Nuclear Theory·nucl-th

Tuesday·January 31, 2017

12 papers—6 primary·6 cross-listed

01
[Submitted on 27 Jan 2017]
A microscopic nucleon spectral function for finite nuclei featuring two- and trhee-nucleon short-range correlations: I. The model vs. ab-initio calculations for the three-nucleon systems
Claudio Ciofi degli Atti · Chiara Benedetta Mezzetti · Hiko Morita
The main features of the convolution model which, in the region of two-nucleon (2N) and three-nucleon (3N) short-range correlations (SRC), describes the one-nucleon momentum distribution n(k_1) and the spectral function P(k_1,E) in terms of a convolution integral involving the relative n_{rel}(k_{rel}) and the center-of-mass n_{c.m.}(K_{c.m.}) momentum distributions of a nucleon-nucleon pair, are illustrated in detail. It is stressed that the model, which stems from the universal property of factorization exhibited by the nuclear wave function at short inter-nucleon distances, is only applicable in a well-defined region of k_{rel} and K_{c.m.}; it is shown, in particular, that the requirement of factorization introduces a severe constraint on the values of k_{rel} and K_{c.m.} that appear in the convolution integral. Using ab-initio relative and c.m. momentum distributions for ^3He, the validity of the convolution model is investigated by comparing the model spectral function and momentum distributions with the ones resulting from ab-initio calculations performed with realistic local NN interaction of the Argonne family. It is shown that when the constraint on the value of k_{rel} and K_{c.m.} are correctly taken into account and only 2N SRC are taken into account, the convolution model is in good agreement with the ab-initio spectral function in the region of the peak exhibited by the latter, whereas far from the peak, particularly at high values of the removal energy, the model spectral function can be qualitatively reconciled with the ab-initio spectral function only by considering the effects of 3N SRC. As for the nucleon momentum distribution, the effects of 3N SRC appears to be very small.
Comments:
25 pages, 8 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1701.08211 [pdf]
PRC(2017)·13 citations
02
[Submitted on 28 Jan 2017]
Derivative Expansion of Wave Function Equivalent Potentials
Takuya Sugiura🇯🇵 · Noriyoshi Ishii🇯🇵 · Makoto Oka🇯🇵
Properties of the wave function equivalent potentials introduced by HAL QCD collaboration are studied in a non-relativistic coupled-channel model. The derivative expansion is generalized, and then applied to the energy-independent and non-local potentials. The expansion coefficients are determined from analytic solutions to the Nambu-Bethe-Salpeter wave functions. The scattering phase shifts computed from these potentials are compared with the exact values to examine the convergence of the expansion. It is confirmed that the generalized derivative expansion converges in terms of the scattering phase shift rather than the functional structure of the non-local potentials. It is also found that the convergence can be improved by tuning either the choice of interpolating fields or expansion scale in the generalized derivative expansion.
Comments:
16 pages, 17 figures
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Lattice (hep-lat); High Energy Physics — Phenomenology (hep-ph)
arXiv:
1701.08268 [pdf]
PRD(2017)·5 citations
03
[Submitted on 29 Jan 2017]
Reproduction of exact solutions of Lipkin model by nonlinear random-phase approximation
J. Terasaki · A. Smetana · F. Šimkovic · M. I. Krivoruchenko
It is shown that the random-phase approximation (RPA) method with its nonlinear generalization, which was previously considered as approximation, reproduces the exact solutions of the Lipkin model. The nonlinear RPA is based on an equation nonlinear on eigenvectors and includes many-particle-many-hole components in the creation operator of the excited states. We demonstrate the exact character of solutions analytically for the particle number $N$ = 2 and, numerically, for $N$ = 20. This finding indicates that the nonlinear RPA is equivalent to the exact Schrödinger equation, which opens up new possibilities for realistic calculations in many-body problems.
