arXiv subjects
Publications and source records attributed to G. Clement.
In the context of gravitational collapse and black hole formation, we reconsider the problem to describe analytically the critical collapse of a massless and minimally coupled scalar field in $2+1$ gravity.
We construct black hole solutions to three-dimensional Einstein-Maxwell theory with both gravitational and electromagnetic Chern-Simons terms. These intrinsically rotating solutions are geodesically complete, and causally regular within a certain parameter range. Their mass, angular momentum and entropy are found to satisfy the first law of black hole thermodynamics. These Chern-Simons black holes admit a four-parameter local isometry algebra, which generically is $sl(2,R)\times R$, and may be generated from the corresponding vacua by local coordinate transformations.
We compute exactly the semi-classical radiation spectrum for a class of non-asymptotically flat charged dilaton black holes, the so-called linear dilaton black holes. In the high frequency regime, the temperature for these black holes generically agrees with the surface gravity result. In the special case where the black hole is massless, we show that, although the surface gravity remains finite, there is no radiation, in agreement with the fact that massless objects cannot radiate.
Recently it was found that the complete integration of the Einstein-dilaton-antisymmetric form equations depending on one variable and describing static singly charged $p$-branes leads to two and only two classes of solutions: the standard asymptotically flat black $p$-brane and the asymptotically non-flat $p$-brane approaching the linear dilaton background at spatial infinity. Here we analyze this issue in more details and generalize the corresponding uniqueness argument to the case of partially delocalized branes. We also consider the special case of codimension one and find, in addition to the standard domain wall, the black wall solution. Explicit relations between our solutions and some recently found $p$-brane solutions ``with extra parameters'' are presented.
We show that the Letelier-Gal'tsov (LG) metric describing multiple crossed strings in relative motion does solve the Einstein equations, in spite of the discontinuity uncovered recently by Krasnikov [gr-qc/0502090] provided the strings are straight and moving with constant velocities.
Contrary to a recent claim by Anderson ["The Mathematical Theory of Cosmic Strings", I.O.P. Publishing, Bristol 2003], we show that the Letelier-Gal'tsov metric does represent a system of crossed straight infinite cosmic strings moving with arbitrary constant velocities.
Static black holes of dilaton-axion gravity become singular in the extreme limit, which prevents a direct determination of their near-horizon geometry. This is addressed by first taking the near-horizon limit of extreme rotating NUT-less black holes, and then going to the static limit. The resulting four-dimensional geometry may be lifted to a Bertotti-Robinson-like solution of six-dimensional vacuum gravity, which also gives the near-horizon geometry of extreme Kaluza-Klein black holes in five dimensions.
We investigate the family of electrostatic spherically symmetric solutions of the five-dimensional Kaluza-Klein theory. Besides black holes and wormholes, a new class of geodesically complete solutions is identified. A monopole perturbation is carried out, enabling us to prove analytically the stability of a large class of solutions, including all black holes and neutral solutions.
We derive and analyze exact static solutions to the gravitating O(3) $σ$ model with cosmological constant in (2+1) dimensions. Both signs of the gravitational and cosmological constants are considered. Our solutions include geodesically complete spacetimes, and two classes of black holes.
We investigate the family of electrostatic spherically symmetric solutions of the five-dimensional Kaluza-Klein theory. Both charged and neutral cases are considered. The analysis of the solutions, through their geometrical properties, reveals the existence of black holes, wormholes and naked singularities. A new class of regular solutions is identified. A monopole perturbation study of all these solutions is carried out, enabling us to prove analytically the stability of large classes of solutions. In particular, the black hole solutions are stable, while for the regular solutions the stability analysis leads to an eigenvalue problem.
We study the structure and stability of spherically symmetric Brans-Dicke black-hole type solutions with an infinite horizon area and zero Hawking temperature, existing for negative values of the coupling constant $ω$. These solutions split into two classes, depending on finite (B1) or infinite (B2) proper time needed for an infalling particle to reach the horizon. Class B1 metrics can be extended through the horizon only for discrete values of mass and scalar charge, depending on two integers m and n. For even m-n, the space-time is globally regular; for odd m, the metric changes its signature on the horizon but remains Lorentzian. Geodesics are smoothly continued across the horizon, but for odd m timelike geodesics become spacelike and vice versa. Causality problems, arising in some cases, are discussed. Tidal forces are shown to grow infinitely near type B1 horizons. All vacuum static, spherically symmetric solutions of the Brans-Dicke theory with $ω<-3/2$ are found to be linearly stable against spherical perturbations. This result extends to the generic case of the Bergmann-Wagoner class of scalar-tensor theories with the coupling function $ω(ϕ) < -3/2$.