Frontiers in Physics | Nuclear Physics section | New and Recent Articles
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RSS Feed for Nuclear Physics section in the Frontiers in Physics journal | New and Recent Articlesen-usFrontiers Feed Generator,version:12020-08-15T15:20:40.4621727+00:0060https://www.frontiersin.org/articles/10.3389/fphy.2020.00307
https://www.frontiersin.org/articles/10.3389/fphy.2020.00307
Lattice QCD and Baryon-Baryon Interactions: HAL QCD Method2020-08-14T00:00:00ZSinya AokiTakumi DoiIn this article, we review the HAL QCD method to investigate baryon-baryon interactions, such as nuclear forces in lattice QCD. We first explain our strategy in detail to investigate baryon-baryon interactions by defining potentials in field theories, such as QCD. We introduce the Nambu-Bethe-Salpeter (NBS) wave functions in QCD for two baryons below the inelastic threshold. We then define the potential from NBS wave functions in terms of the derivative expansion, which is shown to reproduce the scattering phase shifts correctly below the inelastic threshold. Using this definition, we formulate a method to extract the potential in lattice QCD. Secondly, we discuss pros and cons of the HAL QCD method, by comparing it with the conventional method, where one directly extracts the scattering phase shifts from the finite volume energies through the Lüscher's formula. We give several theoretical and numerical evidences that the conventional method combined with the naive plateau fitting for the finite volume energies in the literature so far fails to work on baryon-baryon interactions due to contaminations of elastic excited states. On the other hand, we show that such a serious problem can be avoided in the HAL QCD method by defining the potential in an energy-independent way. We also discuss systematics of the HAL QCD method, in particular errors associated with a truncation of the derivative expansion. Thirdly, we present several results obtained from the HAL QCD method, which include (central) nuclear force, tensor force, spin-orbital force, and three nucleon force. We finally show the latest results calculated at the nearly physical pion mass, m_{π} ≃ 146 MeV, including hyperon forces which lead to form ΩΩ and NΩ dibaryons.]]>https://www.frontiersin.org/articles/10.3389/fphy.2020.00285
https://www.frontiersin.org/articles/10.3389/fphy.2020.00285
Coupled-Cluster Computations of Optical Potential for Medium-Mass Nuclei2020-07-31T00:00:00ZJimmy RotureauRecent progress in the numerical solution of the nuclear many-body problem and in the development of nuclear Hamiltonians rooted in Quantum Chromodynamics, has opened the door to first-principle computations of nuclear reactions. In this article, we discuss the current status of ab initio calculations of nucleon-nucleus optical potentials for medium-mass systems, with a focus on results obtained with the coupled-cluster method.]]>https://www.frontiersin.org/articles/10.3389/fphy.2020.00218
https://www.frontiersin.org/articles/10.3389/fphy.2020.00218
Parity- and Time-Reversal-Violating Nuclear Forces2020-07-21T00:00:00ZJordy de VriesEvgeny EpelbaumLuca GirlandaAlex GnechEmanuele MereghettiMichele VivianiParity-violating and time-reversal conserving (PVTC) and parity-violating and time-reversal-violating (PVTV) forces in nuclei form only a tiny component of the total interaction between nucleons. The study of these tiny forces can nevertheless be of extreme interest because they allow one to obtain information on fundamental symmetries using nuclear systems. The PVTC interaction derives from the weak interaction between the quarks inside nucleons and nuclei, therefore the study of PVTC effects opens a window on the quark-quark weak interaction. The PVTV interaction is sensitive to more exotic interactions at the fundamental level, in particular to strong CP violation in the Standard Model Lagrangian, or even to exotic phenomena predicted in various beyond-the-Standard-Model scenarios. The presence of these interactions can be revealed either by studying various asymmetries in polarized scattering of nuclear systems, or by measuring the presence of non-vanishing permanent electric dipole moments of nucleons, nuclei and diamagnetic atoms and molecules. In this contribution, we review the derivation of the nuclear PVTC and PVTV interactions within various frameworks. We focus in particular on the application of chiral effective field theory, which allows for a more strict connection with the fundamental interactions at the quark level. We investigate PVTC and PVTV effects induced by these potentials on several few-nucleon observables, such as the longitudinal asymmetries in proton-proton scattering and the ^{3}He(n→,p)^{3}H reaction, the radiative neutron-proton capture, and the electric dipole moments of the deuteron and the trinucleon system.]]>https://www.frontiersin.org/articles/10.3389/fphy.2020.00233
