New physical parameterizations of monopole solutions in five-dimensional general relativity and the role of negative scalar field energy in vacuum solutions

Novel parameterizations are presented for monopole solutions to the static, spherically-symmetric vacuum field equations of five-dimensional general relativity. First proposed by Kaluza, 5D general relativity unites gravity and classical electromagnetism with a scalar field. These monopoles correspond to bodies carrying mass, electric charge, and scalar charge. The new parameterizations provide physical insight into the nature of electric charge and scalar field energy. The Reissner-Nordstr\"om limit is compared with alternate physical interpretations of the solution parameters. The new parameterizations explore the role of scalar field energy and the relation of electric charge to scalar charge. The Kaluza vacuum equations imply the scalar field energy density is the negative of the electric field energy density for all known solutions, so the total electric and scalar field energy of the monopole is zero. The vanishing of the total electric and scalar field energy density for vacuum solutions seems to imply the scalar field can be understood as a negative-energy foundation on which the electric field is built.

A brief note on the limit ω →∞ in Weyl geometrical scalar–tensor theory

We obtain vacuum solutions in the presence of a cosmological constant in the context of the Weyl geometrical scalar–tensor theory. We investigate the limit when [Formula: see text] goes to infinity and show by working out the solutions that in this limit there are some cases in which the scalar field tends to a constant (with the implicit consequence of the geometry becoming Riemannian), although the solutions do not reduce to the corresponding Einstein solutions. We have also extended a previous result, known in the literature, by showing that in the case of vacuum with cosmological constant the field equations of the Weyl geometrical scalar–tensor theory are formally identical to Brans–Dicke field equations, even though these theories are not physically equivalent.

Spherically Symmetric Exact Vacuum Solutions in Einstein-Aether Theory

We study spherically symmetric spacetimes in Einstein-aether theory in three different coordinate systems, the isotropic, Painlevè-Gullstrand, and Schwarzschild coordinates, in which the aether is always comoving, and present both time-dependent and time-independent exact vacuum solutions. In particular, in the isotropic coordinates we find a class of exact static solutions characterized by a single parameter c14 in closed forms, which satisfies all the current observational constraints of the theory, and reduces to the Schwarzschild vacuum black hole solution in the decoupling limit (c14=0). However, as long as c14≠0, a marginally trapped throat with a finite non-zero radius always exists, and on one side of it the spacetime is asymptotically flat, while on the other side the spacetime becomes singular within a finite proper distance from the throat, although the geometric area is infinitely large at the singularity. Moreover, the singularity is a strong and spacetime curvature singularity, at which both of the Ricci and Kretschmann scalars become infinitely large.

Minimally deformed wormholes

This work is devoted to the study of wormhole solutions in the framework of gravitational decoupling by means of the minimal geometric deformation scheme. As an example, to analyze how this methodology works in this scenario, we have minimally deformed the well-known Morris–Thorne model. The decoupler function f(r) and the $$\theta $$ θ -sector are determined considering the following approaches: (i) the most general linear equation of state relating the $$\theta _{\mu \nu }$$ θ μ ν components is imposed and (ii) the generalized pseudo-isothermal dark matter density profile is mimicked by the temporal component of the $$\theta $$ θ -sector. It is found that the first approach leads to a non-asymptotically flat space-time with an unbounded mass function. To address this issue we have matched both the wormhole and the Schwarzschild vacuum solutions, via a thin-shell at the junction surface. Using the second approach, it can be seen that, on one hand, the solution for $$\gamma =1$$ γ = 1 does not give place to a bounded mass and it presents a topological defect at large distances; on the other hand, the wormhole manifold is asymptotically flat in the $$\gamma =2$$ γ = 2 case. In order to satisfy the flare-out condition, we have found restrictions on the value of the $$\alpha $$ α parameter, which is related with the amount of exotic matter distribution. Finally, the averaged weak energy condition has been analyzed by using the volume integral quantifier.

