* Astronomy

Blobrana · L

RE: Dark matter

Blobrana · L

Dark Matter Just Got More Mysterious

Reporting in the Astrophysical Journal, scientists write of a massive collision between two galaxy clusters. By studying the cosmic remnants of that smashup, they say leftover dark matter isn't behaving as current theory predicts. Astrophysicist Andisheh Mahdavi discusses this dark matter mystery.
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Title: Earthly measurements of the smallest dark matter halos
Authors: Jonathan M. Cornell, Stefano Profumo

Dark matter kinetic decoupling involves elastic scattering of dark matter off of leptons and quarks in the early universe, the same process relevant for direct detection and for the capture rate of dark matter in celestial bodies; the resulting size of the smallest dark matter collapsed structures should thus correlate with quantities connected with direct detection rates and with the flux of high-energy neutrinos from dark matter annihilation in the Sun or in the Earth. In this paper we address this general question in the context of two widely studied and paradigmatic weakly-interacting particle dark matter models: the lightest neutralino of the minimal supersymmetric extension of the Standard Model, and the lightest Kaluza-Klein particle of Universal Extra Dimensions (UED). We argue and show that while the scalar neutralino-nucleon cross section correlates poorly with the kinetic decoupling temperature, the spin-dependent cross section exhibits a strong correlation in a wide range of models. In UED models the correlation is present for both cross sections, and is extraordinarily tight for the spin-dependent case. A strong correlation is also found, for both models, for the flux of neutrinos from the Sun, especially for fluxes large enough to be at potentially detectable levels. We provide analytic guidance and formulae that illustrate our findings.

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Dark Matter Core Defies Explanation in NASA Hubble Image

Astronomers using data from NASA's Hubble Telescope have observed what appears to be a clump of dark matter left behind from a wreck between massive clusters of galaxies. The result could challenge current theories about dark matter that predict galaxies should be anchored to the invisible substance even during the shock of a collision.
Abell 520 is a gigantic merger of galaxy clusters located 2.4 billion light-years away. Dark matter is not visible, although its presence and distribution is found indirectly through its effects. Dark matter can act like a magnifying glass, bending and distorting light from galaxies and clusters behind it. Astronomers can use this effect, called gravitational lensing, to infer the presence of dark matter in massive galaxy clusters.
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Blobrana · L

Title: Matter-Dark-Matter Correspondence in Left-Right Symmetry
Authors: Ernest Ma (UC Riverside)

In an unconventional realization of left-right symmetry, the particle corresponding to the left-handed neutrino nu_L (with SU(2)_L interactions) in the right-handed sector, call it n_R (with SU(2)_R interactions), is not its Dirac mass partner, but a different particle which may be a dark-matter candidate. In parallel to leptogenesis in the SU(2)_L sector, asymmetric production of n_R may occur in the SU(2)_R sector. This mechanism is especially suited for n_R mass of order 1 to 10 keV, i.e. warm dark matter, which is a possible new paradigm for explaining the structure of the Universe at all scales.

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Missing dark matter located - Inter-galactic space is filled with dark matter

Researchers at IPMU and Nagoya University used large-scale computer simulations and recent observational data of gravitational lensing to reveal how dark matter is distributed around galaxies.
Galaxies have no definite "edges", the new research concludes. Instead galaxies have long outskirts of dark matter that extend to their nearby galaxies; the inter-galactic space is not empty but filled with dark matter.
The research article has been published in the February 10th issue of The Astrophysical Journal.
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Title: Oscillating Asymmetric Dark Matter
Authors: Sean Tulin, Hai-Bo Yu, Kathryn M. Zurek

We study the dynamics of dark matter (DM) particle-antiparticle oscillations within the context of asymmetric DM. Oscillations arise due to small DM number-violating Majorana-type mass terms, and can lead to recoupling of annihilation after freeze-out and washout of the DM density. We derive the density matrix equations for DM oscillations and freeze-out from first principles using nonequilibrium field theory, and our results are qualitatively different than in previous studies. DM dynamics exhibits particle-vs-antiparticle "flavour" effects, depending on the interaction type, analogous to neutrino oscillations in a medium. "Flavour-sensitive" DM interactions include scattering or annihilation through a new vector boson, while "flavour-blind" interactions include scattering or s-channel annihilation through a new scalar boson, or annihilation to pairs of bosons. In particular, we find that flavour-sensitive annihilation does not recouple when coherent oscillations begin, and that flavour-blind scattering does not lead to decoherence.

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Title: Direct Detection of Dark Matter Debris Flows
Authors: Michael Kuhlen, Mariangela Lisanti, David N. Spergel

Tidal stripping of dark matter from subhalos falling into the Milky Way produces narrow, cold tidal streams as well as more spatially extended "debris flows" in the form of shells, sheets, and plumes. Here we focus on the debris flow in the Via Lactea II simulation, and show that this incompletely phase-mixed material exhibits distinctive high-velocity behaviour. Unlike tidal streams, which may not necessarily intersect the Earth's location, debris flow is spatially uniform at 8 kpc and thus guaranteed to be present in the dark matter flux incident on direct detection experiments. At Earth-frame velocities greater than 450 km/s, debris flow comprises more than half of the dark matter at the Sun's location, and up to 80% at even higher velocities. Therefore, debris flow is most important for experiments that are particularly sensitive to the high velocity tail of the dark matter distribution, such as searches for light or inelastic dark matter or experiments with directional sensitivity. We show that debris flow yields a distinctive recoil energy spectrum and a broadening of the distribution of incidence direction.

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Title: Asymmetric Dark Matter from Spontaneous Cogenesis in the Supersymmetric Standard Model
Authors: Kohei Kamada, Masahide Yamaguchi

The observational relation between the density of baryon and dark matter in the Universe, \Omega_DM/\Omega_B\simeq 5, is one of the most difficult problems to solve in modern cosmology. We discuss a scenario that explains this relation by combining the asymmetric dark matter scenario and the spontaneous baryogenesis associated with the flat direction in the supersymmetric standard model. A part of baryon asymmetry is transferred to charge asymmetry D that dark matter carries, if a symmetry violating interaction that works at high temperature breaks not only B-L but also D symmetries simultaneously. In this case, the present number density of baryon and dark matter can be same order if the symmetric part of dark matter annihilates sufficiently. Moreover, the baryon number density can be enhanced as compared to that of dark matter if another B-L violating interaction is still in thermal equilibrium after the spontaneous genesis of dark matter, which accommodates a TeV scale asymmetric dark matter model.

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Blobrana · L

Researchers have released the biggest images yet detailing dark matter, the mysterious substance that makes up three-quarters of the Universe's mass.

The team from the Canada-France Hawaii Telescope inferred the dark matter's existence by the way it bends light.
The images were presented at the 219th meeting of the American Astronomical Society in Austin, US.

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