Nuclear Theory·nucl-th

Tuesday·June 16, 2020

17 papers—10 primary·7 cross-listed

01
Entanglement and correlation in two-nucleon systems
A T Kruppa · J Kovács · P Salamon · Ö Legeza
We examine the mode entanglement and correlation of two fermionic particles. We study the one- and two-mode entropy and a global characteristic, the one-body entanglement entropy. We consider not only angular momentum coupled states with single configuration but use the configuration interaction method. With the help of the Slater decomposition, we derive analytical expressions for the entanglement measures. We show that when the total angular momentum is zero specific single configurations describe maximally entangled states. It turns out that for a finite number of associated modes the one- and two-mode entropies have identical values. In the shell model framework, we numerically study two valence neutrons in the $s d$ shell. The one-body entanglement entropy of the ground state is close to the maximal value and the associated modes have the largest mutual information.
nucl-thcond-mat.str-elJ.Phys.G(2021)·39 citations
02
Least action and the maximum-coupling approximations in the theory of spontaneous fission
K. Hagino · G.F. Bertsch
We investigate the dynamics of spontaneous fission in a configuration-interaction (CI) approach. In that formalism the decay rate is governed by an effective interaction coupling the ground-state configuration and a fission doorway configuration, with the interaction strength determined by inverting a high-dimensioned CI Hamiltonian matrix that may have a block-tridiagonal structure. It is shown that the decay rate decreases exponentially with the number of blocks at a rate determined by the largest eigenvalue of a matrix in the block space for Hamiltonians with identical off-diagonal blocks. The theory is greatly simplified by approximations similar in spirit to the adiabatic and the least-action approximations in continuum representations. Here each block is replaced by a single matrix element. While the adiabatic reduction underestimates the coupling, a reduction based on a maximum-coupling approximation works well in a schematic CI model.
nucl-thPRC(2020)·6 citations
03
Nuclear-Elastic Scattering of $^{9}$ Be+ $^{4}$ He using the Proximity Potential
Austin A. Morris
A nuclear-elastic $^{9}$ Be+ $^{4}$ He reaction is investigated. A tangential literature overview of the proximity potential is presented, necessitated by an approximate method for calculating $l -values$ . The model is surveyed intensively, from classical conception (liquid drop model) to physical implication (fusion barrier height), leading to a second-part calculation of the $^{9}$ Be+ $^{4}$ He angular distribution. The results obtained are limited by the exclusion of phase variation, but provide enough accuracy to give order-of-magnitude estimates for nuclei interacting peripherally, in agreement with experiment.
nucl-th0 citations
04
Force and pressure in many-particle quantum dynamics
G.F. Bertsch
The Newtonian concept of force may be useful in some aspects of the dynamics of many-particle quantum systems such as fissioning nuclei. Following Ehrenfest's method, we show that the quantum kinetic force between parts of an extended quantum system can be described by an operator acting on the boundary between the two subsystems. The contribution to the force due to a short-ranged particle interaction can also be treated in the same way. This includes interaction effects treated in density functional theory by local functionals. The force operators are applied to several simple models to demonstrate the method.
nucl-thquant-ph0 citations
05
Bulk Viscous Damping of Density Oscillations in Neutron Star Mergers
Mark Alford🇺🇸 · Arus Harutyunyan🇦🇲 · Armen Sedrakian🇩🇪
In this paper, we discuss the damping of density oscillations in dense nuclear matter in the temperature range relevant to neutron star mergers. This damping is due to bulk viscosity arising from the weak interaction ``Urca'' processes of neutron decay and electron capture. The nuclear matter is modelled in the relativistic density functional approach. The bulk viscosity reaches a resonant maximum close to the neutrino trapping temperature, then drops rapidly as temperature rises into the range where neutrinos are trapped in neutron stars. We investigate the bulk viscous dissipation timescales in a post-merger object and identify regimes where these timescales are as short as the characteristic timescale $\sim$ 10 ms, and, therefore, might affect the evolution of the post-merger object. Our analysis indicates that bulk viscous damping would be important at not too high temperatures of the order of a few MeV and densities up to a few times saturation density.
