695 research outputs found

### Gravitino dark matter from gluino late decay in split supersymmetry

In split-supersymmetry (split-SUSY), gluino is a metastable particle and thus
can freeze out in the early universe. The late decay of such a long-life gluino
into the lightest supersymmetric particle (LSP) may provide much of the cosmic
dark matter content. In this work, assuming the LSP is gravitino produced from
the late decay of the metastable gluino, we examine the WMAP dark matter
constraints on the gluino mass. We find that to provide the full abundance of
dark matter, the gluino must be heavier than about 14 TeV and thus not
accessible at the CERN Large Hadron Collider (LHC).Comment: discussions added (version in PRD

### Dynamical Dark Matter: II. An Explicit Model

In a recent paper (arXiv:1106.4546), we introduced "dynamical dark matter," a
new framework for dark-matter physics, and outlined its underlying theoretical
principles and phenomenological possibilities. Unlike most traditional
approaches to the dark-matter problem which hypothesize the existence of one or
more stable dark-matter particles, our dynamical dark-matter framework is
characterized by the fact that the requirement of stability is replaced by a
delicate balancing between cosmological abundances and lifetimes across a vast
ensemble of individual dark-matter components. This setup therefore
collectively produces a time-varying cosmological dark-matter abundance, and
the different dark-matter components can interact and decay throughout the
current epoch. While the goal of our previous paper was to introduce the broad
theoretical aspects of this framework, the purpose of the current paper is to
provide an explicit model of dynamical dark matter and demonstrate that this
model satisfies all collider, astrophysical, and cosmological constraints. The
results of this paper therefore constitute an "existence proof" of the
phenomenological viability of our overall dynamical dark-matter framework, and
demonstrate that dynamical dark matter is indeed a viable alternative to the
traditional paradigm of dark-matter physics. Dynamical dark matter must
therefore be considered alongside other approaches to the dark-matter problem,
particularly in scenarios involving large extra dimensions or string theory in
which there exist large numbers of particles which are neutral under
Standard-Model symmetries.Comment: 45 pages, LaTeX, 10 figures. Replaced to match published versio

### Redshift distribution of {\bf Ly-$\alpha$} lines and metal systems

The observed redshift distribution of Ly-$\alpha$ lines and metal systems is
examined in order to discriminate and to trace the evolution of structure
elements observed in the galaxy distribution, at small redshifts, and to test
the theoretical description of structure evolution. We show that the expected
evolution of filamentary component of structure describes quite well the
redshift distribution of metal systems and stronger Ly-$\alpha$ lines with
$\log(N_{HI})\geq$14, at $z\leq$ 3. The redshift distribution of weaker
Ly-$\alpha$ lines can be attributed to the population of poorer structure
elements (Zel'dovich pancakes), which were formed at high redshifts from the
invisible DM and non luminous baryonic matter, and at lower redshifts they
mainly merged and dispersed.Comment: 13 pages, 5 figures, accepted in MNRA

### Cross-correlation of the CMB and foregrounds phases derived from the WMAP data

We present circular and linear cross-correlation tests and the
"friend-of-friend" analysis for phases of the Internal Linear Combination Map
(ILC) and the WMAP foregrounds for all K--W frequency bands at the range of
multipoles $\ell\le100$. We compare also Tegmark, de Oliveira-Costa and
Hamilton (2003) and Naselsky et al. (2003) cleaned maps with corresponding
foregrounds. We have found significant deviations from the expected Poissonian
statistics for all the cleaned maps and foregrounds. Our analysis shows that,
for a low multipole range of the cleaned maps, power spectra contains some of
the foregrounds residuals mainly from the W band.Comment: 11 pages, 10 figures. Submitted to MNRA

