This advert should have read "this Friday 10 November" - the coming
Friday, rather than the one just past.
Thanks to Bernard Carr for spotting this.
The rest of the advert is probably correct.
Apologies for clogging your inboxes,
Joe Zuntz
> Dear London Cosmologists,
>
> There will be a cosmology seminar at Imperial College this Friday 3
> November at 12 noon in the Huxley Building Room 503.
> All would be very welcome.
>
> Speaker : Gianluca Calcagni
> Title : Ghost conditions for Gauss-Bonnet cosmologies (hep-th/
> 0604201)
>
> Abstract:
> We investigate the stability against inhomogeneous perturbations
> and the appearance of ghost modes in Gauss-Bonnet gravitational
> theories with a non-minimally coupled scalar field, which can be
> regarded as either the dilaton or a compactification modulus in the
> context of string theory.
>
> Through cosmological linear perturbations we extract four no-ghost
> and two sub-luminal constraint equations, written in terms of
> background quantities, which must be satisfied for consistency. We
> also argue that, for a general action with quadratic Riemann
> invariants, homogeneous and inhomogeneous perturbations are, in
> general, inequivalent, and that attractors in the phase space can
> have ghosts. Single-field models as candidates for dark energy are
> explored numerically and severe bounds on the parameter space of
> initial conditions are placed.
>
> A number of cases proposed in the literature are tested and most of
> them are found to be unstable or observationally unviable.
>
>
> Joe Zuntz
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