Nuclear Theory·nucl-th

Tuesday·February 23, 2021

22 papers—12 primary·10 cross-listed

01
In-medium $k$ -body reduction of $n$ -body operators
Mikael Frosini🇫🇷 · Thomas Duguet🇫🇷 · Benjamin Bally🇪🇸 · Yann Beaujeault-Taudière🇫🇷 · Jean-Paul Ebran🇫🇷 · Vittorio Somà🇫🇷
The computational cost of ab initio nuclear structure calculations is rendered particularly acute by the presence of (at least) three-nucleon interactions. This feature becomes especially critical now that many-body methods aim at extending their reach beyond mid-mass nuclei. Consequently, state-of-the-art ab initio calculations are typically performed while approximating three-nucleon interactions in terms of effective, i.e. system-dependent, zero-, one- and two-nucleon operators. While straightforward in doubly closed-shell nuclei, existing approximation methods based on normal-ordering techniques involve either two- and three-body density matrices or a symmetry-breaking one-body density matrix in open-shell systems. In order to avoid such complications, a simple, flexible, universal and accurate approximation technique involving the convolution of the initial operator with a sole symmetry-invariant one-body matrix is presently formulated and tested numerically. Employed with a low-resolution Hamiltonian, the novel approximation method is shown to induce errors below $2 - 3%$ across a large range of nuclei, observables and many-body methods.
nucl-thEPJA(2021)·57 citations
02
Elastic scattering of twisted neutrons by nuclei
A.V. Afanasev · D.V. Karlovets · V.G. Serbo
We present a theoretical formalism for scattering of the twisted neutrons by nuclei in a kinematic regime where interference between Coulomb interaction and the strong interaction is essential. Twisted neutrons have definite quantized values of an angular momentum projection along the direction of propagation, and we show that it results in novel observable effects for the scattering cross section, spin asymmetries and polarization of the scattered neutrons. We demonstrate that additional capabilities provided by beam's orbital angular momentum enable new techniques for measuring both real and imaginary parts of the scattering amplitude. Several possible observables are considered, for which the targets may be either well-localized with respect to the spatial beam profile, or the scattering occurs incoherently on nuclei in a bulk target. The developed approach can be applied to other nuclear reactions with strongly interacting twisted particles.
nucl-thquant-phPRC(2021)·23 citations
03
Self-consistent calculations of electron-capture decays in Z=118, 119, and 120 superheavy isotopes
Pedro Sarriguren🇪🇸
Weak decays in superheavy nuclei with proton numbers Z = 118 - 120 and neutron numbers N = 175 - 184 are studied within a microscopic formalism based on deformed self-consistent Skyrme Hartree-Fock mean-field calculations with pairing correlations. The half-lives of beta+ decay and electron capture are compared with alpha-decay half-lives obtained from phenomenological formulas. The sensitivity of the half-lives to the unknown Q-energies is studied by comparing the results obtained from different approaches for the masses. It is shown that alpha-decay is always dominant in this mass region. The competition between alpha and beta+/EC decay modes is studied in seven alpha-decay chains starting at different isotopes of Z=118, 119, and 120.
nucl-thnucl-exPLB(2021)·10 citations
04
Differential analysis of incompressibility in neutron-rich nuclei
Bao-An Li · Wen-Jie Xie
Both the incompressibility \Ka of a finite nucleus of mass A and that ( $K_{\infty}$ ) of infinite nuclear matter are fundamentally important for many critical issues in nuclear physics and astrophysics. While some consensus has been reached about the $K_{\infty}$ , accurate theoretical predictions and experimental extractions of $K_{τ}$ characterizing the isospin dependence of \Ka have been very difficult. We propose a differential approach to extract the \Kt and \Ki independently from the \Ka data of any two nuclei in a given isotope chain. Applying this new method to the \Ka data from isoscalar giant monopole resonances (ISGMR) in even-even Pb, Sn, Cd and Ca isotopes taken by U. Garg {\it et al.} at the Research Center for Nuclear Physics (RCNP), Osaka University, Japan, we find that the $^{106}$ Cd- $^{116}$ Cd and $^{112}$ Sn- $^{124}$ Sn pairs having the largest differences in isospin asymmetries in their respective isotope chains measured so far provide consistently the most accurate up-to-date \Kt value of $K_{τ} = - 616 \pm 59$ MeV and $K_{τ} = - 623 \pm 86$ MeV, respectively, largely independent of the remaining uncertainties of the surface and Coulomb terms in expanding the $K_{A}$ , while the $K_{\infty}$ values extracted from different isotopes chains are all well within the current uncertainty range of the community consensus for $K_{\infty}$ . Moreover, the size and origin of the "Soft Sn Puzzle" is studied with respect to the "Stiff Pb Phenomenon". It is found that the latter is favored due to a much larger (by $\sim 380$ MeV) \Kt for Pb isotopes than for Sn isotopes, while the \Ki from analyzing the \Ka data of Sn isotopes is only about 5 MeV less than that from analyzing the Pb data.
