* Astronomy

Blobrana · L

RE: Dark matter

Blobrana · L

Title: Can Neutron stars constrain Dark Matter?
Authors: Chris Kouvaris, Peter Tinyakov
(5 Apr 2010)

We argue that observations of old neutron stars can impose constraints on dark matter candidates even with very small elastic or inelastic cross section, and self-annihilation cross section. We find that old neutron stars close to the galactic center or in globular clusters can maintain a surface temperature that could in principle be detected. Due to their compactness, neutron stars can acrete WIMPs efficiently even if the WIMP-to-nucleon cross section obeys the current limits from direct dark matter searches, and therefore they could constrain a wide range of dark matter candidates.

Read more (255kb, PDF)

Blobrana · L

Title: Constraints on Decaying Dark Matter from Fermi Observations of Nearby Galaxies and Clusters
Authors: Leanna Dugger, Tesla E. Jeltema, Stefano Profumo
(Version v2)

We analyse the impact of Fermi gamma-ray observations (primarily non-detections) of selected nearby galaxies, including dwarf spheroidals, and of clusters of galaxies on decaying dark matter models. We show that the fact that galaxy clusters do not shine in gamma rays puts the most stringent limits available to-date on the lifetime of dark matter particles for a wide range of particle masses and decay final states. In particular, our results put strong constraints on the possibility of ascribing to decaying dark matter both the increasing positron fraction reported by PAMELA and the high-energy feature in the electron-positron spectrum measured by Fermi. Observations of nearby dwarf galaxies and of the Andromeda Galaxy (M31) do not provide as strong limits as those from galaxy clusters, while still improving on previous constraints in some cases.

Read more (50kb, PDF)

Blobrana · L

Title: Hylogenesis: A Unified Origin for Baryonic Visible Matter and Antibaryonic Dark Matter
Authors: Hooman Davoudiasl, David E. Morrissey, Kris Sigurdson, Sean Tulin
(Version v3)

We present a novel mechanism for generating both the baryon and dark matter densities of the Universe. A new Dirac fermion X carrying a conserved baryon number charge couples to the Standard Model quarks as well as a GeV-scale hidden sector. CP-violating decays of X, produced non-thermally in low-temperature reheating, sequester antibaryon number in the hidden sector, thereby leaving a baryon excess in the visible sector. The antibaryonic hidden states are stable dark matter. A spectacular signature of this mechanism is the baryon-destroying inelastic scattering of dark matter that can annihilate baryons at appreciable rates relevant for nucleon decay searches.

Read more (150kb, PDF)

Blobrana · L

Title: Effect of low mass dark matter particles on the Sun
Authors: Marco Taoso, Fabio Iocco, Georges Meynet, Gianfranco Bertone, Patrick Eggenberger
(Version v2)

We study the effect of dark matter (DM) particles in the Sun, focusing in particular on the possible reduction of the solar neutrinos flux due to the energy carried away by DM particles from the innermost regions of the Sun, and to the consequent reduction of the temperature of the solar core. We find that in the very low-mass range between 4 and 10 GeV, recently advocated to explain the findings of the DAMA and CoGent experiments, the effects on neutrino fluxes are detectable only for DM models with very small, or vanishing, self-annihilation cross section, such as the so-called asymmetric DM models, and we study the combination of DM masses and Spin Dependent cross sections which can be excluded with current solar neutrino data. Finally, we revisit the recent claim that DM models with large self-interacting cross sections can lead to a modification of the position of the convective zone, alleviating or solving the solar composition problem. We show that when the 'geometric' upper limit on the capture rate is correctly taken into account, the effects of DM are reduced by orders of magnitude, and the position of the convective zone remains unchanged.

Read more (876kb, PDF)

Blobrana · L

Title: Unified Origin for Baryonic Visible Matter and Antibaryonic Dark Matter
Authors: Hooman Davoudiasl, David E. Morrissey, Kris Sigurdson, and Sean Tulin

We present a novel mechanism for generating both the baryon and dark matter densities of the Universe. A new Dirac fermion X carrying a conserved baryon number charge couples to the standard model quarks as well as a GeV-scale hidden sector. CP-violating decays of X, produced nonthermally in low-temperature reheating, sequester antibaryon number in the hidden sector, thereby leaving a baryon excess in the visible sector. The antibaryonic hidden states are stable dark matter. A spectacular signature of this mechanism is the baryon-destroying inelastic scattering of dark matter that can annihilate baryons at appreciable rates relevant for nucleon decay searches.

Source

Blobrana · L

Two of the biggest mysteries in physics - what dark matter is made of and why matter dominates over antimatter - might be solved in one go
Read more (Subscription)

Blobrana · L

Title: Turning off the Lights: How Dark is Dark Matter?
Authors: Samuel D. McDermott, Hai-Bo Yu, Kathryn M. Zurek

We consider current observational constraints on the electromagnetic charge of dark matter. The velocity dependence of the scattering cross-section through the photon gives rise to qualitatively different constraints than standard dark matter scattering through massive force carriers. In particular, recombination epoch observations of dark matter density perturbations require that \epsilon, the ratio of the dark matter to electronic charge, is less than 10^{-6} for m_X = 1 GeV, rising to \epsilon < 10^{-4} for m_X = 10 TeV. Though naively one would expect that dark matter carrying a charge well below this constraint could still give rise to large scattering in current direct detection experiments, we show that charged dark matter particles that could be detected with upcoming experiments are expected to be evacuated from the Galactic disk by the Galactic magnetic fields and supernova shock waves, and hence will not give rise to a signal. Thus dark matter with a small charge is likely not a source of a signal in current or upcoming dark matter direct detection experiments.

Read more (28kb, PDF)

Blobrana · L

Hints of a lightweight dark matter particle have been found in the gamma-ray glow at the Milky Way's heart. The particle's apparent mass lines up with tentative signals of dark matter in two direct-detection experiments on Earth, but other researchers caution that conventional sources - such as pulsars - may be responsible for the gamma-ray light instead.
The Milky Way is thought to be awash in dark matter, an as-yet-unidentified substance that makes up more than 80 per cent of the matter in the universe. Although dark matter has been detected by its gravitational tug on stars and galaxies, many of its fundamental properties are still unknown.
Read more

Blobrana · L

In cosmology's standard model, dark matter is cold, made up of relatively heavy low-energy particles, and will happily settle into structures as small as planets. Hot dark matter has already been ruled out because its particles would move too fast for galaxies to form. But warm dark matter has smaller, faster particles that still allow for our familiar starry sky.
Most computer models produce a generic universe that doesn't resemble ours in detail, but Gustavo Yepes at the Autonomous University of Madrid, Spain, and his collaborators on the Constrained Local Universe Simulations (CLUES) project have tuned theirs to resemble the galaxies and clusters nearest Earth.
Read more