Massive Brans Dicke Gravity Research Articles

Study of a Minimally Deformed Anisotropic Solution for Compact Objects with Massive Scalar Field in Brans–Dicke Gravity Admitting the Karmarkar Condition

In the present paper, we focused on exploring the possibility of providing a new class of exact solutions for viable anisotropic stellar systems by means of the massive Brans–Dicke (BD) theory of gravity. In this respect, we used the decoupling of gravitational sources by minimal geometric deformation (MGD) (e−η=Ψ+βh) for compact stellar objects in the realm of embedding class-one space-time to study anisotropic solutions for matter sources through the modified Einstein field equations. For this purpose, we used the ansatz for Ψ relating to the prominent, well-known and well-behaved Finch–Skea model via Karmarkar condition, and the determination scheme for deformation function h(r) was proposed via mimic requirement on radial pressure component: θ11(r)=pr(r) and matter density: θ00(r)=ρ(r) for the anisotropic sector. Moreover, we analyzed the main physical highlights of the anisotropic celestial object by executing several physical tests for the case θ11(r)=pr(r). We have clearly shown how the parameters α, β and ωBD introduced by massive BD gravity via the MGD approach incorporating the anisotropic profile of the matter distribution have an immense effect on many physical parameters of compact bodies such as LMC X-4, LMC X-4, Her X-1, 4U 1820-30, 4U 1608-52, SAX J1808.4–658 and many others that can be fitted.

Binary X-ray Sources in Massive Brans–Dicke Gravity

This study focuses on the X-ray emission of low-mass black hole binaries in massive Brans–Dicke gravity. First, we compute the accretion disk with the well-known Shakura–Sunyaev model for an optically thick, cool, and geometrically thin disk. Moreover, we assume that the gravitational field generated by the stellar-mass black hole is an analogue of the Schwarzschild space-time of Einstein’s theory in massive Brans–Dicke gravity. We compute the most relevant quantities of interest, i.e., (i) the radial velocity, (ii) the energy and surface density, and (iii) the pressure as a function entirely of the radial coordinate. We also compute the soft spectral component of the X-ray emission produced by the disk. Furthermore, we investigate in detail how the mass of the scalar field modifies the properties of the binary as described by the more standard Schwarzschild solution.

Relativistic Models for Strange Stars in Massive Brans–Dicke Gravity

Relativistic Models for Strange Stars in Massive Brans–Dicke Gravity

Post-Newtonian γ -like parameters and the gravitational slip in scalar-tensor and f(R) theories

We review the fundamentals and highlight the differences between some commonly used definitions for the PPN gamma parameter ($\ensuremath{\gamma}$) and the gravitational slip ($\ensuremath{\eta}$). Here we stress the usefulness of a gammalike parameter used by Berry and Gair (${\ensuremath{\gamma}}_{\mathrm{\ensuremath{\Sigma}}}$) that parametrizes the bending of light and the Shapiro time delay in situations in which the standard $\ensuremath{\gamma}$ cannot be promptly used. First we apply our considerations to two well-known cases, but for which some conflicting results can be found: massive Brans-Dicke gravity and $f(R)$ gravity (both the metric and the Palatini versions). Although the slip parameter is always well defined, it has in general no direct relation to either light deflection or the Shapiro time delay, hence care should be taken on imposing the PPN $\ensuremath{\gamma}$ bounds on the slip. We stress that, for any system with a well-posed Newtonian limit, Palatini $f(R)$ theories always have $\ensuremath{\gamma}=1$; while metric $f(R)$ theories can only have two values: either 1 or $1/2$. The extension toward Horndeski gravity shows no qualitative surprises, and ${\ensuremath{\gamma}}_{\mathrm{\ensuremath{\Sigma}}}$ is a constant in this context (only assuming that the Horndeski potentials can be approximated by analytical functions). This implies that a precise study on the bending of light for different impact parameters can in principle be used to rule out the complete Horndeski action as an action for gravity. Also, we comment on the consequences for $\ensuremath{\gamma}$ inferences at external galaxies.

