Nuclear Theory·nucl-th

Tuesday·September 12, 2017

12 papers—5 primary·7 cross-listed

01
[Submitted on 8 Sept 2017]
Emergence of a Brunnian neutron state
Johannes Kirscher
We discuss a quantum-statistical feature of non-relativistic identical fermions whose interaction is predominantly attractive at low energies. Specifically, we consider exotic, multi-neutron nuclei. From the enhancement of an arbitrarily small P-wave interaction between two nucleons, we infer the existence of a particle-stable nucleus composed entirely of neutrons. While we cannot specify the number of neutrons in the system, we predict that none of its substructures is bound. The independence of this deduction from the short-distance structure of the nuclear interaction and its consistency with deuteron, triton, and helium-4 properties is established.
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
1709.02821 [pdf]
4 citations
02
[Submitted on 9 Sept 2017]
Shear viscosity of a pion gas due to $ρ π π$ and $σ π π$ interactions
Sabyasachi Ghosh🇧🇷 · Gastao Krein🇧🇷 · Saurav Sarkar🇮🇳
We have calculated the shear viscosity of pion medium, where propagating pion has some finite thermal width due to interaction with the low mass resonances, $σ$ and $ρ$ . With the help of standard thermal field theoretical technique, the thermal width of the pion has been calculated from the pion self-energy diagram for $π σ$ and $π ρ$ loops, where an effective Lagrangian density has been used for interaction part. We have found a very small value of shear viscosity by entropy density ratio ( $η / s$ ), which is very close to the KSS bound.
Comments:
Published in Proceedings of Science (Conference : ICPAQGP-2015)
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
arXiv:
1709.02902 [pdf]
PoS(2017)·0 citations
03
[Submitted on 10 Sept 2017]
Cluster and toroidal aspects of isoscalar dipole excitations in $^{12}$ C
Yoshiko Kanada-En'yo · Yuki Shikata · Horiyuki Morita
We investigated cluster and toroidal aspects of isoscalar dipole excitations in $^{12}$ C based on the shifted basis antisymmetrized molecular dynamics combined with the generator coordinate method, which can describes 1p-1h excitations and $3 α$ dynamics. In the $E = 10 - 15$ MeV region, we found two low-energy dipole modes separating from the giant dipole resonance. One is the developed $3 α$ -cluster state and the other is the toroidal dipole mode. The cluster state is characterized by the large amplitude cluster motion beyond the 1p-1h model space, whereas the toroidal dipole mode is predominantly described by 1p-1h excitations on the ground state. The low-energy dipole states are remarkably excited by the toroidal dipole operator, which can measure the nuclear vorticity. For compressive dipole transition strengths, a major part is distributed in the $30 - 50$ MeV region for the giant dipole resonance, and 5\% of the total energy weighted sum exist in the $E < 20$ MeV region.
Comments:
9 pages, 7 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1709.03045 [pdf]
PRC(2018)·16 citations
04
[Submitted on 10 Sept 2017]
Mass-15 nuclei and predicting narrow states beyond the proton drip line
P. R. Fraser · K. Amos · L. Canton · S. Karataglidis · D. van der Knijff · J. P. Svenne
In a previous letter (Phys. Rev. Lett. 96, 072502 (2006)), the multi-channel algebraic scattering (MCAS) technique was used to calculate spectral properties for proton-unstable $^{15}$ F and its mirror, $^{15}$ C. MCAS achieved a close match to the then-new data for $p +^{14}$ O elastic scattering and predicted several unusually narrow resonances at higher energies. Subsequently, such narrow resonance states were found. New cross section data has been published characterising the shape of the $J^{π} = \frac{1}{2}^{-}$ resonance. Herein we update that first MCAS analysis and its predictions. We also study the spectra of the set of mass-15 isobars, $^{15}$ C, $^{15}$ N, $^{15}$ O, and $^{15}$ F, using the MCAS method and seeking a consistent Hamiltonian for clusterisation with a neutron and a proton, separately, coupled to core nuclei $^{14}$ C and $^{14}$ O.