nucl-thastro-ph.HEastro-ph.SRParticles(2020)·59 citations
06
Neutrino mixing in nuclear rapid neutron-capture processes
M. M. Saez🇦🇷 · O. Civitarese🇦🇷 · M. E. Mosquera🇦🇷
A possible mechanism for the formation of heavy-mass elements in supernovae is the rapid neutron-capture-mechanism (r-process). It depends upon the electron-fraction $Y_{e}$ , a quantity which is determined by beta-decay-rates. In this paper, we focus on the calculation of electroweak decay-rates in presence of massive neutrinos. The resulting expressions are then used to calculate nuclear reactions entering the rapid-neutron capture. We fix the astrophysical parameters to the case of a core-collapse supernova. The neutrino sector includes a mass scheme and mixing angles for active neutrinos, and also by including the mixing between active and sterile neutrinos. The results of the calculations show that the predicted abundances of heavy-mass nuclei are indeed affected by the neutrino mixing.
nucl-thhep-phIJMPE(2020)·1 citation
07
Structure of the ground and excited states in $_{Λ}^{9}$ Be nucleus
Yu. A. Lashko🇺🇦 · A. V. Nesterov🇺🇦 · V. S. Vasilevsky🇺🇦
We investigate properties of bound and resonance states in the $_{Λ}^{9}$ Be nucleus. To reveal the nature of these states, we use a three-cluster $2 α + Λ$ microscopic model. The model incorporates Gaussian and oscillator basis functions and reduces a three-cluster Schrödinger equation to a two-body like many-channel problem with the two-cluster subsystems ( $_{Λ}^{5}$ He and $^{8}$ Be) being in a bound or a pseudo-bound state. Influence of the cluster polarization on the energy and widths of resonance states in $_{Λ}^{9}$ Be and on elastic and inelastic $_{Λ}^{5}$ He+ $α$ scattering is analyzed.
nucl-thNPA(2021)·4 citations
08
Analytic insights on the information content of new observables
Wei-Chia Chen · J. Piekarewicz
Uncertainty quantification has emerged as a rapidly growing field in nuclear science. Theoretical predictions of physical observables often involve extrapolations to regions that are poorly constrained by laboratory experiments and astrophysical observations. Without properly quantified theoretical errors, such model predictions are of limited value. Also, one often deals with theoretical constructs that involve fundamental quantities that are not accessible to experiment or observation. Particularly relevant in this context is the pressure of pure neutron matter. In this contribution we develop an analytic framework to answer the question of "How can new data reduce uncertainties of current theoretical models?" [P.-G. Reinhard and W. Nazarewicz, Phys. Rev. C81, 051303(R) (2010)]. Simple and insightful expressions are obtained to quantify the impact of one or two new observables on theoretical uncertainties in two critical quantities: the slope of the symmetry energy at saturation density and the pressure of pure neutron matter at twice nuclear matter saturation density.
nucl-thastro-ph.SRnucl-exPRC(2020)·2 citations
09
Spectroscopic factors, overlaps, and isospin symmetry from an $R$ -matrix point of view
Carl R. Brune
Background: Spectroscopic factors, overlaps, and isospin symmetry are often used in conjunction with single-particle wave functions for the phenomenological analysis of nuclear structure and reactions. Many differing prescriptions for connecting these quantities to physically relevant asymptotic normalization constants or widths are available in the literature, but their relationship and degree of validity are not always clear. Purpose: This paper derives relationships among the above quantities of interest using well-defined methodology and starting assumptions. Method: $R$ -matrix theory is used as the primary tool to interoperate between the quantities of interest to this work. Particular attention is paid to effects arising from beyond the nuclear surface, where isospin symmetry is strongly violated. Results: Relationships among the quantities of interest are derived. Example applications of these methods to mirror levels in nucleon+ $^{12} C$ , nucleon+ $^{16} O$ , and nucleon+ $^{26} Al$ are presented. A new approach to multi-level mirror symmetry is derived and applied to the first three $2^{+}$ states of $^{18} O$ and $^{18} Ne$ . Conclusions: The relationship between the quantities of interest is clarified and certain procedures are recommended. It is found that the asymptotic normalization constant of the second $2^{+}$ state in $^{18} Ne$ deduced from the mirror state in $^{18} O$ is significantly larger than found in previous work. This finding has the effect of increasing the $^{17} F (p, γ)^{18} Ne$ reaction rate in novae.
