Nuclear Theory·nucl-th

Tuesday·October 10, 2023

11 papers—5 primary·6 cross-listed

01
Normalizing Flows for Bayesian Posteriors: Reproducibility and Deployment
Yukari Yamauchi · Landon Buskirk · Pablo Giuliani · Kyle Godbey
We present a computational framework for efficient learning, sampling, and distribution of general Bayesian posterior distributions. The framework leverages a machine learning approach for the construction of normalizing flows for the general probability distributions typically encountered in Bayesian uncertainty quantification studies. This normalizing flow can map a trivial distribution to a more complicated one and can be stored more efficiently than the empirical distribution samples themselves. Once the normalized flow is trained, it further enables parallelized and uncorrelated sampling of the learned distribution. We demonstrate our framework with three test distributions with strong non-linear correlations, multi-modality, and heavy tails, as well as with a realistic posterior distribution obtained from a Bayesian calibration of a nuclear relativistic mean-field model. The performance of the framework, as well as its relatively simple implementation, positions it as one fundamental cornerstone in the development and deployment of continuous calibration pipelines of physical models and as a key component of future reproducible science workflows.
nucl-th6 citations
02
Importance of physical information on the prediction of heavy-ion fusion cross section with machine learning
Zhilong Li · Zepeng Gao · Ling Liu · Yongjia Wang · Long Zhu · Qingfeng Li
In this work, the Light Gradient Boosting Machine (LightGBM), which is a modern decision tree based machine-learning algorithm, is used to study the fusion cross section (CS) of heavy-ion reaction. Several basic quantities (e.g., mass number and proton number of projectile and target) and the CS obtained from phenomenological formula are fed into the LightGBM algorithm to predict the CS. It is found that, on the validation set, the mean absolute error (MAE) which measures the average magnitude of the absolute difference between $l o g_{10}$ of the predicted CS and experimental CS is 0.129 by only using the basic quantities as the input, this value is smaller than 0.154 obtained from the empirical coupled channel model. MAE can be further reduced to 0.08 by including an physical-informed input feature. The MAE on the test set (it consists of 280 data points from 18 reaction systems that not included in the training set) is about 0.19 and 0.53 by including and excluding the physical-informed feature, respectively. We further verify the LightGBM predictions by comparing the CS of $^{40, 48} Ca$ + $^{78} Ni$ obtained from the density-constrained time-dependent Hartree-Fock approach. Our study demonstrates the importance of physical information in predicting fusion cross section of heavy-ion reaction with machine learning.
nucl-thnucl-exPRC(2024)·17 citations
03
Impact of choices for center-of-mass correction energy on the surface energy of Skyrme energy density functionals
Philippe Da Costa🇫🇷 · Karim Bennaceur🇫🇷 · Jacques Meyer🇫🇷 · Wouter Ryssens🇧🇪 · Michael Bender🇫🇷
In the framework of nuclear energy density functional (EDF) methods, many nuclear phenomena can be related to the deformation of intrinsic states. Their accurate modeling relies on the correct description of the change of nuclear binding energy with deformation. The two most important contributions to the deformation energy have their origin in shell effects and the surface energy coefficient of nuclear matter. In a first step, we build nine series of parametrizations with a systematically varied surface-energy coefficient a_surf for three frequently-used options for the CM correction (none, one-body term only, full one-body and two-body contributions) combined with three values for the isoscalar effective mass m^*_0/m (0.7, 0.8, 0.85) and analyse how well each of these parametrizations can be adjusted to the properties of spherical nuclei and infinite nuclear matter. In a second step, we performed additional fits without the constraint on surface energy, adding one ``best-fit" parametrization to each of the nine series. We then benchmark these parametrizations to the deformation properties of heavy nuclei by means of three-dimensional Hartree-Fock-Bogoliubov calculations that allow for non-axial and/or non-reflection symmetric configurations. We perform a detailed correlation analysis between surface and volume properties of nuclear matter using the nine series of parametrizations. The best fits out of each series are then benchmarked on the fission barriers of Pu240 and Hg180, as well as on the properties of deformed states at normal and superdeformation for actinides and nuclei in the neutron-deficient Hg region. (see paper for full abstract)
nucl-thPRC(2024)·7 citations
04
Precise neural network predictions of energies and radii from the no-core shell model
Tobias Wolfgruber · Marco Knöll · Robert Roth
