Nuclear Theory·nucl-th

Tuesday·March 12, 2019

13 papers—6 primary·7 cross-listed

01
[Submitted on 9 Mar 2019]
Maximum Mass of Hybrid Stars in the Quark Bag Model
G. B. Alaverdyan🇦🇲 · Yu. L. Vartanyan🇦🇲
The effect of model parameters in the equation of state for quark matter on the magnitude of the maximum mass of hybrid stars is examined. Quark matter is described in terms of the extended MIT bag model including corrections for one-gluon exchange. For nucleon matter in the range of densities corresponding to the phase transition, a relativistic equation of state is used that is calculated with two particle correlations taken into account based on using the Bonn meson-exchange potential. The Maxwell construction is used to calculate the characteristics of the first order phase transition and it is shown that for a fixed value of the strong interaction constant $α_{s}$ , the baryon concentrations of the coexisting phases grow monotonically as the bag constant B increases. It is shown that for a fixed value of the strong interaction constant $α_{s}$ , the maximum mass of a hybrid star increases as the bag constant $B$ decreases. For a given value of the bag parameter $B$ , the maximum mass rises as the strong interaction constant $α_{s}$ increases. It is shown that the configurations of hybrid stars with maximum masses equal to or exceeding the mass of the currently known most massive pulsar are possible for values of the strong interaction constant $α_{s} > 0.6$ and sufficiently low values of the bag constant.
Comments:
9 pages, 3 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1903.03875 [pdf]
Astrophysics(2017)·12 citations
02
[Submitted on 10 Mar 2019]
Cluster structure of light nuclei
R. Bijker · F. Iachello
We review recent studies of the cluster structure of light nuclei within the framework of the algebraic cluster model (ACM) for nuclei composed of k alpha-particles and within the framework of the cluster shell model (CSM) for nuclei composed of k alpha-particles plus x additional nucleons. The calculations, based on symmetry considerations and thus for the most part given in analytic form, are compared with experiments in light cluster nuclei. The comparison shows evidence for Z_2, D_{3h} and T_d symmetry in the even-even nuclei 8Be (k=2), 12C (k=3) and 16O (k=4), respectively, and for the associated double groups Z'_2 and D'_{3h} in the odd nuclei 9Be, 9B (k=2, x=1) and 13C (k=3, x=1), respectively.
Comments:
75 pages, 36 figures, 11 tables, final versión, Progress in Particle and Nuclear Physics (2019), in press
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
1903.04076 [pdf]
PPNP(2020)·49 citations
03
[Submitted on 11 Mar 2019]
Cold dilute nuclear matter with $α$ -particle condensation in a generalized nonlinear relativistic mean-field model
Zhao-Wen Zhang · Lie-Wen Chen
We explore the thermodynamic properties of homogeneous cold (zero-temperature) nuclear matter including nucleons and $α$ -particle condensation at low densities by using a generalized nonlinear relativistic mean-field (gNL-RMF) model. In the gNL-RMF model, the $α$ -particle is included as explicit degree of freedom and treated as point-like particle with its interaction described by meson exchanges and the in-medium effects on the $α$ binding energy is described by density- and temperature-dependent energy shift with the parameters obtained by fitting the experimental Mott density. We find that below the dropping density $n_{drop}$ ( $\sim 3 \times 1 0^{- 3}$ fm $^{- 3}$ ), the zero-temperature symmetric nuclear matter is in the state of pure Bose-Einstein condensate (BEC) of $α$ particles while the neutron-rich nuclear matter is composed of $α$ -BEC and neutrons. Above the $n_{drop}$ , the fraction of $α$ -BEC decreases with density and vanishes at the transition density $n_{t}$ ( $\sim 8 \times 1 0^{- 3}$ fm $^{- 3}$ ). Above the $n_{t}$ , the nuclear matter becomes pure nucleonic matter. Our results indicate that the empirical parabolic law for the isospin asymmetry dependence of nuclear matter equation of state is heavily violated by the $α$ -particle condensation in the zero-temperature dilute nuclear matter, making the conventional definition of the symmetry energy meaningless. We investigate the symmetry energy defined under parabolic approximation for the zero-temperature dilute nuclear matter with $α$ -particle condensation, and find it is significantly enhanced compared to the case without clusters and becomes saturated at about $7$ MeV at very low densities ( $≲ 1 0^{- 3}$ fm $^{- 3}$ ). The critical temperature for $α$ -condensation in homogeneous dilute nuclear matter is also discussed.
Comments:
10 pages, 5 figures. Effects of resonance and continuum states considered effectively, the symmetry energy defined under parabolic approximation investigated, and presentation improved. Accepted version to appear in PRC
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
1903.04108 [pdf]
PRC(2019)·11 citations
04
[Submitted on 11 Mar 2019]
Analysis of nuclear structure in a converging expansion scheme
Hana Gil · Young-Min Kim · Chang Ho Hyun · Panagiota Papakonstantinou · Yongseok Oh