Comments:
11 pages, 5 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1709.03051 [pdf]
PRC(2019)·7 citations
05
[Submitted on 11 Sept 2017]
Excitation energy shift and size difference of low-energy levels in $p$ -shell $Λ$ hypernuclei
Yoshiko Kanada-En'yo🇯🇵
We investigated structures of low-lying $0 s$ -orbit $Λ$ states in $p$ -shell $Λ$ hypernuclei ( $_{Λ}^{A} Z$ ) by applying microscopic cluster models for nuclear structure and a single-channel folding potential model for a $Λ$ particle. For $A > 10$ systems, the size reduction of core nuclei is small, and the core polarization effect is regarded as a higher-order perturbation in the $Λ$ binding. The present calculation qualitatively describes the systematic trend of experimental data for excitation energy change from $^{A - 1} Z$ to $_{Λ}^{A} Z$ , in $A > 10$ systems. The energy change shows a clear correlation with the nuclear size difference between the ground and excited states. In $_{Λ}^{7} Li$ and $_{Λ}^{9} Be$ , the significant shrinkage of cluster structures occurs consistently with the prediction of other calculations.
Comments:
18 pages, 5 figures
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1709.03375 [pdf]
PRC(2018)·12 citations
06
[Submitted on 8 Sept 2017] (cross-list from nucl-ex)
Kaon transverse charge density from space- and timelike data
N.A. Mecholsky🇺🇸 · J. Meija-Ott🇺🇸 · M. Carmignotto🇺🇸 · T. Horn🇺🇸 · G.A. Miller🇺🇸 · I.L. Pegg🇺🇸
We used the world data on the kaon form factor to extract the transverse kaon charge density using a dispersion integral of the imaginary part of the kaon form factor in the timelike region. Our analysis includes recent data from $e^{+} e^{-}$ annihiliation measurements extending the kinematic reach of the data into the region of high momentum transfers conjugate to the region of short transverse distances. To calculate the transverse density we created a superset of both timelike and spacelike data and developed an empirical parameterization of the kaon form factor. The spacelike set includes two new data points we extracted from existing cross section data. We estimate the uncertainty on the resulting transverse density to be 5\% at $b$ =0.025 fm and significantly better at large distances. New kaon data planned with the 12 GeV Jefferson Lab may have a significant impact on the charge density at distances of $b <$ 0.1fm.
Subjects:
Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1709.02853 [pdf]
PRC(2017)·4 citations
07
[Submitted on 8 Sept 2017] (cross-list from hep-ph)
Time-Dependent Observables in Heavy Ion Collisions I: Setting up the Formalism
Bin Wu🇺🇸 · Yuri V. Kovchegov🇺🇸
We adapt the Schwinger-Keldysh formalism to study heavy-ion collisions in perturbative QCD. Employing the formalism, we calculate the two-point gluon correlation function $G_{22}^{a μ, b ν}$ due to the lowest-order classical gluon fields in the McLerran-Venugopalan model of heavy ion collisions and observe an interesting transition from the classical fields to the quasi-particle picture at later times. Motivated by this observation, we push the formalism to higher orders in the coupling and calculate the contribution to $G_{22}^{a μ, b ν}$ coming from the diagrams representing a single rescattering between two of the produced gluons. We assume that the two gluons go on mass shell both before and after the rescattering. The result of our calculation depends on the ordering between the proper time of the rescattering $τ_{Z}$ and the proper time $τ$ when the gluon distribution is measured. For (i) $τ_{Z} ≫ 1/ Q_{s}$ and $τ - τ_{Z} ≫ 1/ Q_{s}$ (with $Q_{s}$ the saturation scale) we obtain the same results as from the Boltzmann equation. For (ii) $τ - τ_{Z} ≫ τ_{Z} ≫ 1/ Q_{s}$ we end up with a result very different from kinetic theory and consistent with a picture of "free-streaming" particles. Due to the approximations made, our calculation is too coarse to indicate whether the ordering (i) or (ii) is the correct one: to resolve this controversy, we shall present a detailed diagrammatic calculation of the rescattering correction in the $φ^{4}$ theory in the second paper of this duplex.
