Nuclear Theory·nucl-th

Thursday·December 10, 2020

13 papers—9 primary·4 cross-listed

01
Superfluid neutron matter with a twist
Georgios Palkanoglou · Alexandros Gezerlis
Superfluid neutron matter is a key ingredient in the composition of neutron stars. The physics of the inner crust is largely dependent on that of its $S$ -wave neutron superfluid which has made its presence known through pulsar glitches and modifications on the neutron star cooling. Moreover, with recent gravitational-wave observations of neutron star mergers, the need for an equation of state for the matter of these compact stars is further accentuated and a model-independent treatment of neutron superfluidity is important. \textit{Ab initio} techniques developed for finite systems can be guided to perform extrapolations to the thermodynamic limit and attain this model-independent extraction of various quantities of infinite superfluid neutron matter. To inform such an extrapolation scheme, we performed calculations of the neutron $^{1} S_{0}$ pairing gap using the model-independent odd-even staggering in the context of the particle-conserving, projected BCS theory under twisted boundary conditions. While the practice of twisted boundary conditions is standard in solid state physics and has been used repeatedly in the past to reduce finite-size effects, this is the first time it is employed in the context of pairing. We find that a twist-averaging approach results in a substantial reduction of the finite-size effects, bringing systems with $N ⪆ 50$ within a $2%$ error margin from the infinite system. This can significantly reduce extrapolation-related errors in the extraction of superfluid neutron matter quantities.
nucl-thcond-mat.quant-gasUniverse(2021)·3 citations
02
Coriolis coupling effects in proton-pickup spectroscopic factors from $^{12}$ B
A. O. Macchiavelli · H. L. Crawford · R. M. Clark · P. Fallon · I. Y. Lee · C. Morse · C. M. Campbell · M. Cromaz · C. Santamaria · J. Chen · C. R. Hoffman · B. P. Kay
Spectroscopic factors to low-lying negative-parity states in $^{11}$ Be extracted from the $^{12}$ B( $d$ , $^{3}$ He) $^{11}$ Be proton-removal reaction are interpreted within the rotational model. Earlier predictions of the $p$ -wave proton removal strengths in the strong coupling limit of the Nilsson model underestimated the spectroscopic factors to the $3/ 2_{1}^{-}$ and $5/ 2_{1}^{-}$ states and suggested that deviations in the $1^{+}$ ground state of the odd-odd $^{12}$ B due to Coriolis coupling should be further explored. In this work we use the Particle Rotor Model to take into account these effects and obtain a good description of the level scheme in $^{11}$ B, with a moderate $K$ -mixing of the proton Nilsson levels [110]1/2 and [101]3/2. This mixing, present in the $1^{+}$ bandhead of $^{12}$ B, is key to explaining the proton pickup data.
nucl-thPRC(2021)·1 citation
03
Single-nucleon properties and pair correlations in nuclear matter from chiral two- and three-nucleon forces
Francesca Sammarruca🇺🇸 · Herbert Muether🇩🇪 · Ruprecht Machleidt🇺🇸
We investigate single-particle properties in infinite nuclear matter using a variety of interactions. One of the focal points is to study the impact of chiral three-nucleon forces on the nucleon self-energy and related quantities, such as spectral function and momentum distribution. We also present results for pairing correlations in nuclear matter. We find characteristic and systematic differences between the predictions obtained with the (softer) chiral interactions and those based on one-boson-exchange or phenomenology.
nucl-th1 citation
04
Elastic $α$ transfer in the $^{16}$ O+ $^{12}$ C scattering and its impact on the nuclear rainbow
Nguyen Hoang Phuc · Dao T. Khoa · Nguyen Tri Toan Phuc
Elastic $^{16}$ O+ $^{12}$ C scattering is known to exhibit the nuclear rainbow pattern at incident energies $E_{lab} ≳ 200$ MeV, with the Airy structure of the far-side scattering cross section clearly seen at medium and large angles. Such a rainbow pattern is well described by the deep real optical potential (OP) given by the double-folding model (DFM). At lower energies, the extensive elastic $^{16}$ O+ $^{12}$ C scattering data show consistently that the nuclear rainbow pattern at backward angles is deteriorated by an oscillating enhancement of elastic cross section that is difficult to describe in the conventional optical model (OM). Given a significant $α$ spectroscopic factor predicted for the dissociation $^{16}$ O $\to α +^{12}$ C by the shell model and $α$ -cluster models, the contribution of the elastic $α$ transfer (or the core-core exchange) to the elastic $^{16}$ O+ $^{12}$ C scattering should not be negligible and is expected to account for the enhanced elastic cross section at backward angles. To reveal the impact of the elastic $α$ transfer, a systematic coupled reaction channels analysis of the elastic $^{16}$ O+ $^{12}$ C scattering has been performed, with the coupling between the elastic scattering and elastic $α$ transfer channels treated explicitly, using the real OP given by the DFM. We found that the elastic $α$ transfer enhances the near-side scattering significantly at backward angles, giving rise to an oscillating distortion of the smooth Airy structure. The dynamic polarization of the OP by the coupling between the elastic scattering and elastic $α$ transfer channels can be effectively taken into account in the OM calculation by an angular-momentum (or parity) dependent potential added to the imaginary OP, as suggested by Frahn and Hussein 40 years ago.
