1,060 research outputs found
Sterile Neutrino Hot, Warm, and Cold Dark Matter
We calculate the incoherent resonant and non-resonant scattering production
of sterile neutrinos in the early universe. We find ranges of sterile neutrino
masses, vacuum mixing angles, and initial lepton numbers which allow these
species to constitute viable hot, warm, and cold dark matter (HDM, WDM, CDM)
candidates which meet observational constraints. The constraints considered
here include energy loss in core collapse supernovae, energy density limits at
big bang nucleosynthesis, and those stemming from sterile neutrino decay:
limits from observed cosmic microwave background anisotropies, diffuse
extragalactic background radiation, and Li-6/D overproduction. Our calculations
explicitly include matter effects, both effective mixing angle suppression and
enhancement (MSW resonance), as well as quantum damping. We for the first time
properly include all finite temperature effects, dilution resulting from the
annihilation or disappearance of relativistic degrees of freedom, and the
scattering-rate-enhancing effects of particle-antiparticle pairs (muons,
tauons, quarks) at high temperature in the early universe.Comment: 24 pages, including 8 figures. v3: to match version in PRD, added
references and numerous minor changes. High resolution color figures
available at http://superbeast.ucsd.edu/~kev/nucd
High-energy Astrophysics and the Virtual Observatory
The Virtual Observatory (VO) will revolutionise the way we do Astronomy by
allowing easy access to all astronomical data and by making the handling and
analysis of datasets at various locations across the globe much simpler and
faster. I report here on the need for the VO and its status in Europe,
concentrating on the recently started EURO-VO project, and then give two
specific applications of VO tools to high-energy astrophysics.Comment: 12 pages, 3 figures, invited talk at the Workshop ``Multifrequency
Behaviour of High Energy Cosmic Sources'', Vulcano, Italy, May 2005, F.
Giovannelli et al., in pres
Empirical Color Transformations Between SDSS Photometry and Other Photometric Systems
We present empirical color transformations between the Sloan Digital Sky
Survey (SDSS) ugriz photometry and Johnson-Cousins UBVRI system and Becker's
RGU system, respectively. Owing to the magnitude of data that is becoming
available in the SDSS photometric system it is particularly important to be
able to convert between this new system and traditional photometric systems.
Unlike earlier published transformations we based our calculations on stars
actually measured by the SDSS with the SDSS 2.5-m telescope. The photometric
database of the SDSS provides in a sense a single-epoch set of 'tertiary
standards' covering more than one quarter of the sky. Our transformations
should facilitate their use to easily and reliably derive the corresponding
approximate Johnson-Cousins or RGU magnitudes. The SDSS survey covers a number
of areas that were previously established as standard fields in the
Johnson-Cousins system, in particular, fields established by Landolt and by
Stetson. We used these overlapping fields to create well-photometered star
samples on which our calculated transformations are based. For the RGU
photometry we used fields observed in the framework of the new Basel
high-latitude field star survey. We calculated empirical color transformations
between SDSS photometry and Johnson-Cousins UBVRI and Becker's RGU system. For
all transformations we found linear relations to be sufficient. Furthermore we
showed that the transformations between the Johnson-Cousins and the SDSS system
have a slight dependence on metallicity.Comment: 11 pages, 7 figures, Accepted for publication in A&
Oscillation Induced Neutrino Asymmetry Growth in the Early Universe
We study the dynamics of active-sterile neutrino oscillations in the early
universe using full momentum-dependent quantum-kinetic equations. These
equations are too complicated to allow for an analytical treatment, and
numerical solution is greatly complicated due to very pronounced and narrow
structures in the momentum variable introduced by resonances. Here we introduce
a novel dynamical discretization of the momentum variable which overcomes this
problem. As a result we can follow the evolution of neutrino ensemble
accurately well into the stable growing phase. Our results confirm the
existence of a "chaotic region" of mixing parameters, for which the final sign
of the asymmetry, and hence the SBBN prediction of He(4)-abundance cannot be
accurately determined.Comment: 23 pages, 9 eps-figs, Latex, uses JHEP clas
Chaos, Determinacy and Fractals in Active-Sterile Neutrino Oscillations in the Early Universe
The possibility of light sterile neutrinos allows for the resonant production
of lepton number in the early universe through matter-affected neutrino mixing.
For a given a mixing of the active and sterile neutrino states it has been
found that the lepton number generation process is chaotic and strongly
oscillatory. We undertake a new study of this process' sensitivity to initial
conditions through the quantum rate equations. We confirm the chaoticity of the
process in this solution, and moreover find that the resultant lepton number
and the sign of the asymmetry produces a fractal in the parameter space of
mass, mixing angle and initial baryon number. This has implications for future
searches for sterile neutrinos, where arbitrary high sensitivity could not be
determinate in forecasting the lepton number of the universe.Comment: 6 pages, 3 figure
Finding Galaxy Groups In Photometric Redshift Space: the Probability Friends-of-Friends (pFoF) Algorithm
We present a structure finding algorithm designed to identify galaxy groups
in photometric redshift data sets: the probability friends-of-friends (pFoF)
algorithm. This algorithm is derived by combining the friends-of-friends
algorithm in the transverse direction and the photometric redshift probability
densities in the radial dimension. The innovative characteristic of our
group-finding algorithm is the improvement of redshift estimation via the
constraints given by the transversely connected galaxies in a group, based on
the assumption that all galaxies in a group have the same redshift. Tests using
the Virgo Consortium Millennium Simulation mock catalogs allow us to show that
the recovery rate of the pFoF algorithm is larger than 80% for mock groups of
at least 2\times10^{13}M_{\sun}, while the false detection rate is about 10%
for pFoF groups containing at least net members. Applying the algorithm
to the CNOC2 group catalogs gives results which are consistent with the mock
catalog tests. From all these results, we conclude that our group-finding
algorithm offers an effective yet simple way to identify galaxy groups in
photometric redshift catalogs.Comment: AJ accepte
Gravitational collapse due to dark matter and dark energy in the brane world scenario
Gravitational collapse of FRW brane world embedded in a conformaly flat bulk
is considered for matter cloud consists of dark matter and dark energy with
equation of state . The effect of dark
matter and dark energy is being considered first separately and then a
combination of them both with and without interaction. In some cases the
collapse leads to black hole in some other cases naked singularity appears.Comment: 10 Latex Pages, RevTex style, 4 figure
Leptogenesis in models with keV sterile neutrino dark matter
We analyze leptogenesis in gauge extensions of the Standard Model with keV
sterile neutrino dark matter. We find that both the observed dark matter
abundance and the correct baryon asymmetry of the Universe can simultaneously
emerge in these models. Both the dark matter abundance and the leptogenesis are
controlled by the out of equilibrium decays of the same heavy right handed
neutrino.Comment: 6 pages, 1 figur
Dynamical Evolution of Interacting Modified Chaplygin Gas
The cosmological model of the modified Chaplygin gas interacting with cold
dark matter is studied. Our attention is focused on the final state of universe
in the model. It turns out that there exists a stable scaling solution, which
provides the possibility to alleviate the coincidence problem. In addition, we
investigate the effect of the coupling constants and on the
dynamical evolution of this model from the statefinder viewpoint. It is found
that the coupling constants play a significant role during the dynamical
evolution of the interacting MCG model. Furthermore, we can distinguish this
interacting model from other dark energy models in the plane.Comment: 10 pages, 6 figures, accepted for publication in Int. J. Mod. Phys.
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