* Astronomy

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Dark-matter halos

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RE: Dark matter

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Title: Number-Theory Dark Matter
Authors: Kazunori Nakayama, Fuminobu Takahashi, Tsutomu T. Yanagida

We propose that the stability of dark matter is ensured by a discrete subgroup of the U(1)B-L gauge symmetry, Z_2(B-L). We introduce a set of chiral fermions charged under the U(1)B-L in addition to the right-handed neutrinos, and require the anomaly-cancellation conditions associated with the U(1)B-L gauge symmetry. We find that the possible number of fermions and their charges are tightly constrained, and that non-trivial solutions appear when at least five additional chiral fermions are introduced. The Fermat theorem in the number theory plays an important role in this argument. Focusing on one of the solutions, we show that there is indeed a good candidate for dark matter, whose stability is guaranteed by Z_2(B-L).

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Title: Isospin-Violating Dark Matter
Authors: Jonathan L. Feng, Jason Kumar, Danny Marfatia, David Sanford

Searches for dark matter scattering off nuclei are typically compared assuming that the dark matter's spin-independent couplings are identical for protons and neutrons. This assumption is neither innocuous nor well motivated. We consider isospin-violating dark matter (IVDM) with one extra parameter, the ratio of neutron to proton couplings. For a single choice of this ratio, the DAMA and CoGeNT signals are consistent with each other and with XENON constraints, and unambiguously predict a signal at CRESST. We provide a quark-level realization of IVDM as WIMPless dark matter that is consistent with all collider and low-energy bounds.

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Title: Xogenesis
Authors: Matthew R. Buckley, Lisa Randall
(Version v2)

We present a new paradigm for dark matter in which a dark matter asymmetry is established in the early universe that is then transferred to ordinary matter. We show this scenario can fit naturally into weak scale physics models, with a dark matter candidate mass of this order. We present several natural suppression mechanisms, including bleeding dark matter number density into lepton number, which occurs naturally in models with lepton-violating operators transferring the asymmetry.

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Scientists weigh out ingredients for the perfect galaxy

Astronomers working with Europe's Herschel Space Observatory have found out just how much dark matter it takes to make a new galaxy bursting with stars.
The discovery is a key step in understanding how dark matter - an invisible substance that pervades our universe - contributed to the creation of massive galaxies early in the life of the Universe, about 13.7 billion years ago.
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Herschel Measures Dark Matter for Star-Forming Galaxies

The Herschel Space Observatory has revealed how much dark matter it takes to form a new galaxy bursting with stars. Herschel is a European Space Agency cornerstone mission supported with important NASA contributions.
The findings are a key step in understanding how dark matter, an invisible substance permeating our universe, contributed to the birth of massive galaxies in the early universe.
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Dark Matter Reconstruction From Radio Experiments.

As photons move through the universe they get gravitationally lensed as the pass by large clumps of matter. Dark matter, being the dominant form of matter, lenses these photons more than anything. Therefore, by studying the lensing properties of incoming photons, in principle we can reconstruct what the profiles of the dark matter doing that lensing.

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In 1969, an astronomer named Jeremiah Ostriker realised that the Milky Way was spinning too fast. That may sound odd, given that it takes the sun 230 million years to make a full orbit. But when Ostriker tried to simulate the Milky Way on a computer, he found that it was spinning so quickly that it should have ripped itself apart long ago. There weren't enough stars to hold it together.
Other astronomers didn't want to believe it. After all, they had spent the past four centuries learning about the universe by collecting its light in their telescopes. Now it seemed they were missing most of the cosmic show. But as Richard Panek chronicles in his fascinating new book, "The 4 Percent Universe," it turned out that there was a lot more wrong with the universe than even Ostriker had realised and that his and Peebles's work was only the beginning of an enormous undertaking by many scientists.
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Study finds 'no link between dark matter, black holes'

A new study has found that there is no direct connection between black holes and dark matter.
The theory first took root when massive black holes were found at the centres of almost all galaxies, where the largest galaxies - which are also the ones embedded in the largest halos of dark matter - harbour the most massive black holes.
Scientists at the Max Planck Institute of Extraterrestrial Physics, the University Observatory Munich, and the University of Texas in Austin, have found otherwise.
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