Nuclear Theory·nucl-th

Friday·April 28, 2017

13 papers—11 primary·2 cross-listed

01
[Submitted on 27 Apr 2017]
Extension of the Bjorken energy density formula of the initial state for relativistic heavy ion collisions
Zi-Wei Lin🇺🇸
For relativistic heavy ion collisions, the Bjorken formula is very useful for estimating the initial energy density once an initial time $τ_{0}$ is specified. However, it cannot be trusted at low energies, e.g. well below $s_{_{NN}} \approx 50$ GeV for central Au+Au collisions, when $τ_{0}$ is smaller than the finite time it takes for the two nuclei to cross each other. Here I extend the Bjorken formula by including the finite time duration of the initial energy production. Analytical solutions for the formed energy density in the central spacetime-rapidity region are derived for several time profiles. Compared to the Bjorken formula at low energies, the maximum energy density reached is much lower, increases much faster with the collision energy, and is much less sensitive to the uncertainty of the formation time, while the energy density time evolution is much longer. Comparisons with results from a multi-phase transport confirm the key features of these solutions. The effect of the finite longitudinal width of the initial energy production, which is neglected in the analytical results, is investigated with the transport model and shown to be small. This work thus provides a general model for the initial energy production of relativistic heavy ion collisions that is also valid at low energies.
Comments:
6 pages, 6 figures, added new figures and discussions, corrected typos in and below Eq.(13); final version to appear on Phys Rev C
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
1704.08418 [pdf]
PRC(2018)·22 citations
02
[Submitted on 27 Apr 2017]
Behaviour of pf shell under RMF+BCS Description
G. Saxena · M. Kaushik
We have employed RMF+BCS (relativistic mean-field plus BCS) approach to study behaviour of pf shell with the help of ground state properties of even-even nuclei. Our present investigations include separation energies , deformations, single particle energies, wavefunction, potential as well etc density distribution. As per recent experiments showing neutron magicity at N = 32 for Ca isotopes, our results with mass dependent pairing indicate a shell closure at N = 32 in Ca isotopes and a more strong shell closure at N = 34 in proton deficient 48Si because of reorganization of neutron pf shell. In a similar manner, proton pf shell structure is more likely to produce shell closure at Z = 34 with a doubly magic character for 84,116Se. We have also included N = 40 isotones and Z = 40 isotopes for our study and predicted 60Ca and 68Ni as doubly magic nuclei out of which 60Ca is found near dripline of Ca and a potential candidate for future studies in the chain of Ca isotopes next to doubly magic 52Ca.
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1704.08421 [pdf]
Chin.J.Phys.(2017)·12 citations
03
[Submitted on 27 Apr 2017]
Study of N = 16 shell closure within RMF+BCS approach
G. Saxena · M. Kaushik
We have employed RMF+BCS (relativistic mean-field plus BCS) ap- proach to study behaviour of N = 16 shell closure with the help of ground state properties of even-even nuclei. Our present investigations include sin- gle particle energies, deformations, separation energies as well as pairing energies etc. As per recent experiments showing neutron magicity at N = 16 for O isotopes, our results indicate a strong shell closure at N = 16 in 22C and 24O. A large gap is found in between neutron 2s1/2 and 1d3/2 states for 22C and 24O. These results are also supported by a sharp increase in two neutron shell gap, zero pairing energy contribution and with excellent agreement with available experimental data. Moreover, our calculations of N = 16 isotones are however found at variance for higher Z isotones like 36Ca, where experiments show high lying first excited 2+ state indicating shell closure at N = 16.
