19 research outputs found
On exact solutions for quintessential (inflationary) cosmological models with exponential potentials
We first study dark energy models with a minimally-coupled scalar field and
exponential potentials, admitting exact solutions for the cosmological
equations: actually, it turns out that for this class of potentials the
Einstein field equations exhibit alternative Lagrangians, and are completely
integrable and separable (i.e. it is possible to integrate the system
analytically, at least by quadratures). We analyze such solutions, especially
discussing when they are compatible with a late time quintessential expansion
of the universe. As a further issue, we discuss how such quintessential scalar
fields can be connected to the inflationary phase, building up, for this class
of potentials, a quintessential inflationary scenario: actually, it turns out
that the transition from inflation toward late-time exponential quintessential
tail admits a kination period, which is an indispensable ingredient of this
kind of theoretical models. All such considerations have also been done by
including radiation into the model.Comment: Revtex4, 10 figure
Inverse Power Law Quintessence with Non-Tracking Initial Conditions
A common property of popular models of quintessence dark energy is the
convergence to a common solution from a large range of the initial conditions.
We re-examine the popular inverse power-law model of quintessence (where the
common solution is dubbed as the 'tracker') with particular attention to the
initial conditions for the field and their influence on the evolution. We find
that previously derived limits on the parameters of the potential in this model
are valid only in a range of initial conditions. A reasonably sharp boundary
lies where the initial energy density of the scalar field is equal to that of
the background radiation component. An initial quintessence energy density
above this equipartition value lead to a solution that will not have joined the
tracker solution by the present epoch. These non-tracker solutions possess the
property that their present equation of state is very compatible with the
observed bounds and independent of the exponent of the potential.Comment: RevTEX4, 9 figure
Measuring the metric: a parametrized post-Friedmanian approach to the cosmic dark energy problem
We argue for a ``parametrized post-Friedmanian'' approach to linear
cosmology, where the history of expansion and perturbation growth is measured
without assuming that the Einstein Field Equations hold. As an illustration, a
model-independent analysis of 92 type Ia supernovae demonstrates that the curve
giving the expansion history has the wrong shape to be explained without some
form of dark energy or modified gravity. We discuss how upcoming lensing,
galaxy clustering, cosmic microwave background and Lyman alpha forest
observations can be combined to pursue this program, which generalizes the
quest for a dark energy equation of state, and forecast the accuracy that the
proposed SNAP satellite can attain.Comment: Replaced to match accepted PRD version. References and another
example added, section III omitted since superceded by astro-ph/0207047. 11
PRD pages, 7 figs. Color figs and links at
http://www.hep.upenn.edu/~max/gravity.html or from [email protected]