Theophanes Grammenos

The symmetric Landau–Lifshitz and Weinberg energy–momentum complexes are utilized in order to determine the energy distribution in a four-dimensional, static and spherically symmetric regular Simpson–Visser space-time geometry. For different values of the metric parameter a, the static Simpson–Visser space-time geometry corresponds to the Schwarzschild black hole solution, to a regular black hole solution with a one-way spacelike throat, to a one-way wormhole solution with an extremal null throat, or to a traversable Morris–Thorne wormhole solution. Both symmetric prescriptions yield a zero momentum, while the energy distributions calculated have an expression dependent on the mass m, the radial coordinate r, and the metric parameter a. Some special limiting cases of the results derived are considered, while a possible astrophysical application to questions of gravitational lensing is indicated.

The possibility of strange stars mixed with dark energy to be one of the candidates for dark energy stars is the main issue of the present study. Our investigation shows that quark matter acts as dark energy after a certain yet unknown critical condition inside the quark stars. Our proposed model reveals that strange stars mixed with dark energy feature a physically acceptable stable model mimic characteristics of dark energy stars. The plausible connections are shown through the mass-radius relation as well as the entropy and temperature. We particularly note that a two-fluid distribution is a major reason for the anisotropic nature of the spherical stellar system.

Energy-momentum localization for the four-dimensional static and spherically symmetric, regular Simpson–Visser black hole solution is studied by use of the Einstein and Møller energy-momentum complexes. According to the particular values of the parameter of the metric, the static Simpson–Visser solution can possibly describe the Schwarzschild black hole solution, a regular black hole solution with a one-way spacelike throat, a one-way wormhole solution with an extremal null throat, or a traversable wormhole solution of the Morris–Thorne type. In both prescriptions it is found that all the momenta vanish, and the energy distribution depends on the mass m, the radial coordinate r, and the parameter a of the Simpson–Visser metric. Several limiting cases of the results obtained are discussed, while the possibility of astrophysically relevant applications to gravitational lensing issues is pointed out.

The energy-momentum localization for a new four-dimensional and spherically symmetric, charged black hole solution that through a coupling of general relativity with non-linear electrodynamics is everywhere non-singular while it satisfies the weak energy condition, is investigated. The Einstein and Møller energy-momentum complexes have been employed in order to calculate the energy distribution and the momenta for the aforesaid solution. It is found that the energy distribution depends explicitly on the mass and the charge of the black hole, on two parameters arising from the space-time geometry considered, and on the radial coordinate. Further, in both prescriptions all the momenta vanish. In addition, a comparison of the results obtained by the two energy-momentum complexes is made, whereby some limiting and particular cases are pointed out.

(2020). Metaphysical experiments – Physics and the invention of the universe. International Studies in the Philosophy of Science. Ahead of Print.

The energy-momentum localization for a new four-dimensional and spherically symmetric, charged black hole solution that through a coupling of general relativity with non-linear electrodynamics is everywhere non-singular while it satisfies the weak energy condition is investigated. The Einstein and M\{o} ller energy-momentum complexes have been employed in order to calculate the energy distribution and the momenta for the aforesaid solution. It is found that the energy distribution depends explicitly on the mass and the charge of the black hole, on two parameters arising from the space-time geometry considered, and on the radial coordinate. Further, in both prescriptions all the momenta vanish.In addition, a comparison of the results obtained by the two energy-momentum complexes is made, whereby some limiting and particular cases are pointed out.

The behaviour of massive and massless test particles around asymptotically flat and spherically symmetric, charged black holes in the context of generalized dilaton-axion gravity in four dimensions is studied. All the possible motions are investigated by calculating and plotting the corresponding effective potential for the massless and massive particles as well. Further, the motion of massive (charged or uncharged) test particles in the gravitational field of charged black holes in generalized dilaton-axion gravity for the cases of static and non-static equilibrium is investigated by applying the Hamilton-Jacobi approach.