Nuclear Theory·nucl-th

Wednesday·March 28, 2018

12 papers—7 primary·5 cross-listed

01
The nuclear symmetry energy and the breaking of the isospin symmetry: how do they reconcile with each other?
X. Roca-Maza (1) · G. Colo' (1) · H. Sagawa (2) ((1) Universita' degli Studi and INFN, Via Celoria 16, 20133 Milano, Italy (2) RIKEN Nishina Center, Wako 351-0198, Japan and University of Aizu, Aizu-Wakamatsu, Fukushima 965-8560, Japan)
We analyze and propose a solution to the apparent inconsistency between our current knowledge of the Equation of State of asymmetric nuclear matter, the energy of the Isobaric Analog State (IAS) in a heavy nucleus such as 208Pb, and the isospin symmetry breaking forces in the nuclear medium. This is achieved by performing state-of-the-art Hartree-Fock plus Random Phase Approximation calculations of the IAS that include all isospin symmetry breaking contributions. To this aim, we propose a new effective interaction that is successful in reproducing the IAS excitation energy without compromising other properties of finite nuclei.
nucl-thnucl-exPRL(2018)·53 citations
02
The $0 ν β β$ -decay nuclear matrix element for light and heavy neutrino mass mechanisms from deformed QRPA cacluations for $^{76}$ Ge, $^{82}$ Se, $^{130}$ Te, $^{136}$ Xe and $^{150}$ Nd with isospin restoration
Dong-Liang Fang🇨🇳 · Amand Faessler🇩🇪 · Fedor Šimkovic🇷🇺
In this work, with restored isospin symmetry, we evaluated the neutrinoless double beta decay nuclear matrix elements for $^{76}$ Ge, $^{82}$ Se, $^{130}$ Te, $^{136}$ Xe and $^{150}$ Nd for both the light and heavy neutrino mass mechanisms using the deformed QRPA approach with realistic forces. We give detailed decompositions of the nuclear matrix elements over different intermediate states and nucleon pairs, and discuss how these decompositions are affected by the model space truncations. Compared to the spherical calculations, our results show reductions from $30%$ to about $60%$ of the nuclear matrix elements for the calculated isotopes mainly due to the presence of BCS overlap factor between the initial and final ground states. The comparison between different nucleon-nucleon forces with corresponding Short-Range-Correlations (src) shows, that the choice of the NN force gives roughly $20%$ deviations for light exchange neutrino mechanism and much larger deviations for the heavy neutrino exchange mechanism.
nucl-thhep-phPRC(2018)·118 citations
03
Low-lying states in even Gd isotopes studied with five-dimensional collective Hamiltonian based on covariant density functional theory
Z. Shi · Q. B. Chen · S. Q. Zhang
Five-dimensional collective Hamiltonian based on the covariant density functional theory has been applied to study the the low-lying states of even-even $^{148 - 162}$ Gd isotopes. The shape evolution from $^{148}$ Gd to $^{162}$ Gd is presented. The experimental energy spectra and intraband $B (E 2)$ transition probabilities for the $^{148 - 162}$ Gd isotopes are reproduced by the present calculations. The relative $B (E 2)$ ratios in present calculations are also compared with the available interacting boson model results and experimental data. It is found that the occupations of neutron $1 i_{13/2}$ orbital result in the well-deformed prolate shape, and are essential for Gd isotopes.
nucl-thEPJA(2018)·11 citations
04
Nucleon internal degrees of freedom and the uniqueness of the Gamow-Teller state
N. Auerbach
The Gamow-Teller strength in nuclei can be strongly affected by the internal degrees of freedom of the nucleon. It is demonstrated that this feature is unique to the Gamow-Teller. Excitation modes that involve spatial degrees of freedom are much less influenced by the internal excitation of nucleons. The fact that the observed Gamow-Teller strength is quenched by 30-40 percent in all nuclei suggests that indeed this is due to the nucleon excitation in nuclei.
nucl-thnucl-ex1 citation
05
Three-nucleon force in chiral EFT with explicit $Δ (1232)$ degrees of freedom: Longest-range contributions at fourth order
H. Krebs🇩🇪 · A. M. Gasparyan🇩🇪 · E. Epelbaum🇩🇪
We analyze the longest-range two-pion exchange contributions to the three-nucleon force at leading-loop order in the framework of heavy-baryon chiral effective field theory with explicit $Δ (1232)$ degrees of freedom. All relevant low-energy constants which appear in the calculation are determined from pion-nucleon scattering. Comparing our results with the ones obtained in the $Δ$ -less theory at N4LO, we find effects of the $Δ$ isobar for this particular topology to be rather well represented in terms of resonance saturation of various low-energy constants in the $Δ$ -less approach.
nucl-thPRC(2018)·47 citations
06
Effect of thresholds on the width of three-body resonances
H. Garcilazo · A. Valcarce
It has been recently reported an intriguing theoretical result of a narrow three-body resonance with a large available phase space. The resonance was reported in the $N ΛΛ - Ξ N N$ system near the $Ξ d$ threshold, having a very small width in spite of the open $N ΛΛ$ channel lying around 23 MeV below the $Ξ N N$ channel. We use first-order perturbation theory as a plausible argument to explain this behavior. We apply our result to realistic local interactions. Other systems involving several thresholds are likely to follow the same behavior.
nucl-thhep-phPLB(2017)·5 citations
07
New algorithm in the variation after projection calculations for non-yrast nuclear states
Jia-Qi Wang · Zao-Chun Gao · Ying-Jun Ma · Y.S. Chen
