Sterile neutrinos in the Milky Way: Observational constraints

We consider the possibility of constraining decaying dark matter by looking out through the Milky Way halo. Specifically we use Chandra blank sky observations to constrain the parameter space of sterile neutrinos. We find that a broad band in parameter space is still open, leaving the sterile neutrino as an excellent dark matter candidate.Comment: Submitted to ApJL, 4 pages, 4 figure

ETHICAL GUIDELINES FOR BLOCKCHAIN SYSTEMS

Today, enterprise architects and IT systems developers must decide ad hoc how to identify, assess and mitigate ethical issues of autonomous, rule-based systems based on blockchain technology. As blockchain systems are decentralized and immutable, developers must assess ethical risks, not only on an individual and context-based level but on a network level and for all life-cycle stages of a blockchain system. Furthermore, these ethical issues should be addressed in a context of clearly defined values, as the developer otherwise risks encoding their own worldviews and values in the system. We have chosen the European Union as a use case for analysing the identified ethical risks of blockchain systems. This empirical work presents a top-down approach that establishes ethical guidelines for blockchain systems based on ethical issues mapped against European values

Searching for decaying axion-like dark matter from clusters of galaxies

We consider the possibility of constraining the lifetime of radiatively decaying dark matter particles in clusters of galaxies inspired from generic axions of the Kaluza-Klein type. Such axions have been invoked as a possible explanation for the coronal X-ray emission from the Sun. These axions, or similar particles, can be produced inside stars and some of them remain confined by the deep gravitational potential of clusters of galaxies. Specifically, we consider regions within merging galaxy clusters (Abell 520 and the "Bullet Cluster"), where gravitational lensing observations have identified massive, but baryon poor, structures. From an analysis of X-ray observations of these mass concentrations, and the expected photon spectrum of decaying solar KK-axions, we derive lower limits to the lifetime of such axions of tau approx. 10^23 sec. However, if KK-axions constitute less than a few percent of the dark matter mass, this lifetime constraint is similar to that derived from solar KK-axions.Comment: Submitted to PRL, 4 pages, 3 figure