Comments:
17 pages, 9 figures
Subjects:
Nuclear Theory (nucl-th); Strongly Correlated Electrons (cond-mat.str-el)
arXiv:
1701.08368 [pdf]
IJMPE(2017)·3 citations
04
[Submitted on 30 Jan 2017]
Three-body halo states in effective field theory
Emil Ryberg · Christian Forssén · Lucas Platter
In this paper we study the renormalization of Halo effective field theory applied to the Helium-6 halo nucleus seen as an alpha-neutron-neutron three-body state. We include the 0+ dineutron channel together with both the 3/2- and 1/2- neutron-alpha channels into the field theory and study all of the six lowest-order three-body interactions that are present. Furthermore, we discuss three different prescriptions to handle the unphysical poles in the P-wave two-body sector. In the simpler field theory without the 1/2- channel present we find that the bound-state spectrum of the field theory is renormalized by the inclusion of a single three-body interaction. However, in the field theory with both the 3/2- and 1/2- included, the system can not be renormalized by only one three-body operator.
Comments:
13 pages, 6 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1701.08576 [pdf]
Few Body Syst.(2017)·15 citations
05
[Submitted on 30 Jan 2017]
Study of Low-Lying Baryons with Hamiltonian Effective Field Theory
Zhan-Wei Liu🇦🇺 · Jonathan M. M. Hall🇦🇺 · Waseem Kamleh🇦🇺 · Derek B. Leinweber🇦🇺 · Finn M. Stokes🇦🇺 · Anthony W. Thomas🇦🇺 · Jia-Jun Wu🇦🇺
Drawing on experimental data for baryon resonances, Hamiltonian effective field theory (HEFT) is used to predict the positions of the finite-volume energy levels to be observed in lattice QCD simulations. We have studied the low-lying baryons $N^{*} (1535)$ , $N^{*} (1440)$ , and $Λ (1405)$ . In the initial analysis, the phenomenological parameters of the Hamiltonian model are constrained by experiment and the finite-volume eigenstate energies are a prediction of the model. The agreement between HEFT predictions and lattice QCD results obtained at finite volume is excellent. These lattice results also admit a more conventional analysis where the low-energy coefficients are constrained by lattice QCD results, enabling a determination of resonance properties from lattice QCD itself. The role and importance of various components of the Hamiltonian model are examined in the finite volume. The analysis of the lattice QCD data can help us to undertand the structure of these states better.
Comments:
8 pages, 6 figures, proceeding of INPC 2016
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
arXiv:
1701.08582 [pdf]
PoS(2017)·2 citations
06
[Submitted on 30 Jan 2017]
Extracting three-body breakup observables from CDCC calculations with core excitations
R. de Diego · R. Crespo · A.M. Moro
Core-excitation effects in the scattering of two-body halo nuclei have been investigated in previous works. In particular, these effects have been found to affect in a significant way the breakup cross sections of neutron-halo nuclei with a deformed core. To account for these effects, appropriate extensions of the continuum-discretized coupled-channels (CDCC) method have been recently proposed. We aim to extend these studies to the case of breakup reactions measured under complete kinematics or semi-inclusive reactions in which only the angular or energy distribution of one of the outgoing fragments is measured. We use the standard CDCC method as well as its extended version with core excitations (XCDCC), assuming a pseudo-state basis for describing the projectile states. Two- and three-body observables are computed by projecting the discrete two-body breakup amplitudes, obtained within these reaction frameworks, onto two-body scattering states with definite relative momentum of the outgoing fragments and a definite state of the core nucleus. The presented method provides a tool to compute double and triple differential cross sections for outgoing fragments following the breakup of a two-body projectile, and might be useful to analyze breakup reactions with other deformed weakly-bound nuclei, for which core excitations are expected to play a role. We have found that, while dynamical core excitations are important for the proton target at intermediate energies, they are very small for the Zn target at energies around the Coulomb barrier.
Comments:
12 pages, 8 figures, submitted to Physical Review C
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1701.08616 [pdf]
PRC(2017)·15 citations
07
[Submitted on 28 Jan 2017] (cross-list from hep-th)
The ideal relativistic fluid limit for a medium with polarization
David Montenegro🇧🇷 · Leonardo Tinti🇺🇸 · Giorgio Torrieri🇧🇷
We use Lagrangian effective field theory techniques to construct the equations of motion for an ideal relativistic fluid whose constituent degrees of freedom have microscopic polarization. We discuss the meaning of such a system, and argue that it is the first term in the EFT appropriate for describing polarization observables in heavy ion collisions, such as final state particle polarization and chiral magnetic and vortaic effects. We show that this system will generally require non-dissipative dynamics at higher order in gradient than second order, leading to potential stability issues known with such systems. We comment on the significance of this in the light of conjectured lower limits on viscosity.