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1704.08422 [pdf]
Acta Phys.Polon.B(2017)·1 citation
04
[Submitted on 27 Apr 2017]
Nuclear response Functions with Realistic Interactions
H.S. Köhler
Linear density response functions are calculated for symmetric nuclear matter of normal density by time-evolving two-time Green's functions in real time. The feasability and convenience of this approach to this particular problem has been shown in previous publications. Calculations are here improved by using more 'realistic' interactions derived from phase-shifts by inverse scattering. Of particular interest is the effect of the strong correlations in the nuclear medium on the response. This as well as the related energy weighted sum rule, dependence on mean field and effective mass are some of the main objects of this investigation. Comparisons are made with the collision-less limit, the HF+RPA method. The importance of vertex corrections is demonstrated.
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1704.08428 [pdf]
0 citations
05
[Submitted on 27 Apr 2017]
From chiral NN(N) interactions to giant and pygmy resonances via extended RPA
P. Papakonstantinou · R. Trippel · R. Roth
The properties of giant and pygmy resonances are calculated starting from chiral two-and three-nucleon interactions. The aim is to assess the predictive power of modern Hamiltonians and especially the role of the three-nucleon force. Methods based on the random-phase approximation (RPA) provide an optimal description of the modes of interest with minimal computational requirements. Here we discuss the giant resonances (GRs) of 40,48Ca isotopes and their low-energy dipole response. A comparison with previous results obtained with a transformed Argonne V18 two-nucleon potential points to certain improvements.
Comments:
4 pages, 1 figure; from a talk at the 2016 Zakopane Conference on Nuclear Physics, September 2016
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1704.08429 [pdf]
Acta Phys.Polon.B(2017)·5 citations
06
[Submitted on 27 Apr 2017]
From bare interactions, low--energy constants and unitary gas to nuclear density functionals without free parameters: application to neutron matter
Denis Lacroix🇫🇷 · Antoine Boulet🇫🇷 · Marcella Grasso🇫🇷 · C.-J. Yang🇫🇷
We further progress along the line of Ref. [Phys. Rev. {\bf A 94}, 043614 (2016)] where a functional for Fermi systems with anomalously large $s$ -wave scattering length $a_{s}$ was proposed that has no free parameters. The functional is designed to correctly reproduce the unitary limit in Fermi gases together with the leading-order contributions in the s- and p-wave channels at low density. The functional is shown to be predictive up to densities $\sim 0.01$ fm $^{- 3}$ that is much higher densities compared to the Lee-Yang functional, valid for $ρ < 1 0^{- 6}$ fm $^{- 3}$ . The form of the functional retained in this work is further motivated. It is shown that the new functional corresponds to an expansion of the energy in $(a_{s} k_{F})$ and $(r_{e} k_{F})$ to all orders, where $r_{e}$ is the effective range and $k_{F}$ is the Fermi momentum. One conclusion from the present work is that, except in the extremely low--density regime, nuclear systems can be treated perturbatively in $- (a_{s} k_{F})^{- 1}$ with respect to the unitary limit. Starting from the functional, we introduce density--dependent scales and show that scales associated to the bare interaction are strongly renormalized by medium effects. As a consequence, some of the scales at play around saturation are dominated by the unitary gas properties and not directly to low-energy constants. For instance, we show that the scale in the s-wave channel around saturation is proportional to the so-called Bertsch parameter $ξ_{0}$ and becomes independent of $a_{s}$ . We also point out that these scales are of the same order of magnitude than those empirically obtained in the Skyrme energy density functional. We finally propose a slight modification of the functional such that it becomes accurate up to the saturation density $ρ ≃ 0.16$ fm $^{- 3}$ .
