Dark Matter in the Milky Way's Dwarf Spheroidal Satellites

The Milky Way's dwarf spheroidal satellites include the nearest, smallest and least luminous galaxies known. They also exhibit the largest discrepancies between dynamical and luminous masses. This article reviews the development of empirical constraints on the structure and kinematics of dSph stellar populations and discusses how this phenomenology translates into constraints on the amount and distribution of dark matter within dSphs. Some implications for cosmology and the particle nature of dark matter are discussed, and some topics/questions for future study are identified.Comment: A version with full-resolution figures is available at http://www.cfa.harvard.edu/~mwalker/mwdsph_review.pdf; 70 pages, 22 figures; invited review article to be published in Vol. 5 of the book "Planets, Stars, and Stellar Systems", published by Springe

A4 Flavor Models in Split Seesaw Mechanism

A seesaw mechanism in an extra-dimension, known as the split seesaw mechanism, provides a natural way to realize a splitting mass spectrum of right-handed neutrinos. It leads to one keV sterile neutrino as a dark matter candidate and two heavy right-handed neutrinos being responsible for leptogenesis to explain the observed baryon asymmetry of the Universe. We study models based on $A_4$ flavor symmetry in the context of the split seesaw mechanism. It is pointed out that most of known $A_4$ flavor models with three right-handed neutrinos being $A_4$ triplet suffer from a degeneracy problem for the bulk mass terms, which disturbs the split mechanism for right-handed neutrino mass spectrum. Then we construct a new $A_4$ flavor model to work in the split seesaw mechanism. In the model, the experimentally observed neutrino masses and mixing angles can be realized from both type I+II seesaw contributions. The model predicts the $\mu-\tau$ symmetry in the neutrino mass matrix at the leading order, resulting in the vanishing $\theta_{13}$ and maximal $\theta_{23}$. The flavor symmetry $A_4$ is broken via the flavon vacuum alignment which can be obtained from the orbifold compactification. The model can be consistent with all data of neutrino oscillation experiments, cosmological discussions of dark matter abundance, leptogenesis, and recent astrophysical data.Comment: 21 pages, 1 figure, version to appear in JHE

Neuroprotective Effects of Rosmarinic Acid on Ciguatoxin in Primary Human Neurons

International audienceCiguatoxin (CTX), is a toxic compound produced by microalgae (dinoflagellate) Gambierdiscus spp., and is bio-accumulated and bio-transformed through the marine food chain causing neurological deficits. To determine the mechanism of CTX-mediated cytotoxicity in human neurons, we measured extracellular lactate dehydrogenase (LDH) activity, intracellular levels of nicotinamide adenine dinucleotide (NAD(+)) and H2AX phosphorylation at serine 139 as a measure for DNA damage in primary cultures of human neurons treated with Pacific (P)-CTX-1B and P-CTX-3C. We found these marine toxins can induce a time and dose-dependent increase in extracellular LDH activity, with a concomitant decline in intracellular NAD(+) levels and increased DNA damage at the concentration range of 5-200 nM. We also showed that pre- and post-treatment with rosmarinic acid (RA), the active constituent of the Heliotropium foertherianum (Boraginaceae) can attenuate CTX-mediated neurotoxicity. These results further highlight the potential of RA in the treatment of CTX-induced neurological deficits