Exact solutions of the gravitational field equations for a mixture of a null charged strange quark fluid and radiation are obtained in a Vaidya space-time. The conditions for the formation of a naked singularity are analyzed by considering the behavior of radial geodesics originating from the central singularity.

Collapsing strange quark matter in Vaidya geometry

We present a new class of black hole solutions in third-order Lovelock gravity whose horizons are Einstein space with two supplementary conditions on their Weyl tensors. The existence of these solutions is due to the higher curvature terms in Lovelock gravity. We find that while the solution of third-order Lovelock gravity with constant-curvature horizon in the absence of a mass parameter is the anti--de Sitter (AdS) metric, this kind of solution with nonconstant-curvature horizon is only asymptotically AdS and may have horizon. We also find that one may have an extreme black hole with nonconstant-curvature horizon whose Ricci scalar is zero or a positive constant, while there is no such black hole with constant-curvature horizon. Furthermore, the thermodynamics of the black holes in the two cases of constant- and nonconstant-curvature horizons are different drastically. Specially, we consider the thermodynamics of black holes with vanishing Ricci scalar and find that in contrast to the case of black holes of Lovelock gravity with constant-curvature horizon, the area law of entropy is not satisfied. Finally, we investigate the stability of these black holes both locally and globally and find that while the black holes with constant-curvature horizons are stable both locally and globally, those with nonconstant-curvature horizons have unstable phases.

Lovelock black holes with nonmaximally symmetric horizons

Abstract It has been suggested that the Einstein–Gauss–Bonnet theory coupled with a scalar field (EGBS) may allow us to obtain physically viable models of celestial phenomena such that the scalar field effect is active in standard four dimensions. We consider the spherically symmetric and static configuration of the compact star and explain the consequences of the EGBS theory in the frame of stellar modeling. In our formulation, for any given static profile of energy density $$\rho $$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>ρ</mml:mi> </mml:math> with spherical symmetry and the arbitrary equation of state (EoS) of matter, we can construct a model which reproduces the profile. Because the profile of the energy density determines the mass M and the radius $$R_s$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>R</mml:mi> <mml:mi>s</mml:mi> </mml:msub> </mml:math> of the compact star, an arbitrary relation between the mass M and the radius $$R_s$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>R</mml:mi> <mml:mi>s</mml:mi> </mml:msub> </mml:math> of the compact star can be realized by adjusting the potential and the coefficient function of the Gauss–Bonnet term in the action of EGBS theory. This could be regarded as a degeneracy between the EoS and the functions characterizing the model, which indicates that the mass–radius relation alone is insufficient to constrain the model. Here, we investigate a novel class of analytic spherically symmetric interior solutions by the polytropic EoS. We discuss our model in detail and show that it is in agreement with the necessary physical conditions required for any realistic compact star, confirming that EGBS theory is consistent with observations. 

/pdf/isotropic-compact-stars-in-four-dimensional-einstein-gauss-3nwdrp2u.pdf

Isotropic compact stars in four-dimensional Einstein–Gauss–Bonnet gravity coupled with scalar field: reconstruction of model

/pdf/holographic-dark-energy-satisfying-the-energy-conditions-in-2o8096hf.pdf

Holographic dark energy satisfying the energy conditions in Lovelock gravity

Topologically nontrivial black holes of Lovelock gravity sourced by logarithmic electrodynamics

Static and radiating solutions of Lovelock gravity in the presence of a perfect fluid

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Static and radiating solutions of Lovelock gravity in the presence of a perfect fluid