857 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
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 . 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
Decaying warm dark matter and neutrino masses
Neutrino masses may arise from spontaneous breaking of ungauged lepton
number. Due to quantum gravity effects the associated Goldstone boson - the
majoron - will pick up a mass. We determine the lifetime and mass required by
cosmic microwave background observations so that the massive majoron provides
the observed dark matter of the Universe. The majoron DDM scenario fits nicely
in models where neutrino masses arise a la seesaw, and may lead to other
possible cosmological implications.Comment: 4 pages, 3 figures. Replaced to match published version. Minor
changes made to address referees' comments. References adde
Redshift distribution of {\bf Ly-} lines and metal systems
The observed redshift distribution of Ly- 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- lines with
14, at 3. The redshift distribution of weaker
Ly- 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
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
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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