Narrow Results

In this paper, we explore the possibility of formation of a traversable wormhole in General Relativity supported by particle creation mechanism. The repulsive back-reaction pressure generated through this mechanism can be thought of as a source of sustaining a traversable wormhole. In the first part of this paper, we model a wormhole geometry by assuming an inverse powerlaw variation of particle creation pressure within the wormhole geometry, and the shape function for the wormhole is obtained, assuming a finite redshift function. By stabilizing the wormhole structure, based on the causality of sound-speed we obtained the existence range of the parameter $\beta$ associated with particle creation mechanism. The general shape function obtained is found to adhere to the feasibility conditions of a viable wormhole geometry. Then we studied the 2D and 3D embedding derived for the obtained shape function. In the second part of the paper, we followed the reverse approach of the aforementioned treatment, where we derived the particle creation pressures by assuming three commonly utilized toy shape-functions. The energy conditions are then investigated for all these cases. In essence, particle creation phenomena inside the wormhole may indeed provide for the possibility of sustenance of stable wormhole structure.

The f(G) gravity is a theory to modify the general relativity and it can explain the present cosmic accelerating expansion without the need of dark energy. In this paper the f(G) gravity is tested with the energy conditions. Using the Raychaudhuri equation along with the requirement that the gravity is attractive in the FRW background, we obtain the bounds on f(G) from the SEC and NEC. These bounds can also be found directly from the SEC and NEC within the general relativity context by the transformations: ρ → ρ_m + ρ_E and p → p_m + p_E, where ρ_E and p_E are the effective energy density and pressure in the modified gravity. With these transformations, the constraints on f(G) from the WEC and DEC are obtained. Finally, we examine two concrete examples with WEC and obtain the allowed region of model parameters.

In the present paper, the modeling of traversable wormholes, proposed by Morris and Thorne [Am. J. Phys.56, 395 (1988)], is performed within the $f(R)$ gravity with particular viable case $f(R)=R-\mu R_c{(\frac{R}{R_c})}^p$, where $\mu$, $R_c>0$ and $0<p<1$. The energy conditions are analyzed using the shape function $b(r)=\frac{rlog(r+1)}{log(r_0+1)}$ defined by Godani and Samanta [Int. J. Mod. Phys. D28, 1950039 (2018)] and the geometric nature of wormholes is analyzed.

First, we illustrate that a conformally flat generalized Ricci recurrent spacetime is a perfect fluid spacetime. As a consequence, we prove that such a spacetime represents a dust matter fluid, stiff matter and dark energy era under certain restrictions on the Ricci scalar. Then we establish that such a spacetime is a Robertson–Walker spacetime. Also, we note that in a conformally flat generalized Ricci recurrent spacetime, the fluid is shear-free, vorticity-free and its flow vector is hypersurface orthogonal. We investigate a conformally flat generalized Ricci recurrent spacetime as a solution of curvature-squared gravity theory. In this study, various energy conditions in terms of the Ricci scalar are examined and state that the Universe is in an accelerating phase and satisfies the weak, null, dominant, and strong energy conditions.

In this paper, we delve into the cosmological assessments concerning the deceleration parameter $q=\kappa -\frac{\gamma }{H}$ in the context of the Bianchi type-III cosmological model within the framework of the Saez–Ballester theory of gravitation. By postulating a proportional relationship between the shear scalar ($\sigma$) and the expansion scalar ($\theta$), we derive solutions for the corresponding field equations. Additionally, we conduct an examination and evaluation of the model’s physical and kinematic parameters, including the jerk parameter and snap parameter, while also discussing the energy condition of the model. Through the depiction of graphical representations, we illustrate the variations of the cosmological parameters for specific sets of constants.

In this paper, the strong gravitational lensing is explored for traversable wormholes in $f(R,T)$ theory of gravity with minimally-coupled massless scalar field. First, the effective wormhole solutions are obtained using the model $f(R,T)=R+2\lambda T$, where $\lambda$ is constant, $R$ is scalar curvature and $T$ is the trace of stress-energy tensor. Furthermore, three different shape functions namely, $b(r)=\frac{r_0}{exp(r-r_0)}$ (Ref. 36), $b(r)=\frac{r_0(log(r+1))}{log(r_0+1)}$ (Refs. 35 and 37) and $b(r)=r_0{\left(\frac{r}{r_0}\right)}^{\gamma }$, $0<\gamma <1$ (Refs. 34, 35, 39, 73) are considered and studied their qualitative behavior for the construction of wormhole geometry respectively. Subsequently, gravitational lensing effect is implemented to detect the existence of photon spheres at or outside the throat of wormholes.