nucl-thPRC(2020)·11 citations
10
Influence of pairing and deformation on charge exchange transitions
A. Carranza M.🇲🇽 · S. Pittel🇺🇸 · Jorge G. Hirsch🇲🇽
We describe the importance of charge-exchange reactions, and in particular Gamow-Teller transitions, in astrophysical processes and double beta decay, and in understanding of nuclear structure. We first provide an overview of the central role played by the isovector pairing and the quadrupole-quadrupole channels in the description of energy spectra and in the manifestation of collective modes, some associated with deformation of the nuclear shape. We then turned our focus to Gamow-Teller (GT) transitions in relatively light nuclei, especially in the 2p1f shell, where isoscalar pairing may be playing a role in competition with the isovector pairing that dominates in heavier regions. Following a summary of the progress made in recent years on this subject, we report a systematic shell model study aimed at providing further clarification as to how these pairing modes compete. In this study, we use a schematic Hamiltonian that contains a quadrupole-quadrupole interaction as well as both isoscalar and isovector pairing interactions. We first find an optimal set of Hamiltonian parameters for the model, to provide a starting point from which to vary the relevant pairing strengths and thus assess how this impacts the behavior of GT transitions and the corresponding energy spectra and rotational properties of the various nuclei involved in the decays. The analysis includes as an important theme a comparison with experimental data. The need to suppress the isoscalar pairing mode when treating nuclei with a neutron excess to avoid producing spurious results for the ground state spin and parity with the simplified Hamiltonian is highlighted. Varying the strength parameters for the two pairing modes is found to exhibit different but systematic effects on GT transition properties and on the corresponding energy spectra, which are detailed. (abridged)
nucl-thRev.Mex.Fis.(2020)·0 citations
11
Power expansion for heavy quarkonium production at next-to-leading order in $e^{+} e^{-}$ annihilation
Kyle Lee🇺🇸 · George Sterman🇺🇸
We study heavy quarkonium production associated with gluons in $e^{+} e^{-}$ annihilation as an illustration of the perturbative QCD (pQCD) factorization approach, which incorporates the first nonleading power in the energy of the produced heavy quark pair. We show how the renormalization of the four-quark operators that define the heavy quark pair fragmentation functions using dimensional regularization induces "evanescent" operators that are absent in four dimensions. We derive closed forms for short-distance coefficients for quark pair production to next-to-leading order ( $α_{s}^{2}$ ) in the relevant color singlet and octet channels. Using non-relativistic QCD (NRQCD) to calculate the heavy quark pair fragmentation functions up to $v^{4}$ in the velocity expansion, we derive analytical results for the differential energy fraction distribution of the heavy quarkonium. Calculations for $^{3} S_{1}^{[1]}$ and $^{1} S_{0}^{[8]}$ channels agree with analogous NRQCD analytical results available in the literature, while several color-octet calculations of energy fraction distributions are new. We show that the remaining corrections due to the heavy quark mass fall off rapidly in the energy of the produced state. To explore the importance of evolution at energies much larger than the mass of the heavy quark, we solve the renormalization group equation perturbatively to two-loop order for the $^{3} S_{1}^{[1]}$ case.
↳ hep-phnucl-thJHEP(2020)·5 citations
12
Anomalous scattering and transport in chiral matter
Kirill Tuchin🇺🇸
Chiral anomaly modifies the scattering processes in chiral systems which can be computed using the Maxwell-Chern-Simons theory that couples electrodynamics to the pseudoscalar field $θ$ describing the topological charge induced be external sources. Assuming slow variation of the topological charge density, the fermion scattering cross section is computed in the Born approximation and is found to have a resonance at the scattering angles proportional to the chiral conductivity. As a result, the transport coefficients are suppressed at high temperatures. The anisotropy of the cross section arises due to the spatial variation of the topological charge; its effect on the electrical conductivity is discussed.
