Nuclear Theory·nucl-th

Tuesday·December 1, 2015

18 papers—11 primary·7 cross-listed

01
[Submitted on 28 Nov 2015]
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.
Comments:
9 pages, three figures, Proceedings of the Eighth European Summer school on Experimental Nuclear Astrophysics, 2015, edited by C. Spitaleri, L. Lamia and R.G. Pizzone
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1511.08859 [pdf]
J.Phys.Conf.Ser.(2016)·12 citations
02
[Submitted on 28 Nov 2015]
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.
Subjects:
Nuclear Theory (nucl-th); Quantum Gases (cond-mat.quant-gas)
arXiv:
1511.08906 [pdf]
PRC(2016)·7 citations
03
[Submitted on 29 Nov 2015]
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.
Comments:
8 pages, 5 figures. arXiv admin note: text overlap with arXiv:1504.00756
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
1511.08965 [pdf]
SCPMA(2016)·15 citations
04
[Submitted on 30 Nov 2015]
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.
Subjects:
Nuclear Theory (nucl-th); High Energy Astrophysical Phenomena (astro-ph.HE); Solar and Stellar Astrophysics (astro-ph.SR); High Energy Physics — Phenomenology (hep-ph)
arXiv:
1511.09136 [pdf]
PRC(2016)·126 citations
05
[Submitted on 30 Nov 2015]
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.
Comments:
7 pages, 9 figures. To appear on Physical Review C
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
1511.09140 [pdf]
PRC(2015)·6 citations
06
[Submitted on 30 Nov 2015]
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.
Comments:
12 pages, submitted to the special issue weakly bound exotic nuclei on Few-Body Systems
Subjects:
Nuclear Theory (nucl-th); Quantum Gases (cond-mat.quant-gas)
arXiv:
1511.09184 [pdf]
Few Body Syst.(2016)·27 citations
07
[Submitted on 30 Nov 2015]
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.
Comments:
4 pages, 2 eps figures. A talk given at the 12th International Conference on Hypernuclear and Strange Particle Physics (HYP2015), September 7-12, 2015, Sendai, Japan
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
1511.09306 [pdf]
JPS Conf.Proc.(2017)·0 citations
08
[Submitted on 13 Oct 2015]
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.
Comments:
6 pages, 3 figures, contribution to NN2015
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1511.09326 [pdf]
EPJ Web Conf.(2016)·1 citation
09
[Submitted on 30 Nov 2015]
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.
Comments:
9 pages, 5 figures, to appear in proceedings of International Workshop "Shapes and Dynamics of Atomic Nuclei: Contemporary Aspects" (SDANCA-15), 8-10 October 2015, Sofia, Bulgaria
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1511.09366 [pdf]
Bulg.J.Phys.(2015)·1 citation
10
[Submitted on 30 Nov 2015]
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.
Comments:
Submitted to Physica Scripta for the Focus Issue on Nuclear Structure: Celebrating the 75 Nobel Prize
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1511.09373 [pdf]
Phys.Scripta(2016)·10 citations
11
[Submitted on 30 Nov 2015]
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.
Comments:
10 pages, 2 figures, Proc. Int. Workshop "Shapes and Dynamics of Atomic Nuclei: Contemporary Aspects" (SDANCA-15), October 8-10, 2015, Sofia, Bulgaria
Subjects:
Nuclear Theory (nucl-th); Quantum Physics (quant-ph)
arXiv:
1511.09387 [pdf]
Bulg.J.Phys.(2015)·0 citations
12
[Submitted on 27 Nov 2015] (cross-list from astro-ph.SR)
Order-of-magnitude physics of neutron stars
Andreas Reisenegger · Felipe S. Zepeda
We use basic physics and simple mathematics accessible to advanced undergraduate students to estimate the main properties of neutron stars. We set the stage and introduce relevant concepts by discussing the properties of "everyday" matter on Earth, degenerate Fermi gases, white dwarfs, and scaling relations of stellar properties with polytropic equations of state. Then, we discuss various physical ingredients relevant for neutron stars and how they can be combined in order to obtain a couple of different simple estimates of their maximum mass, beyond which they would collapse, turning into black holes. Finally, we use the basic structural parameters of neutron stars to briefly discuss their rotational and electromagnetic properties.
