Nuclear Theory·nucl-th

Monday·April 19, 2021

10 papers—6 primary·4 cross-listed

01
Skyrme pseudopotentials at next-to-next-to-leading order Construction of local densities and first symmetry-breaking calculations
Wouter Ryssens🇧🇪 · Michael Bender🇫🇷
There is an ongoing quest to improve on the spectroscopic quality of nuclear energy density functionals (EDFs) of the Skyrme type through extensions of its traditional form. One direction for such activities is the inclusion of terms of higher order in gradients in the EDF. We report on exploratory symmetry-breaking calculations performed for an extension of the Skyrme EDF that includes central terms with four gradients at next-to-next-to-leading order (N2LO) and for which the high-quality parametrization SN2LO1 has been constructed recently [P. Becker et al, Phys. Rev. C 96, 044330 (2017)]. Up to now, the investigation of such functionals with higher-order terms was limited to infinite matter and spherically symmetric configurations of singly- and doubly-magic nuclei. We address here nuclei and phenomena that require us to consider axial and non-axial deformation, both for reflection-symmetric and also reflection-asymmetric shapes, as well as the breaking of time-reversal invariance. Achieving these calculations demanded a number of formal developments. These all resulted from the formulation of the N2LO EDF requiring the introduction of new local densities with additional gradients that are not present in the EDF at NLO. Their choice is not unique, but can differ in the way the gradients are coupled. While designing a numerical implementation of N2LO EDFs in Cartesian 3d coordinate-space representation, we have developed a novel definition and a new unifying notation for normal and pair densities that contain gradients at arbitrary order. The resulting scheme resolves several issues with some of the choices that have been made for local densities in the past, in particular when breaking time-reversal symmetry. Guided by general practical considerations, we propose an alternative form of the N2LO contribution to the Skyrme EDF that is built from a different set of densities.
nucl-thPRC(2021)·10 citations
02
The X17 boson and the $^{3}$ H $(p, e^{+} e^{-})^{4}$ He and $^{3}$ He $(n, e^{+} e^{-})^{4}$ He processes: a theoretical analysis
M. Viviani🇮🇹 · E. Filandri🇮🇹 · L. Girlanda🇮🇹 · C. Gustavino🇮🇹 · A. Kievsky🇮🇹 · L.E. Marcucci🇮🇹 · R. Schiavilla🇺🇸
The present work deals with $e^{+}$ - $e^{-}$ pair production in the four-nucleon system. We first analyze the process as a purely electromagnetic one in the context of a state-of-the-art approach to nuclear strong-interaction dynamics and nuclear electromagnetic currents, derived from chiral effective field theory ( $χ$ EFT). Next, we examine how the exchange of a hypothetical low-mass boson would impact the cross section for such a process. We consider several possibilities, that this boson is either a scalar, pseudoscalar, vector, or axial particle. The ab initio calculations use exact hyperspherical-harmonics methods to describe the bound state and low-energy spectrum of the $A$ = $4$ continuum, and fully account for initial state interaction effects in the $3 + 1$ clusters. While electromagnetic interactions are treated to high orders in the chiral expansion, the interactions of the hypothetical boson with nucleons are modeled in leading-order $χ$ EFT (albeit, in some instances, selected subleading contributions are also accounted for). We also provide an overview of possible future experiments probing pair production in the $A$ = $4$ system at a number of candidate facilities.facilities.
nucl-thnucl-exPRC(2022)·45 citations
03
Anisotropic flow decorrelation in heavy-ion collisions with event-by-event viscous hydrodynamics
Jakub Cimerman🇨🇿 · Iurii Karpenko🇨🇿 · Boris Tomášik🇨🇿 · Barbara Antonina Trzeciak🇨🇿
Decorrelation of the elliptic flow in rapidity is calculated within a hybrid approach which includes event-by-event viscous fluid dynamics and final state hadronic cascade model. The simulations are performed for Au+Au collisions at center-of-mass collision energies of 27 and 200 GeV per nucleon pair, as well as various colliding systems at 72 GeV per nucleon pair. Initial conditions determined by an extended Monte Carlo Glauber model show better agreement with experimental data than initial conditions from the UrQMD transport model. We show how the observed decorrelation is connected with the decorrelation of initial state spatial anisotropies. We also study how the effect is increased by the final state hadronic cascade.