nucl-thastro-ph.HEnucl-exPRC(2021)·11 citations
05
On nonadditive anisotropic relativistic hydrodynamics
A.V. Leonidov🇷🇺
Non-additive generalisation of relativistic anisotropic anisotropic hydrodynamics is described. In the particular case of 0+1 boost-invariant hydrodynamics additional entropy production due to non-additivity is calculated.
nucl-thJETP Lett.(2021)·2 citations
06
ADG: Automated generation and evaluation of many-body diagrams III. Bogoliubov in-medium similarity renormalization group formalism
A. Tichai🇩🇪 · P. Arthuis🇩🇪 · H. Hergert🇺🇸 · T. Duguet🇫🇷
The goal of the present paper is twofold. First, a novel expansion many-body method applicable to superfluid open-shell nuclei, the so-called Bogoliubov in-medium similarity renormalization group (BIMSRG) theory, is formulated. This generalization of standard single-reference IMSRG theory for closed-shell systems parallels the recent extensions of coupled cluster, self-consistent Green's function or many-body perturbation theory. Within the realm of IMSRG theories, BIMSRG provides an interesting alternative to the already existing multi-reference IMSRG (MR-IMSRG) method applicable to open-shell nuclei. The algebraic equations for low-order approximations, i.e., BIMSRG(1) and BIMSRG(2), can be derived manually without much difficulty. However, such a methodology becomes already impractical and error prone for the derivation of the BIMSRG(3) equations, which are eventually needed to reach high accuracy. Based on a diagrammatic formulation of BIMSRG theory, the second objective of the present paper is thus to describe the third version (v3.0.0) of the ADG code that automatically (1) generates all valid BIMSRG(n) diagrams and (2) evaluates their algebraic expressions in a matter of seconds. This is achieved in such a way that equations can easily be retrieved for both the flow equation and the Magnus expansion formulations of BIMSRG. Expanding on this work, the first future objective is to numerically implement BIMSRG(2) (eventually BIMSRG(3)) equations and perform ab initio calculations of mid-mass open-shell nuclei.
nucl-thcond-mat.str-elcond-mat.supr-conphysics.chem-phEPJA(2022)·20 citations
07
Crust-core interface and bulk neutron star properties
Ch. Margaritis · P.S. Koliogiannis · A. Kanakis-Pegios · Ch.C. Moustakidis
The nuclear symmetry energy plays an important role in the description of the properties of finite nuclei as well as neutron stars. Especially, for low values of baryon density, the accurate description of the crust-core interface strongly depends on the symmetry energy. Usually, the well known parabolic approximation is employed for the definition of the symmetry energy without avoiding some drawbacks. In the present paper, a class of nuclear models, suitable for the description of the inner and outer core of neutron stars, is applied in studying the effect of higher orders of the expansion of the energy on the location of the crust-core transition. The thermodynamical and dynamical methods are used for the determination of the transition density $n_{t}$ and pressure $P_{t}$ . The corresponding energy density functional is applied for the study of some relevant properties of both nonrotating and slowly rotating neutron stars. We found that the larger the value of the slope parameter $L$ , the slower the convergence of the expansion. In addition, a universal relation is presented between $n_{t}$ and $L$ , by employing the full expression and dynamical approach. The crustal moment of inertia is very sensitive to the location of the transition while the effects are moderated concerning the critical angular velocity of the $r$ -mode instability and minimum mass configuration. The effect on the tidal deformability is less but not negligible. In any case, the use of the parabolic approximation leads to the overestimation of $n_{t}$ and $P_{t}$ and consequently, on inaccurate predictions. Moreover, in some cases, even the matching process at the interface may affect considerably the predictions, introducing errors of the same order with the one due to the employed method.
nucl-thastro-ph.HEPRC(2021)·13 citations
08
$γ γ$ decay as a probe of neutrinoless $β β$ decay nuclear matrix elements
B. Romeo🇪🇸 · J. Menéndez🇪🇸 · C. Peña🇪🇸
We study double gamma ( $γ γ$ ) decay nuclear matrix elements (NMEs) for a wide range of nuclei from titanium to xenon, and explore their relation to neutrinoless double-beta ( $0 ν β β$ ) NMEs. To favor the comparison, we focus on double-magnetic dipole transitions in the final $β β$ nuclei, in particular the $γ γ$ decay of the double isobaric analog of the initial $β β$ state into the ground state. For the decay with equal-energy photons, our large-scale nuclear shell model results show a good linear correlation between the $γ γ$ and $0 ν β β$ NMEs. Our analysis reveals that the correlation holds for $γ γ$ transitions driven by the spin or orbital angular momentum due to the dominance of zero-coupled nucleon pairs, a feature common to $0 ν β β$ decay. Our shell-model findings point out the potential of future $γ γ$ decay measurements to constrain $0 ν β β$ NMEs, which are key to answer fundamental physics questions based on $0 ν β β$ experiments.
