A new framework for studying spherically symmetric static solutions in f(R) gravity (2009)
Nzioki, Anne Marie, Carloni, Sante, Goswami, Rituparno, Dunsby, Peter K. S.
We develop a new covariant formalism to treat spherically symmetric spacetimes in f(R) theories of gravity. Using this formalism we derive the general equations for a static and spherically symmetric...
Power-law cosmic expansion in f(R) gravity models (2009)
Goheer, Naureen, Larena, Julien, Dunsby, Peter K. S.
We show that within the class of f(R) gravity theories, FLRW power-law perfect fluid solutions only exist for R^n gravity. This significantly restricts the set of exact cosmological solutions which...
On the co-existence of matter dominated and accelerating solutions in f(G)-gravity (2009)
Goheer, Naureen, Goswami, Rituparno, Dunsby, Peter K. S., Ananda, Kishore
Working within the theory of modified Gauss-Bonnet gravity, we show that FLRW--like power--law solutions only exist for a very special class of f(G)theories. Furthermore, we point out that any...
Unifying the study of background dynamics and perturbations in $f(R)$-gravity (2008)
Carloni, Sante, Ananda, Kishore N., Dunsby, Peter K. S., Abdelwahab, Mohamed E. S.
In this paper we show how the covariant gauge invariant equations for the evolution of scalar, vector and tensor perturbations for a generic $f(R)$-gravity theory can be recast in order to exploit...
A characteristic signature of fourth order gravity (2008)
Ananda, Kishore N., Carloni, Sante, Dunsby, Peter K. S.
We present for the first time the complete matter power spectrum for $R^n$ gravity which has been derived from the fourth order scalar perturbation equations. This leads to the discovery of a...
Dynamics of f(R)-cosmologies containing Einstein static models (2008)
Goheer, Naureen, Goswami, Rituparno, Dunsby, Peter K. S.
We study the dynamics of homogeneous isotropic FRW cosmologies with positive spatial curvature in $f(R)$-gravity, paying special attention to the existence of Einstein static models and only study...
A detailed analysis of structure growth in $f(R)$ theories of gravity (2008)
Ananda, Kishore N., Carloni, Sante, Dunsby, Peter K. S.
We investigate the connection between dark energy and fourth order gravity by analyzing the behavior of scalar perturbations around a Friedmann-Robertson-Walker background. The evolution equations...
Goswami, Rituparno, Goheer, Naureen, Dunsby, Peter K. S.
We investigate whether or not an Einstein Static universe is a solution to the cosmological equations in $f(R)$ gravity. It is found that only one class of $f(R)$ theories admits an Einstein Static...
Dynamical systems analysis of anisotropic cosmologies in $R^n$-gravity (2007)
Goheer, Naureen, Leach, Jannie A., Dunsby, Peter K. S.
In this paper we study the dynamics of {\it orthogonal spatially homogeneous} Bianchi cosmologies in $R^n$-gravity. We construct a compact state space by dividing the state space into different...
Compactifying the state space for alternative theories of gravity (2007)
Goheer, Naureen, Leach, Jannie A., Dunsby, Peter K. S.
In this paper we address important issues surrounding the choice of variables when performing a dynamical systems analysis of alternative theories of gravity. We discuss the advantages and...
An analysis of the shear dynamics in Bianchi I cosmologies with $R^n$-gravity (2007)
Leach, Jannie A., Dunsby, Peter K. S., Carloni, Sante
We consider the case of $R^n$-gravity and perform a detailed analysis of the dynamics in Bianchi I cosmologies which exhibit {\it local rotational symmetry} (LRS). We find exact solutions and study...
The evolution of tensor perturbations in scalar-tensor theories of gravity (2006)
Carloni, Sante, Dunsby, Peter K. S.
The evolution equations for tensor perturbations in a generic scalar tensor theory of gravity are presented. Exact solution are given for a specific class of theories and...
A dynamical system approach to higher order gravity (2006)
Carloni, Sante, Dunsby, Peter K. S.
The dynamical system approach has recently acquired great importance in the investigation on higher order theories of gravity. In this talk I review the main results and I give brief comments on the...
