Related papers: Exotic compact objects in Einstein-scalar-Maxwell …
We obtain lagrangian for $k$-essence scalar field $\phi(r,t)$ with scalar curvature $k$ of Friedmann-Lemaitre-Robertson-Walker (FLRW) metric . Obtained lagrangian has two generalised co-ordinates $\phi$ and logarithm of scale factor ($q=\ln…
Background fields of electromagnetic and gravitational type emerge in the low kinetic energy limit of any regular Lagrangian system and, in particular, in the corresponding limit of any spacetime theory in which the free motion of test…
It is known that dynamical solutions of the $k$-essence equation of motion change the metric for the perturbations around these solutions and the perturbations propagate in an emergent spacetime with metric $\tilde G^{\mu\nu}$ different…
A constraint of vanishing energy-momentum tensor is motivated by a variety of perspectives on quantum gravity. We demonstrate in a concrete example how this constraint leads to a metric-independent theory in which quantum gravity emerges as…
We generally investigate the scalar field model with the lagrangian $L=F(X)-V(\phi)$, which we call it {\it General Non-Canonical Scalar Field Model}. We find that it is a special square potential(with a negative minimum) that drives the…
Considering the general Lagrangian of k-essence models, we study and classify them through variables connected to the fluid equation of state parameter w_\kappa. This allows to find solutions around which the scalar field describes a…
We investigate the properties of high density compact objects in a vector type theory, inspired by Einstein's 1919 theory of elementary particles, in which Einstein assumed that elementary particles are held together by gravitational as…
In this paper, we generalize the Schwarzschild-Melvin solution within Einstein-Maxwell-dilaton theories to include non-null scalar charges, while remaining embedded in a magnetic or electric field \textit{\`a la Melvin}. We then use this…
We study linear perturbations about static and spherically symmetric black holes with a time-independent background scalar field in shift-symmetric Horndeski theories, whose Lagrangian is characterized by coupling functions depending only…
Self-gravitating horizonless ultra-compact objects that possess light rings have attracted the attention of physicists and mathematicians in recent years. In the present compact paper we raise the following physically interesting question:…
In this article we try to present spherically symmetric isotropic strange star model under the framework of $f(R,\mathcal{T})$ theory of gravity. To this end, we consider that the Lagrangian density is an arbitrary linear function of the…
We derive a condition for converging a common evolutionary track for k-essence (a scalar field dark energy with non-canonical kinetic terms). For the Lagrangian density V(phi)W(X) with X=dot{phi}^2/2, we find tracker solutions with w_{phi}…
We consider a scalar field action for which the Lagrangian density is a power of the massless Klein-Gordon Lagrangian. The coupling of gravity to this matter action is considered. In this case, we show the existence of nontrivial scalar…
In this paper, we discuss the existence of ghost star models in the Einstein-Maxwell framework. In order to explore these objects, we put forward the idea of Zeldovich and Novikov by keeping in mind that the energy density of such models…
A nearly-massless, slowly-rolling scalar field $\phi$ may provide most of the energy density of the current universe. One potential difficulty with this idea is that couplings to ordinary matter, even if suppressed by the Planck scale,…
In the Einstein-Cartan space $U_4$, an axial vector torsion together with a scalar field connected to a local scale factor have been considered. By combining two particular terms from the SO(4,1) Pontryagin density and then modifying it in…
Nullification of the Einstein tensor curvature for the elementary material space with active gravitational field (radial source) and passive field distribution of its inertial particle (radial sink) maintains the conceptual equivalence of…
We derive the equation of matter density perturbations on sub-horizon scales for a general Lagrangian density f(R, phi, X) that is a function of a Ricci scalar R, a scalar field phi and a kinetic term X=-(nabla phi)^2/2. This is useful to…
We study the properties of possible static, spherically symmetric configurations in k-essence theories with the Lagrangian functions of the form $F(X)$, $X \equiv \phi_{,\alpha} \phi^{,\alpha}$. A no-go theorem has been proved, claiming…
Three non-existence results are established for self-gravitating solitons in Einstein-Maxwell-scalar models, wherein the scalar field is, generically, non-minimally coupled to the Maxwell field via a scalar function $f(\Phi)$. Firstly, a…