nucl-thnucl-exPRC(2021)·9 citations
04
Microscopic description of quadrupole-octupole coupling in neutron-rich actinides and superheavy nuclei with the Gogny-D1M energy density functional
R. Rodriguez-Guzman🇰🇼 · L.M. Robledo🇪🇸
The interplay between quadrupole and octupole degrees of freedom is discussed in a series of neutron-rich actinides and superheavy nuclei with $92 \leq$ Z $\leq 110$ and $186 \leq$ N $\leq 202$ . In addition to the static Hartree-Fock-Bogoliubov approach, dynamical beyond-mean-field correlations are taken into account via both parity restoration and symmetry-conserving Generator Coordinate Method calculations based on the Gogny-D1M energy density functional. Physical properties such as correlation energies, negative-parity excitation energies as well as reduced transition probabilities $B (E 1)$ and $B (E 3)$ are discussed in detail. It is shown that, for the studied nuclei, the quadrupole-octupole coupling is weak and to a large extent the properties of negative parity states can be reasonably well described in terms of the octupole degree of freedom alone.
nucl-thPRC(2021)·23 citations
05
Estimation of nuclear matrix elements of double- $β$ decay from shell model and quasiparticle random-phase approximation
J. Terasaki🇨🇿 · Y. Iwata🇯🇵
The nuclear matrix element (NME) of the neutrinoless double- $β$ ( $0 ν β β$ ) decay is an essential input for determining the neutrino effective mass, if the half-life of this decay is measured. The reliable calculation of this NME has been a long-standing problem because of the diversity of the predicted values of the NME depending on the calculation method. In this paper, we focus on the shell model and the QRPA. The shell model have a rich amount of the many-particle many-hole correlations, and the QRPA can obtain the convergence of the result of calculation with respect to the extension of the single-particle space. It is difficult for the shell model to obtain the convergence of the $0 ν β β$ NME with respect to the valence single-particle space. The many-body correlations of the QRPA are insufficient depending on nuclei. We propose a new method to modify phenomenologically the results of the shell model and the QRPA compensating the insufficient point of each method by using the information of other method complementarily. Extrapolations of the components of the $0 ν β β$ NME of the shell model are made toward a very large valence single-particle space. We introduce a modification factor to the components of the $0 ν β β$ NME of the QRPA. Our modification method gives similar values of the $0 ν β β$ NME of the two methods for $^{48}$ Ca. The NME of the two-neutrino double- $β$ decay is also modified in a similar but simpler manner, and the consistency of the two methods is improved.
nucl-thnucl-exEur.Phys.J.Plus(2021)·9 citations
06
Solution of universal nonrelativistic nuclear DFT equations in the Cartesian deformed harmonic-oscillator basis. (IX) HFODD (v3.06h): a new version of the program
J. Dobaczewski🇬🇧 · P. Bączyk🇵🇱 · P. Becker🇬🇧 · M. Bender🇫🇷 · K. Bennaceur🇫🇷 · J. Bonnard🇬🇧 · Y. Gao🇫🇮 · A. Idini🇸🇪 · M. Konieczka🇵🇱 · M. Kortelainen🇫🇮 · L. Próchniak🇵🇱 · A.M. Romero🇬🇧 and 4 other authors
We describe the new version (v3.06h) of the code HFODD that solves the universal nonrelativistic nuclear DFT Hartree-Fock or Hartree-Fock-Bogolyubov problem by using the Cartesian deformed harmonic-oscillator basis. In the new version, we implemented the following new features: (i) zero-range three- and four-body central terms, (ii) zero-range three-body gradient terms, (iii) zero-range tensor terms, (iv) zero-range isospin-breaking terms, (v) finite-range higher-order regularized terms, (vi) finite-range separable terms, (vii) zero-range two-body pairing terms, (viii) multi-quasiparticle blocking, (ix) Pfaffian overlaps, (x) particle-number and parity symmetry restoration, (xi) axialization, (xii) Wigner functions, (xiii) choice of the harmonic-oscillator basis, (xiv) fixed Omega partitions, (xv) consistency formula between energy and fields, and we corrected several errors of the previous versions.
nucl-thJ.Phys.G(2021)·34 citations
07
Global Analysis of Leptophilic Z' Bosons
Andrzej J. Buras🇩🇪 · Andreas Crivellin🇨🇭 · Fiona Kirk🇨🇭 · Claudio Andrea Manzari🇨🇭 · Marc Montull🇨🇭