We present a novel and simple algorithm in the variation after projection (VAP) approach for the non-yrast nuclear states. It is for the first time that the yrast state and non-yrast states can be varied on the same footing. The orthogonality among the calculated states is automatically fulfilled by solving the Hill-Wheeler equation. This avoids the complexity of the frequently used Gram-Schmidt orthogonalization, as adopted by the excited VAMPIR method. Thanks to the Cauchy's interlacing theorem in the matrix theory, the sum of the calculated lowest projected energies with the same quantum numbers can be safely minimized. Once such minimization is converged, all the calculated energies and the corresponding states can be obtained, simultaneously. The present VAP calculations are performed with time-odd Hartree-Fock Slater determinants. It is shown that the calculated VAP energies (both yrast and non-yrast) are very close to the corresponding ones from the full shell model calculations. It looks the present algorithm is not limited to the VAP, but should be universal, i.e., one can do the variation with different forms of the many-body wavefunctions to calculate the excited states in different quantum many-body systems.
nucl-thPRC(2018)·12 citations
08
Angular Momentum Sum Rule Violation in QCD Due to Confinement and The Proton Spin Crisis
Gouranga C Nayak🇺🇸
The proton spin crisis remains an unsolved problem in physics. In this paper we find that due to the confinement of partons inside the hadron the angular momentum sum rule in QCD is violated. Hence we find that the non-vanishing angular momentum flux contribution of the partons in QCD should be added to the spin and angular momentum of the partons to solve the proton spin crisis.
↳ hep-phhep-latnucl-th5 citations
09
On the use of running $α_{s}$ in calculations of radiative energy loss of fast partons in a quark-gluon plasma
B.G. Zakharov🇷🇺
The incorporation of running $α_{s}$ for the gluon emission vertex in calculations of radiative parton energy loss in a quark-gluon plasma is discussed. It is argued that the virtuality scale for running $α_{s}$ for induced gluon emission is determined by the square of the transverse momentum of the emitted gluon rather than by the square of the invariant mass of the final two-parton state often used in the literature.
↳ hep-phnucl-thJETP Lett.(2018)·1 citation
10
Entanglement in Reggeized Scattering using AdS/CFT
Yizhuang Liu🇨🇳 · Ismail Zahed🇺🇸
The eikonalized parton-parton scattering amplitude at large $s$ and large impact parameter, is dominated by the exchange of a hyperbolic surface in walled AdS. Its analytical continuation yields a worldsheet instanton that is at the origin of the Reggeization of the amplitude and a thermal-like quantum entropy $S_{T}$ . We explicitly construct the entangled density matrix following from the exchanged surface, and show that its von-Neumann entanglement entropy $S_{E}$ coincides with the thermal-like entropy, i.e. $S_{T} = S_{E}$ . The ratio of the entanglement entropy to the transverse growth of the exchanged surface is similar to the Bekenstein entropy ratio for a black-hole, with a natural definition of saturation and the on-set of chaos in high energy collisions. The largest eigenvalues of the entangled density matrix obey a cascade equation in rapidity, reminiscent of non-linear QCD evolution of wee-dipoles at low-x and weak coupling. We suggest that the largest eigenvalues describe the probability distributions of wee-quanta at low-x and strong coupling that maybe measurable at present and future pp and ep colliders.
↳ hep-phhep-thnucl-thPRD(2019)·35 citations
11
Electrical Resistivity and Hall Effect in Binary Neutron-Star Mergers
Arus Harutyunyan · Antonios Nathanail · Luciano Rezzolla · Armen Sedrakian
We examine the range of rest-mass densities, temperatures and magnetic fields involved in simulations of binary neutron-star mergers and identify the conditions under which the ideal-magnetohydrodynamics approximation breaks down and hence the magnetic-field decay should be accounted for. We use recent calculations of the conductivities of warm correlated plasma in envelopes of compact stars and find that the magnetic-field decay timescales are much larger than the characteristic timescales of the merger process for lengthscales down to a meter. Because these are smaller than the currently available resolution in numerical simulations, the ideal-magnetohydrodynamics approximation is effectively valid for all realistic simulations. At the same time, we find that the Hall effect can be important at low densities and low temperatures, where it can induce a non-dissipative rearrangement of the magnetic field. Finally, we mark the region in temperature and density where the hydrodynamic description breaks down.
↳ astro-ph.HEnucl-thEPJA(2018)·37 citations
12
Are small radii of compact stars ruled out by GW170817/AT2017gfo?
G. F. Burgio🇮🇹 · A. Drago🇮🇹 · G. Pagliara🇮🇹 · H.-J. Schulze🇮🇹 · J.-B. Wei🇮🇹
The detection of GW170817 and its electromagnetic counterparts allows to constrain the equation of state of dense matter in new and complementary ways. Very stiff equations of state are ruled out by the upper limit on the average tidal deformability, $Λ ~ ≲ 800$ , imposed by the detected gravitational wave signal. A lower limit, $Λ ~ ≳ 400$ , can also be extracted by considering the large amount of ejected matter which powers the kilonova AT2017gfo. By using several microscopic nucleonic equations of state, we first confirm the existence of a monotonic relation between $R_{1.5}$ (the radius of the $1.5 M_{⊙}$ configuration) and $Λ ~$ . This translates the limits on $Λ ~$ into limits on the radius: $11.8 km ≲ R_{1.5} ≲ 13.1$ km. We then show that the monotonic relation is violated, if a second branch of compact stars composed of quark matter exists, as in the two-families or the twin-stars scenarios. In particular, it is possible to fulfill the limits on $Λ ~$ while having $R_{1.5}$ significantly smaller than $12$ km. In both those scenarios the event GW170817/AT2017gfo originates from the merger of a hadronic star and a star containing quark matter.
↳ astro-ph.HEhep-phnucl-thApJ(2018)·128 citations

Affiliations

first authorsco-authorsvia INSPIRE