https://www.frontiersin.org/articles/10.3389/fphy.2020.00233
The Time-Dependent Generator Coordinate Method in Nuclear Physics2020-07-03T00:00:00ZMarc VerriereDavid RegnierThe emergence of collective behaviors and the existence of large amplitude motions are both central features in the fields of nuclear structure and reactions. From a theoretical point of view, describing such phenomena requires increasing the complexity of the many-body wavefunction of the system to account for long-range correlations. One of the challenges, when going in this direction, is to keep the approach tractable within our current computational resources while gaining a maximum of predictive power for the phenomenon under study. In the Generator Coordinate Method (GCM), the many-body wave function is a linear superposition of (generally non-orthogonal) many-body states (the generator states) labeled by a few collective coordinates. Such a method has been widely used in structure studies to restore the symmetries broken by single-reference approaches. In the domain of reactions, its time-dependent version (TDGCM) has been developed and applied to predict the dynamics of heavy-ion collisions or fission where the collective fluctuations play an essential role. In this review, we present the recent developments and applications of the TDGCM in nuclear reactions. We recall the formal derivations of the TDGCM and its most common approximate treatment, the Gaussian Overlap Approximation. We also emphasize the Schrödinger Collective-Intrinsic Model (SCIM) variant focused on the inclusion of quasiparticle excitations into the description. Finally, we highlight several exploratory studies related to a TDGCM built on time-dependent generator states.]]>https://www.frontiersin.org/articles/10.3389/fphy.2020.00154
https://www.frontiersin.org/articles/10.3389/fphy.2020.00154
Solitons in Nuclear Time-Dependent Density Functional Theory2020-06-30T00:00:00ZYoritaka IwataThe soliton existence in sub-atomic many-nucleon systems will be discussed. In many nucleon dynamics represented by the nuclear time-dependent density functional formalism, much attention is paid to energy and mass dependence of the soliton existence. In conclusion, the existence of nuclear soliton is clarified if the temperature of nuclear system ranges from 10 to 30 MeV. With respect to the mass dependence ^{4}He and ^{16}O are suggested to be the candidates for the self-bound states exhibiting the property of nuclear soliton.]]>https://www.frontiersin.org/articles/10.3389/fphy.2020.00164
https://www.frontiersin.org/articles/10.3389/fphy.2020.00164
Many-Body Perturbation Theories for Finite Nuclei2020-06-05T00:00:00ZAlexander TichaiRobert RothThomas DuguetIn recent years many-body perturbation theory encountered a renaissance in the field of ab initio nuclear structure theory. In various applications it was shown that perturbation theory, including novel flavors of it, constitutes a useful tool to describe atomic nuclei, either as a full-fledged many-body approach or as an auxiliary method to support more sophisticated non-perturbative many-body schemes. In this work the current status of many-body perturbation theory in the field of nuclear structure is discussed and novel results are provided that highlight its power as a efficient and yet accurate (pre-processing) approach to systematically investigate medium-mass nuclei. Eventually a new generation of chiral nuclear Hamiltonians is benchmarked using several state-of-the-art flavors of many-body perturbation theory.]]>https://www.frontiersin.org/articles/10.3389/fphy.2020.00174
https://www.frontiersin.org/articles/10.3389/fphy.2020.00174