↳ hep-phcond-mat.mes-hallnucl-thPLB(2020)·7 citations
13
A new consistent Neutron Star Equation of State from a Generalized Skyrme model
Christoph Adam🇪🇸 · Alberto García Martín-Caro🇪🇸 · Miguel Huidobro García🇪🇸 · Ricardo Vázquez🇪🇸 · Andrzej Wereszczynski🇵🇱
We propose a new equation of state for nuclear matter based on a generalized Skyrme model which is consistent with all current constraints on the observed properties of neutron stars. This generalized model depends only on two free parameters related to the ranges of pressure values at which different submodels are dominant, and which can be adjusted so that mass-radius and deformability constraints from astrophysical and gravitational wave measurements can be met. Our results support the Skyrme model and its generalizations as good candidates for a low energy effective field-theoretic description of nuclear matter even at extreme conditions such as those inside neutron stars.
↳ hep-thgr-qcnucl-thPLB(2020)·34 citations
14
Chiral anomaly and the pion properties in the light-front quark model
Ho-Meoyng Choi (Kyungpook National University)🇰🇷 · Chueng-Ryong Ji (North Carolina State University)🇺🇸
We explore the link between the chiral symmetry of QCD and the numerical results of the light-front quark model, analyzing both the two-point and three-point functions of the pion. Including the axial-vector coupling as well as the pseudoscalar coupling in the light-front quark model, we discuss the implication of the chiral anomaly in describing the pion decay constant, the pion-photon transition form factor and the electromagnetic form factor of the pion. In constraining the model parameters, we find that the chiral anomaly plays a critical role and the analysis of $F_{π γ} (Q^{2})$ in timelike region is important. Our results indicate that the constituent quark picture is effective for the low and high $Q^{2}$ ranges implementing the quark mass evolution effect as $Q^{2}$ grows.
↳ hep-phnucl-thPRD(2020)·10 citations
15
Proof of the orthogonal--Pin duality
K. Neergård
This article contains the proof of a theorem on orthogonal-Pin duality that was cited without proof in a previous article in this journal.
↳ math-phmath.MPnucl-thphysics.atom-phBulg.J.Phys.(2023)·3 citations
16
Masses of doubly heavy tetraquarks $T_{Q Q^{'}}$ in a relativized quark model
Qi-Fang Lü🇨🇳 · Dian-Yong Chen🇨🇳 · Yu-Bing Dong🇨🇳
In the present work, the mass spectra of doubly heavy tetraquarks $T_{Q Q^{'}}$ are systematically investigated in a relativized quark model. The four-body systems including the Coulomb potential, confining potential, spin-spin interactions, and relativistic corrections are solved within the variational method. Our results suggest that the $I J^{P} = 0 1^{+}$ $bb u ˉ d ˉ$ state is 54 MeV below the relevant $B ˉ B ˉ$ and $B ˉ B ˉ^{*}$ thresholds, which indicates that both strong and electromagnetic decays are forbidden, and thus this state can be a stable one. Its large hidden color component and small root mean square radius demonstrate that it is a compact tetraquark rather than a loosely bound molecule or point-like diquark-antidiquark structure. Our predictions of the doubly heavy tetraquarks may provide valuable information for future experimental searches.
↳ hep-phhep-exnucl-thPRD(2020)·93 citations
17
Bubble dynamics in a strong first-order quark-hadron transition
Shuying Zhou🇨🇳 · Song Shu🇨🇳 · Hong Mao🇨🇳
We investigate the dynamics of a strong first-order quark-hadron transition driven by cubic interaction via homogeneous bubble nucleation in the Friedberg-Lee model. The one-loop effective thermodynamics potential of the model and the critical bubble profiles have been calculated at different temperatures and chemical potentials. By taking the temperature and the chemical potential as the variables, the evolutions of the surface tension, the typical radius of the critical bubble and the shift in the coarse-grained free energy in the presence of a nucleation bubble are obtained and the limit on the reliability of the thin-wall approximation is also addressed accordingly. Our results are compared to those obtained for a weak first-order quark-hadron phase transition, especially the spinodal decomposition is relevant.
↳ hep-phnucl-thCPC(2021)·8 citations

Affiliations

first authorsco-authorsvia INSPIRE