* Astronomy

Blobrana · L

RE: Dark matter

Blobrana · L

Title: Search for axion-like particles using a variable baseline photon regeneration technique
Authors: A.S. Chou, W. Wester, A. Baumbaugh, H.R. Gustafson, Y. Irizarry-Valle, P.O. Mazur, J.H. Steffen, R. Tomlin, X. Yang, J. Yoo

We report the first results of the GammeV experiment, a search for milli-eV mass particles with axion-like couplings to two photons. The search is performed using a "light shining through a wall" technique where incident photons oscillate into new weakly interacting particles that are able to pass through the wall and subsequently regenerate back into detectable photons. The oscillation baseline of the apparatus is continuously variable, thus allowing probes of different values of particle mass. We find no excess of events above background and are able to constrain the two-photon couplings of possible new scalar (pseudoscalar) particles to be less than 3.2 x 10^{-7} {GeV}^{-1} (3.2 x 10^{-7} {GeV}^{-1}) in the limit of massless particles.

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Title: Search for Dark Matter Annihilation in Draco with STACEE
Authors: STACEE Collaboration: D. D. Driscoll, J. Ball, J. E. Carson, C. E. Covault, P. Fortin, D. M. Gingrich, D. S. Hanna, A. Jarvis, J. Kildea, T. Lindner, C. Mueller, R. Mukherjee, R. A. Ong, K. Ragan, D. A. Williams, J. Zweerink

For some time, the Draco dwarf spheroidal galaxy has garnered interest as a possible source for the indirect detection of dark matter. Its large mass-to-light ratio and relative proximity to the Earth provide favourable conditions for the production of detectable gamma rays from dark matter self-annihilation in its core. The Solar Tower Atmospheric Cherenkov Effect Experiment (STACEE) is an air-shower Cherenkov telescope located in Albuquerque, NM capable of detecting gamma rays at energies above 100 GeV. We present the results of the STACEE observations of Draco during the 2005-2006 observing season totalling 10 hours of livetime after cuts.

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New calculations show at least 2.1 million-billion years must pass for half of the invisible stuff to decay, if it does at all.
While all this theoretical thinking seems awfully abstract, it represents yet another effort to pin down what the heck dark matter might really be.
Scientists proposed the half-life about 150,000 times longer than the current age of the universe after looking at X-rays from the Bullet Cluster, a cosmic collision of galaxies thought to harbour two massive globs of dark matter.
If dark matter can slowly decay, it can also emit radiation, albeit at nearly undetectable levels. The proposed ultra-wimpy signal might help explain why it's practically invisible to our scientific instruments.

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Title: Spinless photon dark matter from two universal extra dimensions
Authors: Bogdan A. Dobrescu, Dan Hooper, Kyoungchul Kong, Rakhi Mahbubani
(Version v2)

We explore the properties of dark matter in theories with two universal extra dimensions, where the lightest Kaluza-Klein state is a spin-0 neutral particle, representing a six-dimensional photon polarized along the extra dimensions. Annihilation of this 'spinless photon' proceeds predominantly through Higgs boson exchange, and is largely independent of other Kaluza-Klein particles. The measured relic abundance sets an upper limit on the spinless photon mass of 500 GeV, which decreases to almost 200 GeV if the Higgs boson is light. The phenomenology of this dark matter candidate is strikingly different from Kaluza-Klein dark matter in theories with one universal extra dimension. Elastic scattering of the spinless photon with quarks is helicity suppressed, making its direct detection challenging, although possible at upcoming experiments. The prospects for indirect detection with gamma rays and antimatter are similar to those of neutralinos. The rates predicted at neutrino telescopes are below the sensitivity of next-generation experiments.

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Title: Dilaton and off-shell (non-critical string) effects in Boltzmann equation for species abundances
Authors: AB Lahanas, NE Mavromatos and DV Nanopoulos

In this work we derive the modifications to the Boltzmann equation governing the cosmic evolution of relic abundances induced by dilaton dissipative-source and non-critical-string terms in dilaton-driven non-equilibrium string Cosmologies. We also discuss briefly the most important phenomenological consequences, including modifications of the constraints on the available parameter space of cosmologically appealing particle physics models, imposed by recent precision data of astrophysical measurements.

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Astronomers using the Hubble Space Telescope have discovered a ghostly ring of dark matter that formed during a titanic collision between two massive galaxy clusters. Because ordinary matter in the cluster shows no evidence of such a ring, this discovery is among the strongest evidence yet for non-baryonic dark matter.
Clusters of galaxies are the largest gravitationally bound structures in the universe. They typically contain hundreds or thousands of galaxies, forming at the knots of the filamentary sponge-like distribution of matter on very large scales. Numerical simulations show how the accretion of matter from the filaments to the knots make galaxy clusters grow in size. This one-dimensional accretion (along a filament) results in frequent, near head-on collisions among clusters or groups of galaxies, whereas interactions between individual galaxies usually occur only when there is significant rotation.

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Report on the Direct Detection and Study of Dark Matter
The Dark Matter Scientific Assessment Group (DMSAG) A Joint Sub-panel of HEPAP and AAAC

DMSAG has been charged to make a detailed examination of the field of direct detection of dark matter and to consider it in the broader context of particle physics and astrophysics.

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A variety of astrophysical measurements [galactic rotation curves, galactic binding, mappings of the cosmic microwave background radiation (CMB)] all point to the fact that nuclear matter only comprises a tiny fraction of the total matter and energy density of the universe. In addition to nuclear matter, there is also a pervasive dark energy component responsible for the apparent accelerating expansion of the universe, and a cold dark matter (CDM) component, which is responsible for large scale structure formation in the universe.

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Title: Searching for Decaying Axionlike Dark Matter from Clusters of Galaxies
Authors: Signe Riemer-Sørensen, Konstantin Zioutas, Steen H. Hansen, Kristian Pedersen, Håkon Dahle, and Anastasios Liolios

We constrain the lifetime of radiatively decaying dark matter in clusters of galaxies inspired by generic Kaluza-Klein axions, which have been invoked as a possible explanation for the solar coronal x-ray emission. These particles can be produced inside stars and remain confined by the gravitational potential of clusters. By analysing x-ray observations of merging clusters, where gravitational lensing observations have identified massive, baryon poor structures, we derive the first cosmological lifetime constraint on this kind of particles of tau >~10²³ sec.

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The mysterious dark matter that fills the universe could be made of the same particles that put the "big" in the big bang - explaining both inflation and dark matter in a single stroke.
Cosmologists believe that the early universe went through a period of expansion, known as inflation, soon after the big bang - although they do not know exactly what caused it. Now cosmologist Andrew Liddle at the University of Sussex, UK, and his colleagues say one particle may be responsible for both inflation and the dark matter that has been perplexing astronomers.

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A computer model of the early Universe indicates the first stars could have formed in spectacular, long filaments. These structures, which may have been thousands of light-years across, would have been shaped by "dark matter". Scientists know very little about this type of matter, even though it accounts for most of the mass in the cosmos.
The researchers told the British Association (BA) Festival of Science that their work could reveal the true nature of dark matter.
Liang Gao and Tom Theuns from Durham University, UK, also reported their findings in the journal Science.

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