Nuclear Theory·nucl-th

Thursday·December 8, 2016

11 papers—5 primary·6 cross-listed

01
Cluster states in stable and unstable nuclei
M. Kimura🇯🇵
In this contribution, I will discuss two topics related to the clustering of atomic nuclei. The first is dual character of the ground state. Recently, it was pointed out that the ground states of atomic nuclei have dual character of shell and cluster implying that both of the single-particle excitation and cluster excitation occur as the fundamental excitation modes. The isoscalar monopole and dipole transitions are regarded as the triggers to induce the cluster excitation. By referring the Hartree-Fock and antisymmetrized molecular dynamics calculations, the dual character and those transitions are explained. The second is the linear-chain state of $^{16} C$ in which the linearly aligned 3 $α$ particles are sustained by the valence neutrons. The rather convincing evidences for this exotic state are very recently reported by several experiments. Here, I introduce a couple of theoretical analysis and predictions.
nucl-thnucl-ex2 citations
02
Internal Charmonium Evolution in the Quark-Gluon Plasma
Baoyi Chen · Xiaojian Du🇺🇸 · Ralf Rapp🇺🇸
We employ a time-dependent Schrödinger equation to study the evolution of a $c c ˉ$ dipole in a quark-gluon plasma (QGP). Medium effects on the heavy-quark potential in the QGP are found to significantly affect the timescales of the internal evolution of the dipole. Color-screening can enhance the overlap of the expanding wavepackage with excited states at high temperature, while it is reduced at lower temperatures where the dipole favors the formation of the charmonium ground state. We investigate the consequences of this mechanism on the double ratio of charmonium nuclear modification factors, $R_{AA}^{ψ (2 S)} / R_{AA}^{J / ψ}$ , in heavy-ion collisions. The impact of the transition mechanisms on this ratio turns out to be rather sensitive to the attractive strength of the potential, and to its temperature dependence.
nucl-thNucl.Part.Phys.Proc.(2017)·6 citations
03
Fission barriers of two odd-neutron actinide nuclei taking into account the time-reversal symmetry breaking at the mean-field level
Meng-Hock Koh🇫🇷 · L. Bonneau🇫🇷 · P. Quentin🇫🇷 · T. V. Nhan Hao🇺🇸 · Wagiran Husin🇲🇾
Background: Fission barriers of actinide nuclei have been mostly and for long been microscopi- cally calculated for even-even fissioning systems. Calculations in the case of odd nuclei have been performed merely within a so-called equal-filling approximation (EFA) as opposed to an approach taking explicitly into account the time reversal breaking properties at the mean field level- and for only one single-particle configuration. Purpose: We study the dependence of the fission barriers on various relevant configurations (e.g. to evaluate the so-called specialization energy). Besides, we want to assess the relevance as a func- tion of the deformation of the EFA approach which has been already found out at ground state deformation. Methods: Calculations within the Hartree-Fock plus BCS with self-consistent particle blocking have been performed using the SkM* Skyrme effective interaction in the particle-hole channel and a seniority force in the particle-particle channel. Axial symmetry has been imposed throughout the whole fission path while the intrinsic parity symmetry has been allowed to be broken in the outer fission barrier region. Results: Potential energy curves have been determined for six different configurations in U-235 and four in Pu-239. Inner and outer fission barriers have been calculated along with some spectroscopic properties in the fission isomeric well. These results have been compared with available data. The influence of time-reversal breaking mean fields on the solutions has been investigated. Conclusions: A sizeable configuration dependence of the fission barrier (width and height) has been demonstrated. A reasonable agreement with available systematic evaluations of fission barrier heights has been found. The EFA approach has been validated at the large elongations occurring at the outer barrier region.
nucl-thPRC(2017)·11 citations
04
Microscopic Study of $^{1} S_{0}$ Superfluidity in Dilute Neutron Matter
G. E. Pavlou · E. Mavrommatis · Ch. Moustakidis · J. W. Clark