Comments:
13 pages, 3 figures, accepted for publication in European Physical Journal A
Subjects:
Solar and Stellar Astrophysics (astro-ph.SR); High Energy Astrophysical Phenomena (astro-ph.HE); General Relativity and Quantum Cosmology (gr-qc); Nuclear Theory (nucl-th)
arXiv:
1511.08813 [pdf]
EPJA(2016)·11 citations
13
[Submitted on 27 Nov 2015] (cross-list from hep-ph)
Spin Decomposition of Electron in QED
Xiangdong Ji🇺🇸 · Andreas Schäfer🇩🇪 · Feng Yuan🇺🇸 · Jian-Hui Zhang🇩🇪 · Yong Zhao🇺🇸
We perform a systematic study on the spin decomposition of an electron in QED at one-loop order. It is found that the electron orbital angular momentum defined in Jaffe-Manohar and Ji spin sum rules agrees with each other, and the so-called potential angular momentum vanishes at this order. The calculations are performed in both dimensional regularization and Pauli-Villars regularization for the ultraviolet divergences, and they lead to consistent results. We further investigate the calculations in terms of light-front wave functions, and find a missing contribution from the instantaneous interaction in light-front quantization. This clarifies the confusing issues raised recently in the literature on the spin decomposition of an electron, and will help to consolidate the spin physics program for nucleons in QCD.
Comments:
8 pages
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Theory (hep-th); Nuclear Theory (nucl-th)
arXiv:
1511.08817 [pdf]
PRD(2016)·25 citations
14
[Submitted on 29 Nov 2015] (cross-list from hep-ph)
The structure of pentaquarks $P_{c}^{+}$ in the chiral quark model
Gang Yang🇨🇳 · Jialun Ping🇨🇳
The recent experimental results of LHCb collaboration suggested the existence of pentaquark states with charmonium. To understand the structure of the states, a dynamical calculation of 5-quark systems with quantum numbers $I J^{P} = \frac{1}{2} (\frac{1}{2})^{\pm}$ , $\frac{1}{2} (\frac{3}{2})^{\pm}$ and $\frac{1}{2} (\frac{5}{2})^{\pm}$ is performed in the framework of chiral quark model with the help of gaussian expansion method. The results show that the negative parity states can be bound states while all of the positive parity states are the scattering states. The $P_{c} (4380)$ state is suggested to be the bound state of $Σ_{c}^{*} D$ . Although the energy of $Σ_{c} D^{*}$ is very close to the mass of $P_{c} (4450)$ , the inconsistent parity prevents the assignment. The calculated distances between quarks confirm the molecular nature of the states. Other five-quark bound states of the combination of $Σ_{c} D$ and $Σ_{c}^{*} D^{*}$ are also found in the region about 4.3GeV and 4.5GeV.
Comments:
6 pages, 1 figure
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1511.09053 [pdf]
PRD(2017)·93 citations
15
[Submitted on 30 Nov 2015] (cross-list from hep-lat)
N* Spectroscopy from Lattice QCD: The Roper Explained
Derek Leinweber🇦🇺 · Waseem Kamleh🇦🇺 · Adrian Kiratidis🇦🇺 · Zhan-Wei Liu🇦🇺 · Selim Mahbub🇦🇺 · Dale Roberts🇦🇺 · Finn Stokes🇦🇺 · Anthony W. Thomas🇦🇺 · Jiajun Wu🇦🇺
This brief review focuses on the low-lying even- and odd-parity excitations of the nucleon obtained in recent lattice QCD calculations. Commencing with a survey of the 2014-15 literature we'll see that results for the first even-parity excitation energy can differ by as much as 1 GeV, a rather unsatisfactory situation. Following a brief review of the methods used to isolate excitations of the nucleon in lattice QCD, and drawing on recent advances, we'll see how a consensus on the low-lying spectrum has emerged among many different lattice groups. To provide insight into the nature of these states we'll review the wave functions and electromagnetic form factors that are available for a few of these states. Consistent with the Luscher formalism for extracting phase shifts from finite volume spectra, the Hamiltonian approach to effective field theory in finite volume can provide guidance on the manner in which physical quantities manifest themselves in the finite volume of the lattice. With this insight, we will address the question; Have we seen the Roper in lattice QCD?