For light nuclei, ab initio many-body methods such as the no-core shell model are the tools of choice for predictive, high-precision nuclear structure calculations. The applicability and the level of precision of these methods, however, is limited by the model-space truncation that has to be employed to make such computations feasible. We present a universal framework based on artificial neural networks to predict the value of observables for an infinite model-space size based on finite-size no-core shell model data. Expanding upon our previous ansatz of training the neural networks to recognize the observable-specific convergence pattern with data from few-body nuclei, we improve the results obtained for ground-state energies and show a way to handle excitation energies within this framework. Furthermore, we extend the framework to the prediction of converged root-mean-square radii, which are more difficult due to the much less constrained convergence behavior. For all observables robust and statistically significant uncertainties are extracted via the sampling over a large number of network realizations and evaluation data samples.
nucl-thPRC(2024)·26 citations
05
Interactions of $ω$ -Mesons in Nuclear Matter and with Nuclei
Horst Lenske🇩🇪
In--medium interactions of $ω$ --mesons are investigated microscopically by coupling to $N N^{- 1}$ and $N^{*} N^{- 1}$ particle--hole excitations of the medium, including elativistic mean--field dynamics by self--consistent scalar and vector fields. The resulting self--energies are transmitted to finite nuclei in local density approximation. Real and imaginary parts of longitudinal and transversal self--energies are discussed. The relation of the present approach to meson cloud models is addressed and an ambiguity is pointed out. Applications to recent data on the in--medium width of $ω$ mesons scattered on a Niobium target serve to determine unknown $N^{*} N ω$ in-medium coupling constants. The data are well described by $N^{*} N^{- 1}$ self--energies containing S--wave and P--wave $N^{*}$ resonances. Exploratory investigations, however, show that the spectroscopic composition of self--energies depends crucially on the near--threshold properties of the width which at present is known only within large error bars. The calculations predict the prevalence of transversal self--energies, implying that vector current conservation is still maintained in the nuclear medium by slightly more than 90\%. Schrödinger--equivalent potentials are derived and scattering lengths and effective range parameters are extracted for the longitudinal and transversal channel. Longitudinal and transversal spectral distributions are discussed and the dependencies on momentum and nuclear density are investigated. Schrödinger--type $ω +^{93}$ Nb optical potentials are constructed. Low--energy parameters are determined, are used to study the pole structure of the S--matrix at threshold. The effective range expansion of the omega--nucleus K--matrix led to a $ω +^{93}$ Nb bound states with binding energy $R e (ε_{B}) = - 448$ ~keV but of width $Γ_{B} = 4445$ ~keV.
nucl-thEPJA(2023)·7 citations
06
Impact of global monopole on heavy mesons in hot-dense medium
M. Abu-Shady🇪🇬 · Faizuddin Ahmed🇮🇳
This research study is primarily focus on investigating how the topological effects influence the eigenvalue solutions in the presence of a hot-dense medium. To accomplish this, we employ the non-relativistic Schrödinger wave equation, taking into consideration both the quantum flux field and an interaction potential. Through this approach, we determine the energy eigenvalues and their corresponding wave functions using the Nikiforov-Uvarov method. Our findings indicate that when we consider both the topological effects and the magnetic flux, $Φ$ , there is a noticeable reduction in the binding energy within the hot-dense medium. Additionally, we analyze the role of the baryonic potential in shaping the binding energy within the $(T, u_{b})$ plane. Interestingly, it is evident that the influence of the baryonic potential becomes more pronounced as its values decrease
↳ hep-thnucl-thquant-phInt.J.Mod.Phys.A(2024)·2 citations
07
Candidate toroidal electric dipole mode in the spherical nucleus $^{58}$ Ni
P. von Neumann-Cosel (1) · V.O. Nesterenko (2,3) · I. Brandherm (1) · P.I. Vishnevskiy (2,4) · P.-G. Reinhard (5) · J. Kvasil (6) · H. Matsubara (7,8) · A. Repko (9) · A. Richter (1) · M. Scheck (10,11) · A. Tamii (7) ((1) Institut für Kernphysik, Technische Universität Darmstadt, Darmstadt, Germany, (2) Laboratory of Theoretical Physics, Joint Institute for Nuclear Research, Dubna, Russia, (3) State University "Dubna", Dubna, Moscow region, Russia, (4) Institute of Nuclear Physics Almaty, Almaty Region, Kazakhstan, (5) Institut für Theoretische Physik II, Universität Erlangen, Erlangen, Germany, (6) Institute of Particle and Nuclear Physics, Charles University, Praha, Czech Republic, (7) Research Center for Nuclear Physics, Osaka University, Ibaraki, Osaka, Japan, (8) Faculty of Radiological Technology, Fujita Health University, Aichi, Japan, (9) Institute of Physics, Slovak Academy of Sciences, Bratislava, Slovakia, (10) School of Computing, Engineering, and Physical Sciences, University of the West of Scotland, Paisley, United Kingdom, (11) Scottish Universities Physics Alliance, United Kingdom)
Dipole toroidal modes appear in many fields of physics. In nuclei, such a mode was predicted more than 50 years ago, but clear experimental evidence was lacking so far. Using a combination of high-resolution inelastic scattering experiments with photons, electrons and protons, we identify for the first time candidates for toroidal dipole excitations in the nucleus $^{58}$ Ni and demonstrate that transverse electron scattering form factors represent a relevant experimental observable to prove their nature.
↳ nucl-exnucl-thPRL(2024)·18 citations
08
On the Microscopic Level Density Models for Nuclei Near Z=28 Shell Closure
