Traversable wormhole in logarithmic f(R) gravity by various shape and redshift functions

In this paper, we study the traversable wormhole solutions for a logarithmic corrected [Formula: see text] model by considering two different statements of shape [Formula: see text] and redshift [Formula: see text] functions. We calculate the parameters of the model including energy density [Formula: see text], tangential pressure [Formula: see text] and radial pressure [Formula: see text] 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.

A new shape function and some specific wormhole solutions in braneworld scenario

Considering an energy density of the form [Formula: see text] (where [Formula: see text] is an arbitrary positive constant with dimension of energy density and [Formula: see text]), a shape function is obtained by using field equations of braneworld gravity theory in this paper. Under isotropic scenario wormhole solutions are obtained considering six different redshift functions along with the obtained new shape function. For anisotropic case, wormhole solutions are obtained under the consideration of five different shape functions along with the redshift function [Formula: see text], where [Formula: see text] is an arbitrary constant. In each case all energy conditions are examined and it is found that for some cases all energy conditions are satisfied in the vicinity of the wormhole throat and for the rest of the cases all energy conditions are satisfied except strong energy condition.

Repulsive gravitational force and quintessence field in f(T) gravity: How anisotropic compact stars in strong energy condition behave

Recently literature is found to be enriched with studies related to anisotropic behaviors of different compact stars in the background of [Formula: see text] gravity in different energy conditions. Quintessence field, as local impacts of cosmic acceleration upon the compact stars, is also very interesting in recent studies. In this paper, the quintessential field effects on the compact stars (mainly on the neutron stars with an wide range of mass distributions), repulsive gravitational effects inside the compact stars due to dark matter distribution in them, charge distribution inside them in strong energy condition, etc. are studied. All required equations of motion using anisotropic property and concept of Massachusetts Institute of Technology bag model are acquired. Black holes surrounded by quintessential matters which satisfy the additive and linearity conditions, with the form of energy tensors were proposed and the corresponding metric was derived by Kiselev.1 The metric, described by Krori and Barua2 with Reissner–Nordström metric3 are compared to find out the different numerical values of unknown parameters. The numerical values are derived and some important parameters like anisotropic stress, adiabatic constant, surface redshift, electric intensity, compactness factor, stability etc. are analyzed deeply to get a clear idea for further study on these types of stars and to understand their nature.

Energy conditions in mimetic-f(R) gravity

The energy conditions of mimetic-[Formula: see text] gravity theory is analyzed. We will obtain the parameter space of the theory in some special forms of [Formula: see text] in which the self-acceleration is allowed. In this sense, the parameter space is obtained in a way that it violates the strong energy condition while satisfying the weak, null and dominant energy conditions. We will also consider the condition that the Dolgov–Kawasaki instability is avoided. This condition will be further imposed in the parameter space of the theory. We will show that the parameter space of the mimetic-[Formula: see text] gravity is larger than [Formula: see text] gravity theory.

Necessary conditions for having wormholes in f(R) gravity

For a generic f(R) which admits a polynomial expansion, we find the near-throat wormhole solution. Necessary conditions for the existence of wormholes in such f(R) theories are derived for both zero and nonzero matter sources. For vanishing external sources, we show that the energy conditions are violated. A particular choice of energy–momentum reveals that the wormhole geometry satisfies the weak energy condition (WEC). For a range of parameters, even the strong energy condition (SEC) is shown to be satisfied.