Dr. Mauricio Martinez, a postdoctoral researcher in the group of Prof. Ulrich Heinz, and collaborators from Kent State, McGill and Sao Paulo Universities discovered a new exact solution of the highly non-linear relativistic Boltzmann equation. Very few such such exact solutions are known. Among them the new solution is the only one that describes exactly a system that expands simultaneously, with different expansion rates, along both the longitudinal and transverse directions of a cylinder. This mimicks the expansion of the quark-gluon plasma created in relativistic heavy-ion collisions along the directions parallel and perpendicular to the beam. The solution was possible with the help of an ingenious mapping of Minkowski space onto a (3+1)-dimensional de Sitter geometry, imposing a specific type of symmetry first discovered by string theorist Steve Gubser (Princeton) which rendered the mathematical problem effectively one-dimensional.

The new solution can be used to test the accuracy of various approximation schemes that describe the microscopic evolution macroscopically using viscous relativistic fluid dynamics. Hydro-dynamic modelling is a key component of any quantitative theoretical description of relativistic heavy-ion collisions. With the work done in Prof. Heinz' group, Ohio State University plays a worldleading role in this effort. To have an exact solution at ones disposal to test the precision of the hydrodynamic models, at least in specific highly symmetric limits, is invaluable. (As an example, the attached figure shows the spacetime evolution of the viscous stress of the system.) The reported work is available at http://arxiv.org/pdf/1408.5646.pdf and will soon appear in Physical Review Letters as an "Editors' Suggestion". It should be acknowledged and emphasized that this work came out of a collaborative exchange between The Ohio State University and the University of Sao Paulo which was supported by a travel grant awarded by OSU and FAPESP to Profs. Heinz (OSU) and Jorge Noronha (USP) last year in connection with the opening of OSU's Brazil Gateway.