* Astronomy

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RE: Dark matter

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Simulated galaxies provide fresh evidence of dark matter

Further evidence of the existence of dark matter - the mysterious substance that is believed to hold the Universe together - has been produced by Cosmologists at Durham University.
Using sophisticated computer modelling techniques, the research team simulated the formation of galaxies in the presence of dark matter and were able to demonstrate that their size and rotation speed were linked to their brightness in a similar way to observations made by astronomers.
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Waterloo astronomers use CFHT to capture first image of a Dark Matter Bridge.

Researchers at the University of Waterloo have been able to capture the first composite image of a dark matter bridge that connects galaxies together. The scientists publish their work in a new paper in Monthly Notices of the Royal Astronomical Society.
The composite image, which combines a number of individual images, confirms predictions that galaxies across the universe are tied together through a cosmic web connected by dark matter that has until now remained unobservable.
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Dark matter took its time to wrap around early galaxies

Natascha Förster Schreiber at the Max Planck Institute for Extraterrestrial Physics in Germany and her colleagues have used the Very Large Telescope in Chile to make the most detailed observations yet of the movement of six massive galactic discs during the peak era of galaxy formation, 10 billion years ago.
They found that, unlike in most modern galaxies, the stars at the edges of these early galaxies move more slowly than those closer in. "This tells us that at early stages of galaxy formation, the relative distribution of the normal matter and the dark matter was significantly different from what it is today," says Förster Schreiber
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Dark Matter Less Influential in Galaxies in Early Universe

New observations indicate that massive, star-forming galaxies during the peak epoch of galaxy formation, 10 billion years ago, were dominated by baryonic or "normal" matter. This is in stark contrast to present-day galaxies, where the effects of mysterious dark matter seem to be much greater. This surprising result was obtained using ESO's Very Large Telescope and suggests that dark matter was less influential in the early Universe than it is today. The research is presented in four papers, one of which will be published in the journal Nature this week.
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Title: Dark Catalysis
Author: Prateek Agrawal, Francis-Yan Cyr-Racine, Lisa Randall, Jakub Scholtz

Recently it was shown that dark matter with mass of order the weak scale can be charged under a new long-range force, decoupled from the Standard Model, with only weak constraints from early Universe cosmology. Here we consider the implications of an additional charged particle C that is light enough to lead to significant dissipative dynamics on galactic times scales. We highlight several novel features of this model, which can be relevant even when the C particle constitutes only a small fraction of the number density (and energy density). We assume a small asymmetric abundance of the C particle whose charge is compensated by a heavy X particle so that the relic abundance of dark matter consists mostly of symmetric X and X¯, with a small asymmetric component made up of X and C. As the universe cools, it undergoes asymmetric recombination binding the free Cs into (XC) dark atoms efficiently. Even with a tiny asymmetric component, the presence of C particles catalyzes tight coupling between the heavy dark matter X and the dark photon plasma that can lead to a significant suppression of the matter power spectrum on small scales and lead to some of the strongest bounds on such dark matter theories. We find a viable parameter space where structure formation constraints are satisfied and significant dissipative dynamics can occur in galactic haloes but show a large region is excluded. Our model shows that subdominant components in the dark sector can dramatically affect structure formation.

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Galactic X-rays could point to dark matter proof

A small but distinctive signal in X-rays from the Milky Way could be key to proving the existence of dark matter.
That is the claim of US scientists who analysed the energy spectrum of X-rays gathered by Nasa's Chandra satellite.
They found more X-ray photons with a particular energy than would be expected if they were produced only by familiar processes.
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Stanford physicist suggests looking for dark matter in unusual places

For decades, particle physics has been the domain of massive colliders that whip particles around at high speeds and smash them into one another while teams of thousands observe the results. These kinds of experiments have produced great insights into forces and particles that make up the physical world.
But Stanford physicist Peter Graham is advocating a much different approach - one that could be faster and cheaper than massive colliders, and that may be able to detect previously elusive forms of physics like dark matter.
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Dark Matter May be Smoother than Expected

Analysis of a giant new galaxy survey, made with ESO's VLT Survey Telescope in Chile, suggests that dark matter may be less dense and more smoothly distributed throughout space than previously thought. An international team used data from the Kilo Degree Survey (KiDS) to study how the light from about 15 million distant galaxies was affected by the gravitational influence of matter on the largest scales in the Universe. The results appear to be in disagreement with earlier results from the Planck satellite.
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Title: Is the dark matter particle its own antiparticle?
Author: Farinaldo S. Queiroz, Werner Rodejohann, Carlos E. Yaguna

We propose a test based on direct detection data that allows to determine if the dark matter particle is different from its antiparticle. The test requires the precise measurement of the dark matter spin-independent direct detection cross sections off three different nuclei, and consists of interpreting such signals in terms of self-conjugate (particle = antiparticle) dark matter to see if such interpretation is consistent. If it is not, the dark matter must be different from its antiparticle. We illustrate this procedure for two sets of target nuclei, {Xe,Ar,Si} and {Xe,Ar,Ge}, identifying the regions of the parameter space where it is particularly feasible. Our results indicate that future signals in direct detection experiments, if sufficiently accurate, might be used to establish that the dark matter particle is not its own antiparticle -- a major step towards the determination of the fundamental nature of the dark matter.

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