Recent Progress in Nuclear Lattice Simulations2020-05-21T00:00:00ZDean LeeWe review several recent results on lattice simulations by the Nuclear Lattice Effective Field Theory Collaboration. In the first part we discuss the implementation of nuclear forces on the lattice using chiral effective field theory. The new development we highlight is the use of non-local lattice operators to achieve a simpler spin channel decomposition, in contrast with previous studies that considered only local interactions. In the second part, we present evidence that nuclear physics is close to a quantum phase transition. This development is also linked to the study of the differences between local and non-local interactions. In the final part we further explore the link between the nuclear forces and nuclear structure. We consider the simplest possible nuclear interaction which can accurately reproduce the ground state energies of neutron matter, light nuclei, and medium-mass nuclei. We discuss what these recent developments say about the emergence of nuclear structure from nuclear forces and the road ahead for nuclear lattice simulations.]]>https://www.frontiersin.org/articles/10.3389/fphy.2020.00153
https://www.frontiersin.org/articles/10.3389/fphy.2020.00153
Quantum Monte Carlo Methods for Astrophysical Applications2020-05-14T00:00:00ZIngo TewsIn recent years, new astrophysical observations have provided a wealth of exciting input for nuclear physics. For example, the observations of two-solar-mass neutron stars put strong constraints on possible phase transitions to exotic phases in strongly interacting matter at high densities. Furthermore, the recent observation of a neutron-star merger in both the electromagnetic spectrum and gravitational waves has provided compelling evidence that neutron-star mergers are an important site for the production of extremely neutron-rich nuclei within the r-process. In the coming years, an abundance of new observations is expected, which will continue to provide crucial constraints on the nuclear physics of these events. To reliably analyze such astrophysical observations and extract information on nuclear physics, it is very important that a consistent approach to nuclear systems is used. Such an approach consists of a precise and accurate method to solve the nuclear many-body problem in nuclei and nuclear matter, combined with modern nuclear Hamiltonians that allow to estimate the theoretical uncertainties. Quantum Monte Carlo methods are ideally suited for such an approach and have been successfully used to describe atomic nuclei and nuclear matter. In this contribution, I will present a detailed description of Quantum Monte Carlo methods focusing on the application of these methods to astrophysical problems. In particular, I will discuss how to use Quantum Monte Carlo methods to describe nuclear matter of relevance to the physics of neutron stars.]]>https://www.frontiersin.org/articles/10.3389/fphy.2020.00079
https://www.frontiersin.org/articles/10.3389/fphy.2020.00079
The Problem of Renormalization of Chiral Nuclear Forces2020-05-05T00:00:00ZU. van KolckEver since quantum field theory was first applied to the derivation of nuclear forces in the mid-twentieth century, the renormalization of pion exchange with realistic couplings has presented a challenge. The implementation of effective field theories (EFTs) in the 1990s promised a solution to this problem but unexpected obstacles were encountered. The response of the nuclear community has been to focus on “chiral potentials” with regulators chosen to produce a good description of data. Meanwhile, a successful EFT without explicit pion exchange—Pionless EFT—has been formulated where renormalization is achieved order by order in a systematic expansion of low-energy nuclear observables. I describe how lessons from Pionless EFT are being applied to the construction of a properly renormalized Chiral EFT.]]>https://www.frontiersin.org/articles/10.3389/fphy.2020.00116
https://www.frontiersin.org/articles/10.3389/fphy.2020.00116
Ab initio Calculations of Lepton-Nucleus Scattering2020-04-29T00:00:00ZNoemi RoccoThe advent of high precision measurements of neutrinos and their oscillations calls for accurate predictions of their interactions with nuclear targets utilized in the detectors. Over the past decade, ab initio methods based on realistic nuclear interactions and current operators were able to provide accurate description of lepton-nucleus scattering processes. Achieving a comprehensive description of the different reaction mechanisms active in the broad range of energies relevant for oscillation experiments required the introduction of controlled approximations of the nuclear many-body models. In this review, we give an overview of recent developments in the description of electroweak interactions within different approaches and discuss the future perspectives to support the experimental effort in this new precision era.]]>https://www.frontiersin.org/articles/10.3389/fphy.2020.00100