This paper deals with some wormhole solutions which are obtained by taking two different shape functions along with zero tidal force. For obtaining wormhole solutions, anisotropic fluid and a equation of state $p_t=-\frac{a}{\rho }$ related by Chaplygin gas are considered, where $\rho$ is the energy density, $p_t$ is tangential pressure and $a$ is positive constant. Energy conditions are examined for two different models, and it is found that major energy conditions are satisfied in a region.

In this paper, we present the first interior solutions representing compact stars in $\kappa ({ℛ},{𝒯})$ gravity by solving the modified field equations in isotropic coordinates. Further, we have assumed the metric potentials in Schwarzschild’s form and a few parameters along with the isotropic condition of pressure. For solving, we use specific choice of the running gravitational constant as $\kappa ({ℛ},{𝒯})=8\pi -\lambda {𝒯}(G=\tilde{c}=1)$. Once arrived at the reduced field equations, we investigate two solutions with $c=1$ and $c\ne 1$, where $c$ denotes here another constant that should not be confused with the speed of light. Then, we investigate each solution by determining the thermodynamics variable viz pressure, density, speed of sound and adiabatic index. We found that these solutions satisfy the Bondi criterion, causality condition and energy conditions. We also found that the $M-R$ curves generated from these solutions satisfy the stringent constraints provided by the gravitational wave observations due to the neutron star merger GW 170817.

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.

Traversable wormholes, tunnel-like structures introduced by Morris and Thorne [Am. J. Phys.56 (1988) 395], have a significant role in connection of two different spacetimes or two different parts of the same spacetime. The characteristics of these wormholes depend upon the redshift and shape functions which are defined in terms of radial coordinate. In literature, several shape functions are defined and wormholes are studied in $f(R)$ gravity with respect to these shape functions [F. S. N. Lobo and M. A. Oliveira, Phys. Rev. D80 (2009) 104012; H. Saiedi and B. N. Esfahani, Mod. Phys. Lett. A26 (2011) 1211; S. Bahamonde, M. Jamil, P. Pavlovic and M. Sossich, Phys. Rev. D94 (2016) 044041]. In this paper, two shape functions (i) $b(r)=\frac{r_{0}log(r+1)}{log(r_0+1)}$ and (ii) $b(r)=r_0{(\frac{r}{r_0})}^{\gamma }$, $0<\gamma <1$, are considered. The first shape function is newly defined, however, the second one is collected from the literature [M. Cataldo, L. Liempi and P. Rodríguez, Eur. Phys. J. C77 (2017) 748]. The wormholes are investigated for each type of shape function in $f(R)$ gravity with $f(R)=R+\alpha R^m-\beta R^{-n}$, where $m$, $n$, $\alpha$ and $\beta$ are real constants. Varying the parameter $\alpha$ or $\beta$, $f(R)$ model is studied in five subcases for each type of shape function. In each case, the energy density, radial and tangential pressures, energy conditions that include null energy condition, weak energy condition, strong energy condition and dominated energy condition and anisotropic parameter are computed. The energy density is found to be positive and all energy conditions are obtained to be violated which support the existence of wormholes. Also, the equation-of-state parameter is obtained to possess values less than $-1$, that shows the presence of the phantom fluid and leads toward the expansion of the universe.

In this paper, we study the traversable wormhole solutions for a logarithmic corrected $f(R)$ model by considering two different statements of shape $b(r)$ and redshift $\mathrm{\Phi }(r)$ functions. We calculate the parameters of the model including energy density $\rho$, tangential pressure $P_t$ and radial pressure $P_r$ for the corresponding forms of the functions. Then, we investigate different energy conditions such as null energy condition, weak energy condition, dominant energy condition and strong energy condition for our considered cases. Finally, we explain the satisfactory conditions of energy of the models by related plots.

In this paper, we characterize weakly Ricci-symmetric (shortly, ${\mathrm{\text{(}}\text{WRS})}_4$) spacetimes and their solutions in $f({ℛ})$-gravity. It is demonstrated that a ${\mathrm{\text{(}}\text{WRS})}_4$ spacetime represents a stiff matter fluid. In addition, we obtain that a conformally flat ${\mathrm{\text{(}}\text{WRS})}_4$ spacetime is a space of quasi-constant sectional curvature. Moreover, we establish that a Ricci symmetric ${\mathrm{\text{(}}\text{WRS})}_4$ spacetime represents a static spacetime. Finally, we investigate the effect of ${\mathrm{\text{(}}\text{WRS})}_4$ spacetime solutions in $f({ℛ})$-gravity.