Gauge invariant perturbations of Scalar-Tensor Cosmologies: The vacuum case (2006)
Carloni, Sante, Dunsby, Peter K. S., Rubano, Claudio
The covariant gauge invariant perturbation theory of scalar cosmological perturbations is developed for a general Scalar-Tensor Friedmann-Lemaitre-Robertson-Walker cosmology in a vacuum. The...
Shear dynamics in Bianchi I cosmologies with R^n-gravity (2006)
Leach, Jannie A, Carloni, Sante, Dunsby, Peter K S
We give the equations governing the shear evolution in Bianchi spacetimes for general f(R)-theories of gravity. We consider the case of R^n-gravity and perform a detailed analysis of the dynamics in...
On inhomogeneous magnetic seed fields and gravitational waves within the MHD limit (2006)
Zunckel, Caroline, Betschart, Gerold, Dunsby, Peter K S, Marklund, Mattias
In this paper we apply second-order gauge-invariant perturbation theory to investigate the possibility that the non-linear coupling between gravitational waves (GW) and a large scale inhomogeneous...
Bounce Conditions in f(R) Cosmologies (2005)
Carloni, Sante, Dunsby, Peter K. S., Solomons, Deon
We investigate the conditions for a bounce to occur in Friedmann-Robertson-Walker cosmologies for the class of fourth order gravity theories. The general bounce criterion is determined and...
Large-scale perturbations on the brane and the isotropy of the cosmological singularity (2004)
Goheer, Naureen, Dunsby, Peter K. S., Coley, Alan, Bruni, Marco
We present the complete set of propagation and constraint equations for the kinematic and non-local first order quantities which describe general linear inhomogeneous and anisotropic perturbations of...
Are braneworlds born isotropic? (2003)
Dunsby, Peter K. S., Goheer, Naureen, Bruni, Marco, Coley, Alan
It has recently been suggested that an isotropic singularity may be a generic feature of brane cosmologies, even in the inhomogeneous case. Using the covariant and gauge-invariant approach we present...
Cosmic magnetic fields from velocity perturbations in the early Universe (2003)
Betschart, Gerold, Dunsby, Peter K. S., Marklund, Mattias
We show, using a covariant and gauge-invariant charged multifluid perturbation scheme, that velocity perturbations of the matter-dominated dust Friedmann-Lemaitre-Robertson-Walker (FLRW) model can...
Charged multifluids in general relativity (2002)
Marklund, Mattias, Dunsby, Peter K. S., Betschart, Gerold, Servin, Martin, Tsagas, Christos
The exact 1+3 covariant dynamical fluid equations for a multi-component plasma, together with Maxwell's equations are presented in such a way as to make them suitable for a gauge-invariant analysis...
Exponential Potentials on the Brane (2002)
Goheer, Naureen, Dunsby, Peter K. S.
In this paper we study the cosmological dynamics of Randall-Sundrum braneworld type scenarios in which the five-dimensional Weyl tensor has a non-vanishing projection onto the three-brane where...
Singularities on the brane aren't isotropic (2002)
Bruni, Marco, Dunsby, Peter K. S.
Recent studies of homogeneous anisotropic universe models in the brane world scenario show that the cosmological singularity in this context is isotropic. It has therefore been suggested that this...
Cosmological Electromagnetic Fields due to Gravitational Wave Perturbations (2000)
Marklund, Mattias, Dunsby, Peter K. S., Brodin, Gert
We consider the dynamics of electromagnetic fields in an almost-Friedmann-Robertson-Walker universe using the covariant and gauge-invariant approach of Ellis and Bruni. Focusing on the situation...
Dynamical Systems Approach to Magnetised Cosmological Perturbations (2000)
Hobbs, Stacey, Dunsby, Peter K. S.
Assuming a large-scale homogeneous magnetic field, we follow the covariant and gauge-invariant approach used by Tsagas and Barrow to describe the evolution of density and magnetic field...
Non-linear gravitational wave interactions with plasmas (2000)
Brodin, Gert, Marklund, Mattias, Dunsby, Peter K. S.
We consider the interactions of a strong gravitational wave with electromagnetic fields using the 1+3 orthonormal tetrad formalism. A general system of equations are derived, describing the influence...
A fully covariant description of CMB anisotropies (1997)
Starting from the exact non-linear description of matter and radiation, a fully covariant and gauge-invariant formula for the observed temperature anisotropy of the cosmic microwave background (CBR)...