https://www.frontiersin.org/articles/10.3389/fphy.2020.00100
Implementing Chiral Three-Body Forces in Terms of Medium-Dependent Two-Body Forces2020-04-24T00:00:00ZJeremy W. HoltMamiya KawaguchiNorbert KaiserThree-nucleon (3N) forces are an indispensable ingredient for accurate few-body and many-body nuclear structure and reaction theory calculations. While the direct implementation of chiral 3N forces can be technically very challenging, a simpler approach is given by employing instead a medium-dependent NN interaction V_{med} that reflects the physics of three-body forces at the two-body normal-ordered approximation. We review the derivation and construction of V_{med} from the chiral 3N interaction at next-to-next-to-leading order (N2LO), consisting of a long-range 2π-exchange term, a mid-range 1π-exchange component, and a short-range contact-term. Several applications of V_{med} to the equation of state of cold nuclear and neutron matter, the nucleon single-particle potential in nuclear matter, and the nuclear quasiparticle interaction are discussed. We also explore differences in using local vs. non-local regulating functions on 3N forces and make direct comparisons to exact results at low order in perturbation theory expansions for the equation of state and single-particle potential. We end with a discussion and numerical calculation of the in-medium NN potential V_{med} from the next-to-next-to-next-to-leading order (N3LO) chiral 3N force, which consists of a series of long-range and short-range terms.]]>https://www.frontiersin.org/articles/10.3389/fphy.2020.00117
https://www.frontiersin.org/articles/10.3389/fphy.2020.00117
Atomic Nuclei From Quantum Monte Carlo Calculations With Chiral EFT Interactions2020-04-24T00:00:00ZStefano GandolfiDiego LonardoniAlessandro LovatoMaria PiarulliQuantum Monte Carlo methods are powerful numerical tools to accurately solve the Schrödinger equation for nuclear systems, a necessary step to describe the structure and reactions of nuclei and nucleonic matter starting from realistic interactions and currents. These ab-initio methods have been used to accurately compute properties of light nuclei—including their spectra, moments, and transitions—and the equation of state of neutron and nuclear matter. In this work we review selected results obtained by combining quantum Monte Carlo methods and recent Hamiltonians constructed within chiral effective field theory.]]>https://www.frontiersin.org/articles/10.3389/fphy.2020.00098
https://www.frontiersin.org/articles/10.3389/fphy.2020.00098
High-Precision Nuclear Forces From Chiral EFT: State-of-the-Art, Challenges, and Outlook2020-04-17T00:00:00ZEvgeny EpelbaumHermann KrebsPatrick ReinertWe review a new generation of nuclear forces derived in chiral effective field theory using the recently proposed semilocal regularization method. We outline the conceptual foundations of nuclear chiral effective field theory, discuss all steps needed to compute nuclear observables starting from the effective chiral Lagrangian and consider selected applications in the two- and few-nucleon sectors. We highlight key challenges in developing high-precision three-body forces, such as the need to maintain consistency between two- and many-body interactions and constraints placed by the chiral and gauge symmetries after regularization.]]>https://www.frontiersin.org/articles/10.3389/fphy.2020.00102
https://www.frontiersin.org/articles/10.3389/fphy.2020.00102
