Research in cosmic rays, magnetic fields and the nature of dark matter

Washington University, Saint Louis MO

Investigators

Abstract

This project focuses on the most energetic particles in the Universe, the Ultra-High Energy Cosmic Rays (UHECRs). Efforts to understand their origin have been on-going for decades, and evidence of an anisotropic distribution suggesting a link to nearby active galactic nuclei has been recently revealed by the Pierre Auger Observatory (PAO). However, the measurements of the composition and arrival directions point to somewhat conflicting results. The research will combine future data of the spectrum and angular distribution to unveil the mechanism hurling these particles around the Universe. The project also is concerned with the nature of the cosmic magnetic fields. Charged particle astronomy relies on the small magnetic smearing of point sources. The origin of the large-scale magnetization in the Universe could provide a signature of the Universe at the electroweak phase transition or at the end of infation. The project spans the period in which the PAO will accumulate a data set exceeding the experiments to date by more than an order of magnitude. The PI's research will include the following: 1. Unified analysis of the directions and spectrum. The PI will extend previous analysis to incorporate the different energy spectrum resulting from sources distributed non-uniformly. 2. Cosmic magnetic fields: The compelling evidence for the existence of magnetization in galaxies, clusters and superclusters poses a theoretical problem. One explanation for the origin of these magnetic fields is thought to be the product of sphaleron decays at the electroweak phase transition which results in a non-zero helicity that could be measured using cosmic ray astronomy. The PI will improve calculations of the expected helicity, using lattice simulations, and will devise observables for its detection. The broader impact is as follows: the proposed research will add to our knowledge of the universe in which we live, and of the most energetic particles reaching the Earth. It will allow us to learn more about the extreme conditions at the acceleration sites, and the processes that took place when the excess of matter over antimatter, that eventually gave rise to our planet and the stars and galaxies surrounding us, was generated. Washington University operates a substantial science outreach program to improve teaching and learning in K-12 science and math: the work carried out as part of the project will be presented to school teachers in the context of existing courses that enhance their professional development by bringing them into contact with cutting-edge research. Many of the local school districts that participate in this outreach program have substantial populations of under-represented minorities.