Nuclear Theory·nucl-th

Wednesday·November 30, 2016

11 papers—4 primary·7 cross-listed

01
Effective restoration of dipole sum rules within the renormalized random-phase approximation
N. Quang Hung · N. Dinh Dang · T. V. Nhan Hao · L. Tan Phuc
The dipole excitations for calcium and zirconium isotopes are studied within the fully self-consistent Hartree-Fock mean field incorporated with the renormalized random-phase approximation (RRPA) using the Skyrme interaction SLy5. The RRPA takes into account the effect of ground-state correlations beyond RPA owing to the Pauli principle between the particle-hole pairs that form the RPA excitations as well as the correlations due to the particle-particle and hole-hole transitions, whose effects are treated here in an effective way. By comparing the RPA results with the RRPA ones, which are obtained for isoscalar (IS) and isovector (IV) dipole excitations in $^{48, 52, 58}$ Ca and $^{90, 96, 110}$ Zr, it is shown that ground-state correlations beyond the RPA reduce the IS transition strengths. They also shift up the energy of the lowest IV dipole state and slightly push down the peak energy of the IV giant dipole resonance. As the result, the energy-weighted sums of strengths of both IS and IV modes decrease, causing the violation of the corresponding energy-weight sum rules (EWSR). It is shown that this sum rule violation can be eliminated by taking into account the contribution of the particle-particle and hole-hole excitations together with the particle-hole ones in a simple and perturbative way. Consequently, the ratio of the energy-weighted sum of strengths of the pygmy dipole resonance to that of the giant dipole resonance increases.
nucl-thPRC(2016)·2 citations
02
The shapes of nuclei
G.F. Bertsch
Gerry Brown initiated some early studies on the coexistence of different nuclear shapes. The subject has continued to be of interest and is crucial for understanding nuclear fission. We now have a very good picture of the potential energy surface with respect to shape degrees of freedom in heavy nuclei, but the dynamics remain problematic. In contrast, the early studies on light nuclei were quite successful in describing the mixing between shapes. Perhaps a new approach in the spirit of the old calculations could better elucidate the character of the fission dynamics and explain phenomena that current theory does not model well.
nucl-thIJMPE(2017)·5 citations
03
Random matrix analysis of the monopole strength distribution in $^{208}$ Pb
A. P. Severyukhin · S. Aberg · N. N. Arsenyev · R. G. Nazmitdinov · K. N. Pichugin
We study statistical properties of the $0^{+}$ spectrum of $^{208}$ Pb in the energy region $E_{x} \leq 20$ MeV. We use the Skyrme interaction SLy4 as our model Hamiltonian to create a single-particle spectrum and to analyze excited states. The finite-rank separable approximation for the particle-hole interaction enables us to perform the calculations in large configuration spaces. We show that while the position of the monopole resonance centroid is determined by one phonon excitations of $0^{+}$ , the phonon-phonon coupling is crucial for the description of a strength distribution of the $0^{+}$ spectrum. In fact, this coupling has an impact on the spectral rigidity $Δ_{3} (L)$ which is shifted towards the random matrix limit of the Gaussian orthogonal ensembles.
nucl-thPhys.Atom.Nucl.(2016)·7 citations
04
Inclusive breakup of three-fragment weakly bound nuclei
Brett V. Carlson · Tobias Frederico · Mahir S. Hussein
The inclusive breakup of three-fragment projectiles is discussed within a four-body spectator model. Both the elastic breakup and the non-elastic breakup are obtained in a unified framework. Originally developed in the 80's for two-fragment projectiles such as the deuteron, in this paper the theory is successfully generalized to three-fragment projectiles. The expression obtained for the inclusive cross section allows the extraction of the incomplete fusion cross section, and accordingly generalizes the surrogate method to cases such as (t,p) and (t,n) reactions. It is found that two-fragment correlations inside the projectile affect in a conspicuous way the elastic breakup cross section. The inclusive non-elastic breakup cross section is calculated and is found to contain the contribution of a three-body absorption term that is also strongly influenced by the two-fragment correlations. This latter cross section contains the so-called incomplete fusion where more than one compound nuclei are formed. Our theory describes both stable weakly bound three-fragment projectiles and unstable ones such as the Borromean nuclei.
