Nuclear Theory·nucl-th

Thursday·May 21, 2020

10 papers—5 primary·5 cross-listed

01
Isoscalar monopole and quadrupole modes in Mo isotopes: microscopic analysis
Gianluca Colo' (1,2) · Danilo Gambacurta (3,4) · Wolfgang Kleinig (5) · Jan Kvasil (6) · Valentin O. Nesterenko (5,7,8) · Alessandro Pastore (9) ((1) Dipartimento di Fisica, Universita degli Studi di Milano, Italy, (2) INFN, Sezione di Milano, Italy, (3) Extreme Light Infrastructure - Nuclear Physics (ELI-NP), Magurele, Romania, (4) LNS-INFN, Catania, Italy, (5) Laboratory of Theoretical Physics, JINR, Dubna, Russia, (6) Institute of Particle and Nuclear Physics, Charles University, Praha, Czech Republic, (7) State University "Dubna'', Russia, (8) Moscow Institute of Physics and Technology, Dolgoprudny, Russia, (9) Department of Physics, University of York, UK)
The recent RCNP $(α, α^{'})$ data on the Isoscalar Giant Monopole Resonance (ISGMR) and Isoscalar Giant Quadrupole Resonance (ISGQR) in $^{92, 94, 96, 98, 100}$ Mo are analyzed within a fully self-consistent Quasiparticle Random Phase Approximation (QRPA) approach with Skyrme interactions, in which pairing correlations and possible axial deformations are taken into account. The Skyrme sets SkM*, SLy6, SVbas and SkP $^{δ}$ , that explore a diversity of nuclear matter properties, are used. We discuss the connection between the line shape of the monopole strength ISGMR and the deformation-induced coupling between the ISGMR and the $K = 0$ branch of the ISGQR. The ISGMR centroid energy is best described by the force SkP $^{δ}$ , having a low incompressibility $K_{\infty}$ = 202 MeV. The ISGQR data are better reproduced by SVbas, that has large isoscalar effective mass $m^{*} / m$ = 0.9. The need of describing simultaneously the ISGMR and ISGQR data is stressed, with the requirement of suitable values of $K_{\infty}$ and $m^{*} / m$ . Possible extensions of the QRPA to deal with soft systems are also envisaged.
nucl-thnucl-exPLB(2020)·19 citations
02
Correlation studies of fission fragment neutron multiplicities
M. Albertsson · B.G. Carlsson · T. Døssing · P. Möller · J. Randrup · S. Åberg
We calculate neutron multiplicities from fission fragments with specified mass numbers for events having a specified total fragment kinetic energy. The shape evolution from the initial compound nucleus to the scission configurations is obtained with the Metropolis walk method on the five-dimensional potential-energy landscape, calculated with the macroscopic-microscopic method for the three-quadratic-surface shape family. Shape-dependent microscopic level densities are used to guide the random walk, to partition the intrinsic excitation energy between the two proto-fragments at scission, and to determine the spectrum of the neutrons evaporated from the fragments. The contributions to the total excitation energy of the resulting fragments from statistical excitation and shape distortion at scission is studied. Good agreement is obtained with available experimental data on neutron multiplicities in correlation with fission fragments from $^{235}$ U(n $_{th}$ ,f). At higher neutron energies a superlong fission mode appears which affects the dependence of the observables on the total fragment kinetic energy.
nucl-thPRC(2021)·24 citations
03
Exact sum rules with approximate ground states
Calvin W. Johnson · Ken A. Luu · Yi Lu
Electromagnetic and weak transitions tell us a great deal about the structure of atomic nuclei. Yet modeling transitions can be difficult: it is often easier to compute the ground state, if only as an approximation, than excited states. One alternative is through transition sum rules, in particular the non-energy-weighted and energy-weighted sum rules, which can be computed as expectation values of operators. We investigate by computing sum rules for a variety of nuclei, comparing the numerically exact full configuration-interaction shell model, as a reference, to Hartree-Fock, projected Hartree-Fock, and the nucleon pair approximation. These approximations yield reasonable agreement, which we explain by prior work on the systematics of transition moments.
nucl-thJ.Phys.G(2020)·6 citations
04
Future of Nuclear Fission Theory
Michael Bender🇫🇷 · Remi Bernard🇦🇺 · George Bertsch🇺🇸 · Satoshi Chiba🇯🇵 · Jacek Dobaczewski🇬🇧 · Noel Dubray🇫🇷 · Samuel Giuliani🇺🇸 · Kouichi Hagino🇯🇵 · Denis Lacroix🇫🇷 · Zhipan Li🇨🇳 · Piotr Magierski🇵🇱 · Joachim Maruhn🇩🇪 and 21 other authors