This research work provides an exhaustive investigation of the viability of different coupled wormhole (WH) geometries with the relativistic matter configurations in the $f(R,G,T)$ extended gravity framework. We consider a specific model in the context of $f(R,G,T)$-gravity for this purpose. Also, we assume a static spherically symmetric spacetime geometry and a unique distribution of matter with a set of shape functions ($\beta (r)$) for analyzing different energy conditions. In addition to this, we examined WH-models in the equilibrium scenario by employing anisotropic fluid. The corresponding results are obtained using numerical methods and then presented using different plots. In this case, $f(R,G,T)$ gravity generates additional curvature quantities, which can be thought of as gravitational objects that maintain irregular WH-situations. Based on our findings, we conclude that in the absence of exotic matter, WH can exist in some specific regions of the parametric space using modified gravity model as $f(R,G,T)=R+\alpha R^2+\beta G^n+\gamma Gln(G)+\lambda T$.

This work is focused on the study of charged wormholes in the following two aspects: (i) to obtain exotic matter free effective charged wormhole solutions and (ii) to determine deflection angle for gravitational lensing effect. We have defined a novel redshift function, obtained wormhole solutions using the background of $f(R)$ theory of gravity and found the regions obeying the weak energy condition. Further, the gravitational lensing effect is analyzed by determining the deflection angle in terms of strong field limit coefficients.

In this paper, traversable wormholes have been studied in $f(R)=R+\alpha R^m+\beta R^{-n}$ gravity, where $\alpha$, $\beta$, $m>0$ and $n>0$ are constant. A simplest form of shape function and a logarithmic form of redshift function is considered to construct wormhole solutions. The range of parameters providing the wormhole solutions free from the matter violating the energy conditions is explored. Further, the effect of charge is analyzed on wormhole solutions.

This paper is focused on the study of charged wormholes which are combinations of Morris–Thorne wormhole and Reissner–Nordström spacetime. Gravitational lensing is an important tool which has been adopted to detect various objects like wormholes using the notion of deflection angle. In this work, we have evaluated deflection angle with and without using the strong field limit coefficients and compared the results. Further, exact charged wormhole solutions are obtained in $f(R,T)$ gravity and the nature of the energy conditions is examined.

This work is aimed at the study of traversable wormholes, proposed by Morris and Thorne [Wormholes in spacetime and their use for interstellar travel: A tool for teaching general relativity, Am. J. Phys. 56 (1988) 395], in the framework of $f(R,T)=R+\alpha R^n+\lambda T$ gravity, where $\alpha$, $\lambda$ and $n$ are constants. The wormhole solutions are obtained and analyzed by using a simplest form of shape function. Further, the existence of photon spheres outside the throat of wormhole due to the gravitational lensing effect is detected.

In this paper, Morris Thorne wormholes are considered in the context of $f(R)$ gravity. A shape function is defined as $b(r)=r_0(1-k)+k\frac{r_0^2}{r}$, where $k$ is constant. The equation of state is considered as $p_t=-\rho$ and $f(R)$ function is derived. The wormhole solutions are obtained and energy conditions are examined. Further, the $f(R)$ model is found to be consistent with local gravity tests and stability of cosmological perturbations and late-time de Sitter point. Cosmological evolution is also explored using Friedman-Robertson-Walker (FRW) metric in $f(R)$ gravity.

Horizonless compact objects with light rings are becoming more popular in recent years for numerous motives. In this paper, the conditions under which the throat of a Morris–Thorne wormhole can act as an effective photon sphere are worked out. A specific example which satisfies all the energy conditions in modified theory of gravity is considered and the formation of relativistic images is studied. We have detected photon spheres for the wormhole modeling due to the effect of strong gravitational lensing. Subsequently, we have found the expression for deflection angle in terms of the angular separation between the image and lens by determining the strong-field limit coefficients. It is found to diverge for the impact parameter corresponding to the photon sphere. We observed that the angle of Einstein ring ${𝜃}_0$ and relativistic Einstein ring ${𝜃}_{n\ge 1}$ are completely distinguishable. Given the configuration of the gravitational lensing and the radii of the Einstein ring and relativistic Einstein rings, we can distinguish between a black hole and a wormhole in principle. The stability of wormholes is examined from the positivity of the shape function and satisfaction of the flare-out condition.

Kim and Lee [Phys. Rev. D 63 (2001) 064014] studied charged wormholes and Morris–Thorne wormholes in the presence of scalar field using the concepts of general relativity. In this paper, we have also considered same wormholes affected with electric charge and scalar field and extended their study using the framework of $f(R,T)$ gravity with $f(R,T)=R+\beta R^2+\lambda T$ gravity model, where $\beta$ and $\lambda$ are constants. We have examined the possibility for minimization of the amount of exotic matter through energy conditions. Further, we have obtained the deflection angle, an important notion in gravitational lensing, by using strong field limit coefficients which may be helpful in the detection of wormholes.