Subjects:
Nuclear Theory (nucl-th); Quantum Gases (cond-mat.quant-gas); Strongly Correlated Electrons (cond-mat.str-el); Nuclear Experiment (nucl-ex)
arXiv:
1704.08454 [pdf]
PRC(2017)·20 citations
07
[Submitted on 27 Apr 2017]
Six-quark structure of $d^{*} (2380)$ in chiral constituent quark model
Qi-Fang Lü🇨🇳 · Fei Huang🇨🇳 · Yu-Bing Dong🇨🇳 · Peng-Nian Shen🇨🇳 · Zong-Ye Zhang🇨🇳
The structure of $d^{*} (2380)$ is re-studied with the single cluster structure in the chiral SU(3) quark model which has successfully been employed to explain the $N - N$ scattering data and the binding energy of deuteron. The binding behavior of such a six quark system is solved by using a variational method. The trial wave function is chosen to be a combination of a basic spherical symmetric component of $[(0 s)^{6}]_{or b}$ in the orbital space with $0ℏ ω$ excitation and an inner structural deformation component of $[(0 s)^{5} (1 s)]_{or b}$ and $[(0 s)^{4} (0 p)^{2}]_{or b}$ in the orbital space with $2ℏ ω$ excitation, both of which are in the spatial [6] symmetry. It is shown that the mass of the system is about $2356$ MeV, which is qualitative consistent with the result both from the two-cluster configuration calculation and from the data measured by the WASA Collaborations. This result tells us that as long as the medium-range interaction due to the chiral symmetry consideration is properly introduced, the mass of system will be reduced in a rather large extent. It also implies that the observed $d^{*}$ is a six-quark bound state with respect to the $ΔΔ$ threshold, which again supports the conclusion that $d^{*}$ is a hexaquark dominant state.
Comments:
6 pages, 3 figures.
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
arXiv:
1704.08503 [pdf]
PRD(2017)·26 citations
08
[Submitted on 27 Apr 2017]
A Lee-Yang--inspired functional with a density--dependent neutron-neutron scattering length
M. Grasso🇫🇷 · D. Lacroix🇫🇷 · C.J. Yang🇫🇷
Inspired by the low--density Lee-Yang expansion for the energy of a dilute Fermi gas of density $ρ$ and momentum $k_{F}$ , we introduce here a Skyrme--type functional that contains only $s$ -wave terms and provides, at the mean--field level, (i) a satisfactory equation of state for neutron matter from extremely low densities up to densities close to the equilibrium point, and (ii) a good--quality equation of state for symmetric matter at density scales around the saturation point. This is achieved by using a density--dependent neutron-neutron scattering length $a (ρ$ ) which satisfies the low--density limit (for Fermi momenta going to zero) and has a density dependence tuned in such a way that the low--density constraint $∣ a (ρ) k_{F} ∣ \leq 1$ is satisfied at all density scales.
Comments:
5 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1704.08510 [pdf]
PRC(2017)·21 citations
09
[Submitted on 27 Apr 2017]
The Two-Nucleon 1S0 Amplitude Zero in Chiral Effective Field Theory
M. Sánchez Sánchez🇫🇷 · C.-J. Yang🇫🇷 · Bingwei Long🇨🇳 · U. van Kolck🇫🇷
We present a new rearrangement of short-range interactions in the $^{1} S_{0}$ nucleon-nucleon channel within Chiral Effective Field Theory. This is intended to reproduce the amplitude zero (scattering momentum $≃$ 340 MeV) at leading order, and it includes subleading corrections perturbatively in a way that is consistent with renormalization-group invariance. Systematic improvement is shown at next-to-leading order, and we obtain results that fit empirical phase shifts remarkably well all the way up to the pion-production threshold. An approach in which pions have been integrated out is included, which allows us to derive analytic results that also fit phenomenology surprisingly well.
Comments:
34 pages, 7 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1704.08524 [pdf]
PRC(2018)·44 citations
10
[Submitted on 27 Apr 2017]
Optimizing phonon space in the phonon-coupling model
V. Tselyaev · N. Lyutorovich · J. Speth · P.-G. Reinhard
We present a new scheme to select the most relevant phonons in the phonon-coupling model, named here time-blocking approximation (TBA). The new criterion, based on the phonon-nucleon coupling strengths rather than on $B (E L)$ values, is more selective and thus produces much smaller phonon spaces in TBA. This is beneficial in two respects: first, it curbs down the computational cost, and second, it reduces the danger of double counting in the expansion basis of TBA. We use here TBA in a form where the coupling strength is regularized to keep the given Hartree-Fock ground state stable. The scheme is implemented in an RPA and TBA code based on the Skyrme energy functional. We first explore carefully the cutoff dependence with the new criterion and can work out a natural (optimal) cutoff parameter. Then we use the freshly developed and tested scheme to a survey of giant resonances and low-lying collective states in six doubly magic nuclei looking also on the dependence of the results when varying the Skyrme parametrization.
