644 research outputs found
Charged anisotropic compact objects by gravitational decoupling
In the present article, we have constructed a static charged anisotropic
compact star model of Einstein field equations for a spherically symmetric
space-time geometry. Specifically, we have extended the charged isotropic
Heintzmann solution to an anisotropic domain. To address this work, we have
employed the gravitational decoupling through the so called minimal geometric
deformation approach. The charged anisotropic model is representing the
realistic compact objects such as and . We
have reported our results in details for the compact star on the
ground of physical properties such as pressure, density, velocity of sound,
energy conditions, stability conditions, Tolman-Oppenheimer-Volkoff equation
and redshift etc
Compact star in Tolman Kuchowicz spacetime in background of Einstein Gauss Bonnet gravity
The present work is devoted to the study of anisotropic compact matter
distributions within the framework of 5-dimensional Einstein-Gauss-Bonnet
gravity. To solve the field equations, we have considered that the inner
geometry is described by Tolman-Kuchowicz spacetime. The Gauss-Bonnet
Lagrangian is coupled to Einstein-Hilbert action through a coupling constant.
When this coupling tends to zero general relativity results are recovered. We
analyze the effect of this parameter on the principal salient features of the
model, such as energy density, radial and tangential pressure and anisotropy
factor.Additionally, the behaviour of the subliminal sound speed of the
pressure waves in the principal direction of the configuration and the conduct
of the energy-momentum tensor throughout the star are analyzed employing
causality condition and energy conditions, respectively. All these subjects are
supported by mean of physical, mathematical and graphical surve
A new model of regular black hole in dimensions
We provide a new regular black hole solution in dimensions with
presence of matter fields in the energy momentum tensor, having its core a flat
or (A)dS structure. Since the first law of thermodynamics for regular black
holes is modified by the presence of the matter fields, we provide a new
version of the first law, where a local definition of the variation of energy
is defined, and, where the entropy and temperature are consistent with the
previously known in literature. It is shown that the signs of the variations of
the local definition of energy and of the total energy coincide. Furthermore,
at infinite, the usual first law is recovered. It is showed that the
formalism used is effective to compute the total energy of regular black holes
in with presence of matter in the energy momentum tensor. This latter
suggests the potential applicability of this formalism to calculate the mass of
other models of regular black holes in dimensions.Comment: accepted for publication in EP
Compact Anisotropic Models in General Relativity by Gravitational Decoupling
Durgapal's fifth isotropic solution describing spherically symmetric and
static matter distribution is extended to an anisotropic scenario. To do so we
employ the gravitational decoupling through the minimal geometric deformation
scheme. This approach allows to split Einstein's field equations in two simply
set of equations, one corresponding to the isotropic sector and other to the
anisotropic sector described by an extra gravitational source. The isotropic
sector is solved by the Dugarpal's model and the anisotropic sector is solved
once a suitable election on the minimal geometric deformation is imposes. The
obtained model is representing some strange stars candidates and fulfill all
the requirements in order to be a well behaved physical solution to the
Einstein's field equations
Quantum aspects of the gravitational-gauge vector coupling in the Ho\v{r}ava-Lifshitz theory at the kinetic conformal point
This work presents the main aspects of the anisotropic gravity-vector gauge
coupling at all energy scales \i.e., from the IR to the UV point. This study is
carry out starting from the 4+1 dimensional Ho\v{r}ava-Lifshitz theory, at the
kinetic conformal point.The Kaluza-Klein technology is employed as a unifying
mechanism to couple both interactions. Furthermore, by assuming the so-called
cylindrical condition, the dimensional reduction to 3+1 dimensions leads to a
theory whose underlying group of symmetries corresponds to the diffeomorphisms
preserving the foliation of the manifold and a U(1) gauge symmetry. The
counting of the degrees of freedom shows that the theory propagates the same
spectrum of Einstein-Maxwell theory. The speed of propagation of tensorial and
gauge modes is the same, in agreement with recent observations. This point is
thoroughly studied taking into account all the terms that
contribute to the action. In contrast with the 3+1 dimensional formulation,
here the Weyl tensor contributes in a non-trivial way to the potential of the
theory. Its complete contribution to the 3+1 theory is explicitly obtained.
Additionally, it is shown that the constraints and equations determining the
full set of Lagrange multipliers are elliptic partial differential equations of
eighth-order. To check and assure the consistency and positivity of the reduced
Hamiltonian some restrictions are imposed on the coupling constants. The
propagator of the gravitational and gauge sectors are obtained showing that
there are not ghost fields, what is more they exhibit the scaling for all
physical modes at the high energy level. By evaluating the superficial degree
of divergence and considering the structure of the second class constraints, it
is shown that the theory is power-counting renormalizable
Unified first law of thermodynamics in Gauss-Bonnet gravity on an FLRW background
Employing the thermodynamic unified first law through the
thermodynamic-gravity conjecture, in this article, we derive for a FLRW
universe the Friedmann equations in the framework of Gauss-Bonnet gravity
theory. To do this, we project this generalized first law along the Kodama
vector field and along the direction of an orthogonal vector to the Kodama
vector. The second Friedmann equation is obtained by projecting on the Kodama
vector, while the first is obtained by projecting along the flux on the Cauchy
hypersurfaces. This result does not assume a priory temperature and an entropy,
so the Clausius relation is not used here. Nevertheless, it is used to obtain
the corresponding Gauss-Bonnet entropy. In this way, the validity of the
generalized second law of thermodynamics is proved for the Gauss-Bonnet gravity
theory.Comment: 10 pages, 2 figure
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