### Wavelength limits on isobaricity of perturbations in a thermally unstable radiatively cooling medium

Nonlinear evolution of one-dimensional planar perturbations in an optically
thin radiatively cooling medium in the long-wavelength limit is studied
numerically. The accepted cooling function generates in thermal equilibrium a
bistable equation of state $P(\rho)$. The unperturbed state is taken close to
the upper (low-density) unstable state with infinite compressibility
($dP/d\rho= 0$). The evolution is shown to proceed in three different stages.
At first stage, pressure and density set in the equilibrium equation of state,
and velocity profile steepens gradually as in case of pressure-free flows. At
second stage, those regions of the flow where anomalous pressure (i.e. with
negative compressibility) holds, create velocity profile more sharp than in
pressure-free case, which in turn results in formation of a very narrow
(short-wavelength) region where gas separates the equilibrium equation of state
and pressure equilibrium sets in rapidly. On this stage, variation in pressure
between narrow dense region and extended environment does not exceed more than
0.01 of the unperturbed value. On third stage, gas in the short-wavelength
region reaches the second (high-density) stable state, and pressure balance
establishes through the flow with pressure equal to the one in the unperturbed
state. In external (long-wavelength) regions, gas forms slow isobaric inflow
toward the short-wavelength layer. The duration of these stages decreases when
the ratio of the acoustic time to the radiative cooling time increases. Limits
in which nonlinear evolution of thermally unstable long-wavelength
perturbations develops in isobaric regime are obtained.Comment: 21 pages with 7 figures, Revtex, accepted in Physics of Plasma

### Dark Radiation Emerging After Big Bang Nucleosynthesis?

We show how recent data from observations of the cosmic microwave background
may suggest the presence of additional radiation density which appeared after
big bang nucleosynthesis. We propose a general scheme by which this radiation
could be produced from the decay of non-relativistic matter, we place
constraints on the properties of such matter, and we give specific examples of
scenarios in which this general scheme may be realized.Comment: v3: 5 pages, 1 figure. References added, typos corrected, notation
changed throughout. v2: 5 pages, 1 figure. Reformatted, references added,
acknowledgments updated, effect of radiation on CMB clarified. v1: 11 pages,
1 figur

### Statistical characteristics of observed Ly-$\alpha$ forest and the shape of linear power spectrum

Properties of $\sim$ 6 000 Ly-$\alpha$ absorbers observed in 19 high
resolution spectra of QSOs are investigated using the model of formation and
evolution of DM structure elements based on the Zel'dovich theory. This model
asserts that absorbers are formed in the course of both linear and nonlinear
adiabatic or shock compression of dark matter (DM) and gaseous matter. It
allows us to link the column density and overdensity of DM and gaseous
components with the observed column density of neutral hydrogen, redshifts and
Doppler parameters of absorbers and demonstrates that at high redshifts we
observe a self similar period of structure evolution with the Gaussian initial
perturbations. We show that the colder absorbers are associated with rapidly
expanded regions of a galactic scale which represent large amplitude negative
density perturbations.
We extend and improve the method of measuring the power spectrum of initial
perturbations proposed in Demia\'nski & Doroshkevich (2003b). Our method links
the observed separations and the DM column density of absorbers with the
correlation function of the initial velocity field. We recover the cold dark
matter (CDM) like power spectrum at scales 10> D > 0.15Mpc/h with a precision
of ~15%. However at scales $\sim 3 - 150 h^{-1}$kpc the measured and CDM--like
spectra are different. This result suggests a possible complex inflation with
generation of excess power at small scales.Comment: 21 pages, 7 figures, MNRAS submitte

### Bulk Viscosity, Decaying Dark Matter, and the Cosmic Acceleration

We discuss a cosmology in which cold dark-matter particles decay into
relativistic particles. We argue that such decays could lead naturally to a
bulk viscosity in the cosmic fluid. For decay lifetimes comparable to the
present hubble age, this bulk viscosity enters the cosmic energy equation as an
effective negative pressure. We investigate whether this negative pressure is
of sufficient magnitude to account fo the observed cosmic acceleration. We show
that a single decaying species in a flat, dark-matter dominated cosmology
without a cosmological constant cannot reproduce the observed
magnitude-redshift relation from Type Ia supernovae. However, a delayed bulk
viscosity, possibly due to a cascade of decaying particles may be able to
account for a significant fraction of the apparent cosmic acceleration.
Possible candidate nonrelativistic particles for this scenario include sterile
neutrinos or gauge-mediated decaying supersymmetric particles.Comment: 7 pages, 4 figure

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