Comments:
9 figures, 3 tables
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1704.08560 [pdf]
PRC(2017)·14 citations
11
[Submitted on 26 Apr 2017]
Clear indication of a strong I=0 Kbar-N attraction in the Lambda (1405) region from the CLAS photo-production data
M. Hassanvand🇮🇷 · Y. Akaishi🇯🇵 · T. Yamazaki🇯🇵
Possible existence of deeply bound kaonic nuclear systems was proposed Akaishi and Yamazaki (2002} more than a decade ago, based on an ansatz that the Lambda* = Lambda(1405) mass is 1405 MeV/c2, where the Lambda* is a Kbar-N quasi-bound state decaying to Sigma-pi. Recently, a large number of data on photo-production of Lambda(1405) in the gamma p to K+ pi{0+-} Sigma{0-+} reaction were provided by the CLAS collaboration Moriya et al.(2013}, and double-pole structure of the Lambda* has been intensively discussed by chiral dynamics analyses {Roca (2013),Mai 2015}, whereas we show that a Lambda* mass of 1405 MeV/c2 is deduced from the same CLAS data.
Comments:
1 page, 2 figures, RIKEN Progress Report
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
1704.08571 [pdf]
11 citations
12
[Submitted on 24 Apr 2017] (cross-list from hep-ph)
Correct Definition of Color Singlet P-Wave Non-Perturbative Matrix Element of Heavy Quarkonium Production
Gouranga C Nayak🇺🇸
Recently we have proved factorization of infrared divergences in NRQCD S-wave heavy quarkonium production at high energy colliders at all orders in coupling constant. One of the problem which still exists in the higher order pQCD calculation of color singlet P-wave heavy quarkonium production/anihillation is the appearance of non-canceling infrared divergences due to real soft gluons exchange, although no such infrared divergences are present in the color singlet S-wave heavy quarkonium. In this paper we find that since the non-perturbative matrix element of the color singlet P-wave heavy quarkonium production contains derivative operators, the gauge links are necessary to make it gauge invariant and be consistent with the factorization of such non-canceling infrared divergences at all orders in coupling constant.
Comments:
18 pages latex, Final Version, Accepted for Publication in JHEP
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Lattice (hep-lat); Nuclear Theory (nucl-th)
arXiv:
1704.07449 [pdf]
JHEP(2017)·26 citations
13
[Submitted on 25 Apr 2017] (cross-list from astro-ph.CO)
Big-bang nucleosynthesis constraints on dark-matter sectors revisited
C.A. Bertulani🇺🇸 · V. Challa🇺🇸 · J.J. He🇨🇳 · S.Q. Hou🇺🇸 · Ravinder Kumar🇺🇸
We extend previous studies of big bang nucleosynthesis, with the assumption that ordinary matter and dark matter sectors are entangled through the number of degrees of freedom entering the Friedmann equations. This conjecture allows us to find a relation between the temperatures of the weakly interacting matter and dark-matter sectors. The constraints imposed by observations are studied by comparison with calculations of big bang nucleosynthesis for the abundance of light elements. It is found that these constraints are compatible with cold dark matter and a wide range number of dark sectors.
Comments:
7 pages, 2 figures
Subjects:
Cosmology and Nongalactic Astrophysics (astro-ph.CO); High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1704.07803 [pdf]
4 citations

Affiliations

first authorsco-authorsvia INSPIRE