demonstrate the cosmic transition using the deceleration parameter and equation of state parameter. The characteristics of deceleration parameter for this model correspond well with the latest findings. The equation of state parameter behaves well and does not cross the phantom line. Depending on the values of Barrow exponent ($\mathrm{\Delta }$), our model is entirely quintessence and is eventually moving towards $\mathrm{\Lambda }\text{-CDM}$ model. We plotted the pressure diagram with various Barrow exponent ($\mathrm{\Delta }$) values to demonstrate dark energy dominance. The scalar field and potential that explain the universe’s accelerating expansion are also reconstructed.

In this paper, we investigate in this paper the Type IV singular bouncing in the framework of $f(R,{𝒢})$ theory of gravity where $R$ and ${𝒢}$ mean the curvature scalar and the Gauss–Bonnet invariant, respectively. Cosmological $f(R,{𝒢})$ models constrained by the slow-roll evolution is reconstructed and their explicit forms are provided near the bounce and far away from it. One obtains finally two models whose stability is numerically analyzed in this work. Our results show that the stability of the reconstructed models is very affected by their parameters. The model far from the singularity recovers stability quickly than the model near the singularity.

In this work, we study the F (R) gravity with f -essence for the flat and homogeneous Friedman-Robertson-Walker universe. For this model, we have presented the point-like Lagrangian and the corresponding field equations. To describe the dynamics of the universe, we have investigated some cosmological solutions for K, F and h functions. It is shown that these solutions describe the late time accelerated expansion of the Universe.

In this paper, an image edge detection algorithm based on FCM clustering and wavelet transform is presented. By this algorithm, we can not only detect the entire edge of original image, but also detect the edge of irregular sub-image that satisfies some characteristics. In the end, we compare it with Prewitt algorithm, Canny algorithm and Laplacia algorithm respectively. Experimental results show that the algorithm proposed in this paper has better performance in image edge detection.