Structure formation in coupled Dark Energy models

1
One of my main interests concerns.
Structure formation in coupled Dark Energy models
DE affects matter density perturbation evolution
both in linear and non-linear regime (halo
concentration, profiles, mass function) Large
scale structure observations can, in principle,
discriminate among different DE models
DE is usually described as a smooth component on
scales well inside the horizon. However its
behavior in presence of high matter
concentrations is not clear
Currently, my research interest focuses on the DE
clustering properties, in particular in presence
of DM-DE coupling (scalar field coupled to DM)
and in post-linear regime (spherical collapse
model). The starting point is one of my main work
of my PhD concerning the spherical collapse in
coupled DE models
Dark Matter-baryon segregation in the non-linear
evolution of coupled Dark Energy models Mainini
Bonometto, 2005, Phys. Rev. D72, 083514
Effects of the coupling modified dynamics for DM
particles
1. Mass of DM particles varies with
time........................violation of
equivalence principle
2. Newtonian interactions
DM-DM............................................
.......................effective gravitational
constant G G(1 4ß2 / 3)
DM-baryon and baryon-baryon......................
........usual gravitational constant G
Roberto Mainini - ITA Friday - December 7, 2007
2
Spherical collapse in coupled (homogeneous) DE
1. Start with a spherical top-hat overdensity in
DM (d?DM) and baryons (d?bar ) initially
expanding with Hubble flow
2. Then consider a set of n concentric shells for
DM and baryons of radii RnDM and Rnbar such that
initially RnDM Rnbar
3. Finally, numerically follow the evolution of
each shells. Because of the coupling the
gravitational infall proceeds more slowly for the
baryons than for DM. At the time t tin ?t
outer layers of halo rich in baryons
d?bar
background
?t
d?DM d?bar
tin
t
d?DM d?bar
?DM ?bar ?DE
?DM ?bar ?DE
Coupling causes DM-baryon segregation. A great
amount of baryons can be expelled from the
fluctuation in halo encounters before its
virialization
Segregation can be related to several
astrophysical problems (missing satellites
problem, formation of galactic disk, excess of X
and EUV emission, L-T relation of cluster, etc.).
Up to now, some of this problem are explained
through hydrodynamics tuning apposite parameters.
Anyway, the physics here considered has no
hydrodynamical origin. It could be remarkable
before the gas hydrodynamics becomes the dominant
effect in structure formation
These issues should be deepened in future works
Roberto Mainini - ITA Friday - December 7, 2007
3
How to use the spherical collapse approach to
investigate the clustering properties of DE
Relax the assumption of homogeneity and consider
a set of concentric shells also for DE, then find
the equations for their evolution As for DM
and baryons 1. Start from relativistic
perturbation equations obtained expanding the
metric tensor to linear order (weak
gravitational field) around a flat FRW metric,
while keeping the full non-linear stress-energy
tensor 2. Then derive the Newtonian limit (small
scales)
Equations for DE shells are complicated by the
presence of additional terms due to the
non-vanishing pressure of DE itself. They could
make equations difficult to integrate.
Equations are currently under investigation
Roberto Mainini - ITA Friday - December 7, 2007