Comments:
Plenary presentation at NSTAR2015, The 10th International Workshop on the Physics of Excited Nucleons, 25-28 May 2015, Osaka University, Osaka, Japan. 8 pages, 6 figures
Subjects:
High Energy Physics — Lattice (hep-lat); High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1511.09146 [pdf]
JPS Conf.Proc.(2016)·31 citations
16
[Submitted on 30 Nov 2015] (cross-list from hep-ph)
Pion in the Medium with a Light-Front Model
J. P. B. C. de Melo🇧🇷 · Kazuo Tsushima (Laboratório de Física Teórica e Computacional - LFTC - Universidade Cruzeiro do Sul)🇧🇷 · Tobias Frederico (Instituto Tecnológico da Aeronáutica/DCTA)🇧🇷
The pion properties in symmetric nuclear matter are investigated with the Quark-Meson Coupling (QMC) Model plus the light-front constituent quark model~(LFCQM). The LFCQM has been quite successful in describing the properties of pseudoscalar mesons in vacuum, such as the electromagnetic elastic form factors, electromagnetic radii, and decay constants. We study the pion properties in symmetric nuclear matter with the in-medium input recalculated through the QMC model, which provides the in-medium modification of the LFCQM.
Comments:
To appear AIP PROCEEDINGS, XVI International Conference on Hadron Spectroscopy. HADRONS 2015, September 13-18, 2015, JLAB, Newport News, VA 6 pages, 4 figures eps, use AIP latex style
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1511.09219 [pdf]
AIP Conf.Proc.(2016)·5 citations
17
[Submitted on 30 Nov 2015] (cross-list from hep-ph)
Light neutrino contribution: is it all there is to neutrinoless double beta decay?
Namit Mahajan🇮🇳
We consider perturbative one loop QCD corrections to the light neutrino contribution to neutrinoless double beta decay and find large enhancement to the rate. QCD corrections also generate structures which mimic new physics contributions usually considered. Within some approximations, the net effect seem to almost saturate the experimental limits, and therefore seems to implt that this is all there is to neutrinoless double beta decay.
Comments:
5 pages, 1 figure. arXiv admin note: text overlap with arXiv:1406.2606
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Theory (nucl-th)
arXiv:
1511.09242 [pdf]
1 citation
18
[Submitted on 30 Nov 2015] (cross-list from cond-mat.quant-gas)
Ground state of the two-dimensional attractive Fermi gas: essential properties from few- to many-body
L. Rammelmüller🇺🇸 · W. J. Porter🇺🇸 · J. E. Drut🇺🇸
We calculate the ground-state properties of unpolarized two-dimensional attractive fermions in the range from few to many particles. Using first-principles lattice Monte Carlo methods, we determine the ground-state energy, Tan's contact, momentum distribution, and single-particle correlation function. We investigate those properties for systems of $N = 4, 8, ..., 40$ particles and for a wide range of attractive couplings. As the attractive coupling is increased, the thermodynamic limit is reached at progressively lower $N$ due to the dominance of the two-body sector. At large momenta $k$ , the momentum distribution displays the expected $k^{- 4}$ behavior, but its onset shifts from $k ≃ 1.8 k_{F}$ at weak coupling towards higher $k$ at strong coupling.
Comments:
7 pages, 4 figures, 3 tables
Subjects:
Quantum Gases (cond-mat.quant-gas); High Energy Physics — Lattice (hep-lat); Nuclear Theory (nucl-th)
arXiv:
1511.09361 [pdf]
PRA(2016)·17 citations

Affiliations

first authorsco-authorsvia INSPIRE