Surayya H.E (1) · Jesmi Sunny (1) · M.M Musthafa (1) · C.V Midhun (1) · S.V Suryanarayana (2) · Jyoti Pandey (3) · A Pal (2) · P.C Rout (2) · S Santra (2) · Antony Joseph (1) · S. Ganesan (4). (Department of Physics, University of Calicut, Kerala, India (1), Nuclear Physics Division, Bhabha Atomic Research Centre, Mumbai 400085, India (2), Inter University Accelerator Centre, New Delhi, Delhi 110067, India (3) and Formarly Raja Ramanna Fellow, Bhabha Atomic Research Centre, Mumbai 400085, India (4))
A comprehensive test of level density models for explaining the decay of excited compound nuclei, 54 Mn, 56 Fe, 58 Co, 60 Ni, 61 Ni and 63 Cu, in the energy range of 28 - 36 MeV has been performed. The compound nuclei of interest in the desired ranges are populated using 6 Li based transfer reactions. The proton decay spectrum for each excitation energy bins has been measured. The measured proton spectrum has been reproduced using statistical model calculations with different level density models. A variance minimised approach has been employed for analysing the prediction capability of different level density models. This approach has been converged to Gogny Hartree-Fock-Bogoliubov(HFB) microscopic level density model and which is attributed as the most accurate model for the desired nuclei.
↳ nucl-exnucl-thPRC(2025)·0 citations
09
Normal mode analysis within a mutilated relaxation time approximation
Jin Hu🇨🇳
In this paper, we present a detailed analysis of normal modes based on the Boltzmann equation within the mutilated relaxation time approximation (RTA). Using this linearized effective kinetic description, our analysis encompasses a complete order calculation in wavenumber k, extending the conventional hydrodynamic mode analysis to intermediate and short-wavelength regions. Furthermore, our linear mode analysis can provide a natural classification of kinetic modes into collective modes and non-collective single-particle excitations. In the case of an energy-independent relaxation time, the behavior of hydrodynamic onset transitions is recovered (Romatschke in Eur Phys J C 76:352, 2016). However, for the case with an energy-dependent relaxation time, the distinct classification becomes less clear, as the location of hydrodynamic modes is not well separated from non-hydrodynamic modes.
↳ hep-phnucl-thEPJC(2025)·4 citations
10
A new approach to the 3-momentum regularization of the in-medium one and two fermion line integrals with applications to cross sections in the Nambu--Jona-Lasinio model
Renan Câmara Pereira🇵🇹 · João Moreira🇵🇹 · Pedro Costa🇵🇹 · Constança Providência🇵🇹
We propose the 3-momentum sphere intersection regularization applied to the one and two fermion line integrals at finite temperature and chemical potential. The quark-antiquark polarization function in this new regularization approach is equivalent to the usual 3-momentum regularization, when the absolute value of the external 3-momentum of the polarization is zero. Additionally, it respects the particle-antiparticle symmetry of meson states in the Nambu $-$ Jona-Lasinio (NJL) model for all values of temperature and chemical potential. Without this symmetry, in-medium cross sections calculated in the 3-momentum regularized NJL model are not consistent. In order to demonstrate the difference between the usual 3-momentum regularization with the one proposed in this work, we study the quark-quark and quark-antiquark cross sections in both regularization schemes. To this end we use the standard $S U (3)$ NJL model, with four and six quark interactions. We observe major quantitative and qualitative differences when comparing quark-quark cross sections in both schemes. The quark-antiquark cross sections, on the other hand, are very similar in both regularizations, owning to the equivalence between the regularizations when the absolute value of the external 3-momentum is zero.
↳ hep-phnucl-thPRC(2024)·1 citation
11
Collective modes of a massive fermion in a magnetized medium with finite anomalous magnetic moment
Nilanjan Chaudhuri🇮🇳 · Snigdha Ghosh🇮🇳 · Pradip Roy🇮🇳 · Sourav Sarkar🇮🇳
We calculate, in a systematic way, the general structure of the self-energy of light massive fermions and the effective propagator in a thermomagnetic medium with the inclusion of anomalous magnetic moment (AMM) of the fermion in the weak field approximation. It is found that the self-energy of a massive fermion in this case consists of five non-trivial structure factors in contrast to the massless case where the self-energy contains only four. We employ the real time formalism (RTF) of thermal field theory within the ambit of hard thermal loop (HTL) approximation in the evaluation of the structure factors. The collective modes are obtained from the poles of the effective propagator of the fermion. The investigation of the dispersion relations for non-degenerate ground state shows that the effect of the magnetic field is more for up quark than the down quark because of the larger charge of the former. The important observation is that in the first excited state the degeneracy, which exists for non-zero magnetic field is lifted due to the inclusion of the AMM. It is also observed that the first excited state becomes less dispersive compared to the case when AMM is not considered, whereas the second excited state becomes more dispersive when both the magnetic field and the AMM are non-zero in comparison to the case with vanishing AMM. These effects are observed in both particle and hole-like excitations. Qualitatively similar behaviour is also seen in the case of down quarks.
↳ hep-phnucl-thPRD(2023)·9 citations

Affiliations

first authorsco-authorsvia INSPIRE