nucl-th0 citations
05
Nuclear shape transitions and elastic magnetic electron scattering
B. Hernandez · P. Sarriguren · O. Moreno · E. Moya de Guerra · D. N. Kadrev · A. N. Antonov
Backward elastic electron scattering from odd-A nuclear targets is characterized by magnetic form factors containing precise information on the nuclear structure. We study the sensitivity of the magnetic form factors to structural effects related to the evolution and shape transitions in both isotopic and isotonic chains. Calculations of magnetic form factors are performed in the plane-wave Born approximation. The nuclear structure is obtained from a deformed self-consistent mean-field calculation based on a Skyrme HF+BCS formalism. Collective effects are included in the cranking approximation, whereas nucleon-nucleon correlations are taken into account in the coherent density fluctuation model. The evolution of the magnetic form factors is found to exhibit signatures of shape transitions that show up in selected isotopic and isotonic chains involving both stable and unstable nuclei. Several cases are identified as suitable candidates for showing such fingerprints of shape transitions. A new generation of electron scattering experiments involving electron-radioactive beam colliders will be available in the near future, leading to a renewed interest in this field.
nucl-thPRC(2021)·11 citations
06
Role of exact treatment of thermal pairing in radiative strength functions of $^{161 - 163}$ Dy nuclei
L. Tan Phuc · N. Quang Hung · N. Dinh Dang · L. T. Quynh Huong · N. Ngoc Anh · N. Ngoc Duy · L. Ngoc Uyen · N. Nhu Le
The enhancement of radiative strength function (RSF) in the region of low $γ$ -rays energy ( $E_{γ} \leq 12$ MeV), which is caused by the pygmy dipole resonance (PDR), is treated within the phonon damping model (PDM) plus exact thermal pairing (EP) without adding any extra PDR strength function. The numerical calculations performed for $^{161 - 163}$ Dy show that, because of the effect of EP, the EP+PDM can describe reasonably well the total RSF data in both low- and high-energy regions of $γ$ -rays. Consequently, as compared to the conventional description within the phenomenological generalized Lorentzian (GLO) and standard Lorentzian (SLO) models, the EP+PDM calculations can eliminate at least eight free parameters. This indicates the important role of microscopic approaches towards the precise description of the RSF. In particular, temperature is found to have significant contributions to the RSF below the neutron separation energy, questioning again the validity of the Brink-Axel hypothesis in this energy region.
nucl-thnucl-exPRC(2020)·5 citations
07
A new boson approach for the wobbling motion in even-odd nuclei
A. A. Raduta · C. M. Raduta · R. Poenaru
A triaxial core rotating around the middle axis, i.e. 2-axis, is cranked around the 1-axis, due to the coupling of an odd proton from a high j orbital. Using the Bargmann representation of a new and complex boson expansion of the angular momentum components, the eigenvalue equation of the model Hamiltonian acquires a Schrödinger form with a fully separated kinetic energy. From a critical angular momentum, the potential energy term exhibits three minima, two of them being degenerate. Spectra of the deepest wells reflects a chiral-like structure. Energies corresponding to the deepest and local minima respectively, are analytically expressed within a harmonic approximation. Based on a classical analysis, a phase diagram is constructed. It is also shown that the transverse wobbling mode is unstable. The wobbling frequencies corresponding to the deepest minimum are used to quantitatively describe the wobbling properties in $^{135}$ Pr. Both energies and e.m. transition probabilities are described.
nucl-thJ.Phys.G(2020)·14 citations
08
New results about the canonical transformation for boson operators
C. M. Raduta · A. A. Raduta
The Bogoliubov transformation for a monopole boson induces an unitary transformation connecting the Fock spaces of initial and correlated boson-s. Here we provide a very simple method for deriving the analytical expression for the overlap matrix of the basis states generating the two boson spaces.
nucl-thIJMPE(2021)·0 citations
09
Jets and elliptic flow correlations at low and high transverse momenta in ultrarelativistic A+A collisions
L.V. Bravina🇳🇴 · G.Kh. Eyyubova🇷🇺 · V.L. Korotkikh🇷🇺 · I.P. Lokhtin🇷🇺 · S.V. Petrushanko🇷🇺 · A.M. Snigirev🇷🇺 · E.E. Zabrodin🇷🇺
Data from the Large Hadron Collider on elliptic flow correlations at low and high $p_{T}$ from Pb+Pb collisions at $s_{N N} = 5.02$ ~TeV are analyzed and interpreted in the framework of the HYDJET++ model. This model allows us to describe simultaneously the region of both low and high transverse momenta and, therefore, to reproduce the experimentally observed nontrivial centrality dependence of elliptic flow correlations. The origin of the correlations between low and high- $p_{T}$ flow components in peripheral lead-lead collisions is traced to correlations of particles in jets.
nucl-thhep-phnucl-exPRC(2021)·11 citations

Affiliations

first authorsco-authorsvia INSPIRE