Studies on Nuclear Structure and Nuclear Dynamics Using Cb-TDHFB2020-04-09T00:00:00ZShuichiro EbataIn this paper, we briefly review the studies on nuclear structure and nuclear dynamics using the Canonical-basis time-dependent Hartree-Fock-Bogoliubov (Cb-TDHFB) theory which is one of the time-dependent mean-field models which deal with nuclear pairing correlation. At first, after a brief introduction of the time-dependent mean-field models, we explain the derivation and the properties of Cb-TDHFB equations. Next, we introduce the methods to study the nuclear linear responses and to simulate the nuclear collision in terms of the time-dependent mean-field models. Then, we display parts of the results obtained by using the time-dependent methods; Strength functions of electric dipole (E1) excitation mode of ^{172}Yb, Systematic study of low-energy E1 mode, and Comparison of the simulations of the fusion reactions using time-dependent mean-field models with and without pairing correlation. Finally, we summarize the Cb-TDHFB activities and discuss its perspectives.]]>https://www.frontiersin.org/articles/10.3389/fphy.2020.00069
https://www.frontiersin.org/articles/10.3389/fphy.2020.00069
The Hyperspherical Harmonics Method: A Tool for Testing and Improving Nuclear Interaction Models2020-04-07T00:00:00ZLaura E. MarcucciJérémy Dohet-EralyLuca GirlandaAlex GnechAlejandro KievskyMichele VivianiThe Hyperspherical Harmonics (HH) method is one of the most accurate techniques to solve the quantum mechanical problem for nuclear systems with a number of nucleons A ≤ 4. In particular, by applying the Rayleigh-Ritz or Kohn variational principle, both bound and scattering states can be addressed, using either local or non-local interactions. Thanks to this versatility, the method can be used to test the two- and three-nucleon components of the nuclear interaction. In the present review we introduce the formalism of the HH method, both for bound and scattering states. In particular, we describe the implementation of the method to study the A = 3 and 4 scattering problems. Second, we present a selected choice of results of the last decade, most representative of the latest achievements. Finally, we conclude with a discussion of what we believe will be the most significant developments within the HH method for the next 5–10 years.]]>https://www.frontiersin.org/articles/10.3389/fphy.2020.00093
https://www.frontiersin.org/articles/10.3389/fphy.2020.00093
TDHF and a Macroscopic Aspect of Low-Energy Nuclear Reactions2020-04-03T00:00:00ZKouhei WashiyamaKazuyuki SekizawaTime-dependent Hartree–Fock (TDHF) method has been applied to various low-energy nuclear reactions, such as fusion, fission, and multinucleon transfer reactions. In this Mini Review, we summarize recent attempts to bridge a microscopic nuclear reaction theory, TDHF, and a macroscopic aspect of nuclear reactions through nucleus–nucleus potentials and energy dissipation from macroscopic degrees of freedom to microscopic ones obtained from TDHF in various colliding systems from light to heavy mass regions.]]>https://www.frontiersin.org/articles/10.3389/fphy.2020.00067
https://www.frontiersin.org/articles/10.3389/fphy.2020.00067
Applications of Time-Dependent Density-Matrix Approach2020-03-25T00:00:00ZMitsuru TohyamaThe equations of motion for reduced density matrices form a coupled chain known as the Bogoliubov-Born-Green-Kirkwood-Yvon (BBGKY) hierarchy. To close the coupled chain at the two-body level, approximations for a three-body density matrix with one-body and two-body density matrices are needed. The time-dependent density-matrix theory (TDDM) assumes that the three-body density matrix is given by the antisymmetrized products of the one-body and two-body density matrices. In this review the truncation schemes of the BBGKY hierarchy beyond TDDM are discussed and a formulation for the study of excited states which is derived from the time-dependent approach is explained. The truncation schemes and the formulation for excited states are applied to the Lipkin model and the Hubbard model to corroborate their validity. Two realistic applications of the TDDM approaches are also presented. One is the dipole and quadrupole excitations of ^{40}Ca and ^{48}Ca and the other the fusion reactions of ^{16}O + ^{16}O.]]>https://www.frontiersin.org/articles/10.3389/fphy.2020.00063
https://www.frontiersin.org/articles/10.3389/fphy.2020.00063
