Lorentzian spacetimes with constant curvature invariants in four dimensions (2009)
Coley, Alan, Hervik, Sigbjorn, Pelavas, Nicos
In this paper we investigate four dimensional Lorentzian spacetimes with constant curvature invariants ($CSI$ spacetimes). We prove that if a four dimensional spacetime is $CSI$, then either the...
Spacetimes characterized by their scalar curvature invariants (2009)
Coley, Alan, Hervik, Sigbjorn, Pelavas, Nicos
In this paper we determine the class of four-dimensional Lorentzian manifolds that can be completely characterized by the scalar polynomial curvature invariants constructed from the Riemann tensor...
Perihelion precession in spherically symmetric Kaluza-Klein theories (2008)
Elgaroy, Oystein, Gron, Oyvind, Hervik, Sigbjorn
We consider the perihelion precession and bending of light in a class of Kaluza-Klein models and show that the "electric redshift" model, proposed in Zhang (2006) to explain the redshift of Quasars,...
Lorentzian spacetimes with constant curvature invariants in three dimensions (2007)
Coley, Alan, Hervik, Sigbjorn, Pelavas, Nicos
In this paper we study Lorentzian spacetimes for which all polynomial scalar invariants constructed from the Riemann tensor and its covariant derivatives are constant (CSI spacetimes) in three...
Ricci Nilsoliton Black Holes (2007)
We follow a constructive approach and find higher-dimensional black holes with Ricci nilsoliton horizons. The spacetimes are solutions to Einstein's equation with a negative cosmological constant and...
On the evolution of universes in quadratic theories of gravity (2006)
Barrow, John D., Hervik, Sigbjorn
We use a dynamical systems approach to investigate Bianchi type I and II universes in quadratic theories of gravity. Due to the complicated nature of the equations of motion we focus on the stability...
Cosmology: a bird's eye view (2006)
Coley, Alan A., Hervik, Sigbjorn, Lim, Woei Chet
In this essay we discuss the difference in views of the Universe as seen by two different observers. While one of the observers follows a geodesic congruence defined by the geometry of the...
ON THE EVOLUTION OF UNIVERSES IN QUADRATIC THEORIES OF GRAVITY (2006)
Barrow, John D., Hervik, Sigbjorn
We use a dynamical systems approach to investigate Bianchi type I and II universes in quadratic theories of gravity. Due to the complicated nature of the equations of motion we focus on the stability...
HIGHER DIMENSIONAL VSI SPACETIMES (2006)
Coley, Alan, Fuster, Andrea, Hervik, Sigbjorn, Pelavas, Nicos
We present the explicit metric forms for higher dimensional vanishing scalar invariant (VSI) Lorentzian spacetimes. We note that all of the VSI spacetimes belong to the higher dimensional Kundt...
The late-time behaviour of vortic Bianchi type VIII Universes (2005)
Hervik, Sigbjorn, Lim, Woei Chet
We use the dynamical systems approach to investigate the Bianchi type VIII models with a tilted $\gamma$-law perfect fluid. We introduce expansion-normalised variables and investigate the late-time...
Anisotropically Inflating Universes (2005)
Barrow, John D., Hervik, Sigbjorn
We show that in theories of gravity that add quadratic curvature invariants to the Einstein-Hilbert action there exist expanding vacuum cosmologies with positive cosmological constant which do not...
On Spacetimes with Constant Scalar Invariants (2005)
Coley, Alan, Hervik, Sigbjorn, Pelavas, Nicos
We study Lorentzian spacetimes for which all scalar invariants constructed from the Riemann tensor and its covariant derivatives are constant ($CSI$ spacetimes). We obtain a number of general results...
Inhomogeneous perturbations of plane-wave spacetimes (2005)
Recently it was shown that the exact cosmological solutions known as the vacuum plane-wave solutions are late-time attractors for an open set of the spatially homogeneous Bianchi universes containing...
On the Comment by Palle (astro-ph/0503562) on the vorticity and shear of the Universe (2005)
We show that a recent comment where Palle criticises works regarding CMBR fluctuations for a particular type of Bianchi models, is incorrect. In particular, in contrast to the claims of Palle, we...
Future Asymptotic Behaviour of Tilted Bianchi models of type IV and VIIh (2004)
Hervik, Sigbjorn, Hoogen, Robert Van Den, Coley, Alan
Using dynamical systems theory and a detailed numerical analysis, the late-time behaviour of tilting perfect fluid Bianchi models of types IV and VII$_h$ are investigated. In particular, vacuum...
A dynamical systems approach to the tilted Bianchi models of solvable type (2004)
We use a dynamical systems approach to analyse the tilting spatially homogeneous Bianchi models of solvable type (e.g., types VI$_h$ and VII$_h$) with a perfect fluid and a linear barotropic...
