Nuclear Theory·nucl-th

Tuesday·August 11, 2015

13 papers—6 primary·7 cross-listed

01
Differential Hanbury-Brown-Twiss for an exact hydrodynamic model with rotation
S. Velle🇳🇴 · L.P. Csernai🇳🇴
We study an exact rotating and expanding solution of the fluid dynamical model of heavy ion reactions, that take into account the rate of slowing down of the rotation due to the longitudinal and transverse expansion of the system. The parameters of the model are set on the basis of realistic 3+1D fluid dynamical calculation at TeV energies, where the rotation is enhanced by the build up of the Kelvin Helmholtz Instability in the flow.
nucl-thPRC(2015)·8 citations
02
Global calculations on the microscopic energies and nuclear deformations: Isospin dependence of the spin-orbit coupling
Zhe-Ying Wu · Chong Qi · Ramon Wyss · Hong-Liang Liu
The microscopic energies and nuclear deformations of about 1850 even-even nuclei are calculated systematically within the macroscopic-microscopic framework using three Woods-Saxon parameterizations, with different isospin dependences, which were constructed mainly for nuclear spectroscopy calculations. Calculations are performed in the deformation space $(β_{2}, γ, β_{4})$ . Both the monopole and doubly stretched quadrupole interactions are considered for the pairing channel. The ground state deformations obtained by the three calculations are quite similar to each other. Large differences are seen mainly in neutron-rich nuclei and in superheavy nuclei. Systematic calculations on the shape-coexisting second minima are also presented. As for the microscopic energies of the ground states, the results are also very close to each other. Only in a few cases the difference is larger than 2 MeV. The total binding energy is estimated by adding the macroscopic energy provided by the usual liquid drop model with its parameters fitted through the least square root and minimax criteria. Calculations are also compared with the results of other macroscopic-microscopic mass models. All the three calculations give similar values for the deformations, microscopic energies and binding energies of most nuclei. One may expect to have a better understanding of the isospin dependence of the spin-orbital force with more data on proton- and neutron-rich nuclei.
nucl-thPRC(2015)·33 citations
03
Density dependence of the pairing interaction and pairing correlation in unstable nuclei
S. A. Changizi · Chong Qi
This work aims at a global assessment of the effect of the density dependence of the zero-range pairing interaction. Systematic Skyrme-Hartree-Fock-Bogoliubov calculations with the volume, surface and mixed pairing forces are carried out to study the pairing gaps in even-even nuclei over the whole nuclear chart. Calculations are also done in coordinate representation for unstable semi-magic even-even nuclei. The calculated pairing gaps are compared with empirical values from four different odd-even staggering formulae. Calculations with the three pairing interactions are comparable for most nuclei close to $β$ -stability line. However, the surface interaction calculations predict neutron pairing gaps in neutron-rich nuclei that are significantly stronger than those given by the mixed and volume pairing. On the other hand, calculations with volume and mixed pairing forces show noticeable reduction of neutron pairing gaps in nuclei far from the stability.
nucl-thPRC(2015)·37 citations
04
Empirical pairing gaps, shell effects, and di-neutron spatial correlation in neutron-rich nuclei
S.A. Changizi · Chong Qi · R. Wyss
The empirical pairing gaps derived from four different odd-even mass staggering formulas are compared. By performing single- $j$ shell and multi-shell seniority model calculations as well as by using the standard HFB approach with Skyrme force we show that the simplest three-point formula $Δ_{C}^{(3)} (N) = \frac{1}{2} [B (N, Z) + B (N - 2, Z) - 2 B (N - 1, Z)]$ can provide a good measure of the neutron pairing gap in even- $N$ nuclei. It removes to a large extent the contribution from the nuclear mean field as well as contributions from shell structure details. It is also less contaminated by the Wigner effect for nuclei around $N = Z$ . We also show that the strength of $Δ_{C}^{(3)} (N)$ can serve as a good indication of the two-particle spatial correlation in the nucleus of concern and that the weakening of $Δ_{C}^{(3)} (N)$ in some neutron-rich nuclei indicates that the di-neutron correlation itself is weak in these nuclei.
nucl-thNPA(2015)·52 citations
05
Partial restoration of isospin symmetry for neutrinoless double beta decay in the deformed nuclear system of $^{150}$ Nd
Dong-Liang Fang🇨🇳 · Amand Faessler🇩🇪 · Fedor Simkovic🇷🇺