Singlet $S$ -wave superfluidity of dilute neutron matter is studied within the correlated BCS method, which takes into account both pairing and short-range correlations. First, the equation of state (EOS) of normal neutron matter is calculated within the Correlated Basis Function (CBF) method in lowest cluster order using the $^{1} S_{0}$ and $^{3} P$ components of the Argonne $V_{18}$ potential, assuming trial Jastrow-type correlation functions. The $^{1} S_{0}$ superfluid gap is then calculated with the corresponding component of the Argonne $V_{18}$ potential and the optimally determined correlation functions. The dependence of our results on the chosen forms for the correlation functions is studied, and the role of the $P$ -wave channel is investigated. Where comparison is meaningful, the values obtained for the $^{1} S_{0}$ gap within this simplified scheme are consistent with the results of similar and more elaborate microscopic methods.
nucl-thastro-ph.HEcond-mat.quant-gascond-mat.supr-conEPJA(2017)·14 citations
05
Study of chiral vortical and magnetic effects in the anomalous transport model
Yifeng Sun🇺🇸 · Che Ming Ko🇺🇸
We extend our recent study of chiral magnetic effect in relativistic heavy ion collisions based on an anomalous transport model by including also the chiral vortical effect. We find that although vorticities in the chirally restored quark matter, which result from the large angular momentum in non-central collisions, can generate an axial charge dipole moment in the transverse plane of a heavy ion collision, it does not produce a difference in the eccentricities of negatively and positively charged particles. As a result, including the chiral vortical effect alone cannot lead to a splitting between the elliptic flows of negatively and positively charged particles. On the other hand, negatively and positively charged particles do develop a splitting in their elliptic flows if the effect due to a strong and long-lived magnetic field is also included. However, to have a positive slope in the dependence of the elliptic flow splitting on the charge asymmetry of the quark matter, as seen in experiments, requires the neglect of the effect of the Lorentz force. In this case, an elliptic flow splitting appears even at vanishing charge asymmetry.
nucl-thPRC(2017)·32 citations
06
Universal description of radially excited heavy and light vector mesons
S. S. Afonin🇷🇺 · I. V. Pusenkov🇷🇺
A new qualitative stringlike picture for mesons is proposed which leads to a simple and intuitively clear generalization of linear radial Regge trajectories to the case of massive quarks. The obtained universal relation is successfully tested in the sector of unflavored vector mesons, where many radial excitations are known. Some new predictions are given. Our results suggest that the quark masses can be easily estimated from the spectra of radially excited mesons.
↳ hep-phnucl-thPRD(2014)·80 citations
07
On the nature of some SGRs and AXPs as rotation-powered neutron stars
Jaziel G. Coelho · D. L. Cáceres · R. C. R. de Lima · M. Malheiro · J. A. Rueda · R. Ruffini
We investigate the possibility that some SGRs/AXPs could be canonical rotation-powered pulsars using realistic NS structure parameters instead of fiducial values. We show that realistic NS parameters lowers the estimated value of the magnetic field and radiation efficiency, $L_{X} / E ˙_{rot}$ , with respect to estimates based on fiducial NS parameters. We show that nine SGRs/AXPs can be described as canonical pulsars driven by the NS rotational energy, for $L_{X}$ computed in the soft (2--10~keV) X-ray band. We compute the range of NS masses for which $L_{X} / E ˙_{rot} < 1$ . We discuss the observed hard X-ray emission in three sources of the group of nine potentially rotation-powered NSs. This additional hard X-ray component dominates over the soft one leading to $L_{X} / E ˙_{rot} > 1$ in two of them. We show that 9 SGRs/AXPs can be rotation-powered NSs if we analyze their X-ray luminosity in the soft 2--10~keV band. Interestingly, four of them show radio emission and six have been associated with supernova remnants (including Swift J1834.9-0846 the first SGR observed with a surrounding wind nebula). These observations give additional support to our results of a natural explanation of these sources in terms of ordinary pulsars. Including the hard X-ray emission observed in three sources of the group of potential rotation-powered NSs, this number of sources with $L_{X} / E ˙_{rot} < 1$ becomes seven. It remains open to verification 1) the accuracy of the estimated distances and 2) the possible contribution of the associated supernova remnants to the hard X-ray emission.
↳ astro-ph.HEastro-ph.SRhep-phnucl-thAstron.Astrophys.(2017)·17 citations