There has been much recent interest in nuclear fission, due in part to a new appreciation of its relevance to astrophysics, stability of superheavy elements, and fundamental theory of neutrino interactions. At the same time, there have been important developments on a conceptual and computational level for the theory. The promising new theoretical avenues were the subject of a workshop held at the University of York in October 2019; this report summarises its findings and recommendations.
nucl-thJ.Phys.G(2020)·163 citations
05
Chirally improved quark Pauli blocking in nuclear matter and applications to quark deconfinement in neutron stars
David Blaschke🇵🇱 · Hovik Grigorian🇷🇺 · Gerd Röpke🇷🇺
The relativistic mean field (RMF) model of the nuclear matter equation of state has been modified by including the effect of Pauli-blocking owing to quark exchange between the baryons. Different schemes of a chiral enhancement of the quark Pauli blocking have been suggested according to the adopted density dependence of the dynamical quark mass. The resulting equations of state for the pressure are compared to the RMF model DD2 with excluded volume correction. On the basis of this comparison a density-dependent nucleon volume is extracted which parametrises the quark Pauli blocking effect in the respective scheme of chiral enhancement. The dependence on the isospin asymmetry is investigated and the corresponding density dependent nuclear symmetry energy is obtained in fair accordance with phenomenological constraints. The deconfinement phase transition is obtained by a Maxwell construction with a quark matter phase described within a higher order NJL model. Solutions for rotating and nonrotating (hybrid) compact star sequences are obtained which show the effect of high-mass twin compact star solutions for the rotating case.
nucl-thastro-ph.HEhep-phParticles(2020)·33 citations
06
Medium modification of $γ$ -jet fragmentation functions in Pb+Pb collisions at LHC
Wei Chen🇨🇳 · Shanshan Cao🇺🇸 · Tan Luo🇪🇸 · Long-Gang Pang🇨🇳 · Xin-Nian Wang🇨🇳
Coupled linear Boltzmann transport and hydrodynamic (CoLBT-hydro) model has been developed for simultaneous simulations of jet propagation and jet-induced medium excitation in heavy-ion collisions. Within this coupled approach, the final reconstructed jets in heavy-ion collisions include not only hadrons from the hadronization of medium modified jet shower partons from the linear Boltzmann transport (LBT) but also hadrons from the freeze-out of the jet-induced medium excitation in the hydrodynamic evolution of the bulk medium. Using the CoLBT-hydro model, we study medium modification of the fragmentation functions of $γ$ -triggered jets in high-energy heavy-ion collisions at the Large Hadron Collider. The CoLBT-hydro model is shown to describe the experimental data not only on the suppression of leading hadrons within the jet cone at large momentum fraction $z_{γ} = p_{T}^{h} / p_{T}^{γ}$ relative to the transverse momentum of the trigger photon due to parton energy loss but also the enhancement of soft hadrons at small $z_{γ}$ and $z_{jet} = p_{T}^{h} / p_{T}^{jet}$ due to jet-induced medium excitation. There is no suppression of the fragmentation function, however, at large momentum fraction $z_{jet}$ relative to the transverse momentum of the reconstructed jet due to trigger bias and medium modification of quark to gluon jet fraction. For jets whose final transverse momenta are comparable to or larger than that of the trigger photon, the trigger bias can lead to enhancement of the jet fragmentation function at large $z_{jet}$ .
↳ hep-phnucl-thPLB(2020)·79 citations
07
Observational appearance of rapidly rotating neutron stars: X-ray bursts, cooling tail method, and radius determination
Valery F. Suleimanov · Juri Poutanen · Klaus Werner
Neutron stars (NSs) in low-mass X-ray binaries rotate at frequencies high enough to significantly deviate from sphericity ( $ν_{*} \sim$ 200--600 Hz). We investigate the effects of rapid rotation on the observational appearance of a NS. We propose analytical formulae relating gravitational mass and equatorial radius of the rapidly rotating NS to the mass $M$ and radius $R$ of a non-rotating NS of the same baryonic mass using accurate fully relativistic computations. We compute spectra from an oblate rotating NS observed at different inclination angles using the modified oblate Schwarzschild (MOS) approximation, where light bending is computed in Schwarzschild metric, but frame dragging and quadrupole moment of a NS are approximately accounted for in the photon redshift calculations. We generalize the cooling tail method to the case of a rapidly rotating NS to obtain the most probable