Nuclear Theory·nucl-th

Tuesday·December 1, 2015

18 papers—11 primary·7 cross-listed

01
Indirect methods in nuclear astrophysics
C.A. Bertulani · Shubhchintak · A. Mukhamedzhanov · A. S. Kadyrov · A. Kruppa · D. Y. Pang
We discuss recent developments in indirect methods used in nuclear astrophysics to determine the capture cross sections and subsequent rates of various stellar burning processes, when it is difficult to perform the corresponding direct measurements. We discuss in brief, the basic concepts of Asymptotic Normalization Coefficients, the Trojan Horse Method, the Coulomb Dissociation Method, (d,p), and charge-exchange reactions.
nucl-thJ.Phys.Conf.Ser.(2016)·12 citations
02
Transport properties of the Fermi hard-sphere system
Angela Mecca · Alessandro Lovato · Omar Benhar · Artur Polls
The transport properties of neutron star matter play an important role in many astrophysical processes. We report the results of a calculation of the shear viscosity and thermal conductivity coefficients of the hard-sphere fermion system of degeneracy $ν$ =2, that can be regarded as a model of pure neutron matter. Our approach is based on the effective interaction obtained from the formalism of correlated basis functions and the cluster expansion technique. The resulting transport coefficients show a strong sensitivity to the quasiparticle effective mass, reflecting the effect of second order contributions to the self-energy that are not taken into account in nuclear matter studies available in the literature.
nucl-thcond-mat.quant-gasPRC(2016)·7 citations
03
Theoretical study of fusion reactions $^{32}$ S + $^{94, 96}$ Zr and $^{40}$ Ca + $^{94, 96}$ Zr and quadrupole deformation of $^{94}$ Zr
Bing Wang🇨🇳 · Wei-Juan Zhao🇨🇳 · En-Guang Zhao🇨🇳 · Shan-Gui Zhou🇨🇳
The dynamic coupling effects on fusion cross sections for reactions $^{32}$ S + $^{94, 96}$ Zr and $^{40}$ Ca + $^{94, 96}$ Zr are studied with the universal fusion function formalism and an empirical coupled channel (ECC) model. An examination of the reduced fusion functions shows that the total effect of couplings to inelastic excitations and neutron transfer channels on fusion in $^{32}$ S + $^{94}$ Zr ( $^{40}$ Ca + $^{94}$ Zr) is almost the same as that in $^{32}$ S + $^{96}$ Zr ( $^{40}$ Ca + $^{96}$ Zr). The enhancements of the fusion cross section at sub-barrier energies due to inelastic channel coupling and neutron transfer channel coupling are evaluated separately by using the ECC model. The results show that effect of couplings to inelastic excitations channels in the reactions with $^{94}$ Zr as target should be similar as that in the reactions with $^{96}$ Zr as target. This implies that the quadrupole deformation parameters $β_{2}$ of $^{94}$ Zr and $^{96}$ Zr should be similar to each other. However, $β_{2}$ 's predicted from the finite-range droplet model, which are used in the ECC model, are quite different. Experiments on $^{48}$ Ca + $^{94}$ Zr or $^{36}$ S + $^{94}$ Zr are suggested to solve the puzzling issue concerning $β_{2}$ for $^{94}$ Zr.
nucl-thnucl-exSCPMA(2016)·15 citations
04
Nucleon-nucleon bremsstrahlung of dark gauge bosons and revised supernova constraints
Ermal Rrapaj🇺🇸 · Sanjay Reddy🇺🇸
We calculate the rate of production of hypothetical light vector bosons (LVBs) from nucleon-nucleon bremsstrahlung reactions in the soft radiation limit directly in terms of the measured nucleon-nucleon elastic cross sections. We use these results and the observation of neutrinos from supernova SN1987a to deduce constraints on the couplings of vector bosons with masses $≲ 200$ MeV to either electric charge (dark photons) or to baryon number. We establish for the first time strong constraints on LVB that couple only to baryon number, and revise earlier constraints on the dark photon. For the latter, we find that the excluded region of parameter space is diminished by about a factor of 10.
nucl-thastro-ph.HEastro-ph.SRhep-phPRC(2016)·126 citations
05
Improved Thermometer from Intermediate Mass Fragments in Heavy-Ion Collisions with Isobaric Yield Ratio Difference
Chun-Wang Ma🇨🇳 · Tian-Tian Ding🇨🇳 · Chun-Yuan Qiao🇨🇳 · Xi-Guang Cao🇨🇳
\item[Background] Temperature is an important parameter in studying many important questions in heavy-ion collisions. A thermometer based on the isobaric yield ratio (IYR) has been proposed [Ma \textit{et al.}, Phys. Rev. C \textbf{86}, 054611 (2012) and Ma \textit{et al.}, \textit{ibid.}, Phys. Rev. C \textbf{88}, 014609 (2013)]. \item[Purpose] An improved thermometer ( $T_{I B}$ ) is proposed based on the difference between IYRs. $T_{I B}$ obtained from isobars in different reactions will be compared. \item[Methods] The yields of three isobars are employed in $T_{I B}$ . The residual free energy of the three isobars are replaced by that of the binding energy. No secondary decay modification for odd $A$ fragment is used in $T_{I B}$ . \item[Results] The measured fragment yields in the 140 $A$ MeV $^{40, 48}$ Ca + $^{9}$ Be ( $^{181}$ Ta) and $^{58, 64}$ Ni + $^{9}$ Be ( $^{181}$ Ta), the 1 $A$ GeV $^{124, 136}$ Xe + Pb, and the $^{112, 124}$ Sn + $^{112, 124}$ Sn reactions have been analyzed to obtain $T_{I B}$ from IMFs. $T_{I B}$ from most of the fragments in the $^{40, 48}$ Ca and $^{58, 64}$ Ni reactions is in the range of 0.6 MeV $< T_{I B} <$ 3.5 MeV. $T_{I B}$ from most of the fragments in the $^{124}$ Xe and $^{112, 124}$ Sn reactions is in the range of 0.5 MeV $< T_{I B} <$ 2.5 MeV, while the range is 0.5 MeV $< T_{I B} <$ 4 MeV from most of the fragments in the $^{136}$ Xe reaction. In general, for most of the fragments $T_{I B}$ in the $^{40, 48}$ Ca and $^{58, 64}$ Ni reactions are very similar (except in the very neutron-rich fragments), and $T_{I B}$ from IMFs in the $^{124, 136}$ Xe and $^{112, 124}$ Sn reactions is also similar. A slightly dependence of $T_{I B}$ on $A$ is found. \item[Conclusions] Using the binding energy of the nucleus, $T_{I B}$ can be obtained without the knowledge of the free energies of fragments. In the investigated reactions, $T_{I B}$ from most of the IMFs is low.