Comments:
45 pages, 9 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1709.02866 [pdf]
JHEP(2018)·12 citations
08
[Submitted on 8 Sept 2017] (cross-list from hep-ph)
Time-Dependent Observables in Heavy Ion Collisions II: in Search of Pressure Isotropization in the $φ^{4}$ Theory
Yuri V. Kovchegov🇺🇸 · Bin Wu🇺🇸
To understand the dynamics of thermalization in heavy ion collisions in the perturbative framework it is essential to first find corrections to the free-streaming classical gluon fields of the McLerran-Venugopalan model. The corrections that lead to deviations from free streaming (and that dominate at late proper time) would provide evidence for the onset of isotropization (and, possibly, thermalization) of the produced medium. To find such corrections we calculate the late-time two-point Green function and the energy-momentum tensor due to a single $2 \to 2$ scattering process involving two classical fields. To make the calculation tractable we employ the scalar $φ^{4}$ theory instead of QCD. We compare our exact diagrammatic results for these quantities to those in kinetic theory and find disagreement between the two. The disagreement is in the dependence on the proper time $τ$ and, for the case of the two-point function, is also in the dependence on the space-time rapidity $η$ : the exact diagrammatic calculation is, in fact, consistent with the free streaming scenario. Kinetic theory predicts a build-up of longitudinal pressure, which, however, is not observed in the exact calculation. We conclude that we find no evidence for the beginning of the transition from the free-streaming classical fields to the kinetic theory description of the produced matter after a single $2 \to 2$ rescattering.
Comments:
46 pages, 9 figures
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1709.02868 [pdf]
JHEP(2018)·8 citations
09
[Submitted on 9 Sept 2017] (cross-list from hep-ph)
Exploring hadrons' partonic structure using ab initio lattice QCD calculations
Yan-Qing Ma🇨🇳 · Jian-Wei Qiu🇺🇸
Following our previous proposal [1], we construct a class of good "lattice cross sections" (LCSs), from which we could study partonic structure of hadrons from ab initio lattice QCD calculations. These good LCSs, on the one hand, can be calculated directly in lattice QCD, and on the other hand, can be factorized into parton distribution functions (PDFs) with calculable coefficients, in the same way as QCD factorization for factorizable hadronic cross sections. PDFs could be extracted from QCD global analysis of the lattice QCD generated data of LCSs. We also show that proposed functions for lattice QCD calculation of PDFs in the literature are special cases of these good LCSs.
Comments:
6 pages, 1 figure, version accepted by Physical Review Letters
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Lattice (hep-lat); Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1709.03018 [pdf]
PRL(2018)·294 citations
10
[Submitted on 10 Sept 2017] (cross-list from hep-th)
Homogeneous isotropization and equilibration of a strongly coupled plasma with a critical point
Renato Critelli (1) · Romulo Rougemont (2) · Jorge Noronha (1) ((1) Sao Paulo U., (2) IIP, Brazil)
We use holography to investigate the process of homogeneous isotropization and thermalization in a strongly coupled $N = 4$ Super Yang-Mills plasma charged under a $U (1)$ subgroup of the global $S U (4)$ R-symmetry which features a critical point in its phase diagram. Isotropization dynamics at late times is affected by the critical point in agreement with the behavior of the characteristic relaxation time extracted from the analysis of the lowest non-hydrodynamic quasinormal mode in the $S O (3)$ quintuplet (external scalar) channel of the theory. In particular, the isotropization time may decrease or increase as the chemical potential increases depending on whether one is far or close enough to the critical point, respectively. On the other hand, the thermalization time associated with the equilibration of the scalar condensate, which happens only after the system has relaxed to a (nearly) isotropic state, is found to always increase with chemical potential in agreement with the characteristic relaxation time associated to the lowest non-hydrodynamic quasinormal mode in the $S O (3)$ singlet (dilaton) channel. These conclusions about the late dynamics of the system are robust in the sense that they hold for different initial conditions seeding the time evolution of the far-from-equilibrium plasma.
