Nuclear Theory·nucl-th

Wednesday·December 2, 2015

11 papers—4 primary·7 cross-listed

01
Structure of the $Λ (1405)$ and the $K^{-} d \to π Σ n$ reaction
Shota Ohnishi🇯🇵 · Yoichi Ikeda🇯🇵 · Tetsuo Hyodo🇯🇵 · Wolfram Weise🇮🇹
The $Λ (1405)$ resonance production reaction is investigated within the framework of the coupled-channels Alt-Grassberger-Sandhas (AGS) equations. We perform full three-body calculations for the $K ˉ N N - π Y N$ amplitudes on the physical real energy axis and investigate how the signature of the $Λ (1405)$ appears in the cross sections of the $K^{-} d \to π Σ n$ reactions, also in view of the planned E31 experiment at J-PARC. Two types of meson-baryon interaction models are considered: an energy-dependent interaction based on chiral $S U (3)$ effective field theory, and an energy-independent version that has been used repeatedly in phenomenological approaches. These two models have different off-shell properties that imply correspondingly different behavior in the three-body system. We investigate how these features show up in differential cross sections of $K^{-} d \to π Σ n$ reactions. Characteristic patterns distinguishing between the two models are found in the invariant mass spectrum of the final $π Σ$ state. The $K^{-} d \to π Σ n$ reaction, with different ( $π^{\pm} Σ^{\mp}$ and $π^{0} Σ^{0}$ ) charge combinations in the final state, is thus demonstrated to be a useful tool for investigating the subthreshold behavior of the $K ˉ N$ interaction.
nucl-thhep-phPRC(2016)·37 citations
02
Two-gluon rapidity correlations of strong colour field in $pp$ , $p A$ and $AA$ collisions
Ye-Yin Zhao🇨🇳 · Ming-Mei Xu🇨🇳 · Heng-Ying Zhang🇨🇳 · Yuan-Fang Wu🇨🇳
Using the CGC formalism, we calculate the two-gluon rapidity correlations of strong colour fields in $pp$ , $p A$ and $AA$ collisions, respectively. If one trigger gluon is fixed at central rapidity, a ridge-like correlation pattern is obtained in symmetry $pp$ and $AA$ collisions, and a huge bump-like correlation pattern is presented in asymmetry $p A$ collisions. It is demonstrated that the ridge-like correlation patterns are caused by the stronger correlation with the gluon of colour source. The transverse momentum and incident energy dependence of the ridge-like correlation pattern is also systematically studied. The ridge is more likely observed at higher incident energy and lower transverse momentum of trigger gluon.
nucl-thhep-phNPA(2016)·5 citations
03
Dipole response in 208Pb within a self-consistent multiphonon approach
F. Knapp🇨🇿 · N. Lo Iudice🇮🇹 · P. Vesely🇨🇿 · F. Andreozzi🇮🇹 · G. De Gregorio🇮🇹 · A. Porrino🇮🇹
Background: The electric dipole strength detected around the particle threshold and commonly associated to the pygmy dipole resonance offers a unique information on neutron skin and symmetry energy, and is of astrophysical interest. The nature of such a resonance is still under debate. Purpose: We intend to describe the giant and pygmy resonances in 208 Pb by enhancing their fragmentation with respect to the random-phase approximation. Method: We adopt the equation of motion phonon method to perform a fully self-consistent calculation in a space spanned by one-phonon and two-phonon basis states using an optimized chiral two-body potential. A phenomenological density dependent term, derived from a contact three-body force, is added in order to get single-particle spectra more realistic than the ones obtained by using the chiral potential only. The calculation takes into full account the Pauli principle and is free of spurious center of mass admixtures. Results: We obtain a fair description of the giant resonance and obtain a dense low-lying spectrum in qualitative agreement with the experimental data. The transition densities as well as the phonon and particle-hole composi- tion of the most strongly excited states support the pygmy nature of the low-lying resonance. Finally, we obtain realistic values for the dipole polarizability and the neutron skin radius. Conclusions: The results emphasize the role of the two-phonon states in enhancing the fragmentation of the strength in the giant resonance region and at low energy, consistently with experiments. For a more detailed agreement with the data, the calculation suggests the inclusion of the three-phonon states as well as a fine tuning of the single-particle spectrum to be obtained by a refinement of the nuclear potential.
