Scientific background and state of the art
Vision for low-energy nuclear physics
The long-term vision is to arrive at a comprehensive and unified description of nuclei and their reactions, grounded in the fundamental interactions between the constituent nucleons. Nuclear theorists seek to replace current phenomenological models of nuclear structure and reactions with a well-founded microscopic theory that delivers maximum predictive power with well-quantified uncertainties. To achieve this ambitious goal, a vibrant interplay between theory and experiment is needed. This interplay should match the research conducted at present and planned experimental facilities, where one of the aims is to study short-lived isotopes. These nuclei convey crucial information about the stability of nuclear matter and the origin of elements, but are difficult to study experimentally due to their extremely short lifetimes and small production cross-sections.
We expect that the new-generation of experimental facilities will offer unprecedented data on weakly bound systems and the limits of nuclear existence. To interpret such a wealth of experimental data and point to new experiments that can shed light on various properties of matter requires a reliable and predictive theory. In view of the high investment costs and limited availability of the most exotic beams, it is also extremely important to use high-quality theoretical modeling to set correct priorities and identify experiments that advance science most and those that can be safely postponed.
Basic nuclear physics research, as conducted today, is very diverse in nature, with experimental facilities that include accelerators, reactors, and underground laboratories. This diversity reflects the complex nature of the nuclear forces acting among protons and neutrons. These generate a broad range of nuclear phenomena in energy and distance ranges that span many decades.
To exemplify this, one may consider the following specific example which spans distances from femtometers (10-15 m) to thousands of meters. In order to understand how a neutron star cools over time, one needs detailed calculations of the thermodynamics of its outer layers, the so-called neutron star crust. The crust can be modeled as a lattice of nuclei, interspersed in a medium of neutrons, protons and electrons. The standard way to model such a system is provided by methods from Molecular Dynamics, a familiar methodology in Materials Science. The typical extension of the crust of a neutron star is one to two kilometers. To make reliable predictions, Molecular Dynamics calculations need robust input in the form of interactions between nucleons and nuclei. To model these interactions acting on a femtometer scale, effective field theory and ab initio methods must be applied. Consequently, to understand how a neutron star cools over time requires physics input which spans over 18 orders of magnitude in length scales!
Nuclear physics is thus an excellent example of what one would call multi-scale physics, with many intellectually demanding problems. These problems are a tough challenge to our current understanding and our capabilities to compute and analyze nuclear systems. A theoretical approach to the physics of multi-scale processes has also strong intellectual parallels with present research in Materials Science or studies of biological systems. In Materials Science one needs to link ab initio methods with density functional theories and Molecular Dynamics approaches in order to be able to predict properties of materials. A multi-scale process program implies also the development of pertinent algorithms and high-performance computing tools. This has in turn consequences for the development of an advanced curriculum for the next generation of nuclear theorists.
Some of the key physics issues addressed by low-energy nuclear theory are:
- How to understand nuclear forces acting between nucleons?
- How does the inter-nucleon force in nuclear medium depend on the proton-to-neutron ratio?
- What are the limits of the chart of the nuclides?
- What is the nature of collective phenomena in nuclei?
- What are the rates of nuclear reactions that cannot be measured in nuclear laboratories?
- Which is the nuclear microphysics needed for comprehensive description of stellar matter?
These are genuine quantum many-body physics questions. They demonstrate that low-energy nuclear theory is a forefront area that makes the connection between fundamental particles, mesoscopic many-body systems and the cosmos.
To address the above challenges, extensive collaborations and contacts between research groups having different expertise are needed. It also requires that these research groups develop a long-range perspective on their activities. Unfortunately, low-energy theory groups in many countries are often sub- critically manned, in many cases they are represented by a single faculty, with obvious consequences for the broadness of the instruction offered. The research and educational network proposed here can therefore function as a starting point for strengthening the educational background of our students and provide a basis for new scientific collaborations and training of a new generation of nuclear scientists.
In order to strengthen the theoretical community in Europe and Northern America, provide solid support to experimental developments in the field and address manpower needs, the proposed network aims at developing a curriculum which responds to many of the above challenges.
