# QCDpQED--QCD Plus QED and the Stability of Matter

**Principal Investigator:** Zoltán Fodor, Institut für Theoretische Physik, FB-C, Universität Wuppertal (Germany)

**HPC Platform:** JUQUEEN of JSC

The mass of our visible universe is to a very large part provided by the strong nuclear interaction between elementary quarks, as described by the theory of quantum chromodynamics (QCD). This long standing assumption has been conclusively proven a few years ago utilizing supercomputer resources through an ab-initio computation of the mass of the proton and other composite nuclear particles (hadrons). Since the required precision in these calculations was a few percent, it was then sufficient to ignore all other forces, notably electromagnetism (QED), and make some simplifying assumptions that would have affected the result at the permil level only.

In order to understand more deeply not only the origin of the mass of the visible universe but also its composition, i.e. to answer the question why the chemical elements as we know them today exist or why stars form the way they do, tiny differences in the particle masses, especially those of protons and neutrons, are essential. These mass differences, caused by QCD and QED effects and the coupling to the Higgs boson (Nobel prize 2013), however, are tiny - in the permil range - and, therefore, require a much more careful treatment of the aforementioned sub-leading effects.

In this project, the scientists have developed and deployed novel methods that allow to perform such a calculation. The physicists developed a method of reliably including the small corrections from the electromagnetic force into the calculations ab-initio. In addition, they removed the two most prominent simplifying assumptions that are usually used (the equivalence of the mass of the two lightest quarks and ignoring the heavy charm quark), thus obtaining a description of nuclear forces that is accurate at the sub-permil level. Through the supercomputing resources of the GCS the scientists were able to put their methods to the test. In particular, they were able to verify that their new methods reduced the autocorrelations of subsequent measurements, in the full strong plus electromagnetic system, by three orders of magnitude. This allows the physicists to cover a large region of the parameter space and to test these new analysis techniques on the generated data.

The project was made possible through the Partnership for Advanced Computing in Europe (PRACE) using the petascale supercomputing resources of GCS centre Jülich Supercomputing Centre.

Copyright: Bergische Universität Wuppertal, Theoretische Physik, Fachbereich C

Zoltan Fodor

Theoretische Physik, Fachbereich C - Bergische Universität Wuppertal

D-42097 Wuppertal/Germany

e-mail: fodor@bodri.elte.hu

*September 2014*