08
Reggeized model for $γ p \to ρ^{-} Δ^{++} (1232)$ photoproduction
Byung-Geel Yu🇰🇷 · Kook-Jin Kong🇰🇷
A model for the reaction $γ p \to ρ^{-} Δ^{++}$ is presented with the $t$ -channel $π + ρ$ exchanges reggeized to describe the reaction up to high energies. Gauge invariance of $ρ$ exchange is discussed in connection with the convergence of the reaction cross section at high energy. The roles of electromagnetic (EM) multipole moments of $Δ^{++}$ baryon and of $ρ^{-}$ meson are analyzed in total and differential cross sections and spin density matrix elements. Photon polarization asymmetry $Σ$ is predicted for a measurement of electromagnetic moments of $ρ^{-}$ and of $Δ^{++}$ .
↳ hep-phnucl-thJ.Phys.G(2020)·3 citations
09
Radiative corrections to elastic proton-electron scattering measured in coincidence
G.I. Gakh🇺🇦 · M.I. Konchatnij🇺🇦 · N.P. Merenkov🇺🇦 · Egle Tomasi-Gustafsson🇫🇷
The differential cross section for elastic scattering of protons on electrons at rest is calculated taking into account the QED radiative corrections to the leptonic part of interaction. These model-independent radiative corrections arise due to emission of the virtual and real soft and hard photons as well as to vacuum polarization. We analyze an experimental setup when both the final particles are recorded in coincidence and their energies are determined within some uncertainties. The kinematics, the cross section, and the radiative corrections are calculated and numerical results are presented.
↳ hep-phnucl-thPRC(2017)·5 citations
10
The effect of magnetization and electric polarization on the anomalous transport coefficients of a chiral fluid
N. Sadooghi🇮🇷 · S.M.A. Tabatabaee🇮🇷
The effects of finite magnetization and electric polarization on dissipative and non-dissipative (anomalous) transport coefficients of a chiral fluid are studied. First, using the second law of thermodynamics as well as Onsager's time reversal symmetry principle, the complete set of dissipative transport coefficients of this medium is derived. It is shown that the properties of the resulting shear and bulk viscosities are mainly affected by the anisotropy induced by external electric and magnetic fields. Then, using the fact that the anomaly induced currents do not contribute to entropy production, the corresponding algebro-differential equations to non-dissipative anomalous transport coefficients are derived in a certain derivative expansion. The solutions of these equations show that, within this approximation, anomalous transport coefficients are, in particular, given in terms of the electric susceptibility of the medium.
↳ hep-thhep-phnucl-thNew J.Phys.(2017)·7 citations
11
Neutrino-induced one-pion production revisited: the $ν_{μ} n \to μ^{-} n π^{+}$ channel
E. Hernández🇪🇸 · J. Nieves🇪🇸
Understanding single pion production reactions on free nucleons is the first step towards a correct description of these processes in nuclei, which are important for signal and background contributions in current and near future accelerator neutrino oscillation experiments. In this work, we reanalyze our previous studies of neutrino-induced one-pion production on nucleons for outgoing $π N$ invariant masses below 1.4 GeV. Our motivation is to get a better description of the $ν_{μ} n \to μ^{-} n π^{+}$ cross section, for which current theoretical models give values significantly below data. This channel is very sensitive to the crossed $Δ (1232)$ contribution and thus to spin 1/2 components in the Rarita-Schwinger $Δ$ propagator. We show how these spin 1/2 components are nonpropagating and give rise to contact interactions. In this context, we point out that the discrepancy with experiment might be corrected by the addition of appropriate extra contact terms and argue that this procedure will provide a natural solution to the $ν_{μ} n \to μ^{-} n π^{+}$ puzzle. To keep our model simple, in this work we propose to change the strength of the spin 1/2 components in the $Δ$ propagator and use the $ν_{μ} n \to μ^{-} n π^{+}$ data to constraint its value. With this modification, we now find a good reproduction of the $ν_{μ} n \to μ^{-} n π^{+}$ cross section without affecting the good results previously obtained for the other channels. We also explore how this change in the $Δ$ propagator affects our predictions for pion photoproduction and find also a better agreement with experiment than with the previous model.
↳ hep-phnucl-thPRD(2017)·39 citations

Affiliations

first authorsco-authorsvia INSPIRE