Nuclear Fission Dynamics: Past, Present, Needs, and Future2020-03-18T00:00:00ZAurel BulgacShi JinIonel StetcuSignificant progress in the understanding of the fission process within a microscopic framework has been recently reported. Even though the complete description of this important nuclear reaction remains a computationally demanding task, recent developments in theoretical modeling and computational power have brought current microscopic simulations to the point where they can provide guidance and constraints to phenomenological models, without making recourse to parameters. An accurate treatment compatible with our understanding of the inter-nucleon interactions should be able to describe the real-time dynamics of the fissioning system and could justify or rule out assumptions and approximations incompatible with the underlying universally accepted quantum-mechanical framework. Of particular importance are applications to observables that cannot be directly measured in experimental setups (such as the angular momentum distribution of the fission fragments, or the excitation energy sharing between the fission fragments, or fission of nuclei formed during the r-process), and their dependence of the excitation energy in the fissioning system. Even if accurate predictions are not within reach, being able to extract the trends with increasing excitation energy is important in various applications. The most advanced microscopic simulations of the fission process do not support the widely used assumption of adiabaticity of the large amplitude collective motion in fission, in particular for trajectories from the outer saddle toward the scission configuration. Hence, the collective potential energy surface and inertia tensor, which are the essential elements of many simplified microscopic theoretical approaches, become irrelevant. In reality, the dynamics of the fissioning system is slower than in the case of pure adiabatic motion by a factor of three to four times and is strongly overdamped. The fission fragment properties are defined only after the full separation, while in most of the current approaches no full separation can be achieved, which increases the uncertainties in describing fission-related observables in such methods.]]>https://www.frontiersin.org/articles/10.3389/fphy.2020.00057
https://www.frontiersin.org/articles/10.3389/fphy.2020.00057
Nucleon-Nucleon Scattering Up to N5LO in Chiral Effective Field Theory2020-03-18T00:00:00ZDavid Rodriguez EntemRuprecht MachleidtYevgen NosykDuring the past few decades a large effort has been made toward describing the NN interaction in the framework of chiral Effective Field Theory (EFT). The main idea is to exploit the symmetries of QCD to obtain an effective theory for low energy nuclear systems. In 2003, the first accurate charge-dependent NN potential in this scheme was developed and it has been applied to many ab-initio calculations, opening the possibility to study nuclear systems in a systematic and accurate way. It was shown that the fourth order (N^{3}LO) was necessary and sufficient to describe the NN scattering data with a χ^{2}/d.o.f on the order of so-called high precision potentials. However the systematics of chiral EFT also allow to relate two- and many-body interactions in a well-defined way. Since many-body forces make their first appearance at higher order, they are substantially smaller than their two-body counterparts, but may never-the-less be crucial for some processes. Thus, there are observables where they can have a big impact and, for example, there are indications that they solve the long standing A_{y} puzzle of N-d scattering. The last few years, have also seen substantial progress toward higher orders of chiral EFT which was motivated by the fact that only three-body forces of rather high order may solve some outstanding issues in microscopic nuclear structure and reactions. In this chapter we will review the latest contributions of the authors to development of chiral EFT based potentials up to N^{4}LO as well as first calculations conducted for NN scattering at N^{5}LO.]]>https://www.frontiersin.org/articles/10.3389/fphy.2020.00014
https://www.frontiersin.org/articles/10.3389/fphy.2020.00014
Fusion Dynamics of Low-Energy Heavy-Ion Collisions for Production of Superheavy Nuclei2020-02-28T00:00:00ZXiao Jun BaoOne of the major motivations for low-energy heavy-ion collision is the synthesis of superheavy nuclei. Based on the following two main aspects, various theoretical and experimental studies have been performed to explore the fusion dynamical process of superheavy nuclei production. The first reason is to elucidate and analyze the synthesis mechanism of superheavy nuclei; the other is to search the favorable incident energy and the best combination of projectile and target to produce new superheavy elements and isotopes of superheavy elements.]]>