Compact stars with MIT bag model in massive Brans-Dicke gravity

Compact stars with MIT bag model in massive Brans-Dicke gravity

Complexity analysis of dynamical cylinder in massive Brans–Dicke gravity

In this paper, a complexity factor is devised for a non-static cylindrical system in the framework of massive Brans–Dicke theory. The definition of complexity is developed by taking into account the essential physical characteristics (such as anisotropy and inhomogeneity.) of the system. In order to determine the complexity factor of the self-gravitating object, we acquire structure scalars from the orthogonal splitting of the Riemann tensor. Moreover, we discuss two patterns of evolution and choose the homologous mode as the simplest pattern under the influence of massive scalar field. We derive solutions in the absence as well as the presence of heat dissipation for a specific form of the scalar field. The factors that induce complexity in an initially complexity-free system are also examined. It is concluded that the massive scalar field as well as heat dissipation contribute to the complexity of the celestial system. Thus, a dynamical cylinder is more complex as compared to its static counterpart.

Analysis of strange quark stars in massive Brans–Dicke gravity

In this paper, we explore the behavior and anisotropic structure of quark stellar models in the framework of massive Brans–Dicke gravity. The system of field equations, representing a static sphere, is formulated by incorporating the MIT bag model. We use the Karmarkar condition for embedding class-one to formulate a relativistic model corresponding to a well-behaved radial metric function. The values of unknown parameters are determined through the matching of internal and external space–times at the hypersurface. The observed masses and radii of the strange star candidates (RXJ 1856-37, Her X-1 and PSR J1614-2230) specify the solution. Further, we evaluate the impact of the massive scalar field on state parameters and investigate the viability as well as stability of the self-gravitating objects. It is found that the obtained values of the bag constant (corresponding to each star) lie within the accepted range. Moreover, the anisotropic structure meets the necessary viability and stability criteria.

Quark Stars in Massive Brans–Dicke Gravity with Tolman–Kuchowicz Spacetime

In this paper, we construct anisotropic model representing salient features of strange stars in the framework of massive Brans–Dicke gravity. We formulate the field equations for Tolman–Kuchowicz ansatz by incorporating the MIT bag model. Junction conditions are applied on the boundary of the stellar model to evaluate the unknown constants in terms of mass and radius of the star. The radius of the strange star candidate PSR J1614-2230 is predicted by assuming maximum anisotropy at the surface of the star for different values of the coupling parameter, mass of the scalar field and bag constant. We examine various properties as well as the viability and stability of the anisotropic sphere. We conclude that the astrophysical model agrees with the essential criteria of a physically realistic model for higher values of the coupling parameter as well as mass of the scalar field.

Anisotropic strange stars through embedding technique in massive Brans–Dicke gravity

This paper investigates the existence and properties of anisotropic strange quark stars in the context of massive Brans–Dicke theory. The field equations are constructed in Jordan frame by assuming a suitable potential function with MIT bag model. We employ the embedding class-one approach as well as junction conditions to determine the unknown metric functions. Radius of the strange star candidate, LMC X-4, is predicted through its observed mass for different values of the bag constant. We analyze the effects of coupling parameter as well as mass of scalar field on state determinants and execute multiple checks on the stability and viability of the spherical system. It is concluded that the resulting stellar structure is physically viable and stable as it satisfies the energy conditions as well as essential stability criteria.

Stability of oscillating gaseous masses in massive Brans–Dicke gravity

This paper explores the instability of gaseous masses for the radial oscillations in post-Newtonian correction of massive Brans–Dicke (BD) gravity. For this purpose, we derive linearized perturbed equation of motion through Lagrangian radial perturbation which leads to the condition of marginal stability. We discuss radius of instability of different polytropic structures in terms of the Schwarzschild radius. It is concluded that our results provide a wide range of difference with those in general relativity and BD gravity.

Shear-free axial model in massive Brans–Dicke gravity

This paper explores the influences of dark energy on the shear-free axially symmetric evolution by considering self-interacting Brans–Dicke gravity as a dark energy candidate. We describe energy source of the model and derive all the effective dynamical variables as well as effective structure scalars. It is found that scalar field is one of the sources of anisotropy and dissipation. The resulting effective structure scalars help to study the dynamics associated with dark energy in any axial configuration. In order to investigate shear-free evolution, we formulate a set of governing equations along with heat transport equation. We discuss consequences of shear-free condition upon different SBD fluid models like dissipative non-geodesic and geodesic models. For dissipative non-geodesic case, the rotational distribution turns out to be the necessary and sufficient condition for radiating model. The dissipation depends upon inhomogeneous expansion. The geodesic model is found to be irrotational and non-radiating. The non-dissipative geodesic model leads to FRW model for positive values of the expansion parameter.