arXiv subjects

D. R. Matravers

Publications and source records attributed to D. R. Matravers.

3 recordsLinked to original sources

arXiv2001

Particle number density fluctuations and pressure effects on structure formation

We provide a covariant and gauge-invariant approach to the question of how a first order pressure can be incorporated self-consistently in a cosmological scenario. The approximation is relevant, in the linear regime, to weakly self-interacting or warm dark matter models. We also derive number density fluctuations in which new modes appear because the number density fluctuations are no longer simply proportional to the density fluctuations.

astro-ph↗

arXiv2000

Matching Spherical Dust Solutions to Construct Cosmological Models

Conditions for smooth cosmological models are set out and applied to inhomogeneous spherically symmetric models constructed by matching together different Lemaitre-Tolman-Bondi solutions to the Einstein field equations. As an illustration the methods are applied to a collapsing dust sphere in a curved background. This describes a region which expands and then collapses to form a black hole in an Einstein de Sitter background. We show that in all such models if there is no vacuum region then the singularity must go on accreting matter for an infinite LTB time.

gr-qc↗

arXiv2000

Cosmic magnetism, curvature and the expansion dynamics

We discuss how a cosmological magnetic field could affect the expansion of the universe, through its interaction with the spacetime geometry. The tension of the field lines means that the magneto-curvature coupling tends to accelerate positively curved regions and decelerate those with negative curvature. Depending on the equation of state of the matter, the effect varies from mimicking that of a cosmological constant to resembling a time-decaying quintessence. Most interestingly, the coupling between magnetism and geometry implies that even weak fields have a significant impact if the curvature contribution is strong. This leads to kinematical complications that can inhibit the onset of the accelerated phase in spatially open inflationary models. We employ a simple cosmological model to illustrate these effects and examine the conditions necessary for them to have a appreciable impact.

astro-ph↗