nucl-thnucl-exPLB(2017)·25 citations
05
The branching ratio $ω \to π^{+} π^{-}$ revisited
C. Hanhart🇩🇪 · S. Holz🇩🇪 · B. Kubis🇩🇪 · A. Kupść🇸🇪 · A. Wirzba🇩🇪 · C. W. Xiao🇩🇪
We analyze the most recent data for the pion vector form factor in the timelike region, employing a model-independent approach based on dispersion theory. We confirm earlier observations about the inconsistency of different modern high-precision data sets. Excluding the BaBar data, we find an updated value for the isospin-violating branching ratio $B (ω \to π^{+} π^{-}) = (1.46 \pm 0.08) \times 1 0^{- 2}$ . As a side result, we also extract an improved value for the pion vector or charge radius, $⟨ r_{V}^{2} ⟩ = 0.6603 (5) (4) fm$ , where the first uncertainty is statistical as derived from the fit, while the second estimates the possible size of nonuniversal radiative corrections. In addition, we demonstrate that modern high-quality data for the decay $η^{'} \to π^{+} π^{-} γ$ will allow for an even improved determination of the transition strength $ω \to π^{+} π^{-}$ .
↳ hep-phhep-exnucl-exnucl-thEPJC(2017)·71 citations
06
Testing the formation scenarios of binary neutron star systems with measurements of the neutron star moment of inertia
William G. Newton · Andrew W. Steiner · Kent Yagi
Two low mass neutron stars, J0737-3039B and the companion to J1756-2251, show strong evidence of being formed from the collapse of an ONeMg core in an electron capture supernova (ECSN) or in an ultra-stripped iron core collapse supernova (FeCCSN). Using three different systematically generated sets of equations of state we explore the relationship between the moment of inertia of J0737-3039A and the binding energy of the two low mass neutron stars. We find this relationship, a less strict variant of the recently discovered I-Love-Q relations, is nevertheless more robust than a previously explored correlation between the binding energy and the slope of the nuclear symmetry energy L. We find that, if either J0737-3039B or the J1756-2251 companion were formed in an ECSN, no more than 0.06 solar masses could have been lost from the progenitor core, more than four times the mass loss predicted by current supernova modeling. A measurement of the moment of inertia of J0737-3039A to within 10% accuracy from pulsar timing, possible within a decade, can discriminate between formation scenarios such as ECSN or ultra-stripped FeCCSN and, given current constraints on the predicted core mass loss, potentially rule them out. Using the I-Love-Q relations we find that an Advanced LIGO can potentially measure the neutron star tidal polarizability to equivalent accuracy in a neutron star-neutron star merger at a distance of 200 Mpc, thus obtaining similar constraints on the formation scenarios. Such information on the occurrence of ECSNe is important for population synthesis calculations, especially for estimating the rate of binary neutron star mergers and resulting electromagnetic and gravitational wave signals. Further progress needs to be made modeling the core collapse process that leads to low-mass neutron stars, particularly in making robust predictions for the mass loss from the progenitor core.
↳ astro-ph.SRastro-ph.HEnucl-thApJ(2018)·9 citations
07
Spatial structure of the modified Coulomb potential in a superstrong magnetic field
S.I. Glazyrin🇷🇺 · S.I. Godunov🇷🇺
The modification of the Coulomb potential due to the enhancement of loop corrections in a superstrong magnetic field is studied numerically. We calculate the modified potential with high precision and obtain the pattern of equipotential lines. The results confirm the general features known from previous studies, however we emphasize some differences in potential structure that can be important for problems with spatially distributed charges.
↳ hep-phnucl-thJETP Lett.(2017)·1 citation
08
Hadron tomography studies by generalized parton distributions and distribution amplitudes
S. Kumano🇯🇵
