2 research outputs found
Towards a future singularity?
We discuss whether the future extrapolation of the present cosmological state
may lead to a singularity even in case of "conventional" (negative) pressure of
the dark energy field, namely . The discussion is based on an
often neglected aspect of scalar-tensor models of gravity: the fact that
different test particles may follow the geodesics of different metric frames,
and the need for a frame-independent regularization of curvature singularities.Comment: 8 pages. Essay written for the "2004 Awards for Essays on
Gravitation" (Gravity Research Foundation, Wellesley Hills, MA, USA), and
selected for "Honorable Mention
Fitting Type Ia supernovae with coupled dark energy
We discuss the possible consistency of the recently discovered Type Ia
supernovae at z>1 with models in which dark energy is strongly coupled to a
significant fraction of dark matter, and in which an (asymptotic) accelerated
phase exists where dark matter and dark energy scale in the same way. Such a
coupling has been suggested for a possible solution of the coincidence problem,
and is also motivated by string cosmology models of "late time" dilaton
interactions. Our analysis shows that, for coupled dark energy models, the
recent data are still consistent with acceleration starting as early as at
(to within 90% c.l.), although at the price of a large "non-universality"
of the dark energy coupling to different matter fields. Also, as opposed to
uncoupled models which seem to prefer a ``phantom'' dark energy, we find that a
large amount of coupled dark matter is compatible with present data only if the
dark energy field has a conventional equation of state w>-1.Comment: 13 pages, 6 figures. Final version, accepted for publication in JCA