Nuclear Theory·nucl-th

Wednesday·October 7, 2015

13 papers—7 primary·6 cross-listed

08
[Submitted on 16 Jul 2015] (cross-list from quant-ph)
High-precision evaluation of Wigner's d-matrix by exact diagonalization
X. M. Feng · P. Wang🇨🇳 · W. Yang🇨🇳 · G. R. Jin
The precise calculations of the Wigner's d-matrix are important in various research fields. Due to the presence of large numbers, direct calculations of the matrix using the Wigner's formula suffer from loss of precision. We present a simple method to avoid this problem by expanding the d-matrix into a complex Fourier series and calculate the Fourier coefficients by exactly diagonalizing the angular-momentum operator $J_{y}$ in the eigenbasis of $J_{z}$ . This method allows us to compute the d-matrix and its various derivatives for spins up to a few thousand. The precision of the d-matrix from our method is about $1 0^{- 14}$ for spins up to $100$ .
Comments:
4 pages, 3 figures; a Fortran90 code is included; resubmitted to Phys. Rev. E
Subjects:
Quantum Physics (quant-ph); Mathematical Physics (math-ph); math.MP (math.MP); Nuclear Theory (nucl-th); Atomic Physics (physics.atom-ph); Computational Physics (physics.comp-ph)
arXiv:
1507.04535 [pdf]
PRE(2015)·15 citations
09
[Submitted on 2 Oct 2015] (cross-list from cond-mat.mes-hall)
Fluctuation Phenomena in Chaotic Dirac Quantum Dots: Artificial Atoms on Graphene Flakes
J. G. G. S. Ramos · M. S. Hussein · A. L. R. Barbosa
We develop the stub model for the Dirac Quantum Dot, an electron confining device on a grapheme surface. Analytical results for the average conductance and the correlation functions are obtained and found in agreement with those found previously using semiclassical calculation. Comparison with available data are presented. The results reported here demonstrate the applicability of Random Matrix Theory in the case of Dirac electrons confined in a stadium.
Comments:
9 pages, 4 figures
Subjects:
Mesoscale and Nanoscale Physics (cond-mat.mes-hall); cond-mat.dis-nn (cond-mat.dis-nn); Nuclear Theory (nucl-th)
arXiv:
1510.00750 [pdf]
PRB(2016)·7 citations
10
[Submitted on 5 Oct 2015] (cross-list from hep-ph)
Status of Chiral-Scale Perturbation Theory
R.J. Crewther🇦🇺 · Lewis C. Tunstall🇨🇭
Chiral-scale perturbation theory $χ$ PT $_{σ}$ has been proposed as an alternative to chiral $S U (3)_{L} \times S U (3)_{R}$ perturbation theory which explains the $Δ I = 1/2$ rule for kaon decays. It is based on a low-energy expansion about an infrared fixed point in three-flavor QCD. In $χ$ PT $_{σ}$ , quark condensation $⟨ q ˉ q ⟩_{vac} \neq = 0$ induces nine Nambu-Goldstone bosons: $π, K, η$ and a QCD dilaton $σ$ which we identify with the $f_{0} (500)$ resonance. Partial conservation of the dilatation and chiral currents constrains low-energy constants which enter the effective Lagrangian of $χ$ PT $_{σ}$ . These constraints allow us to obtain new phenomenological bounds on the dilaton decay constant via the coupling of $σ / f_{0}$ to pions, whose value is known precisely from dispersive analyses of $π π$ scattering. Improved predictions for $σ \to γ γ$ and the $σ N N$ coupling are also noted. To test $χ$ PT $_{σ}$ for kaon decays, we revive a 1985 proposal for lattice methods to be applied to $K \to π$ on-shell.
Comments:
10 pages, 1 figure. Presented at the 8th International Workshop on Chiral Dynamics, 29 June 2015 - 03 July 2015, Pisa, Italy. Revision: references and comment added
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Lattice (hep-lat); Nuclear Theory (nucl-th)
arXiv:
1510.01322 [pdf]
PoS(2015)·24 citations
11
[Submitted on 6 Oct 2015] (cross-list from nucl-ex)
Mass measurement of 56Sc reveals a small A=56 odd-even mass staggering, implying a cooler accreted neutron star crust
Z. Meisel🇺🇸 · S. George🇺🇸 · S. Ahn🇺🇸 · D. Bazin🇺🇸 · B.A. Brown🇺🇸 · J. Browne🇺🇸 · J.F. Carpino🇺🇸 · H. Chung🇺🇸 · A.L. Cole🇺🇸 · R.H. Cyburt🇺🇸 · A. Estradé🇬🇧 · M. Famiano🇺🇸 and 20 other authors
