Violation Of Energy Conditions Research Articles

On energy condition violation for shifting negative mass black holes

On energy condition violation for shifting negative mass black holes

The “Planckonions”

We consider a spherically symmetric stellar configuration with a density profile [Formula: see text]. This configuration satisfies the Schwarzchild black hole condition [Formula: see text] for every [Formula: see text]. We refer to it as “Planckonion”. The interesting thing about the Planckonion is that it has an onion-like structure. The central sphere with radius of the Planck-length [Formula: see text] has one unit of the Planck-mass [Formula: see text]. Subsequent spherical shells of radial width [Formula: see text] contain exactly one unit of [Formula: see text]. We study this stellar configuration using Tolman–Oppenheimer–Volkoff equation and show that the equation is satisfied if pressure [Formula: see text]. On the geometrical side, the space component of the metric blows up at every point. The time component of the metric is zero inside the star but only in the sense of a distribution (generalized function). The Planckonions mimic some features of black holes but avoid appearance of central singularity because of the violation of null energy conditions.

Holographic bounce

We investigate the bounce realization arising from the application of the holographic principle in the early universe, inspired by its well-studied late-time application. We first consider as Infrared cutoffs the particle and future event horizons, and we show that the decrease of the horizons at early times naturally increases holographic energy density at bouncing scales, while we additionally obtain the necessary null energy condition violation. Furthermore, adding a simple correction to the horizons due to the Ultraviolet cutoff we analytically obtain improved nonsingular bouncing solutions, in which the value of the minimum scale factor is controlled by the UV correction. Finally, we construct generalized scenarios, arisen from the use of extended Infrared cutoffs, and as specific examples we consider cutoffs that can reproduce F(R) gravity, and the bounce realization within it.

Non violation of energy conditions in wormholes modeling

Morris and Thorne [M. S. Morris and K. S. Thorne, Am. J. Phys. 56, 395 (1988)] proposed geometrical objects called traversable wormholes that act as bridges in connecting two spacetimes or two different points of the same spacetime. The geometrical properties of these wormholes depend upon the choice of the shape function. In the literature, these are studied in modified gravities for different types of shape functions. In this paper, the traversable wormholes having shape function [Formula: see text] are explored in [Formula: see text] gravity with [Formula: see text], where [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text] are real constants. For different values of constants in function [Formula: see text], the analysis is done in various cases. In each case, the energy conditions, equation of state parameter and anisotropic parameter are determined.

Aspects of nonflat FRW bouncing models with quadratic equation of state

In this paper, we investigate the possibility of a nonsingular model of universe in the framework of general relativity in nonflat FRW geometries with quadratic equation of state and bulk viscosity. We study whether a nonsingular bounce requires violation of energy conditions. We discuss the thermodynamical aspects of the resulting models with equilibrium description. In particular, we discuss the validity of the generalized second law of thermodynamics for resulting cosmologies.

Energy condition respecting warp drives: the role of spin in Einstein–Cartan theory

In this paper we study the so called ‘warp drive’ spacetimes within the U4 Riemann–Cartan manifolds of Einstein–Cartan theory. Specifically, the role that spin may play with respect to energy condition violation is considered. It turns out that with the addition of spin, the torsion terms in Einstein–Cartan gravity do allow for energy condition respecting warp drives. Limits are derived which minimize the amount of spin required in order to have a weak/null-energy condition respecting system. This is done both for the traditional Alcubierre warp drive as well as for the modified warp drive of Van Den Broeck which minimizes the amount of matter required for the drive. The ship itself is in a region of effectively vacuum and hence the torsion, which in Einstein–Cartan theory is localized in matter, does not affect the geodesic nature of the ship’s trajectory. We also comment on the amount of spin and matter required in order for these conditions to hold.

A time machine for free fall into the past

Inspired by some recent works of Tippett–Tsang and Mallary–Khanna–Price, we present a new spacetime model containing closed timelike curves (CTCs). This model is obtained postulating an ad hoc Lorentzian metric on , which differs from the Minkowski metric only inside a spacetime region bounded by two concentric tori. The resulting spacetime is topologically trivial, free of curvature singularities and is both time and space orientable; besides, the inner region enclosed by the smaller torus is flat and displays geodesic CTCs. Our model shares some similarities with the time machine of Ori and Soen but it has the advantage of a higher symmetry in the metric, allowing for the explicit computation of a class of geodesics. The most remarkable feature emerging from this computation is the presence of future-oriented timelike geodesics starting from a point in the outer Minkowskian region, moving to the inner spacetime region with CTCs, and then returning to the initial spatial position at an earlier time; this means that time travel to the past can be performed by free fall across our time machine. The amount of time travelled into the past is determined quantitatively; this amount can be made arbitrarily large keeping non-large the proper duration of the travel. An important drawback of the model is the violation of the classical energy conditions, a common feature of many time machines. Other problems emerge from our computations of the required (negative) energy densities and of the tidal accelerations; these are small only if the time machine is gigantic.