Comments:
Version accepted for publication in Phys.Rev.D Discussion extended and clarified, conclusions and main ideas unchanged
Subjects:
High Energy Physics — Theory (hep-th); High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th); Fluid Dynamics (physics.flu-dyn)
arXiv:
1701.08263 [pdf]
PRD(2017)·162 citations
08
[Submitted on 29 Jan 2017] (cross-list from astro-ph.HE)
Dependence of weak interaction rates on the nuclear composition during stellar core collapse
Shun Furusawa · Hiroki Nagakura · Kohsuke Sumiyoshi · Chinami Kato · Shoichi Yamada
We investigate the influences of the nuclear composition on the weak interaction rates of heavy nuclei during the core collapse of massive stars. The nuclear abundances in nuclear statistical equilibrium (NSE) are calculated by some equation of state (EOS) models including in-medium effects on nuclear masses. We systematically examine the sensitivities of electron capture and neutrino-nucleus scattering on heavy nuclei to the nuclear shell effects and the single nucleus approximation. We find that the washout of shell effects at high temperatures brings significant change to weak rates by smoothing the nuclear abundance distribution: the electron capture rate decreases by $\sim$ 20 $%$ in the early phase and increases by $\sim$ 40 $%$ in the late phase at most, while the cross section for neutrino-nucleus scattering is reduced by $\sim$ 15 $%$ . This is because the open-shell nuclei become abundant instead of those with closed neutron shells as the shell effects disappear. We also find that the single-nucleus description based on the average values leads to underestimations of weak rates. Electron captures and neutrino coherent scattering on heavy nuclei are reduced by $\sim$ 80 $%$ in the early phase and by $\sim$ 5 $%$ in the late phase, respectively. These results indicate that NSE like EOS accounting for shell washout is indispensable for the reliable estimation of weak interaction rates in simulations of core-collapse supernovae.
Comments:
28 pages 14 figures, accepted for publication in Phys. Rev. C
Subjects:
High Energy Astrophysical Phenomena (astro-ph.HE); Nuclear Theory (nucl-th)
arXiv:
1701.08414 [pdf]
PRC(2017)·36 citations
09
[Submitted on 29 Jan 2017] (cross-list from hep-ph)
$D$ - meson production at very forward rapidities: estimating the intrinsic charm contribution
F. Carvalho🇧🇷 · A.V. Giannini🇧🇷 · V.P. Goncalves🇧🇷 · F.S. Navarra🇧🇷
We study $D$ - meson production at forward rapidities taking into account the non - linear effects in the QCD dynamics and the intrinsic charm component of the proton wave function. The total cross section, the rapidity distributions and the Feynman - $x$ distributions are calculated for $pp$ collisions at different center of mass energies. Our results show that, at the LHC, the intrinsic charm component changes the $D$ rapidity distributions in a region which is beyond the coverage of the LHCb detectors. At higher energies the IC component dominates the $y$ and $x_{F}$ distributions exactly in the range where the produced $D$ mesons decay and contribute the most to the prompt atmospheric neutrino flux measured by the ICECUBE Collaboration. We compute the $x_{F}$ - distributions and demonstrate that they are enhanced at LHC energies by approximately one order of magnitude in the $0.2 \leq x_{F} \leq 0.8$ range.
