On Nonlinear σ\sigma-Models arizing in (Super-)Gravity

In a previous paper with Gibbons [CMP 120 (1987) 295] we derived a list of three dimensional symmetric space $\sigma$-model obtained by dimensional reduction of a class of four dimensional gravity theories with abelian gauge fields and scalars. Here we give a detailed analysis of their group theoretical structure leading to an abstract parametrization in terms of `triangular' group elements. This allows for a uniform treatment of all these models. As an interesting application we give a simple derivation of a `Quadratic Mass Formula' for strictly stationary black holes.Comment: 33 pages, 1 tabl

Classification of Static, Spherically Symmetric Solutions of the Einstein-Yang-Mills Theory with Positive Cosmological Constant

We give a complete classification of all static, spherically symmetric solutions of the SU(2) Einstein-Yang-Mills theory with a positive cosmological constant. Our classification proceeds in two steps. We first extend solutions of the radial field equations to their maximal interval of existence. In a second step we determine the Carter-Penrose diagrams of all 4-dimensional space-times constructible from such radial pieces. Based on numerical studies we sketch a complete phase space picture of all solutions with a regular origin.Comment: 49 pages, 19 figures, submitted to Commun. Math. Phy

Non-Universality of Critical Behaviour in Spherically Symmetric Gravitational Collapse

The aim of the present letter is to explain the `critical behaviour' observed in numerical studies of spherically symmetric gravitational collaps of a perfect fluid. A simple expression results for the critical index $\gamma$ of the black hole mass considered as an order parameter. $\gamma$ turns out to vary strongly with the parameter $k$ of the assumed equation of state $p=k\rho$.Comment: 6

Self-similar solutions of semilinear wave equations with a focusing nonlinearity

We prove that in three space dimensions a nonlinear wave equation $u_{tt}-\Delta u = u^p$ with $p\geq 7$ being an odd integer has a countable family of regular spherically symmetric self-similar solutions.Comment: 12 pages, 3 figures, minor corrections to match the published versio

Quantization of the Reissner-Nordstr\"{o}m Black Hole

The Reissner--Nordstr\"{o}m family of solutions can be understood to arise from the spherically symmetric sector of a nonlinear SO(2,1)/SO(1,1) sigma model coupled to three dimensional Euclidean gravity. In this context a group theoretical quantization is performed. We identify the observables of the theory and calculate their spectra.Comment: 8 pages, Late

Bogomol'nyi Equations for Einstein-Yang-Mills-Dilaton theory

A static, spherically symmetric and purely magnetic solution of the Einstein-Yang-Mills-Dilaton theory, found previously by numerical integration is shown to obey a system of first order Bogomol'nyi equations. As common for such equations, there is a tight relation to supersymmetry, in the present case to the N=4 gauged SU(2)$\times$SU(2) supergravity of Freedman and Schwarz. Specifically, the dilaton potential of the latter can be avoided by choosing one of the two gauge coupling constants to be imaginary. It is argued that this corresponds to a hitherto unknown N=4 gauged SU(2)$\times$SU(1,1) supergravity in four Euclidean dimensions leading to Bogomol'nyi equations with asymptotically flat solutions.Comment: 13 pages, LaTeX, 2 epsf figures, uses elsar

Mass inflation and chaotic behaviour inside hairy black holes

We analyze the interior geometry of static, spherically symmetric black holes of the Einstein-Yang-Mills-Higgs theory. Generically the solutions exhibit a behaviour that may be described as ``mass inflation'', although with a remarkable difference between the cases with and without a Higgs field. Without Higgs field the YM field induces a kind of cyclic behaviour leading to repeated cycles of mass inflation - taking the form of violent explosions - interrupted by quiescent periods and subsequent approaches to an almost Cauchy horizon. With the Higgs field no such cycles occur. In addition there are non-generic families with a Schwarzschild resp. Reissner-Nordstr{\o}m type singularity at r=0.Comment: 22 pages, Latex, 5 figures (8 eps files

A Remark on the Instability of the Bartnik-McKinnon Solutions

The aim of the present letter is to critically review the stability of the Bartnik-McKinnon solutions of the Einstein-Yang-Mills theory. The stability question was already studied by several authors, but there seems to be some confusion about the nature and the number of unstable modes. We suggest to distinguish two different kind of instabilities, which we call `gravitational' respectively `sphaleron' instabilities. We claim that the $n^{\rm th}$ Bartnik-McKinnon solution has exactly $2n$ unstable modes, $n$ of either type.Comment: LaTex, 6 p., MPI-PhT/94-6

Rotating Einstein-Maxwell-Dilaton Black Holes in D Dimensions

We construct exact charged rotating black holes in Einstein-Maxwell-dilaton theory in $D$ spacetime dimensions, $D \ge 5$, by embedding the $D$ dimensional Myers-Perry solutions in $D+1$ dimensions, and performing a boost with a subsequent Kaluza-Klein reduction. Like the Myers-Perry solutions, these black holes generically possess $N=[(D-1)/2]$ independent angular momenta. We present the global and horizon properties of these black holes, and discuss their domains of existence.Comment: 12 pages, 6 figue