81 research outputs found
The Growth of Structure in Interacting Dark Energy Models
If dark energy interacts with dark matter, there is a change in the
background evolution of the universe, since the dark matter density no longer
evolves as a^{-3}. In addition, the non-gravitational interaction affects the
growth of structure. In principle, these changes allow us to detect and
constrain an interaction in the dark sector. Here we investigate the growth
factor and the weak lensing signal for a new class of interacting dark energy
models. In these models, the interaction generalises the simple cases where one
dark fluid decays into the other. In order to calculate the effect on structure
formation, we perform a careful analysis of the perturbed interaction and its
effect on peculiar velocities. Assuming a normalization to today's values of
dark matter density and overdensity, the signal of the interaction is an
enhancement (suppression) of both the growth factor and the lensing power, when
the energy transfer in the background is from dark matter to dark energy (dark
energy to dark matter).Comment: 9 pages, 12 figures. Minor improvements to clarify relation to
previous work. Version accepted by JCA
Theoretical Priors On Modified Growth Parametrisations
Next generation surveys will observe the large-scale structure of the
Universe with unprecedented accuracy. This will enable us to test the
relationships between matter over-densities, the curvature perturbation and the
Newtonian potential. Any large-distance modification of gravity or exotic
nature of dark energy modifies these relationships as compared to those
predicted in the standard smooth dark energy model based on General Relativity.
In linear theory of structure growth such modifications are often parameterised
by virtue of two functions of space and time that enter the relation of the
curvature perturbation to, first, the matter over-density, and second, the
Newtonian potential. We investigate the predictions for these functions in
Brans-Dicke theory, clustering dark energy models and interacting dark energy
models. We find that each theory has a distinct path in the parameter space of
modified growth. Understanding these theoretical priors on the
parameterisations of modified growth is essential to reveal the nature of
cosmic acceleration with the help of upcoming observations of structure
formations.Comment: 10 pages, 5 figure
Dynamics of dark energy with a coupling to dark matter
Dark energy and dark matter are the dominant sources in the evolution of the
late universe. They are currently only indirectly detected via their
gravitational effects, and there could be a coupling between them without
violating observational constraints. We investigate the background dynamics
when dark energy is modelled as exponential quintessence, and is coupled to
dark matter via simple models of energy exchange. We introduce a new form of
dark sector coupling, which leads to a more complicated dynamical phase space
and has a better physical motivation than previous mathematically similar
couplings.Comment: 11 pages, 4 figures, revtex, references adde
Quintessence with quadratic coupling to dark matter
We introduce a new form of coupling between dark energy and dark matter that
is quadratic in their energy densities. Then we investigate the background
dynamics when dark energy is in the form of exponential quintessence. The three
types of quadratic coupling all admit late-time accelerating critical points,
but these are not scaling solutions. We also show that two types of coupling
allow for a suitable matter era at early times and acceleration at late times,
while the third type of coupling does not admit a suitable matter era.Comment: 11 pages, 8 figures, revte
Dynamics of interacting dark energy
Dark energy and dark matter are only indirectly measured via their
gravitational effects. It is possible that there is an exchange of energy
within the dark sector, and this offers an interesting alternative approach to
the coincidence problem. We consider two broad classes of interacting models
where the energy exchange is a linear combination of the dark sector densities.
The first class has been previously investigated, but we define new variables
and find a new exact solution, which allows for a more direct, transparent and
comprehensive analysis. The second class has not been investigated in general
form before. We give general conditions on the parameters in both classes to
avoid unphysical behavior (such as negative energy densities).Comment: 11 pages, 5 color figures, revtex; matches version published in PR
Dynamics of interacting dark energy
Dark energy and dark matter are only indirectly measured via their
gravitational effects. It is possible that there is an exchange of energy
within the dark sector, and this offers an interesting alternative approach to
the coincidence problem. We consider two broad classes of interacting models
where the energy exchange is a linear combination of the dark sector densities.
The first class has been previously investigated, but we define new variables
and find a new exact solution, which allows for a more direct, transparent and
comprehensive analysis. The second class has not been investigated in general
form before. We give general conditions on the parameters in both classes to
avoid unphysical behavior (such as negative energy densities).Comment: 11 pages, 5 color figures, revtex; matches version published in PR
Limits on the parameters of the equation of state for interacting dark energy
Under the assumption that cold dark matter and dark energy interact with each
other through a small coupling term, , we constrain the parameter space of
the equation of state of those dark energy fields whose variation of the
field since last scattering do not exceed Planck's mass. We use three
parameterizations of and two different expressions for . Our work
extends previous ones.Comment: 18 pages, 11 figures, accepted for publication on Physics Letters
On the growth of perturbations in interacting dark energy and dark matter fluids
The covariant generalizations of the background dark sector coupling
suggested in G. Mangano, G. Miele and V. Pettorino, Mod. Phys. Lett. A 18, 831
(2003) are considered. The evolution of perturbations is studied with detailed
attention to interaction rate that is proportional to the product of dark
matter and dark energy densities. It is shown that some classes of models with
coupling of this type do not suffer from early time instabilities in strong
coupling regime.Comment: 11 pages, 2 figures. v3: minor changes, typos fixe
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