26 research outputs found
Gamma rays from Dark Matter Annihilation in the Central Region of the Galaxy
In this article, we review the prospects for the Fermi satellite (formerly
known as GLAST) to detect gamma rays from dark matter annihilations in the
Central Region of the Milky Way, in particular on the light of the recent
astrophysical observations and discoveries of Imaging Atmospheric Cherenkov
Telescopes. While the existence of significant backgrounds in this part of the
sky limits Fermi's discovery potential to some degree, this can be mitigated by
exploiting the peculiar energy spectrum and angular distribution of the dark
matter annihilation signal relative to those of astrophysical backgrounds.Comment: v3: corrected typos, content unchange
LSST Science Book, Version 2.0
A survey that can cover the sky in optical bands over wide fields to faint
magnitudes with a fast cadence will enable many of the exciting science
opportunities of the next decade. The Large Synoptic Survey Telescope (LSST)
will have an effective aperture of 6.7 meters and an imaging camera with field
of view of 9.6 deg^2, and will be devoted to a ten-year imaging survey over
20,000 deg^2 south of +15 deg. Each pointing will be imaged 2000 times with
fifteen second exposures in six broad bands from 0.35 to 1.1 microns, to a
total point-source depth of r~27.5. The LSST Science Book describes the basic
parameters of the LSST hardware, software, and observing plans. The book
discusses educational and outreach opportunities, then goes on to describe a
broad range of science that LSST will revolutionize: mapping the inner and
outer Solar System, stellar populations in the Milky Way and nearby galaxies,
the structure of the Milky Way disk and halo and other objects in the Local
Volume, transient and variable objects both at low and high redshift, and the
properties of normal and active galaxies at low and high redshift. It then
turns to far-field cosmological topics, exploring properties of supernovae to
z~1, strong and weak lensing, the large-scale distribution of galaxies and
baryon oscillations, and how these different probes may be combined to
constrain cosmological models and the physics of dark energy.Comment: 596 pages. Also available at full resolution at
http://www.lsst.org/lsst/sciboo
Cosmology: small scale issues
The abundance of dark matter satellites and subhalos, the existence of
density cusps at the centers of dark matter halos, and problems producing
realistic disk galaxies in simulations are issues that have raised concerns
about the viability of the standard cold dark matter (LambdaCDM) scenario for
galaxy formation. This talk reviews these issues, and considers the
implications for cold vs. various varieties of warm dark matter (WDM). The
current evidence appears to be consistent with standard LambdaCDM, although
improving data may point toward a rather tepid version of LambdaWDM - tepid
since the dark matter cannot be very warm without violating observational
constraints.Comment: 7 pages, 1 figure, to appear in the proceedings of the 8th UCLA Dark
Matter Symposium, Marina del Rey, USA, 20-22 February 200
Formation of z similar to 6 quasars from hierarchical galaxy mergers
The discovery of luminous quasars at redshift z ~ 6 indicates the presence of
supermassive black holes (SMBHs) of mass ~10^9 Msun when the Universe was less
than one billion years old. This finding presents several challenges for
theoretical models. Here, we present the first multi-scale simulations that,
together with a self-regulated model for the SMBH growth, produce a luminous
quasar at z ~ 6.5 in the LCDM paradigm. We follow the hierarchical assembly
history of the most massive halo in a ~ 3 Gpc^3 volume, and find that this halo
of ~ 8x 10^{12} Msun forming at z ~ 6.5 after several major mergers is able to
reproduce a number of observed properties of SDSS J1148+5251, the most distant
quasar detected at z =6.42 (Fan et al. 2003). Moreover, the SMBHs grow through
gas accretion below the Eddington limit in a self-regulated manner owing to
feedback. We find that the progenitors experience significant star formation
(up to 10^4 Msun/yr) preceding the major quasar phase such that the stellar
mass of the quasar host reaches 10^{12} Msun at z ~ 6.5, consistent with
observations of significant metal enrichment in SDSS J1148+5251. Our results
provide a viable formation mechanism for z ~ 6 quasars in the standard LCDM
cosmology, and demonstrate a common, merger-driven origin for the rarest
quasars and the fundamental SMBH-host correlation in a hierarchical
Universe.(Abridged)Comment: 25 pages, 15 figures, accepted to ApJ. Version with full resolution
images is available at http://www.cfa.harvard.edu/~yxli/quasar/quasar.pd
Nitrogen and phosphorus effects on water use efficiency of spring wheat grown in a semi-arid region of the Canadian prairies
Reheating neutron stars with the annihilation of self-interacting dark matter
[[abstract]]Compact stellar objects such as neutron stars (NS) are ideal places for capturing dark matter (DM) particles. We study the effect of self-interacting DM (SIDM) captured by nearby NS that can reheat it to an appreciated surface temperature through absorbing the energy released due to DM annihilation. When DM-nucleon cross section σχn is small enough, DM self-interaction will take over the capture process and make the number of captured DM particles increased as well as the DM annihilation rate. The corresponding NS surface temperature resulted from DM self-interaction is about hundreds of Kelvin and is potentially detectable by the future infrared telescopes. Such observations could act as the complementary probe on DM properties to the current DM direct searches.[[notice]]補正完
On the evolution process of two-component dark matter in the Sun
[[abstract]]We introduce dark matter (DM) evolution process in the Sun under a two- component DM (2DM) scenario. Both DM species χ and ξ with masses heavier than 1 GeV are considered. In this picture, both species could be captured by the Sun through DM-nucleus scattering and DM self-scatterings, e.g. χχ and ξξ collisions. In addition, the heterogeneous self-scattering due to χ and ξ collision is essentially possible in any 2DM models. This new introduced scattering naturally weaves the evolution processes of the two DM species that was assumed to evolve independently. Moreover, the heterogeneous self-scattering enhances the number of DM being captured in the Sun mutually. This effect significantly exists in a broad range of DM mass spectrum. We have studied this phenomena and its implication for the solar-captured DM annihilation rate. It would be crucial to the DM indirect detection when the two masses are close. General formalism of the 2DM evolution in the Sun as well as its kinematics are studied.[[notice]]補正完