235 research outputs found
Probing Dynamical Dark Energy with Press-Schechter Mass Functions
Measurement of accelerated expansion in the Universe led to propose a new
cosmic fluid as its cause: dark energy. Its various incarnations offer a wealth
of models whose relevance it is important to discriminate via contacts with
observations. I will present my investigations on the influence of dynamical
dark energy models on the formation of non-linear dark matter structures. In
particular, I will focus on structures traced by the mass function of dark
matter haloes.Comment: submitted to the Proceedings of the 11th Marcel Grossmann Meeting,
MG11, Berlin, Germany, July 23-29, 2006 (2007) to be publishe
A unified solution to the small scale problems of the CDM model II: introducing parent-satellite interaction
We continue the study of the impact of baryon physics on the small scale
problems of the CDM model, based on a semi-analytical model (Del
Popolo, 2009). Withsuch model, we show how the cusp/core, missing satellite
(MSP), Too Big to Fail (TBTF) problems and the angular momentum catastrophe can
be reconciled with observations, adding parent-satellite interaction. Such
interaction between darkmatter (DM) and baryons through dynamical friction (DF)
can sufficiently flattenthe inner cusp of the density profiles to solve the
cusp/core problem. Combining, in our model, a Zolotov et al. (2012)-like
correction, similarly to Brooks et al. (2013), and effects of UV heating and
tidal stripping, the number of massive, luminous satellites, as seen in the Via
Lactea 2 (VL2) subhaloes,is in agreement with the numbers observed in the MW,
thus resolving the MSP and TBTF problems. The model also produces a
distribution of the angular spin parameter and angular momentum in agreement
with observations of the dwarfs studied by van den Bosch, Burkert, \\& Swaters
(2001).Comment: 24pp, 5figs. arXiv admin note: text overlap with arXiv:1404.367
Separating expansion from contraction and generalizing TOV condition in spherically symmetric models with pressure
We investigate spherically symmetric solutions with pressure and discuss the
existence of a dividing shell separating expanding and collapsing regions. We
perform a 3+1 splitting and obtain gauge invariant conditions relating not only
the intrinsic spatial curvature of the shells to the ADM mass, but also a
function of the pressure which we introduce that generalises the
Tolman-Oppenheimer-Volkoff equilibrium condition. We consider the particular
case of a Lema\^itre-Tolman dust models with a cosmological constant (a
-CDM model) as an example of our results.Comment: 4pp, 1fig, AIP Conference: Proc. XXXI Spanish Relat. Meeting, ERE08,
Salamanca, Spain, 15-19 Sept., 2008 Septembre, Salamanca, Espagn
Small scale problems of the CDM model: a short review
The CDM model, or concordance cosmology, as it is often called, is a
paradigm at its maturity. It is clearly able to describe the universe at large
scale, even if some issues remain open, such as the cosmological constant
problem , the small-scale problems in galaxy formation, or the unexplained
anomalies in the CMB. CDM clearly shows difficulty at small scales,
which could be related to our scant understanding, from the nature of dark
matter to that of gravity; or to the role of baryon physics, which is not well
understood and implemented in simulation codes or in semi-analytic models. At
this stage, it is of fundamental importance to understand whether the problems
encountered by the DCM model are a sign of its limits or a sign of our
failures in getting the finer details right. In the present paper, we will
review the small-scale problems of the CDM model, and we will discuss
the proposed solutions and to what extent they are able to give us a theory
accurately describing the phenomena in the complete range of scale of the
observed universe.Comment: 48pp 19 figs, invited review, accepted by Galaxie
Advanced General Relativity Notes
These lecture notes are intended as a guide to Graduate level readers that
are already familiar with basic General Relativity. They present in a concise
way some advanced concepts and problems encountered in the study of
gravitation. In these notes are covered: Alternates forms of the Schwarzschild
Black Hole solution, including the classic Kruskal extension; An account of the
building of Conformal, Carter-Penrose, diagrams; A discussion of Birkhoff
Theorem; A discussion of tools for Geodesics and congruences, including Energy
Conditions; A discussion of Horizons and an approach to some of the singularity
theorems; An exploration of the Kerr Black Hole solution properties, including
the Penrose Process and Black Hole Thermodynamics; A discussion of the Eckart
and Israel-Stewart Relativistic Thermodynamics; A discussion of Tetrads in
Relativity, in Einstein-Cartan theory and in Newman-Penrose formalism; An
explicitation of calculations on Geodesics approach from Hamilton-Jacobi
Formalism; A derivation from Least action of the equation of Motion of a top in
Relativity, the M.P.D. equationsComment: 164pp, 40figs. Lecture notes for Graduates with GR1 knowledge.
