Challenges in the description of the atomic nucleus: Unification and interdisciplinarity

Abstract

Abstract. Nuclear physics, in general, and theoretical nuclear physics, in particular, have provided the physics community at large, among other things, with the paradigm of spontaneous symmetry breaking phenomena in finite many-body systems. The study of the associated mechanisms of symmetry restoration has shed light on the microscopic structure of the corresponding condensates, in particular on the superfluid phase, allowing to study Cooper pair tunnelling into superfluid nuclei (related to the Josephson effect), in terms of individual quantum states and reaching, in doing so, a new milestone: that of unifying structure and reactions, these last processes being found at the basis of the formulation of quantum mechanics (probability interpretation, Born). In the process, nuclear physicists have extended the validity of BCS theory of superconductivity to the single Cooper pair situation, let alone discovering unexpected mechanism to break gauge invariance. The insight obtained from pair transfer research is likely to have important consequences in the study of double charge exchange processes, and thus in the determination of the nuclear matrix element associated with neutrinoless double beta decay, eventually providing an important test of the Standard Model. Time, thus, seems ripe for nuclear theorists to take centre stage, backed by a wealth of experimental information and by their interdisciplinary capacity to connect basic physical concepts across the borders. With the help of these elements they can aim at fully revealing the many facets of their femtometer many-body system, from vacuum zero point fluctuations to new exotic modes of nuclear excitations and of their interweaving, resulting in powerful effective field theories. Unless. Unless they are not able to free themselves from words like ab initio or fundamental, and to adapt a relax attitude concerning Skyrme, tensor, etc., forces, as well as regarding the quest for "the" Hamiltonian.The modern theory of nuclear structure results from the merging of the liquid drop and of the shell model, which contributed to the concepts of collective excitations and of independent-particle motion, respectively. These apparently contradictory views became eventually unified in the paradigm of broken symmetry restoration to determine the elementary modes of nuclear excitation, their interweaving being a consequence of the particle-vibration coupling mechanism [1]. The resulting clothed bosonic and fermionic degrees of freedom constitute the physical, elementary modes of nuclear excitation which diagonalize the many-body nuclear Hamiltonian restoring symmetries spontaneously broken. The associated spectroscopic amplitudes provide, together with the theory of reactions [2][3][4][5], the elements to calculate the absolute value of the differential cross sections and transition rates. In partica e-mail: Pierfrancesco.Bortignon@mi.infn.it ular, those associated with: a) inelastic scattering and Coulomb excitation, b) one-particle and, c) two-particle transfer processes. ...

RETRACTED ARTICLE: On the unification of nuclear-structure theory: A response to Bortignon and Broglia

“…The "challenge" posed by Bortignon and Broglia [1] for achieving unification of specifically nuclear-structure theory with nuclear-reaction data should be applauded by all physicists. Their suggestion for "nuclear theorists to take center stage" is an unusual, but welcome invitation to return to the basics of nuclear physics while using the conceptual and computational tools developed in the 21st century to solve old and yet-unsolved problems.…”

“…a e-mail: cook@res.kutc.kansai-u.ac.jp While many researchers await developments in quark theory for elucidation of the character of the nucleonnucleon interaction, it is worth bearing in mind that nuclear-structure theorists from the heyday of nuclear theory have repeatedly stated their conviction that insights from high-energy particle physics are unlikely to shed light on the relatively low-energy phenomena of nuclear structure. As noted by Bortignon and Broglia [1], the so-called "unified" model of Bohr and Mottelson [3] from the 1960s was a success in providing a means to address both the collective and the independent-particle aspects of nuclei, but the nucleon-clustering phenomena treated in the alpha-cluster and boson models remained outside of the "unified" model and progress in clarifying the nuclear force did not follow from their work. The related problem of the mean-free-path of nucleons in stable nuclei (long, as in a gas?…”

“…In conclusion, while research on the quark constituents of hadrons in high-energy physics has had some success in classifying particles in the Standard Model, it appears that the low-energy realm of nuclear-structure physics requires the attention of "a new type of nuclear theoretician" who "thinks more" about the self-consistency of nuclearstructure theory [1].…”

Nuclear response in a finite-temperature relativistic framework

“…A large corpus of theoretical knowledge and experimental data was summarized in the volume "Giant Resonances: Nuclear Structure at Finite Temperature" by Pier Francesco Bortignon and his co-authors Angela Bracco and Ricardo A. Broglia [18]. In his late years, he was involved in new advancements of the NFT [19,20,21,22], which also open new horizons for future research.…”

Many-body effects in (p,pN) reactions within a unified approach

“…A consistent analysis of available experimental data, for all open reaction channels as well as different probes, with state-of-the art theory is lacking and of utmost importance for the understanding of nuclear structure along the nuclear landscape. Furthermore, it is essential to meet the challenges of new experimental developments and multiphysics research [25].…”