Astronomers have mapped dark matter for the first time on the largest scale ever observed. Edinburgh astronomers studied the way light emitted from 10 million galaxies was bent as it passed massive clumps of dark matter on its journey to Earth. They found web-like strands of dark matter stretching in all directions. Read more
Title: Dark matter powered stars: Constraints from the extragalactic background light Authors: A. Maurer, M. Raue, T. Kneiske, D. Elsässer, P. H. Hauschildt, D. Horns
The existence of predominantly cold non-baryonic dark matter is unambiguously demonstrated by several observations (e.g., structure formation, big bang nucleosynthesis, gravitational lensing, and rotational curves of spiral galaxies). A candidate well motivated by particle physics is a weakly interacting massive particle (WIMP). Self-annihilating WIMPs would affect the stellar evolution especially in the early universe. Stars powered by self-annihilating WIMP dark matter should possess different properties compared with standard stars. While a direct detection of such dark matter powered stars seems very challenging, their cumulative emission might leave an imprint in the diffuse metagalactic radiation fields, in particular in the mid-infrared part of the electromagnetic spectrum. In this work the possible contributions of dark matter powered stars (dark stars; DSs) to the extragalactic background light (EBL) are calculated. It is shown that existing data and limits of the EBL intensity can already be used to rule out some DS parameter sets.
Title: Assisted freeze-out Authors: Genevieve Belanger, Jong-Chul Park
We explore a class of dark matter models with two dark matter candidates, only one interacts with the SM sector. One of the dark matter is thermalised with the assistance of the other stable particle. While both stable particles contribute to the total relic density only one can elastically scatter with nucleis, thus effectively reducing the direct detection rate.
Title: Constraining dark matter models from a combined analysis of Milky Way satellites with the Fermi-LAT Authors: The Fermi-LAT Collaboration: M. Ackermann, M. Ajello, A. Albert, W. B. Atwood, L. Baldini, J. Ballet, G. Barbiellini, D. Bastieri, K. Bechtol, R. Bellazzini, B. Berenji, R. D. Blandford, E. D. Bloom, E. Bonamente, A. W. Borgland, J. Bregeon, M. Brigida, P. Bruel, R. Buehler, T. H. Burnett, S. Buson, G. A. Caliandro, R. A. Cameron, B. Canadas, P. A. Caraveo, J. M. Casandjian, C. Cecchi, E. Charles, A. Chekhtman, J. Chiang, S. Ciprini, R. Claus, J. Cohen-Tanugi, J. Conrad, S. Cutini, A. de Angelis, F. de Palma, C. D. Dermer, S. W. Digel, E. do Couto e Silva, P. S. Drell, A. Drlica-Wagner, L. Falletti, C. Favuzzi, S. J. Fegan, E. C. Ferrara, Y. Fukazawa, S. Funk, P. Fusco, F. Gargano, D. Gasparrini, N. Gehrels, S. Germani, N. Giglietto, F. Giordano, M. Giroletti, T. Glanzman, G. Godfrey, I. A. Grenier, et al. (93 additional authors not shown) (Version v2)
Satellite galaxies of the Milky Way are among the most promising targets for dark matter searches in gamma rays because of their large dynamical mass to light ratio and small expected background from astrophysical sources. We present a search for dark matter consisting of weakly interacting massive particles where we apply a joint likelihood analysis to 10 satellite galaxies with 24 months of data of the Fermi Large Area Telescope. No dark matter signal is detected. Taking into account the uncertainty in the dark matter distribution in the satellites, robust upper limits are placed on dark matter models. The 95% confidence level upper limits on the annihilation cross section range from about 1e-26 cm^3 s^-1 at 5 GeV to about 5e-23 cm^3 s^-1 at 1 TeV, depending on the dark matter annihilation final state. For the first time, using gamma rays, we are able to rule out models with the most generic cross section (~3e-26 cm^3 s^-1 for a purely s-wave cross section), without assuming additional astrophysical or particle physics boost factors.
Title: Dark matter in dwarf galaxies of the Local Group Authors: Ewa L. Lokas
We review basic properties of the population of dwarf galaxies in the Local Group focusing on dwarf spheroidal galaxies found in the immediate vicinity of the Milky Way. The evidence for dark matter in these objects is critically assessed. We describe the methods of dynamical modelling of such objects, using a few examples of the best-studied dwarfs and discuss the sources of uncertainties in mass estimates. We conclude with perspectives for dwarf galaxies as targets for dark matter detection experiments.
Dark matter particles may be heavyweights after all
Dark matter is slowly running out of places to hide. Two new looks at the gamma-ray sky suggest that if the mysterious matter is a particle, it is heavier than 40 gigaelectronvolts, about 44 times the mass of a proton. That contradicts hints from three experiments on Earth that pointed to a lightweight dark matter particle weighing just a quarter as much, although some researchers say such featherweights are still in the running. Read more
Title: Dark Matter searches with H.E.S.S. towards dwarf spheroidal galaxies Authors: A. Viana (for the H.E.S.S. collaboration)
The H.E.S.S. experiment is an array of four identical imaging atmospheric Cherenkov telescopes in the Southern hemisphere, designed to observe very high energy gamma-rays (E > 100 GeV). These high energy gamma-rays can be used to search for annihilations of Dark Matter particles in dense environments. Dwarf galaxy dynamics shows that they are Dark Matter-dominated environments. Several observation campaigns on dwarf satellite galaxies of the Milky Way were launched by H.E.S.S.. The observations are reviewed. In the absence of clear signals, constraints on the Dark Matter particle annihilation cross-section have been derived in different particle physics scenarios. Some possible enhancements of the gamma-ray flux are studied, i.e., the Sommerfeld effect, the internal bremsstrahlung and the substructures in the Dark Matter halo.
Physicists set strongest limit on mass of dark matter
Brown University physicists have set the strongest limit for the mass of dark matter, the mysterious particles believed to make up nearly a quarter of the universe. The researchers report in Physical Review Letters that dark matter must have a mass greater than 40 giga-electron volts. The distinction is important because it casts doubt on recent results from underground experiments that have reported detecting dark matter. Read more
Title: Limits on the local density of dark matter Authors: Silvia Garbari, Justin I. Read, George Lake
We study the systematic problems in determining the local dark matter density ho_{dm}(R_\odot) from kinematics of stars in the Solar Neighbourhood, using a simulated Milky Way-like galaxy. We introduce a new unbiased method for recovering ho_{dm}(R_\odot) based on the moments of the Jeans equations, combined with a Monte Carlo Markov Chain technique and apply it to real data.
Like all galaxies, our Milky Way is home to a strange substance called dark matter. Dark matter is invisible, betraying its presence only through its gravitational pull. Without dark matter holding them together, our galaxy's speedy stars would fly off in all directions. The nature of dark matter is a mystery -- a mystery that a new study has only deepened. The standard cosmological model describes a universe dominated by dark energy and dark matter. Most astronomers assume that dark matter consists of "cold" (i.e. slow-moving) exotic particles that clump together gravitationally. Over time these dark matter clumps grow and attract normal matter, forming the galaxies we see today. Cosmologists use powerful computers to simulate this process. Their simulations show that dark matter should be densely packed in the centers of galaxies. Instead, new measurements of two dwarf galaxies show that they contain a smooth distribution of dark matter. This suggests that the standard cosmological model may be wrong.