Feedback appreciate
A dual null formalism for the collapse of fluids in a cosmological background
In this work we revisit the definition of Matter Trapping Surfaces (MTS)
introduced in previous investigations and show how it can be expressed in the
so-called dual null formalism developed for Trapping Horizons (TH). With the
aim of unifying both approaches, we construct a 2+2 threading from the 1+3
flow, and thus isolate one prefered spatial direction, that allows
straightforward translation into a dual nul subbasis, and to deduce the
geometric apparatus that follows. We remain as general as possible, reverting
to spherical symmetry only when needed, and express the MTS conditions in terms
of 2-expansion of the flow, then in purely geometric form of the dual null
expansions. The Raychadhuri equations that describe both MTS and TH are written
and interpreted using the previously defined gTOV (generalized
Tolman-Oppenheimer-Volkov) functional introduced in previous work. Further
using the Misner-Sharp mass and its previous perfect fluid definition, we
relate the spatial 2-expansion to the fluid pressure, density and acceleration.
The Raychaudhuri equations also allows us to define the MTS dynamic condition
with first order differentials so the MTS conditions are now shown to be all
first order differentials. This unified formalism allows one to realise that
the MTS can only exist in normal regions, and so it can exist only between
black hole horizons and cosmological horizons. Finally we obtain a relation
yielding the sign, on a TH, of the non-vanishing null expansion which
determines the nature of the TH from fluid content, and flow characteristics.
The 2+2 unified formalism here investigated thus proves a powerful tool to
reveal, in the future extensions, more of the very rich and subtle relations
between MTS and TH.Comment: 10pp 1 fig. corrected for equation labels, cross listing correcte
Dark Energy-Dark Matter Interaction from the Abell Cluster A586
We find that deviation from the virial equilibrium of the Abell Cluster A586
yields evidence of the interaction between dark matter and dark energy. We
argue that this interaction might imply a violation of the Equivalence
Principle. Our analysis show that evidence is found in the context of two
different models of dark energy-dark matter interaction.Comment: Talk presented by O.B. at Encuentros Relativistas Espanoles 2007,
Puerto de la Cruz, Tenerife, Spain, 10-14 September 2007. 6 pages, 3 figures
and style fil
Spherically symmetric models: separating expansion from contraction in models with anisotropic pressures
We investigate spherically symmetric spacetimes with an anisotropic fluid and
discuss the existence and stability of a dividing shell separating expanding
and collapsing regions. We find that the dividing shell is defined by a
relation between the pressure gradients, both isotropic and anisotropic, and
the strength of the fields induced by the Misner-Sharpe mass inside the
separating shell and by the pressure fluxes. This balance is a generalization
of the Tolman-Oppenheimer- Volkoff equilibrium condition which defines a local
equilibrium condition, but conveys also a non- local character given the
definition of the Misner-Sharpe mass. We present a particular solution with
dust and radiation that provides an illustration of our results.Comment: 4pp Towards New Paradigms: Proceeding Of The Spanish Relativity
Meeting 2011. AIP Conference Proceedings, Volume 1458, pp. 487-490 (2012).
Published in AIP Conf.Proc. 1458 (2011) 487-49
Black Holes and Galactic Density Cusps Spherically Symmetric Anisotropic Cusps
Aims: In this paper we study density cusps that may contain central black
holes. The actual co-eval self-similar growth would not distinguish between the
central object and the surroundings. Methods: To study the environment of a
growing black hole we seek descriptions of steady `cusps' that may contain a
black hole and that retain at least a memory of self-similarity. We refer to
the environment in brief as the `bulge' and on smaller scales, the `halo'.
Results: We find simple descriptions of the simulations of collisionless matter
by comparing predicted densities, velocity dispersions and distribution
functions with the simulations. In some cases central point masses may be
included by iteration. We emphasize that the co-eval self-similar growth allows
an explanation of the black hole bulge mass correlation between approximately
similar collisionless systems. Conclusions: We have derived our results from
first principles assuming adiabatic self-similarity and either self-similar
virialisation or normal steady virialisation. We conclude that distribution
functions that retain a memory of self-similar evolution provide an
understanding of collisionless systems. The implied energy relaxation of the
collisionless matter is due to the time dependence. Phase mixing relaxation may
be enhanced by clump-clump interactions.Comment: 9 pp, 3 figs, accepted by A\&
Energy transfer from baryons to dark matter as a unified solution to small-scale structure issues of the CDM model
Using a semianalytic code, we show how baryon physics in a CDM
cosmology could solve the discrepancy between numerical predictions of dark
matter haloes and observations, ranging from dwarf galaxies to clusters,
without the need of nonstandard dark matter models as advocated, for example,
by [Kaplinghat et al., Phys. Rev. Lett. 116, 041302, (2016)]. Combining well
established results, we show, for the first time, how accounting for baryon
physics, in particular dynamical friction mechanisms, leads to flat
galaxy-cluster profiles and correlations in several of their properties, solves
the so-called `diversity problem' and reproduces very well the challenging,
extremely low-rising rotation curve of IC2574. We therefore suggest treating
baryonic physics properly before introducing new exotic features, albeit
legitimate, in the standard cosmological model.Comment: 10 pages, 4 figures, matching the accepted version on Phys. Rev.
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