2,901 research outputs found
Cold Dark Matter Halos Must Burn
High-quality optical rotation curves for a sample of low-luminosity spirals
evidence that the dark halos around galaxies are inconsistent with the output
of proper CDM simulations. In fact, dark halos enveloping stellar disks are
structures with approximately a constant density out to the optical edges. This
is in strong disagreement with the characteristic rho(r) ~ r^(-1.5) CDM regime
and severely challenges the "standard" CDM theory, also because the halo
density appears to be heated up, at gross variance with the hierarchical
evolution of collision-free particles.Comment: 2 figures, definitive version to appear in the Proceedings of the
MPA/ESO/MPE/USM Joint Conference: "Lighthouses of the Universe: The Most
Luminous Celestial Objects and their use for Cosmology", August 2001,
Garching, German
The Dark Matter Distribution in Disk Galaxies
We use high-quality optical rotation curves of 9 low-luminosity disk galaxies
to obtain the velocity profile of the surrounding dark matter halos. We find
that they increase linearly with radius at least out to the stellar disk edge,
implying that, over the entire region where the stars reside, the density of
the dark halo is constant. The properties of the halo mass structure found are
similar to that claimed for a number of dwarf and low surface brightness
galaxies, but provide a more substantial evidence of the discrepancy between
the halo mass distribution predicted in standard cold dark matter scenario and
those actually detected around galaxies. We find that the density profile
proposed by Burkert (1995) reproduces the halo rotation curves, with halo
central densities and core radii scaling as .Comment: 8 pages, 6 figures, MNRAS accepted. New section and figures added,
concerning CDM mass models. Minor changes to the rest of the pape
Secondary radiation from the Pamela/ATIC excess and relevance for Fermi
The excess of electrons/positrons observed by the Pamela and ATIC experiments
gives rise to a noticeable amount of synchrotron and Inverse Compton Scattering
(ICS) radiation when the e^+e^- interact with the Galactic Magnetic Field, and
the InterStellar Radiation Field (ISRF). In particular, the ICS signal produced
within the WIMP annihilation interpretation of the Pamela/ATIC excess shows
already some tension with the EGRET data. On the other hand, 1 yr of Fermi data
taking will be enough to rule out or confirm this scenario with a high
confidence level. The ICS radiation produces a peculiar and clean "ICS Haze"
feature, as well, which can be used to discriminate between the astrophysical
and Dark Matter scenarios. This ICS signature is very prominent even several
degrees away from the galactic center, and it is thus a very robust prediction
with respect to the choice of the DM profile and the uncertainties in the ISRF.Comment: 5 pages, 3 figures; v2: improved figures, enlarged discussion on the
gamma signal and data; to appear in ApJ
Ultrahigh energy neutrinos with a mediterranean neutrino telescope
A study of the ultra high energy neutrino detection performances of a km^3
Neutrino Telescope sitting at the three proposed sites for "ANTARES", "NEMO"
and "NESTOR" in the Mediterranean sea is here performed. The detected charged
leptons energy spectra, entangled with their arrival directions, provide an
unique tool to both determine the neutrino flux and the neutrino-nucleon cross
section.Comment: 10 pages, 10 figures, Proceedings of XII International Workshop on
Neutrino Telescopes, Venezia 200
Traps
In lieu of an abstract, below is the essay\u27s first paragraph.
The traps had been good to her that day. Five muskrat, three a good size, and the two smaller ones would still get a decent price. The pelts were thick and full because the winter had been cold. Joey was proud that she could judge a good pelt and she usually came. pretty close on guessing the price the dealers would settle for
Active Debris Removal Mapping Project
Space debris discussions initiated with the start of the space age 55 years ago and have seen special interest in current years. This is due to the large increase in the number of space debris which has led to an increased threat of collision with operational space systems and of unsafe reentry.
Due to this increased interest in this area, many different methods have been proposed in recent years for mitigation and space debris removal, some of which have even secured funding from space agencies for further development. These include ground based lasers and space based systems which use electro-dynamic tethers, solar sails or inflatable components. While each method has its own pros and cons, some of these concepts seem to be more suitable for the short term and others for the long term.
This paper identifies major performance measures for space debris removal systems based on current rules and regulations and maps the performance of the ADR technologies based on these criteria. The map can help prioritize removal concepts and required technologies in order to better meet current needs
Radio constraints on dark matter annihilation in the galactic halo and its substructures
Annihilation of Dark Matter usually produces together with gamma rays
comparable amounts of electrons and positrons. The e+e- gyrating in the
galactic magnetic field then produce secondary synchrotron radiation which thus
provides an indirect mean to constrain the DM signal itself. To this purpose,
we calculate the radio emission from the galactic halo as well as from its
expected substructures and we then compare it with the measured diffuse radio
background. We employ a multi-frequency approach using data in the relevant
frequency range 100 MHz-100 GHz, as well as the WMAP Haze data at 23 GHz. The
derived constraints are of the order =10^{-24} cm3 s^{-1} for a DM
mass m_chi=100 GeV sensibly depending however on the astrophysical
uncertainties, in particular on the assumption on the galactic magnetic field
model. The signal from single bright clumps is instead largely attenuated by
diffusion effects and offers only poor detection perspectives.Comment: 12 pages, 7 figures; v2: some references added, some discussions
enlarged; matches journal versio
Neighbors
In lieu of an abstract, below is the essay\u27s first paragraph.
Sarah and Pa had been up there just a week before. It was a run-down old house that hadn\u27t been lived in since Mrs. Blackert died eleven years before. The wild blackberries grew clear up to the front door, but around to the back of the house the daffodils had gone wild and covered the whole yard including the path that led to the outhouse. Sarah thought they looked like melted, fresh-churned butter and told Pa so, but he pulled her braids and said no, the field looked like it was filled with tiny, bobbing, blonde-haired girls
Stringent constraint on neutrino Lorentz-invariance violation from the two IceCube PeV neutrinos
It has been speculated that Lorentz-invariance violation (LIV) might be
generated by quantum-gravity (QG) effects. As a consequence, particles may not
travel at the universal speed of light. In particular, superluminal
extragalactic neutrinos would rapidly lose energy via the bremssthralung of
electron-positron pairs (nu -> nu e+ e-), damping their initial energy into
electromagnetic cascades, a figure constrained by Fermi-LAT data. We show that
the two cascade neutrino events with energies around 1 PeV recently detected by
IceCube -if attributed to extragalactic diffuse events, as it appears likely-
can place the strongest bound on LIV in the neutrino sector, namely delta
=(v^2-1) ~
10^(-4) M_Pl) for a linear (quadratic) LIV, at least for models inducing
superluminal neutrino effects (delta > 0).Comment: 4 page
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