Browsing by Author "Ward, John"

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    Quintessentially geometric model
    (2006-10-16) Gumjudpai, Burin; Naskar, Tapan; Ward, John
    We consider string inspired cosmology on a solitary D3 brane moving in the background of a ring of branes located on a circle of radius R. The motion of the D3 brane transverse to the plane of the ring gives rise to a radion field which can be mapped to a massive non-BPS Born-Infeld type field with a cosh potential. For certain bounds of the brane tension we find an inflationary phase is possible, with the string scale relatively close to the Planck scale. The relevant perturbations and spectral indices are all well within the expected observational bounds. The evolution of the universe eventually comes to be dominated by dark energy, which we show is a late time attractor of the model. However we also find that the equation of state is time dependent, and will lead to late time Quintessence.
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    Type I singularities and the Phantom Menace
    (2007-04-15) Naskar, Tapan; Ward, John
    We consider the future dynamics of a transient phantom dominated phase of the universe in LQC and in the RS braneworld, which both have a non-standard Friedmann equation. We find that for a certain class of potentials, the Hubble parameter oscillates with simple harmonic motion in the LQC case and therefore avoids any future singularity. For more general potentials we find that damping effects eventually lead to the Hubble parameter becoming constant. On the other hand in the braneworld case we find that although the type I singularity can be avoided, the scale factor still diverges at late times.