743,644 research outputs found
Cusp-core problem and strong gravitational lensing
Cosmological numerical simulations of galaxy formation have led to the cuspy
density profile of a pure cold dark matter halo toward the center, which is in
sharp contradiction with the observations of the rotation curves of cold dark
matter-dominated dwarf and low surface brightness disk galaxies, with the
latter tending to favor mass profiles with a flat central core. Many efforts
have been devoted to resolve this cusp-core problem in recent years, among
them, baryon-cold dark matter interactions are considered to be the main
physical mechanisms erasing the cold dark matter (CDM) cusp into a flat core in
the centers of all CDM halos. Clearly, baryon-cold dark matter interactions are
not customized only for CDM-dominated disk galaxies, but for all types,
including giant ellipticals. We first fit the most recent high resolution
observations of rotation curves with the Burkert profile, then use the
constrained core size-halo mass relation to calculate the lensing frequency,
and compare the predicted results with strong lensing observations.
Unfortunately, it turns out that the core size constrained from rotation curves
of disk galaxies cannot be extrapolated to giant ellipticals. We conclude that,
in the standard cosmological paradigm, baryon-cold dark matter interactions are
not universal mechanisms for galaxy formation, and therefore, they cannot be
true solutions to the cusp-core problem.Comment: 11 pages, 3 figures, references updated, typos correcte
A dark matter solution from the supersymmetric axion model
We study the effect of the late decaying saxino (the scalar superpartner of
the axion) and find out that there is a possible dark matter solution from a
class of supersymmetric extensions of the invisible axion model. In this class
of models, the saxino which decays into two axions acts as the late decaying
particle which reconciles the cold dark matter model with high values of the
Hubble constant. Recent observations of the Hubble constant are converging to
, which would be
inconsistent with the standard mixed dark matter model. This class of models
provides a plausible framework for the alternative cold dark matter plus late
decaying particle model, with the interesting possibility that both cold dark
matter and the extra radiation consist of axion.Comment: 11 pages, no figure, REVTEX 3.
Messenger sneutrinos as cold dark matter
In models where supersymmetry breaking is communicated into the visible
sector via gauge interactions the lightest supersymmetric particle is typically
the gravitino which is too light to account for cold dark matter. We point out
that the lightest messenger sneutrinos with mass in the range of one to three
TeV may serve as cold dark matter over most of the parameter space due to
one-loop electroweak radiative corrections. However, in the minimal model this
mass range has been excluded by the direct dark matter searches. We propose a
solution to this problem by introducing terms that explicitly violate the
messenger number. This results in low detection rate for both direct and
indirect searches and allows messenger sneutrinos to be a valid dark matter
candidate in a wide region of SUSY parameter space.Comment: 12 pages, 2 figures, postscript file available via anonymous
ftp://ucdhep.ucdavis.edu/han/dm/dm.p
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