nucl-thnucl-exPRC(2015)·6 citations
06
Efimov physics with $1/2$ spin-isospin fermions
A. Kievsky · M. Gattobigio
The structure of few-fermion systems having $1/2$ spin-isospin symmetry is studied using potential models. The strength and range of the two-body potentials are fixed to describe low energy observables in the angular momentum $L = 0$ state and spin $S = 0, 1$ channels of the two-body system. Successively the strength of the potentials are varied in order to explore energy regions in which the two-body scattering lengths are close to the unitary limit. This study is motivated by the fact that in the nuclear system the singlet and triplet scattering lengths are both large with respect to the range of the interaction. Accordingly we expect evidence of universal behavior in the three- and four-nucleon systems that can be observed from the study of correlations between observables. In particular we concentrate in the behavior of the first excited state of the three-nucleon system as the system moves away from the unitary limit. We also analyze the dependence on the range of the three-body force of some low-energy observables in the three- and four-nucleon systems.
nucl-thcond-mat.quant-gasFew Body Syst.(2016)·27 citations
07
Beyond-mean-field approach to low-lying spectra of $Λ$ hypernuclei
K. Hagino🇯🇵 · H. Mei🇯🇵 · J.M. Yao🇯🇵 · T. Motoba🇯🇵
Taking the hypernucleus $_{Λ}^{13}$ C as an example, we illustrate the miscroscopic particle-rotor model for low-lying spectra of hypernuclei. This approach is based on the beyond-mean-field method, with the particle number and angular momentum projections. The quantum fluctuation of the mean-field is also taken into account for the core nucleus using the generator coordinate method. We show that the impurity effect of $Λ$ hyperon, such as a change in $B (E 2)$ , is well described with this model. Our calculation indicates that the most important impurity effect in $s d$ -shell hypernuclei is a change in a deformation parameter rather than in a nuclear size.
nucl-thnucl-exJPS Conf.Proc.(2017)·0 citations
08
Effects of symmetry energy and momentum dependent interaction on low-energy reaction mechanisms
H. Zheng · M. Colonna · V. Baran · S. Burrello
We study the dipole response associated with the Pygmy Dipole Resonance (PDR) and the Isovector Giant Dipole Resonance (IVGDR), in connection with specific properties of the nuclear effective interaction (symmetry energy and momentum dependence), in the neutron-rich systems $^{68}$ Ni, $^{132}$ Sn and $^{208}$ Pb. We perform our investigation within a microscopic transport model based on the Landau-Vlasov kinetic equation. We observe that the peak energies of PDR and IVGDR are shifted to higher values when employing momentum dependent interactions, with respect to the results obtained neglecting momentum dependence. The calculated energies are close to the experimental values and similar to the results obtained in Hartree-Fock (HF) with Random Phase Approximation (RPA) calculations.
nucl-thEPJ Web Conf.(2016)·1 citation
09
Shapes and Dynamics from the Time-Dependent Mean Field
P. D. Stevenson · P. M. Goddard · A. Rios
Explaining observed properties in terms of underlying shape degrees of freedom is a well--established prism with which to understand atomic nuclei. Self--consistent mean--field models provide one tool to understand nuclear shapes, and their link to other nuclear properties and observables. We present examples of how the time--dependent extension of the mean--field approach can be used in particular to shed light on nuclear shape properties, particularly looking at the giant resonances built on deformed nuclear ground states, and at dynamics in highly-deformed fission isomers. Example calculations are shown of $^{28}$ Si in the first case, and $^{240}$ Pu in the latter case.
nucl-thBulg.J.Phys.(2015)·1 citation
10
Effective field theory for deformed atomic nuclei
T. Papenbrock · H. A. Weidenmüller
We present an effective field theory (EFT) for a model-independent description of deformed atomic nuclei. In leading order this approach recovers the well-known results from the collective model by Bohr and Mottelson. When higher-order corrections are computed, the EFT accounts for finer details such as the variation of the moment of inertia with the band head and the small magnitudes of interband $E 2$ transitions. For rotational bands with a finite spin of the band head, the EFT is equivalent to the theory of a charged particle on the sphere subject to a magnetic monopole field.
nucl-thPhys.Scripta(2016)·10 citations
11
Partial Dynamical Symmetry in Odd-Mass Nuclei
A. Leviatan
Spectral features of the odd-mass nucleus $^{195}$ Pt are analyzed by means of an interacting boson-fermion Hamiltonian with SO(6) partial dynamical symmetry. For the latter, selected eigenstates are solvable and preserve the symmetry exactly, while other states are mixed. The analysis constitutes a first example of this novel symmetry construction in a mixed Bose-Fermi system.
nucl-thquant-phBulg.J.Phys.(2015)·0 citations

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