Hans und Walter Thirring-Preis 2021

Xiaoyong Chu wird für seine bahnbrechenden Neuansätze zur Physik der Dunklen Materie ausgezeichnet.

The gravitational evidence for dark matter is well established, and deciphering its microphysical properties is one of the most actively pursued goals in fundamental physics. Latest cosmological measurements suggest that there exists an unexpected mass deficit in small dark matter halos that host dwarf and low-surface-brightness galaxies. This is not expected in any simple models of dark matter, but may rather indicate that dark matter is substantially self-interacting. On the other side, however, no such mass deficit is observed in much larger halos that host clusters of galaxies, putting a principal limit on the strength of such self-interaction, which is tighter than what is required for the small haloes.

In a series of work, Xiaoyong Chu and his team propose that the dark matter self-interaction strongly depends on velocity, in a similar way to the interactions between nuclei. This velocity-dependence can be caused by the presence of a resonance, or by the compositeness of dark matter particles. In the resonance model, dark matter particles in small haloes generally have low, yet special velocities that make two-body collisions resonant, significantly enhancing the corresponding cross section. In the composite model, the physical cross section is determined by the quantum summation of the dark matter internal structure, where lower dark matter velocities generate weaker destructive quantum-phase differences and thus stronger collisions. Both models are novel solutions to the mass deficit problem, and thus open up a new avenue for self-interacting dark matter model-building. Furthermore, Xiaoyong Chu and his team adopt the so-called effective-range approach, which was also first formulated to describe nucleon collisions, to obtain a model-independent parametrization of dark matter self-interaction. This parametrization can be simultaneously interpreted in many well-motivated models, with only two parameters. As it allows to consistently take into account the velocity dependence of dark matter self-interactions, it can be very useful in cosmological simulations involving different astrophysical scales, as well as in bridging the observational data and particle models of dark matter.

Der Preisträger

Xiaoyong Chu war von 2005 bis 2007 Forschungsassistent an der University of Science and Technolgy of China. Das Masterstudium im Fach Allgemeine Physik hat er 2009 an der Chalmers University of Technology, Schweden, abgeschlossen; 2013 dissertierte er im Fach Theoretische Physik an der Université Libre de Bruxelles, Belgien. Von 2013 bis 2016 hatte Xiaoyong Chu eine Postdoc-Stelle am International Center for Theoretical Physics in Triest, Italien. Seit 2016 arbeitet er am Institut für Hochenergiephysik der ÖAW: zunächst als Postdoc (2016 bis 2020) und ab 2021 als Research Associate.