Nuclear Physics Research
The TALENT initiative is firmly rooted in the scientific goals of the Nuclear Physics community and matches well ESFRI (the European Strategy Forum on Research Infrastructures) road-map facilities that includes FRIB in Michigan, FAIR in Germany and SPIRAL2 in France, to mention a few of the coming facilities. These facilities for studies of rare exotic isotopes and basic research programs aiming at understanding the limits of stability of matter, represent multi-billion USD/Euro investments in Europe and Northern America, with considerable technological challenges and manpower needs. Measurements of masses and drip lines, nuclear reaction rates, weak decay rates, electron capture rate, etc. at these facilities will provide key information to answer fundamental questions such as:
- What is the nature of the nuclear force that binds protons and neutrons into stable nuclei and rare isotopes?
- How do the building blocks of atomic nuclei self-organize themselves into composite structure and phases.
- What is the origin of elements in the cosmos?,
- What are the nuclear reactions that drive stars and stellar explosions?
- What is the nature of neutron stars and dense nuclear matter?
- How can we best use the unique properties of nuclei to improve our lives?
Theory is crucial to the success of experimental infrastructures. The goal is to build a validated and comprehensive theoretical framework
- having a high predictive power;
- capable of robust extrapolations (applying the validated theory to properties of interest that cannot be measured);
- guiding experimental efforts;
- validating experimental data and assessing their importance.
In addition to the intellectual potential of this research, applications of rare isotopes can benefit the society in many ways. These include:
- Stockpile stewardship and waste transmutation
- Materials science,
- Defense (e.g., nuclear forensics),
- Environmental science, archaeology, etc.
Crucial input from studies of rare exotic isotopes is necessary to build economically competitive, energy efficient, reduced-waste nuclear reactors, which could assure future energy needs. The cutting edge radioisotope studies aim at determining next medically viable isotopes required for enhanced and targeted treatment and diagnosis.
Societal and industrial applications rely often on our ability to select specific designer nuclei, with particular properties optimized for specific needs. Nuclear Physics provides a superb venue for a probably the most important mission to educate and train the next generation of nuclear scientists, who will play key roles not only in basic research itself, but in a myriad of applied fields. This is the vision and objective of the proposed network, which will provide a unique training in modern theoretical nuclear physics and its methods, with a particular emphasis on those aspects, which can be beneficial to other domains of research and applications, outside of the Nuclear Physics.
Project scientific areas
The TALENT initiative addresses early-stage researchers and offers them an advanced training in modern multi-scale nuclear physics and a possibility to broaden research competences with a dedicated research program that will focus upon both exploiting the educational content of the training and the expertise of the participating partners of the network. The research and educational aspects of training young researchers aim at the exploitation of the mutual synergy for the benefit of individual research projects and their early definition in a broad context of the highly competitive world-class research.
The TALENT courses will provide young researchers with numerous opportunities to develop projects under one or more of the five inter-related themes:
- Advanced few- and many-body methods;
- Theoretical modeling of nuclear phenomena;
- Nuclear astrophysics;
- Physics of weakly bound and open quantum systems;
- High-performance computing, numerical methods and advanced algorithms.
The TALENT initiative aims at setting up a curriculum of courses that will provide an essential training in modern low-energy nuclear theory and related fields. An important aspect of the training is a strong emphasis on high-performance computing and numerical algorithms. Each course is planned to run over three weeks, involving 30 hours of lectures, 30 hours of problem solving and 60 hours of the course preparation and the development of an individual project related both to the research topic of each trainee and the specific content of the course. Each three-week module will be complemented by a study/discussion period (typically lasting one week) involving world-leading experts in the field, which will include include:
- The overview of the current research related to the subject of the course;
- The presentation and discussion of an individual research project of each trainee, with a special emphasis on the formulation of the project, discussion of its premises and difficulties, and presentation;
- Discussion in depth of each scientific project with experts. Here the aim is to improve the research project of a trainee and develop collaborations between individuals and groups in different partnerships of the network;
- A seminar on skills needed to prepare a scientific paper/report;
- The preparation and presentation of an exit report (which can be a publishable scientific paper). This will complete each course module.
The TALENT courses cover:
- basic nuclear structure and reaction theory;
- advanced theoretical methods such as effective field theory, configuration interaction approach, coupled cluster theory, density functional theory and extensions, and reaction theory;
- modern theory of nuclear forces;
- computational and numerical methods, and high performance computing.