nucl-thhep-exhep-phnucl-exPLB(2022)·29 citations
09
Implementation of local chiral interactions in the hyperspherical harmonics formalism
Simone Salvatore Li Muli · Sonia Bacca · Nir Barnea
With the goal of using chiral interactions at various orders to explore properties of the few-body nuclear systems, we write the recently developed local chiral interactions as spherical irreducible tensors and implement them in the hyperspherical harmonics expansion method. We devote particular attention to three-body forces at next-to-next-to leading order, which play an important role in reproducing experimental data. We check our implementation by benchmarking the ground-state properties of $^{3}$ H, $^{3}$ He and $^{4}$ He against the available Monte Carlo calculations. We then confirm their order-by-order truncation error estimates and further investigate uncertainties in the charge radii obtained by using the precise muonic atom data for single-nucleon radii. Having local chiral Hamiltonians at various orders implemented in our hyperspherical harmonics suites of codes opens up the possibility to test such interactions on other light-nuclei properties, such as electromagnetic reactions.
nucl-thFront.in Phys.(2021)·4 citations
10
Nonuniform-temperature effects on the phase transition in an Ising-like model
Jun-Hui Zheng🇳🇴 · Lijia Jiang🇨🇳
In this study, we investigate the spatially nonuniform-temperature effects on the QCD chiral phase transition in the heavy-ion collisions. Since the QCD effective theory and the Ising model belong to the same universality class, we start our discussion by mimicking the QCD effective potential with an Ising-like effective potential. In contrast to the dynamical slowing down effects which delays the phase transition from quark-gluon-plasma to hadron gas, the spatially nonuniform-temperature effects show a possibility to lift the phase transition temperature. Besides, both the fluctuations and the correlation length are enhanced in the phase transition region. Furthermore, the critical phenomena is strongly suppressed like as the critical slowing down effects. The underlying mechanism is the nonzero-momentum mode fluctuations of the order parameter induced by the nonuniform temperature. Our study provides a method to evaluate the nonuniform-temperature effects, and illustrate its potential influence on analyzing the QCD phase transition signals at RHIC.
nucl-thhep-phPRD(2021)·4 citations
11
In-medium similarity renormalization group with three-body operators
M. Heinz🇩🇪 · A. Tichai🇩🇪 · J. Hoppe🇩🇪 · K. Hebeler🇩🇪 · A. Schwenk🇩🇪
Over the past decade the in-medium similarity renormalization group (IMSRG) approach has proven to be a powerful and versatile ab initio many-body method for studying medium-mass nuclei. So far, the IMSRG was limited to the approximation in which only up to two-body operators are incorporated in the renormalization group flow, referred to as the IMSRG(2). In this work, we extend the IMSRG(2) approach to fully include three-body operators yielding the IMSRG(3) approximation. We use a perturbative scaling analysis to estimate the importance of individual terms in this approximation and introduce truncations that aim to approximate the IMSRG(3) at a lower computational cost. The IMSRG(3) is systematically benchmarked for different nuclear Hamiltonians for $^{4} He$ and $^{16} O$ in small model spaces. The IMSRG(3) systematically improves over the IMSRG(2) relative to exact results. Approximate IMSRG(3) truncations constructed based on computational cost are able to reproduce much of the systematic improvement offered by the full IMSRG(3). We also find that the approximate IMSRG(3) truncations behave consistently with expectations from our perturbative analysis, indicating that this strategy may also be used to systematically approximate the IMSRG(3).
nucl-thPRC(2021)·94 citations
12
The smallest fluid on earth
Björn Schenke🇺🇸
High energy heavy ion collisions create quark gluon plasmas that behave like almost perfect fluids. Very similar features to those that led to this insight have also been observed in experimental data from collisions of small systems, involving protons or other light nuclei. We describe recent developments aimed at understanding whether, and if so how, systems that produce relatively few particles (orders of magnitude less than in typical heavy ion collisions) and are only one to a few times the size of a proton, can behave like fluids. This involves a deeper understanding of fluid dynamics and its applicability, improvements of our understanding of the initial geometry of the collisions by considering fluctuations of the proton shape, as well as advancements in the calculation of initial state effects within an effective theory of quantum chromodynamics, which can affect the observables that are used to study fluid behavior. We further address open questions and discuss future directions.
nucl-thhep-phnucl-exRept.Prog.Phys.(2021)·108 citations

Affiliations

first authorsco-authorsvia INSPIRE