Description:

Many of the best motivated extensions of the Standard Model of Particle Physics, including String Theories, predict the existence of “axions” and low-mass “axion-like particles” (ALPs). ALPs are increasingly gaining interest as possible dark matter candidates, and sufficiently light ALPs (those with Compton wavelengths comparable to the cosmological horizon) may even be dark energy candidates. So the hunt is on to find these particles! After reviewing the motivation and basic physics of ALPs, this talk will describe how X-ray observations of clusters of galaxies are providing the most stringent constraints to date on the existence of low-mass ALPs, providing limits that already are pushing on the predictions of String Theory. I shall then discuss the promise (and challenges) of advancing these studies with the next generation of X-ray observatories.

 Chris Reynolds, Professor, University of Maryland

Host: Fred Rasio