Collapse and bounce of null fluids

Exact solutions describing the spherical collapse of null fluids can contain regions which violate the energy conditions. Physically the violations occur when the infalling matter continues to move inwards even when non-gravitational repulsive forces become stronger than gravity. In 1991 Ori proposed a resolution for these violations: spacetime surgery should be used to replace the energy condition violating region with an outgoing solution. The matter bounces. We revisit and implement this proposal for the more general Husain null fluids including a careful study of potential discontinuities and associated matter shells between the regions. Along the way we highlight an error in the standard classification of energy condition violations for Type II stress-energy tensors.

On regular rotating black holes

Different proposals for regular rotating black hole spacetimes have appeared recently in the literature. However, a rigorous analysis and proof of the regularity of this kind of spacetimes is still lacking. In this note we analyze rotating Kerr-like black hole spacetimes and find the necessary and sufficient conditions for the regularity of all their second order scalar invariants polynomial in the Riemann tensor. We also show that the regularity is linked to a violation of the weak energy conditions around the core of the rotating black hole.

On a new approach for constructing wormholes in Einstein–Born–Infeld gravity

We study a new approach for the wormhole construction in Einstein-Born-Infeld gravity, which does not require exotic matters in the Einstein equation. The Born-Infeld field equation is not modified from "coordinate independent" conditions of continuous metric tensor and its derivatives, even though the Born-Infeld fields have discontinuities in their derivatives at the throat in general. We study the relation of the newly introduced conditions with the usual continuity equation for the energy-momentum tensor and the gravitational Bianchi identity. We find that there is no violation of energy conditions for the Born-Infeld fields contrary to the usual approaches. The exoticity of energy-momentum tensor is not essential for sustaining wormholes. Some open problems are discussed.

Charged Noncommutative Wormhole Solutions via Power-Law f(T) Models

In this paper, we explore static spherically symmetric charged wormhole solutions in extended teleparallel gravity taking power-law f(T) models. We consider noncommutative geometry under Lorentzian distribution. In order to obtain matter components, we develop field equations using effective energy-momentum tensor for non-diagonal tetrad. We explore solutions by considering various viable power-law f(T) models, which also include teleparallel gravity case. The violation of energy conditions obtain by exotic matter to form wormhole solutions in teleparallel case while, physical acceptable wormhole solutions exist for charged noncommutative wormhole solutions for some cases of power-law models. The effective energy-momentum tensor and charge are responsible for the violation of the energy conditions. Also, we check the equilibrium condition for these solutions. The equilibrium condition meets for the teleparallel case and some power-law solutions while remaining solutions are either in less equilibrium or in disequilibrium situation.

Can Galileons support Lorentzian wormholes?

We discuss the possibility of constructing stable, static, spherically symmetric, asymptotically flat Lorentzian wormhole solutions in General Relativity coupled to a generalized Galileon field $\pi$. Assuming that Minkowski space-time is obtained at $\partial \pi =0$, we find that there is tension between the properties of the energy-momentum tensor required to support a wormhole (violation of average null energy conditions) and stability of the Galileon perturbations about the putative solution (absence of ghosts and gradient instabilities). In 3-dimensional space-time, this tension is strong enough to rule out wormholes with above properties. In higher dimensions, including the most physically interesting case of 4-dimensional space-time, wormholes, if any, must have fairly contrived shapes.

Lorentz distributed noncommutative wormhole solutions in extended teleparallel gravity

In this paper, we study static spherically symmetric wormhole solutions in extended teleparallel gravity with the inclusion of noncommutative geometry under a Lorentzian distribution. We obtain expressions of matter components for a non-diagonal tetrad. The effective energy-momentum tensor leads to the violation of energy conditions which impose a condition on the normal matter to satisfy these conditions. We explore the noncommutative wormhole solutions by assuming a viable power-law $$f(T)$$ and shape function models. For the first model, we discuss two cases in which one leads to teleparallel gravity and the other is for $$f(T)$$ gravity. The normal matter violates the weak energy condition for the first case, while there exists a possibility for micro physically acceptable wormhole solution. There exists a physically acceptable wormhole solution for the power-law $$b(r)$$ model. Also, we check the equilibrium condition for these solutions, which is only satisfied for the teleparallel case, while for the $$f(T)$$ case, these solutions are less stable.

