Illustration of planets.

Studying nuclear matter under Big Bang Conditions 

The study of nuclear matter under extreme temperature and pressure conditions, like those close to the Big Bang, is a central focus of collider experiments in the powerful particle accelerators at CERN and the Brookhaven National Laboratory. 

Rasmus Normann Larsen, at the Department of Mathematics and Physics at Stavanger University and his fellow researchers, study the interactions of particles called Hadrons, which are made up of quarks and anti-quarks and bound together by the strong nuclear force. They were recently awarded computing time on the PRACE Tier-0 systems
 
Larsen and his team are looking for the effective potential that binds the quark and anti-quark together, similar to how planets are bound to the star that they orbit. The researchers also want to know how this binding changes as the temperature reaches billions of degrees Celsius. Computer simulations are used to calculate the effective potential by averaging over the fluctuations of the quantum fields, that is the quarks. However, it is impossible to calculate all possible fluctuations of the quantum fields, so the researchers find the most likely fluctuations using Rational Hybrid Monte-Carlo simulations – a type of random walk algorithm. When the most likely fluctuations have been found, they calculate the probability of the quark and anti-quark to be separated.
 
The code that makes the fluctuations is done by using GPU computations and is written in c++ and CUDA. The code is part of the HotQCD collaboration that explores QCD (quarks and the strong force) at temperatures like in the early universe. These are large computations, and every output file containing only 1 fluctuation each is 10 GB. Thousands of files are generated and used for measurements. This means that the research team need to process files that amount to more than 100 TB. Only supercomputers such as the Juwel Booster, which is the computer the project is granted access to by the Prace award, can handle such vast calculations. 
 

We hope to have a good description of the effective potential between quarks and anti-quarks, at temperatures similar to those observed at the large hadron collider. This should help to better understand the state of matter in the early universe. Currently many proposals for how these interactions behave exist, but there are large uncertainties. We hope to clear up these uncertainties and provide a much more specific description of the quark and anti-quark system.
Rasmus Normann Larsen

In the 22nd PRACE Call, for the first time, two Norwegian-led projects were awarded a total of over 46 million computing hours on PRACE Tier-0 systems. Both projects are on the fundamental constituents of matter, and the awards give these projects access to compute power beyond our national systems.

See also Explaining the dark matter mystery