values of $M$ and $R$ of the corresponding non-rotating NS with the same baryonic mass. We approximate the local spectra from the NS surface by a diluted blackbody using previously computed NS atmosphere models. We show that the NS radius could be overestimated by 3--3.5 km for face-on stars of $R \approx 11$ km rotating at $ν_{*} =$ 700 Hz if the version of the cooling tail method for a non-rotating NS is used. We apply the method to an X-ray burst observed from the NS rotating at $ν_{*} \approx$ 532 Hz in SAX J1810.8 $-$ 2609. The resulting radius of the non-rotating NS (assuming $M = 1.5 M_{⊙}$ ) becomes $11.8 \pm 0.5$ km if it is viewed at inclination i=60 deg and $R = 11.2 \pm 0.5$ km for a face-on view, which are smaller by 0.6 and 1.2 km than the radius obtained using standard cooling tail method ignoring rotation. The corresponding equatorial radii of these rapidly rotating NSs are 12.3 $\pm 0.6$ km (for i=60 deg) and 11.6 $\pm 0.6$ \,km (for i=0 deg).
↳ astro-ph.HEastro-ph.SRnucl-thAstron.Astrophys.(2020)·29 citations
08
T-odd generalized and quasi transverse momentum dependent parton distribution in a scalar spectator model
Xuan Luo🇨🇳 · Hao Sun🇨🇳
Generalized transverse momentum dependent parton distributions (GTMDs), as mother funtions of transverse momentum dependent parton distributions (TMDs) and generalized parton distributions (GPDs), encode the most general parton structure of hadrons. We calculate four twist-two time reversal odd GTMDs of pion in a scalar spectator model. We study the dependence of GTMDs on the longitudinal momentum fraction $x$ carried by the active quark and the transverse momentum $∣ k_{T} ∣$ for different values of skewness $ξ$ defined as the longitudinal momentum transferred to the proton as well as the total momentum $∣ Δ_{T} ∣$ transferred to the proton. In addition, the quasi-TMDs and quasi-GPDs of pion have also been investigated in this paper.
↳ hep-phnucl-thEPJC(2020)·18 citations
09
Compressional-mode resonances in the molybdenum isotopes: Emergence of softness in open-shell nuclei near A=90
K. B. Howard · U. Garg · M. Itoh · H. Akimune · M. Fujiwara · T. Furuno · Y. K. Gupta · M. N. Harakeh · K. Inaba · Y. Ishibashi · K. Karasudani · T. Kawabata and 11 other authors
"Why are the tin isotopes soft?" has remained, for the past decade, an open problem in nuclear structure physics: models which reproduce the isoscalar giant monopole resonance (ISGMR) in the "doubly-closed shell" nuclei, $^{90}$ Zr and $^{208}$ Pb, overestimate the ISGMR energies of the open-shell tin and cadmium nuclei, by as much as 1 MeV. In an effort to shed some light onto this problem, we present results of detailed studies of the ISGMR in the molybdenum nuclei, with the goal of elucidating where--and how--the softness manifests itself between $^{90}$ Zr and the cadmium and tin isotopes. The experiment was conducted using the $^{94, 96, 98, 100}$ Mo( $α, α^{'}$ ) reaction at $E_{α} = 386$ MeV. A comparison of the results with relativistic, self-consistent Random-Phase Approximation calculations indicates that the ISGMR response begins to show softness in the molybdenum isotopes beginning with $A = 92$ .
↳ nucl-exnucl-thPLB(2020)·24 citations
10
Revisiting relativistic magnetohydrodynamics from quantum electrodynamics
Masaru Hongo🇺🇸 · Koichi Hattori🇯🇵
We provide a statistical mechanical derivation of relativistic magnetohydrodynamics on the basis of the $(3 + 1)$ -dimensional quantum electrodynamics; the system endowed with the magnetic one-form symmetry. The conservation laws and the constitutive relations are presented in a manifestly covariant way with respect to the general coordinate transformation. The method of the local Gibbs ensemble (or nonequilibrium statistical operator) combined with the path-integral formula for the thermodynamic functional enables us to obtain an exact form of the constitutive relations. Applying the derivative expansion to the exact formula, we derive the first-order constitutive relations for the relativistic magnetohydrodynamics. The result for the QED plasma preserving the parity and charge-conjugation symmetries is equipped with two electrical resistivities and five (three bulk and two shear) viscosities. We also show that those transport coefficients satisfy the Onsager's reciprocal relation and a set of inequalities, indicating the semi-positivity of the entropy production rate consistent with the local second law of thermodynamics.
↳ hep-thastro-ph.HEcond-mat.stat-mechhep-ph+1JHEP(2021)·16 citations

Affiliations

first authorsco-authorsvia INSPIRE