Spherically symmetric analytic solutions and naked singularities in Einstein–Aether theory

We analyze all the possible spherically symmetric exterior vacuum solutions allowed by the Einstein–Aether theory with static aether. We show that there are three classes of solutions corresponding to different values of a combination of the free parameters, $$c_{14}=c_1+c_4$$ c 14 = c 1 + c 4 , which are: $$ 0< c_{14}<2$$ 0 < c 14 < 2 , $$c_{14} < 0$$ c 14 < 0 , and $$c_{14}=0$$ c 14 = 0 . We present explicit analytical solutions for $$c_{14}=3/2, 16/9, 48/25, -16$$ c 14 = 3 / 2 , 16 / 9 , 48 / 25 , - 16 and 0. The first case has some pathological behavior, while the rest have all singularities at $$r=0$$ r = 0 and are asymptotically flat spacetimes. For the solutions $$c_{14}=16/9, 48/25\, \mathrm {\, and \,}\, -16$$ c 14 = 16 / 9 , 48 / 25 and - 16 we show that there exist no horizons, neither Killing horizon nor universal horizon, thus we have naked singularities. This characteristic is completely different from general relativity. We briefly discuss the thermodynamics for the case $$c_{14}=0$$ c 14 = 0 where the horizon exists.

PHYSICAL PROPERTIES OF THE THIN ACCRETION DISK OF THE TAUB-NUT BLACK HOLE

The Taub-NUT space-time metric is one of the vacuum solutions to Einstein's gravitational field equations. In this metric, the Newman-Unti-Tamburino parameter (NUT) and its effect on the physical properties of a thin accretion disk are of particular interest. In this paper, calculations are performed to determine the physical properties of a thin accretion disk around the Taub-NUT black hole based on the Page-Thorne model. The influence of the NUT parameter on the angular velocity, binding energy, angular momentum of particles, effective potential, energy flow, and temperature of the accretion disk is revealed. According to the data obtained, the temperature of the accretion disk of the Taub-NUT black hole decreases as the value of the NUT parameter increases.

Super Yang-Mills theories with inhomogeneous mass deformations

We construct the 4-dimensional $$ \mathcal{N}=\frac{1}{2} $$ N = 1 2 and $$ \mathcal{N} $$ N = 1 inhomogeneously mass-deformed super Yang-Mills theories from the $$ \mathcal{N} $$ N = 1* and $$ \mathcal{N} $$ N = 2* theories, respectively, and analyse their supersymmetric vacua. The inhomogeneity is attributed to the dependence of background fluxes in the type IIB supergravity on a single spatial coordinate. This gives rise to inhomogeneous mass functions in the $$ \mathcal{N} $$ N = 4 super Yang-Mills theory which describes the dynamics of D3-branes. The Killing spinor equations for those inhomogeneous theories lead to the supersymmetric vacuum equation and a boundary condition. We investigate two types of solutions in the $$ \mathcal{N}=\frac{1}{2} $$ N = 1 2 theory, corresponding to the cases of asymptotically constant mass functions and periodic mass functions. For the former case, the boundary condition gives a relation between the parameters of two possibly distinct vacua at the asymptotic boundaries. Brane interpretations for corresponding vacuum solutions in type IIB supergravity are also discussed. For the latter case, we obtain explicit forms of the periodic vacuum solutions.

5-dimensional space-periodic solutions of the static vacuum Einstein equations

An affirmative answer is given to a conjecture of Myers concerning the existence of 5-dimensional regular static vacuum solutions that balance an infinite number of black holes, which have Kasner asymptotics. A variety of examples are constructed, having different combinations of ring S1 × S2 and sphere S3 cross-sectional horizon topologies. Furthermore, we show the existence of 5-dimensional vacuum solitons with Kasner asymptotics. These are regular static space-periodic vacuum spacetimes devoid of black holes. Consequently, we also obtain new examples of complete Riemannian manifolds of nonnegative Ricci curvature in dimension 4, and zero Ricci curvature in dimension 5, having arbitrarily large as well as infinite second Betti number.