19,381 research outputs found
Cold dark matter halos in Multi-coupled Dark Energy cosmologies: structural and statistical properties
The recently proposed Multi-coupled Dark Energy (McDE) scenario -
characterised by two distinct Cold Dark Matter (CDM) particle species with
opposite couplings to a Dark Energy scalar field - introduces a number of novel
features in the small-scale dynamics of cosmic structures, most noticeably the
simultaneous existence of both attractive and repulsive fifth-forces. Such
small-scale features are expected to imprint possibly observable footprints on
nonlinear cosmic structures, that might provide a direct way to test the
scenario. In order to unveil such footprints, we have performed the first suite
of high-resolution N-body simulations of McDE cosmologies, covering the
coupling range . We find that for coupling values corresponding
to fifth-forces weaker than standard gravity, the impact on structure formation
is very mild, thereby showing a new type of screening mechanism for long-range
scalar interactions. On the contrary, for fifth-forces comparable to or
stronger than standard gravity a number of effects appear in the statistical
and structural properties of CDM halos. Collapsed structures start to fragment
into pairs of smaller objects that move on different trajectories, providing a
direct evidence of the violation of the weak equivalence principle.
Consequently, the relative abundance of halos of different masses is
significantly modified. For sufficiently large coupling values, the expected
number of clusters is strongly suppressed, which might alleviate the present
tension between CMB- and cluster-based cosmological constraints. Finally, the
internal structure of halos is also modified, with a significant suppression of
the inner overdensity, and a progressive segregation of the two CDM species.Comment: 38 pages, 8 figures, 1 table. Accepted for publication in Physics of
the Dark Univers
The nonlinear evolution of large scale structures in Growing Neutrino cosmologies
We present the results of the first N-body simulations of the Growing
Neutrino scenario, as recently discussed in Baldi et al. (2011). Our results
have shown for the first time how neutrino lumps forming in the context of
Growing Neutrino cosmologies are expected to pulsate as a consequence of the
rapid oscillations of the dark energy scalar field. We have also computed for
the first time a realistic statistical distribution of neutrino halos and
determined their impact on the underlying Cold Dark Matter structures.Comment: 4 pages, 2 Figures. To appear in the Proceedings Volume of the
Conference "Advances in computational astrophysics", Cefalu' (Italy), 13-17
June 201
Time dependent couplings in the dark sector: from background evolution to nonlinear structure formation
We present a complete numerical study of cosmological models with a time
dependent coupling between the dark energy component driving the present
accelerated expansion of the Universe and the Cold Dark Matter (CDM) fluid.
Depending on the functional form of the coupling strength, these models show a
range of possible intermediate behaviors between the standard LCDM background
evolution and the widely studied case of interacting dark energy models with a
constant coupling. These different background evolutions play a crucial role in
the growth of cosmic structures, and determine strikingly different effects of
the coupling on the internal dynamics of nonlinear objects. By means of a
suitable modification of the cosmological N-body code GADGET-2 we have
performed a series of high-resolution N-body simulations of structure formation
in the context of interacting dark energy models with variable couplings.
Depending on the type of background evolution, the halo density profiles are
found to be either less or more concentrated with respect to LCDM, contrarily
to what happens for constant coupling models where concentrations can only
decrease. However, for some specific choice of the interaction function the
reduction of halo concentrations can be larger than in constant coupling
scenarios. In general, we find that time dependent interactions between dark
energy and CDM can in some cases determine stronger effects on structure
formation as compared to the constant coupling case, with a significantly
weaker impact on the background evolution of the Universe, and might therefore
provide a more viable possibility to alleviate the tensions between
observations and the LCDM model on small scales than the constant coupling
scenario. [Abridged]Comment: 27 pages, 17 figures, 3 tables. Minor revisions. MNRAS accepte
Periodic solutions of forced Kirchhoff equations
We consider Kirchhoff equations for vibrating bodies in any dimension in
presence of a time-periodic external forcing with period 2pi/omega and
amplitude epsilon, both for Dirichlet and for space-periodic boundary
conditions.
We prove existence, regularity and local uniqueness of time-periodic
solutions of period 2pi/omega and order epsilon, by means of a Nash-Moser
iteration scheme. The results hold for parameters (omega, epsilon) in Cantor
sets having measure asymptotically full as epsilon tends to 0.
(What's new in version 2: the case of finite-order Sobolev regularity, the
case of space-periodic boundary conditions, a different iteration scheme in the
proof, some references).Comment: 23 page
The new class of FR0 radio galaxies
Are the FRI and FRII radio galaxies representative of the radio-loud (RL) AGN
population in the local Universe? Recent studies on the local low-luminosity
radio sources cast lights on an emerging population of compact radio galaxies
which lack extended radio emission. In a pilot JVLA project, we study the
high-resolution images of a small but representative sample of this population.