We discuss hadron-tomography studies for the nucleon and exotic hadrons by high-energy hadron reactions. First, the constituent-counting rule is explained for determining internal quark configurations of exotic-hadron candidates by scaling properties of high-energy exclusive cross sections. Next, possibilities are discussed for investigating the generalized parton distributions (GPDs) of the nucleon and exotic hadrons at J-PARC. In particular, we study hadronic $2 \to 3$ process $p + p \to N + π + B$ , exclusive Drell-Yan process, and exotic-hadron GPDs. For determining three-dimensional structure of unstable exotic hadrons, we consider $s$ - $t$ crossed quantities of the GPDs called generalized distribution amplitudes (GDAs), which can be investigated at KEKB. We explain possible studies of the GDAs by two-photon processes.
↳ hep-phhep-exhep-latnucl-ex+1EPJ Web Conf.(2017)·1 citation
09
Investigating convergence of the reaction $γ p \to π^{\pm} Δ$ and tensor meson $a_{2}$ exchange at high energy
Byung-Geel Yu🇰🇷 · Kook-Jin Kong🇰🇷
A Regge approach to the reaction processes $γ p \to π^{-} Δ^{++}$ and $γ p \to π^{+} Δ^{0}$ is presented for the description of existing data up to $E_{γ} = 16$ GeV. The model consists of the $t$ -channel $π (139) + ρ (775) + a_{2} (1320)$ exchanges which are reggeized from the relevant Born amplitude. Discussion is given on the minimal gauge prescription for the $π$ exchange to render convergent the divergence of the $u$ -channel $Δ$ -pole in the former process. A new Lagrangian is constructed for the $a_{2} N Δ$ coupling in this work and applied to the process for the first time with the coupling constant deduced from the duality plus vector dominance. It is shown that, while the $π$ exchange dominates over the process, the role of the $a_{2}$ exchange is crucial rather than the $ρ$ in reproducing the cross sections for total, differential, and photon polarization asymmetry to agree with data at high energy.
↳ hep-phnucl-thPLB(2017)·13 citations
10
Nucleon-Nucleon Correlations, Short-lived Excitations, and the Quarks Within
O. Hen🇺🇸 · G. A. Miller🇺🇸 · E. Piasetzky🇮🇱 · L. B. Weinstein🇺🇸
This article reviews our current understanding of how the internal quark structure of a nucleon bound in nuclei differs from that of a free nucleon. We focus on the interpretation of measurements of the EMC effect for valence quarks, a reduction in the Deep Inelastic Scattering (DIS) cross-section ratios for nuclei relative to deuterium, and its possible connection to nucleon-nucleon Short-Range Correlations (SRC) in nuclei. Our review and new analysis (involving the amplitudes of non-nucleonic configurations in the nucleus) of the available experimental and theoretical evidence shows that there is a phenomenological relation between the EMC effect and the effects of SRC that is not an accident. The influence of strongly correlated neutron-proton pairs involving highly virtual nucleons is responsible for both effects. These correlated pairs are temporary high-density fluctuations in the nucleus in which the internal structure of the nucleons is briefly modified. This conclusion needs to be solidified by the future experiments and improved theoretical analyses that are discussed herein.
↳ nucl-exhep-phnucl-thRMP(2017)·420 citations
11
Mott-hadron resonance gas and lattice QCD thermodynamics
D. Blaschke🇷🇺 · A. Dubinin🇵🇱 · L. Turko🇵🇱
A unified equation of state for quark-hadron matter is presented in the generalized Beth-Uhlenbeck form. It follows from a $Φ -$ derivable approach to the thermodynamic potential where the ansatz for the $Φ$ functional contains all 2PI diagrams at two-loop order formed with quark cluster Green's functions for quark, diquark, meson and baryon propagators. We present numerical results using an effective model for the generic behaviour of hadron masses and phase shifts at finite temperature which shares basic features with recent developments within the PNJL model for correlations in quark matter. We obtain the transition between a hadron resonance gas phase and the quark gluon plasma where the Mott dissociation of hadrons is encoded in the hadronic phase shifts. The resulting thermodynamics is in very good agreement with recent lattice QCD simulations.
↳ hep-phnucl-th8 citations

Affiliations

first authorsco-authorsvia INSPIRE