We present the mass excesses of 52-57Sc, obtained from recent time-of-flight nuclear mass measurements at the National Superconducting Cyclotron Laboratory at Michigan State University. The masses of 56Sc and 57Sc were determined for the first time with atomic mass excesses of -24.85(59)(+0 -54) MeV and -21.0(1.3) MeV, respectively, where the asymmetric uncertainty for 56Sc was included due to possible contamination from a long-lived isomer. The 56Sc mass indicates a small odd-even mass staggering in the A = 56 mass-chain towards the neutron drip line, significantly deviating from trends predicted by the global FRDM mass model and favoring trends predicted by the UNEDF0 and UNEDF1 density functional calculations. Together with new shell-model calculations of the electron-capture strength function of 56Sc, our results strongly reduce uncertainties in model calculations of the heating and cooling at the 56Ti electron-capture layer in the outer crust of accreting neutron stars. We found that, in contrast to previous studies, neither strong neutrino cooling nor strong heating occurs in this layer. We conclude that Urca cooling in the outer crusts of accreting neutron stars that exhibit superbursts or high temperature steady-state burning, which are predicted to be rich in A=56 nuclei, is considerably weaker than predicted. Urca cooling must instead be dominated by electron capture on the small amounts of adjacent odd-A nuclei contained in the superburst and high temperature steady-state burning ashes. This may explain the absence of strong crust Urca cooling inferred from the observed cooling light curve of the transiently accreting x-ray source MAXI J0556-332.
Comments:
Accepted to Physical Review Letters
Subjects:
Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1510.01510 [pdf]
PRL(2015)·31 citations
12
[Submitted on 6 Oct 2015] (cross-list from hep-ph)
Diffractive $ρ$ production at small $x$ in future Electron - Ion Colliders
V. P. Goncalves🇸🇪 · F. S. Navarra🇧🇷 · D. Spiering🇧🇷
The future Electron - Ion ( $e A$ ) Collider is expected to probe the high energy regime of the QCD dynamics, with the exclusive vector meson production cross section being one of the most promising observables. In this paper we complement previous studies of exclusive processes presenting a comprehensive analysis of diffractive $ρ$ production at small $x$ . We compute the coherent and incoherent cross sections taking into account non-linear QCD dynamical effects and considering different models for the dipole - proton scattering amplitude and for the vector meson wave function. The dependence of these cross sections with the energy, photon virtuality, nuclear mass number and squared momentum transfer is analysed in detail. Moreover, we compare the non-linear predictions with those obtained in the linear regime. Finally, we also estimate the exclusive photon, $J /Ψ$ and $ϕ$ production and compare with the results obtained for $ρ$ production. Our results demonstrate that the analysis of diffractive $ρ$ production in future electron - ion colliders will be important to understand the non-linear QCD dynamics.
Comments:
12 pages, 8 figures, 1 table. Enlarged and revised version to be published in the Journal of Physics G. arXiv admin note: text overlap with arXiv:1503.00647
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Experiment (hep-ex); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1510.01512 [pdf]
J.Phys.G(2016)·13 citations
13
[Submitted on 6 Oct 2015] (cross-list from nucl-ex)
Strangeness Photoproduction on Quasifree Neutrons
Dominik Werthmüller🇬🇧
Strangeness photoproduction in the elementary reactions $γ N \to K Y$ offers the possibility to study nucleon resonances in the mass region above 1.7 GeV, where the number of states and their properties are still under debate. These reactions could allow the first 'complete' experiment in pseudoscalar meson photoproduction due to the easier access to recoil polarization observables in experiments. In addition to measurements on proton targets, a full isospin decomposition of the $I = 1/2$ electromagnetic amplitudes requires also data obtained from quasifree neutron targets. This contribution shows first preliminary results on feasibility studies for such measurements at the A2 experiment at MAMI.
Comments:
Contribution to the proceedings of the 10th International Workshop on the Physics of Excited Nucleons - NSTAR2015, 25-28 May 2015, Osaka, Japan, to be published in JPS conference proceedings
Subjects:
Nuclear Experiment (nucl-ex); High Energy Physics — Experiment (hep-ex); Nuclear Theory (nucl-th)
arXiv:
1510.01660 [pdf]
JPS Conf.Proc.(2016)·3 citations

Affiliations

first authorsco-authorsvia INSPIRE

High-precision evaluation of Wigner's d-matrix by exact diagonalization

Fluctuation Phenomena in Chaotic Dirac Quantum Dots: Artificial Atoms on Graphene Flakes

Status of Chiral-Scale Perturbation Theory

Mass measurement of 56Sc reveals a small A=56 odd-even mass staggering, implying a cooler accreted neutron star crust

Diffractive ρ production at small x in future Electron - Ion Colliders

Strangeness Photoproduction on Quasifree Neutrons

Affiliations

Diffractive $ρ$ production at small $x$ in future Electron - Ion Colliders