The radio maps reveal compact unresolved or slightly resolved radio structures
on a scale of 1-3 kpc. We find that these RL AGN live in red massive early-type
galaxies, with large black hole masses (10 M), and
spectroscopically classified as Low Excitation Galaxies, all characteristics
typical of FRI radio galaxies which they also share the same nuclear luminosity
with. However, they are more core dominated (by a factor of 30) than FRIs
and show a clear deficit of extended radio emission. We call these sources
'FR0' to emphasize their lack of prominent extended radio emission. A
posteriori, other compact radio sources found in the literature fulfill the
requirements for a FR0 classification. Hence, the emerging FR0 population
appears to be the dominant radio class of the local Universe. Considering their
properties we speculate on their possible origins and the possible cosmological
scenarios they imply.Comment: 5 pages, 3 figures. Submitted for publication in Astronomische
Nachrichten. Contribution to the proceedings of the 5th Workshop on CSS and
GPS radio sources, held in Rimini (Italy) in May 201
Early massive clusters and the bouncing coupled dark energy
The abundance of the most massive objects in the Universe at different epochs
is a very sensitive probe of the cosmic background evolution and of the growth
history of density perturbations, and could provide a powerful tool to
distinguish between a cosmological constant and a dynamical dark energy field.
In particular, the recent detection of very massive clusters of galaxies at
high redshifts has attracted significant interest as a possible indication of a
failure of the standard LCDM model. Several attempts have been made in order to
explain such detections in the context of non-Gaussian scenarios or interacting
dark energy models, showing that both these alternative cosmologies predict an
enhanced number density of massive clusters at high redshifts, possibly
alleviating the tension. However, all the models proposed so far also
overpredict the abundance of massive clusters at the present epoch, and are
therefore in contrast with observational bounds on the low-redshift halo mass
function. In this paper we present for the first time a new class of
interacting dark energy models that simultaneously account for an enhanced
number density of massive clusters at high redshifts and for both the standard
cluster abundance at the present time and the standard power spectrum
normalization at CMB. The key feature of this new class of models is the
"bounce" of the dark energy scalar field on the cosmological constant barrier
at relatively recent epochs. We present the background and linear perturbations
evolution of the model, showing that the standard amplitude of density
perturbations is recovered both at CMB and at the present time, and we
demonstrate by means of large N-body simulations that our scenario predicts an
enhanced number of massive clusters at high redshifts without affecting the
present halo abundance. (Abridged)Comment: 11 pages, 6 figures, 2 tables. Minor changes, references added.
Accepted for publication in MNRA
Logics of variable inclusion and the lattice of consequence relations
In this paper, firstly, we determine the number of sublogics of variable
inclusion of an arbitrary finitary logic L with partition function. Then, we
investigate their position into the lattice of consequence relations over the
language of L.Comment: arXiv admin note: text overlap with arXiv:1804.08897,
arXiv:1809.0676
Structure formation in Multiple Dark Matter cosmologies with long-range scalar interactions
(Abridged) An interaction between Cold Dark Matter (CDM) and a classical
scalar field playing the role of the cosmic dark energy (DE) might provide
long-range dark interactions without conflicting with solar system bounds.
Although presently available observations allow to constrain such interactions
to a few percent of the gravitational strength, some recent studies have shown
that if CDM is composed by two different particle species having opposite
couplings to the DE field, such tight constraints can be considerably relaxed,
allowing for long-range scalar forces of order gravity without significantly
affecting observations both at the background and at the linear perturbations
level. In the present work, we extend the investigation of such Multiple Dark
Matter scenarios to the nonlinear regime of structure formation, by presenting
the first N-body simulations ever performed for these cosmologies. Our results
highlight some characteristic footprints of long-range scalar forces that arise
only in the nonlinear regime for specific models that would be otherwise
practically indistinguishable from the standard LCDM scenario both in the
background and in the growth of linear density perturbations. Among these
effects, the formation of "mirror" cosmic structures in the two CDM species,
the suppression of the nonlinear matter power spectrum at k > 1 h/Mpc, and the
fragmentation of collapsed halos, represent peculiar features that might
provide a direct way to constrain this class of cosmological models.Comment: 11 pages, 4 figures. Submitted to MNRA
Some characterizations of the spherical harmonics coefficients for isotropic random fields
In this paper we provide some simple characterizations for the spherical
harmonics coefficients of an isotropic random field on the sphere. The main
result is a characterization of isotropic gaussian fields through independence
of the coefficients of their development in spherical harmonics.Comment: 9 pages. Submitted June 200
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