In this work, we calculate the matrix elements of $0 ν β β$ -decay of $^{150}$ Nd with the deformed pn-QRPA method. We adopted the approach introduced by Rodin, Faessler [Phys. Rev. C84, 014322 (2011)] and Simkovic {\it et. al.} [Phys. Rev. C87,045501(2013)] to restore the isospin symmetry by enforcing $M_{F}^{2 ν} = 0$ . We found that with this restoration, the Fermi matrix elements are reduced by about 30\% while the more important Gamow-Teller matrix elements remains the same. The results of an enlarged model space is also presented, which changes the matrix elements by less than 10\%.
nucl-thPRC(2015)·35 citations
06
Probing Pb+Pb collisions at $S_{N N} = 2760$ GeV with spectators
Vipul Bairathi🇮🇳 · Sandeep Chatterjee🇮🇳 · Md. Rihan Haque🇮🇳 · Bedangadas Mohanty🇮🇳
There is event by event geometric as well as quantum fluctuations in the initial condition of heavy-ion collisions. The standard technique of analysing heavy-ion collisions in bins of centrality obtained from final state multiplicity averages out the various initial configurations and thus restricts the study to only a limited range of initial conditions. In this paper, we propose an additional binning in terms of total spectator neutrons in an event. This offers us a key control parameter to probe events with broader range of initial conditions providing us an opportunity to peep into events with rarer initial conditions which otherwise get masked when analysed by centrality binning alone. We find that the inclusion of spectator binning allows one to vary $ε_{2}$ and $ε_{3}$ independently. We observe that the standard scaling relation between $v_{2} / ε_{2}$ and $\frac{1}{S} \frac{d N _{ch}}{d η}$ exhibited by centrality bins is broken by the spectator neutron bins. However, the acoustic scaling relation between $ln (v_{n} / ε_{n})$ and transverse system size holds for both centrality as well as spectator bins for central to mid-central collisions. The introduction of the spectator binning allows us to tune over a wide range viscosity driven effects for events with varying initial states but similar final state multiplicity.
nucl-thhep-exhep-phnucl-exPLB(2016)·5 citations
07
New Photodisintegration Model of GEANT4 for the $d γ \to n p$ Reaction with a Dibaryon Effective Field Theory
Jae Won Shin🇰🇷 · Chang Ho Hyun🇰🇷
We develop a new hadronic model for GEANT4 that is specialized for the disintegration of the deuteron by photons, $d γ \to n p$ . For the description of two-nucleon interactions, we employ a pionless effective field theory with dibaryon fields (dEFT). We apply the new model of GEANT4 (G4dEFT) to the calculations of the total and the differential cross sections in $d γ \to n p$ and compare the results with empirical data. As an application of the new model, we calculate the neutron yield from the $γ + CD_{2}$ process. G4dEFT predicts peaks for the neutron yield, but the existing model of GEANT4 does not show such behavior.
↳ nucl-exnucl-thJ.Korean Phys.Soc.(2016)·1 citation
08
Possible identifications of newly observed magnetar quasi-periodic oscillations as crustal shear modes
Hajime Sotani🇯🇵 · Kei Iida🇯🇵 · Kazuhiro Oyamatsu🇯🇵
Quasi-periodic oscillations (QPOs) discovered in soft-gamma repeaters (SGRs) are expected to help us to study the properties of matter in neutron stars. In earlier investigations, we identified the QPOs of frequencies below $\sim 100$ Hz observed in giant flares of SGR 1806 $-$ 20 and SGR 1900+14 as the crustal torsional oscillations. For this purpose, we calculated the frequencies of the fundamental torsional oscillations with various angular indices $ℓ$ , by changing the stellar mass and radius. In this work, we try to explain the additional QPO frequencies recently reported by Huppenkothen et al. (2014a,b) within the same framework as before except that we newly take into account the effect of electron screening, which acts to decrease the frequencies by a small amount. Those QPOs were discovered in two different SGRs, i.e., SGR 1806 $-$ 20 and SGR J1550 $-$ 5418. Then, we find that the newly observed QPO frequency in SGR 1806 $-$ 20 can be still identified as one of the frequencies of the fundamental torsional oscillations, while those in SGR J1550 $-$ 5418 can also be explained in terms of the torsional oscillations although the relevant angular indices are difficult to identify.
↳ astro-ph.HEnucl-thNew Astron.(2016)·50 citations
09
On $m_{T}$ dependence of femtoscopy scales for meson and baryon pairs
Yu. M. Sinyukov🇺🇦 · V. M. Shapoval🇺🇦 · V. Yu. Naboka🇺🇦
