2,476 research outputs found
Neutrino Constraints on the Dark Matter Total Annihilation Cross Section
In the indirect detection of dark matter through its annihilation products,
the signals depend on the square of the dark matter density, making precise
knowledge of the distribution of dark matter in the Universe critical for
robust predictions. Many studies have focused on regions where the dark matter
density is greatest, e.g., the Galactic Center, as well as on the cosmic signal
arising from all halos in the Universe. We focus on the signal arising from the
whole Milky Way halo; this is less sensitive to uncertainties in the dark
matter distribution, and especially for flatter profiles, this halo signal is
larger than the cosmic signal. We illustrate this by considering a dark matter
model in which the principal annihilation products are neutrinos. Since
neutrinos are the least detectable Standard Model particles, a limit on their
flux conservatively bounds the dark matter total self-annihilation cross
section from above. By using the Milky Way halo signal, we show that previous
constraints using the cosmic signal can be improved on by 1-2 orders of
magnitude; dedicated experimental analyses should be able to improve both by an
additional 1-2 orders of magnitude.Comment: 8 pages, 4 figures; Matches version published in Phys. Rev.
Cosmic Neutrino Bound on the Dark Matter Annihilation Rate in the Late Universe
How large can the dark matter self-annihilation rate in the late universe be?
This rate depends on (rho_DM/m_chi)^2 , where rho_DM/m_chi is the
number density of dark matter, and the annihilation cross section is averaged
over the velocity distribution. Since the clustering of dark matter is known,
this amounts to asking how large the annihilation cross section can be.
Kaplinghat, Knox, and Turner proposed that a very large annihilation cross
section could turn a halo cusp into a core, improving agreement between
simulations and observations; Hui showed that unitarity prohibits this for
large dark matter masses. We show that if the annihilation products are
Standard Model particles, even just neutrinos, the consequent fluxes are ruled
out by orders of magnitude, even at small masses. Equivalently, to invoke such
large annihilation cross sections, one must now require that essentially no
Standard Model particles are produced.Comment: 4 pages, 2 figures; to appear in the proceedings of the TeV Particle
Astrophysics II Workshop, Madison, Wisconsin, 28-31 Aug 200
Nucleon Flow and Fragment Flow in Heavy Ion Reactions
The collective flow of nucleons and that of fragments in the 12C + 12C
reaction below 150 MeV/nucleon are calculated with the antisymmetrized version
of molecular dynamics combined with the statistical decay calculation. Density
dependent Gogny force is used as the effective interaction. The calculated
balance energy is about 100 MeV/nucleon, which is close to the observed value.
Below the balance energy, the absolute value of the fragment flow is larger
than that of nucleon flow, which is also in accordance with data. The
dependence of the flow on the stochastic collision cross section and its origin
are discussed. All the results are naturally understood by introducing the
concept of two components of flow: the flow of dynamically emitted nucleons and
the flow of the nuclear matter which contributes to both the flow of fragments
and the flow of nucleons due to the statistical decay.Comment: 20 pages, PostScript figures, LaTeX with REVTeX and EPSF, KUNS 121
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