In the framework of the KIDS generalized energy density functional (EDF), the nuclear equation of state (EoS) is expressed as an expansion in powers of the Fermi momentum or the cubic root of the density ( $ρ^{1/3}$ ). Although an optimal number of converging terms was obtained in specific cases of fits to empirical data and pseudodata, the degree of convergence remains to be examined not only for homogeneous matter but also for finite nuclei. One goal of the present work is to validate the minimal and optimal number of EoS parameters required for the description of homogeneous nuclear matter over a wide range of densities relevant for astrophysical applications. The major goal is to examine the validity of the adopted expansion scheme for an accurate description of finite nuclei. To this end we vary the values of the high-order derivatives of the EoS, namely the skewness of the energy of symmetric nuclear matter and the kurtosis of the symmetry energy, at saturation and examine the relative importance of each term in $ρ^{1/3}$ expansion for homogeneous matter. For given sets of EoS parameters determined in this way, we define equivalent Skyrme-type functionals and examine the convergence in the description of finite nuclei focusing on the masses and charge radii of closed-shell nuclei. The EoS of symmetric nuclear matter is found to be efficiently parameterized with only 3 parameters and the symmetry energy (or the energy of pure neutron matter) with 4 parameters when the EoS is expanded in the power series of the Fermi momentum. Higher-order EoS parameters do not produce any improvement, in practice, in the description of nuclear ground-state energies and charge radii, which means that they cannot be constrained by bulk properties of nuclei.
Comments:
15 pages, 10 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1903.04123 [pdf]
PRC(2019)·30 citations
05
[Submitted on 11 Mar 2019]
On calculating response functions via their Lorentz integral transforms
Victor D. Efros · Winfried Leidemann · Veronika Yu. Shalamova
The accuracy of reconstruction of a response function from its Lorentz integral transform is studied in an exactly solvable model. An inversion procedure is elaborated in detail and features of the procedure are studied. Unlike results in the literature pertaining to the same model, the response function is reconstructed from its Lorentz integral transform with rather high accuracy.
Comments:
18 pages, 5 figures, submitted to FBS
Subjects:
Nuclear Theory (nucl-th); Computational Physics (physics.comp-ph)
arXiv:
1903.04189 [pdf]
Few Body Syst.(2019)·3 citations
06
[Submitted on 11 Mar 2019]
Three-body problem with velocity-dependent optical potentials: a case of $(d, p)$ reactions
N.K. Timofeyuk
The change in mass of a nucleon, arising from its interactions with other nucleons inside the target, results in velocity-dependent terms in the Schrödinger equation that describes nucleon scattering. It has recently been suggested in a number of publications that introducing and fitting velocity-dependent terms improves the quality of the description of nucleon scattering data for various nuclei. The present paper discusses velocity-dependent optical potentials in a context of a three-body problem used to account for deuteron breakup in the entrance channel of $(d, p)$ reactions. Such potentials form a particular class of nonlocal optical potentials which are a popular object of modern studies. It is shown here that because of a particular structure of the velocity-dependent terms the three-body problem can be formulated in two different ways. Solving this problem within an adiabatic approximation results in a significant difference between the two approaches caused by contributions from the high $n$ - $p$ momenta in deuteron in one of them. Solving the three-body problem beyond the adiabatic approximation may remove such contributions, which is indirectly confirmed by replacing the adiabatic approximation by the folding Watanabe model where such contributions are suppressed. Discussion of numerical results is carried out for the $^{40}$ Ca( $d, p)^{41}$ Ca reaction where experimental data both on elastic scattering in entrance and exit channels and on nucleon transfer are available.
Comments:
Accepted for publications in Journal of Physics G
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
1903.04216 [pdf]
J.Phys.G(2019)·2 citations

Affiliations

first authorsco-authorsvia INSPIRE

Maximum Mass of Hybrid Stars in the Quark Bag Model

Cluster structure of light nuclei

Cold dilute nuclear matter with α-particle condensation in a generalized nonlinear relativistic mean-field model

Analysis of nuclear structure in a converging expansion scheme

On calculating response functions via their Lorentz integral transforms

Three-body problem with velocity-dependent optical potentials: a case of (d,p) reactions

Affiliations

Cold dilute nuclear matter with $α$ -particle condensation in a generalized nonlinear relativistic mean-field model

Three-body problem with velocity-dependent optical potentials: a case of $(d, p)$ reactions