Comments:
66 pages, 27 figures, calculation of the QNMs of the dilaton channel added, revised conclusions. Accepted for publication in JHEP. v4-v7: several typos corrected; v8: one more typo corrected in Eq. (3.15)
Subjects:
High Energy Physics — Theory (hep-th); High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1709.03131 [pdf]
JHEP(2017)·38 citations
11
[Submitted on 11 Sept 2017] (cross-list from nucl-ex)
Evidence for Z=6 `magic number' in neutron-rich carbon isotopes
D.T. Tran · H.J. Ong · G. Hagen · T. D. Morris · N. Aoi · T. Suzuki · Y. Kanada-En'yo · L.S. Geng · S. Terashima · I. Tanihata · T.T. Nguyen · Y. Ayyad and 28 other authors
The nuclear shell structure, which originates in the nearly independent motion of nucleons in an average potential, provides an important guide for our understanding of nuclear structure and the underlying nuclear forces. Its most remarkable fingerprint is the existence of the so-called `magic numbers' of protons and neutrons associated with extra stability. Although the introduction of a phenomenological spin-orbit (SO) coupling force in 1949 helped explain the nuclear magic numbers, its origins are still open questions. Here, we present experimental evidence for the smallest SO-originated magic number (subshell closure) at the proton number 6 in 13-20C obtained from systematic analysis of point-proton distribution radii, electromagnetic transition rates and atomic masses of light nuclei. Performing ab initio calculations on 14,15C, we show that the observed proton distribution radii and subshell closure can be explained by the state-of-the-art nuclear theory with chiral nucleon-nucleon and three-nucleon forces, which are rooted in the quantum chromodynamics.
Comments:
7 pages, 5 figures
Subjects:
Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1709.03355 [pdf]
Nature Commun.(2018)·39 citations
12
[Submitted on 11 Sept 2017] (cross-list from hep-ph)
Asymptotically Free Theory with Scale Invariant Thermodynamics
Gabriel N. Ferrari🇧🇷 · Jean-Loic Kneur🇫🇷 · Marcus B. Pinto🇧🇷 · Rudnei O. Ramos🇧🇷
A recently developed variational resummation technique, incorporating renormalization group properties consistently, has been shown to solve the scale dependence problem that plagues the evaluation of thermodynamical quantities, e.g., within the framework of approximations such as in the hard-thermal-loop resummed perturbation theory. This method is used in the present work to evaluate thermodynamical quantities within the two-dimensional nonlinear sigma model, which, apart from providing a technically simpler testing ground, shares some common features with Yang-Mills theories, like asymptotic freedom, trace anomaly and the nonperturbative generation of a mass gap. The present application confirms that nonperturbative results can be readily generated solely by considering the lowest-order (quasi-particle) contribution to the thermodynamic effective potential, when this quantity is required to be renormalization group invariant. We also show that when the next-to-leading correction from the method is accounted for, the results indicate convergence, apart from optimally preserving, within the approximations here considered, the sought-after scale invariance.
Comments:
24 pages, 10 figures. v2: some corrections in a few figures, more explanations on the difference with standard optimized perturbation or hard thermal loop resummation. One reference added. To appear in Phys. Rev. D
Subjects:
High Energy Physics — Phenomenology (hep-ph); High Energy Physics — Theory (hep-th); Nuclear Theory (nucl-th)
arXiv:
1709.03457 [pdf]
PRD(2017)·9 citations

Affiliations

first authorsco-authorsvia INSPIRE