nucl-thPRC(2015)·34 citations
04
Role of $ω$ -meson exchange in scaling of the $γ p \to π^{0} p$ process from a Regge-type model with resonances
Kook-Jin Kong🇰🇷 · Tae Keun Choi🇰🇷 · Byung-Geel Yu🇰🇷
The scaling of photoproduction $γ p \to π^{0} p$ is investigated in the Reggeized model with $N^{*}$ and $Δ$ resonances included to describe resonance peaks up to photon energy $E_{γ}$ = 3 GeV. Given the $t$ -channel exchanges $ρ (770) + ω (780) + b_{1} (1235) + h_{1} (1170)$ Reggeized for the background contribution, the resonances of the Breit-Wigner form are introduced to agree with cross sections for total, differential and beam asymmetry in the low energy region. The scaled differential-cross sections $s^{7} d σ / d t$ are reproduced to agree with the recent JLab data, revealing the production mechanism of the big bump structure around $W \approx 2.2$ GeV by the deep-dip pattern of the $ω$ exchange that originates from the zeros of the trajectory $α_{ω} (t) = 0$ in the canonical phase, $\frac{1}{2} (- 1 + e^{- iπ α_{ω} (t)})$ .
nucl-thhep-phPRC(2016)·4 citations
05
Initial-state splitting kernels in cold nuclear matter
Grigory Ovanesyan🇺🇸 · Felix Ringer🇺🇸 · Ivan Vitev🇺🇸
We derive medium-induced splitting kernels for energetic partons that undergo interactions in dense QCD matter before a hard-scattering event at large momentum transfer $Q^{2}$ . Working in the framework of the effective theory $SCET_{G}$ , we compute the splitting kernels beyond the soft gluon approximation. We present numerical studies that compare our new results with previous findings. We expect the full medium-induced splitting kernels to be most relevant for the extension of initial-state cold nuclear matter energy loss phenomenology in both p+A and A+A collisions.
↳ hep-phnucl-thPLB(2016)·14 citations
06
Aspects of QCD Current Algebra on a Null Plane
Silas R. Beane🇺🇸 · Timothy J. Hobbs🇺🇸
Consequences of QCD current algebra formulated on a light-like hyperplane are derived for the forward scattering of vector and axial-vector currents on an arbitrary hadronic target. It is shown that current algebra gives rise to a special class of sum rules that are direct consequences of the independent chiral symmetry that exists at every point on the two-dimensional transverse plane orthogonal to the lightlike direction. These sum rules are obtained by exploiting the closed, infinite-dimensional algebra satisfied by the transverse moments of null-plane axial-vector and vector charge distributions. In the special case of a nucleon target, this procedure leads to the Adler-Weisberger, Gerasimov-Drell-Hearn, Cabbibo-Radicatti and Fubini-Furlan-Rossetti sum rules. Matching to the dispersion-theoretic language which is usually invoked in deriving these sum rules, the moment sum rules are shown to be equivalent to algebraic constraints on forward S-matrix elements in the Regge limit.
↳ hep-phnucl-thAnnals Phys.(2016)·5 citations
07
Electron capture and beta-decay rates for sd-shell nuclei in stellar environments relevant to high density O-Ne-Mg cores
Toshio Suzuki · Hiroshi Toki · Ken'ichi Nomoto
Electron capture and beta-decay rates for nuclear pairs in sd-shell are evaluated at high densities and high temperatures relevant to the final evolution of electron-degenerate O-Ne-Mg cores of stars with the initial masses of 8-10 solar mass. Electron capture induces a rapid contraction of the electron-degenerate O-Ne-Mg core. The outcome of rapid contraction depends on the evolutionary changes in the central density and temperature, which are determined by the competing processes of contraction, cooling, and heating. The fate of the stars are determined by these competitions, whether they end up with electron-capture supernovae or Fe core-collapse supernovae. Since the competing processes are induced by electron capture and beta-decay, the accurate weak rates are crucially important. The rates are obtained for pairs with A=20, 23, 24, 25 and 27 by shell-model calculations in sd-shell with the USDB Hamiltonian. Effects of Coulomb corrections on the rates are evaluated. The rates for pairs with A=23 and 25 are important for nuclear URCA processes that determine the cooling rate of O-Ne-Mg core, while those for pairs with A=20 and 24 are important for the core-contraction and heat generation rates in the core. We provide these nuclear rates at stellar environments in tables with fine enough meshes at various densities and temperatures for the studies of astrophysical processes sensitive to the rates. In particular, the accurate rate tables are crucially important for the final fates of not only O-Ne-Mg cores but also a wider range of stars such as C-O cores of lower mass stars.