Comments:
11 pages, 8 figures. v2: new references added, minor changes in the text, changes in the figures; v3: new results with better treatment for the fragmentation function of partons into D0/D0bar mesons; conclusions unchanged; matches the version published in Phys. Rev. D
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1701.08451 [pdf]
PRD(2017)·20 citations
10
[Submitted on 30 Jan 2017] (cross-list from astro-ph.HE)
Strangeon and Strangeon Star
Xiaoyu Lai (HUE)🇨🇳 · Renxin Xu (PKU)🇨🇳
The nature of pulsar-like compact stars is essentially a central question of the fundamental strong interaction (explained in quantum chromo-dynamics) at low energy scale, the solution of which still remains a challenge though tremendous efforts have been tried. This kind of compact objects could actually be strange quark stars if strange quark matter in bulk may constitute the true ground state of the strong-interaction matter rather than Fe^56 (the so-called Witten's conjecture). From astrophysical points of view, however, it is proposed that strange cluster matter could be absolutely stable and thus those compact stars could be strange cluster stars in fact. This proposal could be regarded as a general Witten's conjecture: strange matter in bulk could be absolutely stable, in which quarks are either free (for strange quark matter) or localized (for strange cluster matter). Strange cluster with three-light-flavor symmetry is renamed strangeon, being coined by combining "strange nucleon" for the sake of simplicity. A strangeon star can then be thought as a 3-flavored gigantic nucleus, and strangeons are its constituent as an analogy of nucleons which are the constituent of a normal (micro) nucleus. The observational consequences of strangeon stars show that different manifestations of pulsar-like compact stars could be understood in the regime of strangeon stars, and we are expecting more evidence for strangeon star by advanced facilities (e.g., FAST, SKA, and eXTP).
Comments:
Proceedings CSQCD5, 23-27 May 2016 GSSI and LNGS (L'Aquila, Italy)
Subjects:
High Energy Astrophysical Phenomena (astro-ph.HE); Nuclear Theory (nucl-th)
arXiv:
1701.08463 [pdf]
J.Phys.Conf.Ser.(2017)·40 citations
11
[Submitted on 30 Jan 2017] (cross-list from hep-ph)
First Results with HIJING++ in High-Energy Heavy-Ion Collisions
Gergely Gábor Barnaföldi🇭🇺 · Gábor Bíró🇭🇺 · Miklos Gyulassy🇭🇺 · Szilveszter Miklós Haranozó🇭🇺 · Péter Lévai🇭🇺 · Guoyang Ma🇨🇳 · Gábor Papp🇭🇺 · Xin-Nian Wang🇺🇸 · Ben-Wei Zhang🇨🇳
First calculated results with the new HIJING++ are presented for identified hadron production in high-energy heavy ion collisions. The recently developed HIJING++ version is based on the latest version of PYTHIA8 and contains all the nuclear effects has been included in the HIJING2.552, which will be improved by a new version of the shadowing parametrization and jet quenching module. Here, we summarize the major changes of the new program code beside the comparison between experimental data for some specific high-energy nucleus-nucleus collisions.
Comments:
4 pages, 3 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1701.08496 [pdf]
Nucl.Part.Phys.Proc.(2017)·12 citations
12
[Submitted on 30 Jan 2017] (cross-list from hep-lat)
Finite temperature gluon spectral functions from $N_{f} = 2 + 1 + 1$ lattice QCD
Ernst-Michael Ilgenfritz🇷🇺 · Jan M. Pawlowski🇩🇪 · Alexander Rothkopf🇩🇪 · Anton Trunin🇷🇺
We investigate gluon spectral functions at finite temperature in Landau gauge, based on a subset of lattice QCD ensembles with $N_{f} = 2 + 1 + 1$ dynamical twisted mass quarks flavors, generated by the tmfT collaboration. Our study uses a novel Bayesian approach for the extraction of non-positive definite spectral functions, which for each binned spatial momentum takes into account the gluon correlation functions at all available discrete imaginary frequencies. The spectral functions are extracted at three different lattice spacing, where for each of them, a scan of temperatures around the crossover transition is carried out at fixed scale. We find indications for the existence of a well defined quasi-particle peak. Due to a relatively small number of imaginary frequencies available, we focus on the momentum and temperature dependence of the position of this spectral feature. This dispersion relation reveals different in-medium masses for longitudinal and transversal gluons at high temperatures, qualitatively consistent with weak coupling expectations.
Comments:
23 pages, 30 figures
Subjects:
High Energy Physics — Lattice (hep-lat); High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Theory (hep-th); Nuclear Theory (nucl-th)
arXiv:
1701.08610 [pdf]
EPJC(2018)·32 citations

Affiliations

first authorsco-authorsvia INSPIRE