Nuclear physics: Fostering nuclear theory in Europe

The European Centre for Theoretical Studies in Nuclear Physics and Related Areas

The European Centre for Theoretical Studies in Nuclear Physics and Related Areas (ECT*) plays a key role in Europe, as Professor Jochen Wambach explains.

From the hot and dense soup of quarks and gluons in the first microseconds after the Big Bang, through to the formation of protons and neutrons which began the evolution of the chemical elements, the physics of nuclei is fundamental to our understanding of the Universe. Now, nuclear physicists are creating new forms of matter in the laboratory and are producing isotopes of elements that, hitherto, have only existed in stellar explosions or in the mergers of neutron stars.

The overarching goal of nuclear physics is to unravel the fundamental properties of nuclei from their building blocks (protons and neutrons), and ultimately to determine the emergent complexity from the underlying quark- and gluon degrees of freedom of Quantum Chromodynamics (QCD), the fundamental theory of the strong nuclear force. This requires a detailed knowledge of the structure of hadrons, the nature of the residual forces between nucleons resulting from their constituents, and the limits of the existence of bound nuclei and ultimately of hadrons themselves.

A thorough understanding is vital for the complex structure of nuclei, nuclear reactions, and the properties of strong-interaction matter under extreme conditions in astrophysical settings and in the laboratory. Nuclei also constitute a unique laboratory for a variety of investigations of fundamental symmetries in nature which, in many cases, are complementary to particle physics. Substantial experimental and theoretical efforts are being made worldwide to address the central questions of nuclear physics, which include:

• How is the visible mass in the universe generated in QCD and what are the static and dynamical properties of hadrons?
• How does the strong force between nucleons emerge from the underlying quark-gluon structure?
• How does the complexity of nuclear structure arise from the interaction between nucleons?
• What are the limits of nuclear stability?
• How and where in the Universe are the chemical elements produced?
• What are the properties of nuclei and strong-interaction matter as encountered shortly after the Big Bang, in catastrophic cosmic events, and in compact neutron stars?

These fascinating topics in basic science require concerted efforts in the development of new and increasingly sophisticated tools such as accelerators and detectors but also significant advances in theory. Knowledge and technical progress in basic, curiosity-driven nuclear physics has significant societal benefits, including the training of a highly skilled workforce.

Nuclear theory

Advances in nuclear theory underpin the goal of truly understanding how nuclei and strong-interaction matter in all its forms behave, meaning that we can then predict their behaviour in new settings. Nuclear theory is making major conceptual and computational advances to address the fundamental questions in the strong-interaction sector of the Standard Model. These include the high-temperature and high-density behaviour of matter as encountered in cosmological settings and the emergence of hadrons and nuclei from the complex dynamics of QCD. They are driven by discoveries such as the detection of perhaps the most exotic state of matter, the quark-gluon plasma, which is believed to have existed in the very first moments of the Universe.

The recent detection of gravitational waves from a neutron-star merger focuses attention on the equation of state at high baryon densities, which is still not well understood. High-precision measurements of the quark structure of the nucleon are challenging existing theoretical understanding. Nuclei also serve as an indispensable testing ground for the fundamental symmetries of Nature. These include searches for dark matter, neutrinoless double-beta decay and others that require strong guidance from nuclear theory.

High-performance computing

Accompanying the experimental developments, qualitative changes in the theoretical understanding of strong-interaction matter have taken place through significant improvements in computational algorithms and high-performance computing. Numerical simulations of the QCD thermodynamics have entered the precision era, now providing stringent predictions of the equation of state near the quark-hadron transition for moderate baryon chemical potentials. Similarly, numerical studies of hadron structure and spectroscopy have led to major advances on a quantitative level, and are indispensable for precision observables exploring the limits of the Standard Model.

