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Register a new userEnergy conditions outside a dielectric ball
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We show analytically that the vacuum electromagnetic stress-energy tensor outside a ball with constant dielectric constant and permeability always obeys the weak, null, dominant, and strong energy conditions. There are still no known examples in quantum field theory in which the averaged null energy condition in flat spacetime is violated.
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Energy conditions for matter fields are comprehensively investigated in arbitrary $n(ge 3)$ dimensions without specifying future and past directions locally. We classify an energy-momentum tensor into $n$-dimensional counterparts of the Hawking-Ellis type I to IV, where type III is defined by a more useful form than those adopted by Hawking and Ellis and other authors to identify the type-III energy-momentum tensor in a given spacetime. We also provide necessary and sufficient conditions for types I and II as inequalities for the orthonormal components of the energy-momentum tensor in a canonical form and show that types III and IV violate all the standard energy conditions. Lastly, we study energy conditions for a set of physically motivated matter fields.
A complete theory of gravity impels us to go beyond Einsteins General Relativity. One promising approach lies in a new class of teleparallel theory of gravity named $f(Q)$, where the nonmetricity $Q$ is responsible for the gravitational interaction. The important roles any of these alternative theories should obey are the energy condition constraints. Such constraints establish the compatibility of a given theory with the causal and geodesic structure of space-time. In this work, we present a complete test of energy conditions for $f(Q)$ gravity models. The energy conditions allowed us to fix our free parameters, restricting the families of $f(Q)$ models compatible with the accelerated expansion our Universe passes through. Our results straight the viability of $f(Q)$ theory, leading us close to the dawn of a complete theory for gravitation.
The recently proposed $f(Q, T)$ gravity (Xu et al. Eur. Phys. J. C textbf{79} (2019) 708) is an extension of the symmetric teleparallel gravity. The gravitational action $L$ is given by an arbitrary function $f$ of the non-metricity $Q$ and the trace of the matter-energy momentum tensor $T$. In this paper, we examined the essence of some well prompted forms of $f(Q,T)$ gravity models i.e. $f(Q,T)= mQ+bT$ and $f(Q,T)= m Q^{n+1}+b T$ where $m$, $b$, and $n$ are model parameters. We have used the proposed deceleration parameter, which predicts both decelerated and accelerated phases of the Universe, with the transition redshift by recent observations and obtains energy density ($rho$) and pressure ($p$) to study the various energy conditions for cosmological models. The equation of state parameter ($omegasimeq -1$) in the present model also supports the accelerating behavior of the Universe. In both, the models, the null, weak, and dominant energy conditions are obeyed with violating strong energy conditions as per the present accelerated expansion.
We present a simple static spacetime which describes a spherically symmetric traversable wormhole characterized by a length parameter $l$ and reduces to Minkowski in the limit $lto 0$. The wormhole connects two distinct asymptotically flat regions with vanishing ADM mass and the areal radius of its throat is exactly $l$. All the standard energy conditions are respected outside the proper radial distance approximately $1.60l$ from the wormhole throat. If $l$ is identified as the Planck length $l_{rm p}$, the total amount of the negative energy supporting this wormhole is only $Esimeq -2.65m_{rm p}c^2$, which is the rest mass energy of about $-5.77times 10^{-5}{rm g}$.
We are living in a golden age for experimental cosmology. New experiments with high accuracy precision are been used to constrain proposals of several theories of gravity, as it has been never done before. However, important roles to constrain new theories of gravity in a theoretical perspective are the energy conditions. Throughout this work, we carefully constrained some free parameters of two different families of $f(Q,T)$ gravity using different energy conditions. This theory of gravity combines the gravitation effects through the non-metricity scalar function $Q$, and manifestations from the quantum era of the Universe in the classical theory (due to the presence of the trace of the energy-momentum tensor $T$). Our investigation unveils the viability of $f(Q,T)$ gravity to describe the accelerated expansion our Universe passes through. Besides, one of our models naturally provides a phantom regime for dark energy and satisfies the dominant energy condition. The results here derived strength the viability of $f(Q,T)$ as a promising complete theory of gravity, lighting a new path towards the description of the dark sector of the Universe.
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