1,949 research outputs found

### A rotating black lens solution in five dimensions

It has recently been shown that a stationary, asymptotically flat vacuum
black hole in five space-time dimensions with two commuting axial symmetries
must have an event horizon with either a spherical, ring or lens-space
topology. In this paper, we study the third possibility, a so-called black lens
with L(n,1) horizon topology. Using the inverse scattering method, we construct
a black lens solution with the simplest possible rod structure, and possessing
a single asymptotic angular momentum. Its properties are then analysed; in
particular, it is shown that there must either be a conical singularity or a
naked curvature singularity present in the space-time.Comment: 25 pages, 2 figures, LaTe

### A generalisation of the Heckmann - Schucking cosmological solution

An exact solution of the Einstein equations for a Bianchi -I universe in the
presence of dust, stiff matter and cosmological constant, generalising the
well-known Heckmann-Schucking solution is presented. PACS: 04.20-q; 04.20.Dw
Keywords: Exact cosmological solutionsComment: LaTeX file, 10 pages. Physics Letters B, to appea

### Chaos and Quantum Chaos in Cosmological Models

Spatially homogeneous cosmological models reduce to Hamiltonian systems in a
low dimensional Minkowskian space moving on the total energy shell $H=0$. Close
to the initial singularity some models (those of Bianchi type VIII and IX) can
be reduced further, in a certain approximation, to a non-compact triangular
billiard on a 2-dimensional space of constant negative curvature with a
separately conserved positive kinetic energy. This type of billiard has long
been known as a prototype chaotic dynamical system. These facts are reviewed
here together with some recent results on the energy level statistics of the
quantized billiard and with direct explicit semi-classical solutions of the
Hamiltonian cosmological model to which the billiard is an approximation. In
the case of Bianchi type IX models the latter solutions correspond to the
special boundary conditions of a `no-boundary state' as proposed by Hartle and
Hawking and of a `wormhole' state.Comment: 23 pages, Late

### Thermodynamic black di-rings

Previously the five dimensional $S^1$-rotating black rings have been
superposed in a concentric way by some solitonic methods, and regular systems
of two $S^1$-rotating black rings were constructed by the authors and then
Evslin and Krishnan (we called these solutions "black di-rings"). In this place
we show some characteristics of the solutions of five dimensional black
di-rings, especially in thermodynamic equilibrium. After the summary of the
di-ring expressions and their physical quantities, first we comment on the
equivalence of the two different solution sets of the black di-rings. Then the
existence of thermodynamic black di-rings is shown, in which both isothermality
and isorotation between the inner black ring and the outer black ring are
realized. We also give detailed analysis of peculiar properties of the
thermodynamic black di-ring including discussion about a certain kind of
thermodynamic stability (instability) of the system.Comment: 26 pages,10 figures; references added, typos corredte

### Gravitational fields with a non Abelian bidimensional Lie algebra of symmetries

Vacuum gravitational fields invariant for a bidimensional non Abelian Lie
algebra of Killing fields, are explicitly described. They are parameterized
either by solutions of a transcendental equation (the tortoise equation) or by
solutions of a linear second order differential equation on the plane.
Gravitational fields determined via the tortoise equation, are invariant for a
3-dimensional Lie algebra of Killing fields with bidimensional leaves. Global
gravitational fields out of local ones are also constructed.Comment: 8 pagese, latex, no figure

### Naturalness in Cosmological Initial Conditions

We propose a novel approach to the problem of constraining cosmological
initial conditions. Within the framework of effective field theory, we classify
initial conditions in terms of boundary terms added to the effective action
describing the cosmological evolution below Planckian energies. These boundary
terms can be thought of as spacelike branes which may support extra
instantaneous degrees of freedom and extra operators. Interactions and
renormalization of these boundary terms allow us to apply to the boundary terms
the field-theoretical requirement of naturalness, i.e. stability under
radiative corrections. We apply this requirement to slow-roll inflation with
non-adiabatic initial conditions, and to cyclic cosmology. This allows us to
define in a precise sense when some of these models are fine-tuned. We also
describe how to parametrize in a model-independent way non-Gaussian initial
conditions; we show that in some cases they are both potentially observable and
pass our naturalness requirement.Comment: 35 pages, 8 figure

### Symplectic Gravity Models in Four, Three and Two Dimensions

A class of the $D=4$ gravity models describing a coupled system of $n$
Abelian vector fields and the symmetric $n \times n$ matrix generalizations of
the dilaton and Kalb-Ramond fields is considered. It is shown that the
Pecci-Quinn axion matrix can be entered and the resulting equations of motion
possess the $Sp(2n, R)$ symmetry in four dimensions. The stationary case is
studied. It is established that the theory allows a $\sigma$-model
representation with a target space which is invariant under the $Sp[2(n+1), R]$
group of isometry transformations. The chiral matrix of the coset $Sp[2(n+1),
R]/U(n+1)$ is constructed. A K\"ahler formalism based on the use of the Ernst
$(n+1) \times (n+1)$ complex symmetric matrix is developed. The stationary
axisymmetric case is considered. The Belinsky-Zakharov chiral matrix depending
on the original field variables is obtained. The Kramer-Neugebauer
transformation, which algebraically maps the original variables into the target
space ones, is presented.Comment: 21 pages, RevTex, no figurie

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