2,272 research outputs found

### Martian atmospheric compositional analysis- its biological significance first quarterly progress report, 15 may - 15 aug. 1965

Biological significance of Martian atmospheric compositional analysis, and life detection studies of chemical free energy in surface matte

### On the static Lovelock black holes

We consider static spherically symmetric Lovelock black holes and generalize
the dimensionally continued black holes in such a way that they asymptotically
for large r go over to the d-dimensional Schwarzschild black hole in dS/AdS
spacetime. This means that the master algebraic polynomial is not degenerate
but instead its derivative is degenerate. This family of solutions contains an
interesting class of pure Lovelock black holes which are the Nth order Lovelock
{\Lambda}-vacuum solu- tions having the remarkable property that their
thermodynamical parameters have the universal character in terms of the event
horizon radius. This is in fact a characterizing property of pure Lovelock
theories. We also demonstrate the universality of the asymptotic Einstein limit
for the Lovelock black holes in general.Comment: 19 page

### Galactic Potentials

The information contained in galactic rotation curves is examined under a
minimal set of assumptions. If emission occurs from stable circular geodesic
orbits of a static spherically symmetric field, with information propagated to
us along null geodesics, observed rotation curves determine galactic potentials
without specific reference to any metric theory of gravity. Given the
potential, the gravitational mass can be obtained by way of an anisotropy
function of this field. The gravitational mass and anisotropy function can be
solved for simultaneously in a Newtonian limit without specifying any specific
source. This procedure, based on a minimal set of assumptions, puts very strong
constraints on any model of the "dark matter".Comment: A somewhat longer form of the final version to appear in Physical
Review Letters.Clarification and further reference

### Charged gravitational instantons in five-dimensional Einstein-Gauss-Bonnet-Maxwell theory

We study a solution of the Einstein-Gauus-Bonnet theory in 5 dimensions
coupled to a Maxwell field, whose euclidean continuation gives rise to an
instanton describing black hole pair production. We also discuss the dual
theory with a 3-form field coupled to gravity.Comment: 8 pages, plain Te

### Some aspects of field equations in generalised theories of gravity

A class of theories of gravity based on a Lagrangian which depends on the
curvature and metric - but not on the derivatives of the curvature tensor - is
of interest in several contexts including in the development of the paradigm
that treats gravity as an emergent phenomenon. This class of models contains,
as an important subset, all Lanczos-Lovelock models of gravity. I derive
several identities and properties which are useful in the study of these models
and clarify some of the issues that seem to have received insufficient
attention in the past literature.Comment: latex; 11 pages; no figures; ver 2: references added; to appear in
Phys. Rev.

### Gauss-Bonnet lagrangian G ln G and cosmological exact solutions

For the lagrangian L = G ln G where G is the Gauss-Bonnet curvature scalar we
deduce the field equation and solve it in closed form for 3-flat Friedman
models using a statefinder parametrization. Further we show, that among all
lagrangians F(G) this L is the only one not having the form G^r with a real
constant r but possessing a scale-invariant field equation. This turns out to
be one of its analogies to f(R)-theories in 2-dimensional space-time. In the
appendix, we systematically list several formulas for the decomposition of the
Riemann tensor in arbitrary dimensions n, which are applied in the main
deduction for n=4.Comment: 18 pages, amended version, accepted by Phys. Rev.

### The Lanczos potential for Weyl-candidate tensors exists only in four dimensions

We prove that a Lanczos potential L_abc for the Weyl candidate tensor W_abcd
does not generally exist for dimensions higher than four. The technique is
simply to assume the existence of such a potential in dimension n, and then
check the integrability conditions for the assumed system of differential
equations; if the integrability conditions yield another non-trivial
differential system for L_abc and W_abcd, then this system's integrability
conditions should be checked; and so on. When we find a non-trivial condition
involving only W_abcd and its derivatives, then clearly Weyl candidate tensors
failing to satisfy that condition cannot be written in terms of a Lanczos
potential L_abc.Comment: 11 pages, LaTeX, Heavily revised April 200

### Black Hole Entropy and the Dimensional Continuation of the Gauss-Bonnet Theorem

The Euclidean black hole has topology $\Re^2 \times {\cal S}^{d-2}$. It is
shown that -in Einstein's theory- the deficit angle of a cusp at any point in
$\Re^2$ and the area of the ${\cal S}^{d-2}$ are canonical conjugates. The
black hole entropy emerges as the Euler class of a small disk centered at the
horizon multiplied by the area of the ${\cal S}^{d-2}$ there.These results are
obtained through dimensional continuation of the Gauss-Bonnet theorem. The
extension to the most general action yielding second order field equations for
the metric in any spacetime dimension is given.Comment: 7 pages, RevTe

### Volume elements and torsion

We reexamine here the issue of consistency of minimal action formulation with
the minimal coupling procedure (MCP) in spaces with torsion. In Riemann-Cartan
spaces, it is known that a proper use of the MCP requires that the trace of the
torsion tensor be a gradient, $T_\mu=\partial_\mu\theta$, and that the modified
volume element $\tau_\theta = e^\theta \sqrt{g} dx^1\wedge...\wedge dx^n$ be
used in the action formulation of a physical model. We rederive this result
here under considerably weaker assumptions, reinforcing some recent results
about the inadequacy of propagating torsion theories of gravity to explain the
available observational data. The results presented here also open the door to
possible applications of the modified volume element in the geometric theory of
crystalline defects.Comment: Revtex, 8 pages, 1 figure. v2 includes a discussion on
$\lambda$-symmetr

### Five-Dimensional Eguchi-Hanson Solitons in Einstein-Gauss-Bonnet Gravity

Eguchi-Hanson solitons are odd-dimensional generalizations of the
four-dimensional Eguchi-Hanson metric and are asymptotic to
AdS$_5$\mathbb{Z}_p$ when the cosmological constant is either positive or
negative. We find soliton solutions to Lovelock gravity in 5 dimensions that
are generalizations of these objects.Comment: 26 pages, 11 figure

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