↳ astro-ph.SRnucl-thApJ(2016)·70 citations
08
Hamiltonian effective field theory study of the $N^{*} (1535)$ resonance in lattice QCD
Zhan-Wei Liu🇦🇺 · 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 of the lowest-lying $J^{P} = 1/ 2^{-}$ nucleon excitation. 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 on volumes with spatial lengths of 2 and 3 fm 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. Finally, the role and importance of various components of the Hamiltonian model are examined.
↳ hep-lathep-phnucl-thPRL(2016)·98 citations
09
Expected impact from weak reactions with light nuclei in core-collapse supernova simulations
T. Fischer · G. Martínez-Pinedo · M. Hempel · L. Huther · G. Röpke · S. Typel · A. Lohs
We study the role of light nuclear clusters in simulations of core-collapse supernovae. Expressions for the reaction rates are developed for a large selection of charged current absorption and scattering processes with light clusters. Medium modifications are taken into account at the mean-field level. We explore the possible impact on the supernova dynamics and the neutrino signal during the mass accretion phase prior to the possible explosion onset as well as during the subsequent protoneutron star deleptnoization after the explosion onset has been launched.
↳ astro-ph.HEnucl-thEPJ Web Conf.(2016)·20 citations
10
Particle production in high-energy collisions beyond the shockwave limit
Tolga Altinoluk🇪🇸 · Adrian Dumitru🇺🇸
We compute next to eikonal (NE) and next to next to eikonal (NNE) corrections to the Lipatov vertex due to a finite target thickness. These arise from electric field insertions into the eikonal Wilson lines. We then derive a $k_{T}$ -factorization formula for single inclusive gluon production at NNE accuracy and find that nuclear effects are absent. We also analyze NNE corrections to two-gluon production where some of the contributions are found to exhibit corrections proportional to $A^{2/3}$ .
↳ hep-phnucl-thPRD(2016)·48 citations
11
Structures of the Vela pulsar and the glitch crisis from the Brueckner theory
A. Li · J. M. Dong · J. B. Wang · R. X. Xu
Detailed structures of the Vela pulsar (PSR B0833-45, with a period of $89.33$ milliseconds) are predicted by adopting a recently-constructed unified treatment of all parts of neutron stars: the outer crust, the inner crust and the core based on modern microscopic Brueckner-Hartree-Fock calculations. To take the pulsar mass ranging from $1.0 M_{⊙}$ to $2.0 M_{⊙}$ , we calculate the central density, the core/crust radii, the core/crust mass, the core/crustal thickness, the moment of inertia, and the crustal moment of inertia. Among them, the crustal moment of inertia could be effectively constrained from the accumulated glitch observations, which has been a great debate recently, known as "glitch crisis". Namely, superfluid neutrons contained in the inner crust, which are regarded as the origin of the glitch in the standard two-component model, could be largely entrained in the nuclei lattices, then there may not be enough superfluid neutrons ( $\sim 4/5$ less than the previous value) to trigger the large glitches ( $Δ ν / ν_{0} \sim 1 0^{- 6}$ ) in the Vela pulsar. We then provide the first analysis of the crisis based on the microscopic basis, by confronting the glitch observations with the theoretical calculations for the crustal moment of inertia. We find that despite some recent opposition to the crisis argument, the glitch crisis is still present, which means that besides the crust superfluid neutrons, core neutrons might be necessary for explaining the large glitches of the Vela pulsar.
↳ astro-ph.SRastro-ph.HEnucl-thAstrophys.J.Suppl.(2016)·38 citations

Affiliations

first authorsco-authorsvia INSPIRE