New neutral heavy gauge bosons ( $Z^{'}$ ) are predicted within many extensions of the Standard Model. While in case they couple to quarks the LHC bounds are very stringent, leptophilic $Z^{'}$ bosons (even with sizable couplings) can be much lighter and therefore lead to interesting quantum effects in precision observables (like $(g - 2)_{μ}$ ) and generate flavour violating decays of charged leptons. In particular, $ℓ \to ℓ^{'} ν ν ˉ$ decays, anomalous magnetic moments of charged leptons, $ℓ \to ℓ^{'} γ$ and $ℓ \to 3 ℓ^{'}$ decays place stringent limits on leptophilic $Z^{'}$ bosons. Furthermore, in case of mixing $Z^{'}$ with the SM $Z$ , $Z$ pole observables are affected. In light of these many observables we perform a global fit to leptophilic $Z^{'}$ models with the main goal of finding the bounds for the $Z^{'}$ couplings to leptons. To this end we consider a number of scenarios for these couplings. While in generic scenarios correlations are weak, this changes once additional constraints on the couplings are imposed. In particular, if one considers an $L_{μ} - L_{τ}$ symmetry broken only by left-handed rotations, or considers the case of $τ - μ$ couplings only. In the latter setup, on can explain the $(g - 2)_{μ}$ anomaly and the hint for lepton flavour universality violation in $τ \to μν ν ˉ / τ \to e ν ν ˉ$ without violating bounds from electroweak precision observables.
↳ hep-phhep-exnucl-exnucl-thJHEP(2021)·82 citations
08
Efficiency corrections for mutually inclusive variables and particle identification effect for mixed-cumulants in heavy-ion collisions
Arghya Chatterjee🇨🇳 · Toshihiro Nonaka🇯🇵 · ShinIchi Esumi🇯🇵 · Xiaofeng Luo🇨🇳
Mix-cumulants of conserved charge distributions are sensitive observables for probing properties of the QCD medium and phase transition in heavy-ion collisions. To perform precise measurements, efficiency correction is one of the most important step. In this study, using the binomial efficiency model, we derive efficiency correction formulas for mutually exclusive and inclusive variables. The UrQMD model is applied to verify the validity of these formulas for different types of correlations. Furthermore, we investigate the effect of the multiplicity loss and contamination emerging from the particle identifications. This study provides an important step toward future measurements of mixed-cumulants in relativistic heavy-ion collisions.
↳ physics.data-annucl-thCPC(2021)·2 citations
09
Collective flow in single-hit QCD kinetic theory
Aleksi Kurkela🇨🇭 · Aleksas Mazeliauskas🇨🇭 · Robin Törnkvist🇸🇪
Motivated by recent interest in collectivity in small systems, we calculate the harmonic flow response to initial geometry deformations within weakly coupled QCD kinetic theory using the first correction to the free-streaming background. We derive a parametric scaling formula that relates harmonic flow in systems of different sizes and different generic initial gluon distributions. We comment on similarities and differences between the full QCD effective kinetic theory and the toy models used previously. Finally we calculate the centrality dependence of the integrated elliptic flow $v_{2}$ in oxygen-oxygen, proton-lead and proton-proton collision systems.
↳ hep-phnucl-thJHEP(2021)·38 citations
10
Calculation of generating function in many-body systems with quantum computers: technical challenges and use in hybrid quantum-classical methods
Edgar Andres Ruiz Guzman🇫🇷 · Denis Lacroix🇫🇷
The generating function of a Hamiltonian $H$ is defined as $F (t) = ⟨ e^{- i t H} ⟩$ , where $t$ is the time and where the expectation value is taken on a given initial quantum state. This function gives access to the different moments of the Hamiltonian $⟨ H^{K} ⟩$ at various orders $K$ . The real and imaginary parts of $F (t)$ can be respectively evaluated on quantum computers using one extra ancillary qubit with a set of measurement for each value of the time $t$ . The low cost in terms of qubits renders it very attractive in the near term period where the number of qubits is limited. Assuming that the generating function can be precisely computed using quantum devices, we show how the information content of this function can be used a posteriori on classical computers to solve quantum many-body problems. Several methods of classical post-processing are illustrated with the aim to predict approximate ground or excited state energies and/or approximate long-time evolutions. This post-processing can be achieved using methods based on the Krylov space and/or on the $t$ -expansion approach that is closely related to the imaginary time evolution. Hybrid quantum-classical calculations are illustrated in many-body interacting systems using the pairing and Fermi-Hubbard models.
↳ quant-phcond-mat.str-elnucl-th18 citations

Affiliations

first authorsco-authorsvia INSPIRE