Bianchi Cosmologies: A Tale of Two Tilted fluids (2004)
Coley, Alan A., Hervik, Sigbjorn
We use a dynamical systems approach to study Bianchi type VI$_0$ cosmological models containing two tilted $\gamma$-law perfect fluids. The full state space is 11-dimensional, but the existence of a...
Coley, Alan A., Hervik, Sigbjorn
In brane-world cosmology gravitational waves can propagate in the higher dimensions (i.e., in the `bulk'). In some appropriate regimes the bulk gravitational waves may be approximated by plane waves....
Solvegeometry gravitational waves (2004)
In this paper we construct negatively curved Einstein spaces describing gravitational waves having a solvegeometry wave-front (i.e., the wave-fronts are solvable Lie groups equipped with a...
The Asymptotic Behaviour of Tilted Bianchi type VI$_0$ Universes (2004)
We study the asymptotic behaviour of the Bianchi type VI$_0$ universes with a tilted $\gamma$-law perfect fluid. The late-time attractors are found for the full 7-dimensional state space and for...
Einstein metrics: Homogeneous solvmanifolds, generalised Heisenberg groups and Black Holes (2003)
In this paper we construct Einstein spaces with negative Ricci curvature in various dimensions. These spaces -- which can be thought of as generalised AdS spacetimes -- can be classified in terms of...
Homogeneous Plane-wave Spacetimes and their Stability (2003)
Hervik, Sigbjorn, Kunduri, Hari K., Lucietti, James
We consider the stability of spatially homogeneous plane-wave spacetimes. We carry out a full analysis for plane-wave spacetimes in (4+1) dimensions, and find there are two cases to consider; what we...
The Future of Tilted Bianchi Universes (2003)
Barrow, John D., Hervik, Sigbjorn
An asymptotic stability analysis of spatially homogeneous models of Bianchi type containing tilted perfect fluids is performed. Using the known attractors for the non-tilted Bianchi type universes,...
Brane-world Singularities (2003)
Coley, Alan A., Hervik, Sigbjorn
We study the behavior of spatially homogeneous brane-worlds close to the initial singularity in the presence of both local and nonlocal stresses. It is found that the singularity in these...
Indefinite Information Processing in Ever-expanding Universes (2003)
Barrow, John D., Hervik, Sigbjorn
We show that generic anisotropic universes arbitrarily close to the open Friedmann universe allow information processing to continue into the infinite future if there is no cosmological constant or...
Vacuum Plane Waves in 4+1 D and Exact solutions to Einstein's Equations in 3+1 D (2002)
In this paper we derive homogeneous vacuum plane-wave solutions to Einstein's field equations in 4+1 dimensions. The solutions come in five different types of which three generalise the vacuum...
The early time behaviour of brane-world models is analysed in the presence of anisotropic stresses. It is shown that that the initial singularity cannot be isotropic, unless there is also an...
Multidimensional Cosmology: Spatially Homogeneous models of dimension 4+1 (2002)
In this paper we classify all 4+1 cosmological models where the spatial hypersurfaces are connected and simply connected homogeneous Riemannian manifolds. These models come in two categories,...
The Weyl tensor in Spatially Homogeneous Cosmological Models (2002)
Barrow, John D., Hervik, Sigbjorn
We study the evolution of the Weyl curvature invariant in all spatially homogeneous universe models containing a non-tilted gamma-law perfect fluid. We investigate all the Bianchi and Thurston type...
The Weyl Curvature Conjecture (2002)
Gron, Oyvind, Hervik, Sigbjorn
In this paper we review Penrose's Weyl curvature conjecture which states that the concept of gravitational entropy and the Weyl tensor is somehow linked, at least in a cosmological setting. We give a...
Barrow, John D., Hervik, Sigbjorn
We investigate brane-worlds with a pure magnetic field and a perfect fluid. We extend earlier work to brane-worlds, and find new properties of the Bianchi type I brane-world. We find new asymptotic...
Discrete Symmetries in Translation Invariant Cosmological Models (2001)
In this paper we investigate a class of (d+1) dimensional cosmological models with a cosmological constant possessing an R^d simply transitive symmetry group and show that it can be written in a form...
Quantum creation of an Inhomogeneous universe (2000)
In this paper we study a class of inhomogeneous cosmological models which is a modified version of what is usually called the Lema\^itre-Tolman model. We assume that we have a space with...
The Bianchi Type I minisuperspace model (2000)
The minisuperspace model of a Bianchi Type I universe with compact spatial sections is investigated. The classical solutions are brought onto a form were the difference between compact and infinite...