Connecting horizon pixels and interior voxels of a black hole

In this paper we discuss to what extent one can infer details of the interior structure of a black hole based on its horizon. Recalling that black hole thermal properties are connected to the non-classical nature of gravity, we circumvent the restrictions of the no-hair theorem by postulating that the black hole interior is singularity free due to violations of the usual energy conditions. Further these conditions allow one to establish a one-to-one, holographic projection between Planckian areal “bits” on the horizon and “voxels”, representing the gravitational degrees of freedom in the black hole interior. We illustrate the repercussions of this idea by discussing an example of the black hole interior consisting of a de Sitter core postulated to arise from the local graviton quantum vacuum energy. It is shown that the black hole entropy can emerge as the statistical entropy of a gas of voxels.

No superluminal propagation for classical relativistic and relativistic quantum fields

A criterion is proposed to ensure that classical relativistic fields do not propagate superluminally. If this criterion does indeed serve as a sufficient condition for no superluminal propagation it follows that various other criteria found in the physics literature cannot serve as necessary conditions since they can fail although the proffered condition holds. The rejected criteria rely on energy conditions that are believed to hold for most classical fields used in actual applications. But these energy conditions are known to fail at small scales for quantum fields. It is argued that such a failure is not necessarily a cause for concern about superluminal propagation in the quantum regime since the proffered criterion of no superluminal propagation for classical fields has a natural analog for quantum fields and, further, this quantum analog condition provably holds for some quantum fields despite the violation of energy conditions. The apparatus developed here also offers a different approach to treating the Reichenbach–Salmon cases of “pseudo-causal processes” and helps to clarify the issue of whether relativity theory is consistent with superluminal propagation.

Primeval acceleration and bounce conditions within induced gravity

A model of induced gravity with Higgs potential is analyzed for the FLRW cosmology. Conditions of acceleration and signatures for the primeval universe along with inflation are discussed. It is shown that the scalar-field excitations act quintessentially within effective pressure terms for a negative deceleration parameter. A violation of energy conditions and primeval acceleration appear naturally in the present model in view of the notions for inflationary universe with avoidance of the Big Bang singularity.

Galactic Halo Wormhole Solutions inf(T)Gravity

The proposal of galactic halo region is based on the idea that dark halos contain some characteristics needed to support traversable wormhole solutions. We explore wormhole solutions in this region in the framework of generalized teleparallel gravity. We consider static spherically symmetric wormhole spacetime with flat galactic rotational curves and obtain expressions of matter components for nondiagonal tetrad. The effective energy-momentum tensor leads to the violation of energy conditions which may impose condition on the normal matter to satisfy these conditions. We take two well-knownf(T)models in exponential and logarithmic forms to discuss wormhole solutions as well as the equilibrium condition. It is concluded that wormhole solutions violating weak energy condition are obtained for both models with stable configuration.

Wormhole solutions inf(T)gravity with noncommutative geometry

The objective of this paper is to study static spherically symmetric noncommutative wormhole solutions in the framework of $f(T)$ gravity. We construct $f(T)$ field equations in covariant and effective energy-momentum tensor forms to make a correspondence with general relativity. It is observed that the violation of energy conditions to support the nonstandard wormhole is due to the effective energy-momentum tensor. We explore the noncommutative wormhole solutions for two cases: (i) assume a viable power-law $f(T)$ model to construct the shape function and (ii) a particular shape function is taken to construct the $f(T)$ model. In the first case, only exotic matter forms a wormhole structure in teleparallel gravity, whereas for $f(T)$ gravity, normal matter threads these structures except for a particular range of $r$. For the constructed $f(T)$ model, there does not exist a physically acceptable wormhole solution similar to the teleparallel case.

Dynamical wormhole solutions in $$f(T)$$ f ( T ) gravity

We study dynamical wormhole solutions in the framework of $$f(T)$$ theory of gravity with anisotropic fluid. We assume a general dynamical spherically symmetric wormhole spacetime with specific form of the shape function and scale factor. The scale factor is taken in the power-law form in order to meet the accelerated expansion of the universe. We discuss the behavior of energy conditions for three particular choices of equation of state, i.e., radial and transverse pressures in linear form with energy density and traceless fluid. The energy conditions satisfy for certain time intervals in all cases. The radial coordinate does not play any role in graphs and the validity or violation of energy conditions depend upon the time coordinate only. The graphical behavior of the energy conditions become equivalent for radial and transverse pressures in all the three cases.

Dirac-Born-Infeld genesis: an improved violation of the null energy condition.

We show that the Dirac-Born-Infeld conformal galileons, derived from the world-volume theory of a 3-brane moving in an anti-de Sitter bulk, admit a background, stable under quantum corrections, which violates the null energy condition. The perturbations around this background are stable and propagate subluminally. Unlike other known examples of null energy condition violation, such as ghost condensation and conformal galileons, this theory also admits a stable, Poincaré-invariant vacuum. The 2 → 2 amplitude satisfies standard analyticity conditions. The full S matrix is likely not analytic, however, since perturbations around deformations of the Poincaré invariant vacuum propagate superluminally.