The $m_{T}$ -dependencies of the femto-scales, the so-called interferometry and source radii, are investigated within the hydrokinetic model for different types of particle pairs - pion-pion, kaon-kaon, proton-proton and proton-lambda, - produced in Pb+Pb and $p + p$ collisions at the LHC. In particular, such property of the femto-scales momentum behavior as $m_{T}$ -scaling is studied for the systems with (w) and without (w/o) intensive transverse flow, and also w and w/o re-scattering at the final afterburner stage of the matter evolution. The detail spatiotemporal description obtained within hydrokinetic model is compared with the simple analytical results for the spectra and longitudinal interferometry radii depending on the effective temperature on the hypersurface of maximal emission, proper time of such emission, and intensity of transverse flow. The derivation of the corresponding analytical formulas and discussion about a possibility for their utilization by the experimentalists for the simple femtoscopy data analysis is the main aim of this theoretical investigation.
↳ hep-phhep-exnucl-exnucl-thNPA(2016)·34 citations
10
A Comparative study of hyperon equations of state in supernova simulations
Prasanta Char🇮🇳 · Sarmistha Banik🇮🇳 · Debades Bandyopadhyay🇮🇳
A comparative study of the $Λ$ hyperon equations of state of Banik, Hempel and Banyopadhyay (BHB) \citep{bhb} and \citet{shen11} (denoted as HShen $Λ$ ) for core collapse supernova (CCSN) simulations is carried out in this work. The dynamical evolution of a protoneutron star (PNS) into a black hole is investigated in core collapse supernova simulations in the general relativistic one dimensional code using the BHB $Λ ϕ$ and HShen $Λ$ equation of state (EoS) tables and different progenitor models from Woosley and Heger \citep{Woos}. Radial profiles of the mass fractions of baryons, the density as well as the temperature in the PNS at different moments in time, are compared for both EoS tables. The behaviour of the central density of the PNS with time is demonstrated for those two $Λ$ hyperon EoS tables and compared with their corresponding nuclear EoS tables. It is observed that the black hole formation time is higher in the BHB $Λ ϕ$ case than in the HShen $Λ$ EoS for the entire set of progenitor models adopted here, because the repulsive $Λ$ - $Λ$ interaction makes the BHB $Λ ϕ$ EoS stiffer. Neutrino emission with the $Λ$ hyperon EoS ceases earlier than that of its nuclear counterpart. The long duration evolution of the shock radius and gravitational mass of the PNS after a successful supernova explosion with enhanced neutrino heating are studied with the BHB $Λ ϕ$ EoS and $s$ 20WH07 progenitor model. The PNS is found to remain stable for 4 s and might evolve into a cold neutron star.
↳ astro-ph.HEnucl-thApJ(2015)·27 citations
11
The Lamb shift in muonic hydrogen and the proton radius from effective field theories
Clara Peset🇪🇸 · Antonio Pineda🇪🇸
We comprehensively analyse the theoretical prediction for the Lamb shift in muonic hydrogen, and the associated determination of the proton radius. We use effective field theories. This allows us to relate the proton radius with well-defined objects in quantum field theory, eliminating unnecessary model dependence. The use of effective field theories also helps us to organize the computation so that we can clearly state the parametric accuracy of the result. In this paper we review all (and check several of) the contributions to the energy shift of order $α^{5}$ , as well as those that scale like $α^{6} \times$ logarithms in the context of non-relativistic effective field theories of QED.
↳ hep-phnucl-thphysics.atom-phEPJA(2015)·34 citations
12
Semi-relativistic wave-phase approximation for two-body spinless bound states in 1+1 dimensions
K.-E. Thylwe · S. Belov
An approximate quantum-mechanical two-body equation for spinless particles incorporating relativistic kinematics is derived. The derivation is based on the relativistic energy-momentum relation $m c^{2} + ϵ = m^{2} c^{4} + p^{2} c^{2} + V$ for each single particle, where $m c^{2}$ is the particle rest mass energy, $p$ its linear momentum, $ϵ$ its dynamical energy, and $V$ being the time-like vector interaction potential. The resulting two-body equation assumes rapid wave oscillations in a single, slowly varying potential well. A Bohr-Sommerfeld-type quantization condition is obtained. The approximation is compared to exact results for the harmonic potential.
↳ quant-phmath-phmath.MPnucl-th0 citations
13
Simple way to the high-temperature expansion of relativistic Fermi-Dirac integrals
A.S. Khvorostukhin🇷🇺
The pressure of an ideal relativistic Fermi gas is computed as an infinite series for high temperatures at nonzero chemical potentials. The expansion of the particle number density, scalar density, and entropy density as first derivatives of the pressure is also found.
↳ math-phhep-phhep-thmath.MP+1PRD(2015)·4 citations

Affiliations

first authorsco-authorsvia INSPIRE