Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userGravitationally decoupled strange star model beyond standard maximum mass limit in Einstein-Gauss-Bonnet gravity
65
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
In this work we employ the Minimal Geometric Deformation (MGD) method to model a strange star within the context of Einstein-Gauss-Bonnet gravity. Starting off with the Tolman ansatz together with the MIT Bag model equation of state, anisotropy is introduced via the superposition of the seed source and the decoupled energy-momentum tensor. The solution of the governing systems of equations bifurcates into two distinct models, namely the mimicking of the $theta$ sector to the seed radial pressure and energy density, respectively. Each of these models can be interpreted as self-gravitating static, compact objects with the exterior described by the vacuum Boulware-Deser solution. Utilising observational data for three stellar candidates, viz., PSR J1614-2230, PSR J1903+317, and LMC X-4 we subject our solutions to rigorous viability tests based on regularity and stability. We find that the Einstein-Gauss-Bonnet parameter and the decoupling constant compete against each other for ensuring physically realizable stellar structures. The novel feature of work is the demonstration of stable compact objects with stellar masses in excess of $M= 2 M_{odot}$ without appealing to exotic matter.
rate research
Read More
We discuss the cosmological evolution of a braneworld in five dimensional Gauss-Bonnet gravity. Our discussion allows the fifth (bulk) dimension to be space-like as well as time-like. The resulting equations of motion have the form of a cubic equation in the (H^2,(rho+sigma)^2) plane, where sigma is the brane tension and rho is the matter density. This allows us to conduct a comprehensive pictorial analysis of cosmological evolution for the Gauss-Bonnet brane. The many interesting properties of this braneworld include the possibility of accelerated expansion at late times. For a finite region in parameter space the accelerated expansion can be phantom-like so that w < -1. At late times, this branch approaches de Sitter space (w = -1) and avoids the big-rip singularities usually present in phantom models. For a time-like extra dimension the Gauss-Bonnet brane can bounce and avoid the initial singularity.
We study a specific model of anisotropic strange stars in the modified $fleft(R,mathcal{T}right)$-type gravity by deriving solutions to the modified Einstein field equations representing a spherically symmetric anisotropic stellar object. We take a standard assumption that $f(R,mathcal{T})=R+2chimathcal{T}$, where $R$ is Ricci scalar, $mathcal{T}$ is the trace of the energy-momentum tensor of matter, and $chi$ is a coupling constant. To obtain our solution to the modified Einstein equations, we successfully apply the `embedding class 1 techniques. We also consider the case when the strange quark matter (SQM) distribution is governed by the simplified MIT bag model equation of state given by $p_r=frac{1}{3}left(rho-4Bright)$, where $B$ is bag constant. We calculate the radius of the strange star candidates by directly solving the modified TOV equation with the observed values of the mass and some parametric values of $B$ and $chi$. The physical acceptability of our solutions is verified by performing several physical tests. Interestingly, besides the SQM, another type of matter distribution originates due to the effect of coupling between the matter and curvature terms in the $fleft(R,mathcal{T}right)$ gravity theory. Our study shows that with decreasing the value of $chi$, the stellar systems under investigations become gradually massive and larger in size, turning them into less dense compact objects. It also reveals that for $chi<0$ the $fleft(R,mathcal{T}right)$ gravity emerges as a suitable theory for explaining the observed massive stellar objects like massive pulsars, super-Chandrasekhar stars and magnetars, etc., which remain obscure in the standard framework of General Relativity (GR).
We present results from a numerical study of spherical gravitational collapse in shift symmetric Einstein dilaton Gauss-Bonnet (EdGB) gravity. This modified gravity theory has a single coupling parameter that when zero reduces to general relativity (GR) minimally coupled to a massless scalar field. We first show results from the weak EdGB coupling limit, where we obtain solutions that smoothly approach those of the Einstein-Klein-Gordon system of GR. Here, in the strong field case, though our code does not utilize horizon penetrating coordinates, we nevertheless find tentative evidence that approaching black hole formation the EdGB modifications cause the growth of scalar field hair, consistent with known static black hole solutions in EdGB gravity. For the strong EdGB coupling regime, in a companion paper we first showed results that even in the weak field (i.e. far from black hole formation), the EdGB equations are of mixed type: evolution of the initially hyperbolic system of partial differential equations lead to formation of a region where their character changes to elliptic. Here, we present more details about this regime. In particular, we show that an effective energy density based on the Misner-Sharp mass is negative near these elliptic regions, and similarly the null convergence condition is violated then.
The current trend concerning dense matter physics at sufficiently high densities and low temperatures is expected to behave as a degenerate Fermi gas of quarks forming Cooper pairs, namely a color superconductor, in the core of compact objects. In this context, we study the anisotropy of quark stars (QSs) assuming the internal composition to be comprised of homogeneous, charge neutral 3-flavor interacting quark matter with $mathcal{O}(m_s^4)$ corrections. Using the equation of state (EoS) with the Tolmann-Oppenheimer-Volkoff (TOV) structure equations, we perform numerical calculation for quark stars and determine the maximum mass-radius relation in the context of $4D$ Einstein-Gauss-Bonnet (EGB) gravity. In particular, we consider the effects of Gauss-Bonnet (GB) coupling constant on the diagrams related to mass-radius $(M-R)$ relation and the mass-central mass density $(M-rho_c)$ relation of QSs. We pay particular attention to the influence of the anisotropy in the equilibrium and stability of strange stars. We also study the other properties of QSs related to compactness and binding energy. Interestingly, our result provides circumstantial evidence in favor of super-massive pulsars in $4D$ EGB gravity.
We present the $d+1$ formulation of Einstein-scalar-Gauss-Bonnet (ESGB) theories in dimension $D=d+1$ and for arbitrary (spacelike or timelike) slicings. We first build an action which generalizes those of Gibbons-Hawking-York and Myers to ESGB theories, showing that they can be described by a Dirichlet variational principle. We then generalize the Arnowitt-Deser-Misner (ADM) Lagrangian and Hamiltonian to ESGB theories, as well as the resulting $d+1$ decomposition of the equations of motion. Unlike general relativity, the canonical momenta of ESGB theories are nonlinear in the extrinsic curvature. This has two main implications: (i) the ADM Hamiltonian is generically multivalued, and the associated Hamiltonian evolution is not predictable; (ii) the $d+1$ equations of motion are quasilinear, and they may break down in strongly curved, highly dynamical regimes. Our results should be useful to guide future developments of numerical relativity for ESGB gravity in the nonperturbative regime.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