A combination of techniques has also provided links between numerical QCD calculations of nuclear few-body systems and ab-initio methods for the solution of the nuclear many-body problem through effective field theories rooted in QCD. The theoretical tools have matured such that they begin to span the strong-interaction landscape from the elementary constituents, quarks and gluons, as the building blocks for the computation of hadrons and nuclei to the computation of the equation of state for infinite nuclear matter and neutron-star matter. In all areas of theoretical nuclear physics algorithmic and computational advances thus hold promise for breakthroughs in predictive power. Recent developments in quantum computing platforms and algorithms hold the potential for new breakthrough solutions.

Nuclear theory is a significant driving force in the utilisation of high-performance computing facilities and the exploration of rapidly growing opportunities in quantum computing at the national and European level. The planning of future computer installations and the exploration of quantum computation possibilities is recognised as being of strategic importance for Europe. Being ready to exploit new computational concepts and capabilities will be mandatory for the competitiveness of European nuclear theory.

With continued major conceptional and computational advances, nuclear theory plays a crucial role in shaping existing experimental programmes in Europe and provides guidance to new initiatives in nuclear physics. Combining theory initiatives in a concerted effort is essential for the optimal use of the available resources, in particular by providing platforms for scientific exchange and the training of the next generation of nuclear theorists.

The role of ECT

The European Centre for Theoretical Studies in Nuclear Physics and Related Areas (ECT*) started operating in 1993 as a ‘bottom up’, community-driven initiative of the European nuclear physics community and has since developed into a very successful research centre for nuclear physics in a broad sense. ECT* is unique and the only centre of its kind in Europe. It is similar in scope and mission to the Institute for Nuclear Theory in Seattle (INT), USA, and collaborates with European universities, institutes and laboratories. It is an institutional member of NuPECC, the Associated Nuclear Physics Expert Committee of the European Science Foundation. With around 700 scientific visitors each year, from all over the world, spending from a week to several months at the Centre, ECT* has gained a high visibility. As stipulated in its statutes, ECT* assumes a co-ordinating function in the European and international scientific community by:

• Conducting in-depth research on topical problems at the forefront of contemporary developments in theoretical nuclear physics
• Fostering interdisciplinary contacts between nuclear physics and neighbouring fields such as particle physics, astrophysics, condensed matter physics, statistical and computational physics, and the quantum physics of small systems
• Encouraging talented young physicists by arranging for them to participate in the activities of the ECT*, by organising training programs and establishing networks of active young researchers
• Strengthening the interaction between theoretical and experimental physicists

These goals are reached through international workshops and collaboration meetings, advanced doctoral training programmes and schools, and research carried out by postdoctoral fellows and senior research associates as well as long-term visitors. Co-operations exist with the Physics Department and the Center for Bose-Einstein Condensation (BEC) at the University of Trento and with the Interdisciplinary Laboratory for Computational Science (LISC) of the Bruno Kessler Foundation, Italy. There are now co-operative agreements with other scientific institutions, in particular the Extreme Matter Institute (EMMI) in Darmstadt, the Helmholtz International Center for FAIR, Germany, the JINR in Dubna, Russia, the research Center RIKEN, Japan, the National Astronomical Observatory of Japan, the ITP of the Chinese Academy of Science and the Asia Pacific Center for Theoretical Physics in Korea.

ECT* is institutionally embedded in and sponsored by the ‘Fondazione Bruno Kessler’ in co-operation with the ‘Assessorato alla Cultura’ (Provincia Autonoma di Trento) and receives substantial funding from EU Member and Associated States. It is also supported by various instruments of the Framework Programmes of the European Commission.

With the emergence of a common European Research Area (ERA) and growing international co-operation, ECT* faces new opportunities and challenges. Significant European and global investments are now being made in accelerator centres and other experimental facilities. Their efficient utilisation requires co-ordination and the exchange of ideas – experiments stimulating theory and vice versa. Interdisciplinary contacts between the various subfields covered by ECT* and with related areas of physics and science is beneficial to all parties.

Professor Jochen Wambach
+39 0461 314 760

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