Nuclear Theory·nucl-th

Monday·September 5, 2016

9 papers—7 primary·2 cross-listed

01
[Submitted on 1 Sept 2016]
Dynamical Screening of $α$ - $α$ Resonant Scattering and Thermal Nuclear Scattering Rate in a Plasma
Xiaojun Yao🇺🇸 · Thomas Mehen🇺🇸 · Berndt Müller🇺🇸
We use effective field theory and thermal field theory to study the dynamical screening effect in the QED plasma on the $α$ - $α$ scattering at the $^{8}$ Be resonance. Dynamical screening leads to an imaginary part of the potential which results in a thermal width for the resonance and dominates over the previously considered static screening effect. As a result, both the resonance energy and width increase with the plasma temperature. Furthermore, dynamical screening can have a huge impact on the $α$ - $α$ thermal nuclear scattering rate. For example, when the temperature is around $10$ keV, the rate is suppressed by a factor of about $900$ . We expect similar thermal suppressions of nuclear reaction rates to occur in those reactions dominated by an above threshold resonance with a thermal energy. Dynamical screening effects on nuclear reactions can be relevant to cosmology and astrophysics.
Comments:
20 pages, 7 figures, published version with an appendix to justify the hard-thermal-loop approximation with finite electron mass
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
arXiv:
1609.00383 [pdf]
PRD(2017)·5 citations
02
[Submitted on 1 Sept 2016]
Net Baryon Fluctuations from a Crossover Equation of State
J. Kapusta🇺🇸 · M. Albright🇺🇸 · C. Young🇺🇸
We have constructed an equation of state which smoothly interpolates between an excluded volume hadron resonance gas at low energy density to a plasma of quarks and gluons at high energy density. This crossover equation of state agrees very well with lattice calculations at both zero and nonzero baryon chemical potential. We use it to compute the variance, skewness, and kurtosis of fluctuations of baryon number, and compare to measurements of proton number fluctuations in central Au-Au collisions as measured by the STAR collaboration in a beam energy scan at the Relativistic Heavy Ion Collider. The crossover equation of state can reproduce the data if the fluctuations are frozen out at temperatures well below than the average chemical freeze-out.
Comments:
5 pages, 7 figures. arXiv admin note: substantial text overlap with arXiv:1506.03408
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1609.00398 [pdf]
EPJA(2016)·10 citations
03
[Submitted on 1 Sept 2016]
Lattice methods and the nuclear few- and many-body problem
Dean Lee🇺🇸
We begin with a brief overview of lattice calculations using chiral effective field theory and some recent applications. We then describe several methods for computing scattering on the lattice. After that we focus on the main goal, explaining the theory and algorithms relevant to lattice simulations of nuclear few- and many-body systems. We discuss the exact equivalence of four different lattice formalisms, the Grassmann path integral, transfer matrix operator, Grassmann path integral with auxiliary fields, and transfer matrix operator with auxiliary fields. Along with our analysis we include several coding examples and a number of exercises for the calculations of few- and many-body systems at leading order in chiral effective field theory.
Comments:
20 pages, 3 figures, Submitted to Lect. Notes Phys., "An advanced course in computational nuclear physics: Bridging the scales from quarks to neutron stars", M. Hjorth-Jensen, M. P. Lombardo, U. van Kolck, Editors
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Lattice (hep-lat)
arXiv:
1609.00421 [pdf]
Lect.Notes Phys.(2017)·16 citations
04
[Submitted on 2 Sept 2016]
The role of $a_{1} (1260)$ in $π^{-} p \to a_{1}^{-} (1260) p$ and $π^{-} p \to π^{-} ρ^{0} p$ reactions near threshold
Chen Cheng🇨🇳 · Ju-Jun Xie🇨🇳 · Xu Cao🇨🇳
We report on a theoretical study of the $π^{-} p \to a_{1}^{-} (1260) p$ and $π^{-} p \to π^{-} ρ^{0} p$ reactions near threshold within an effective Lagrangian approach. The production process is described by $t$ -channel $ρ^{0}$ meson exchange. For the $π^{-} p \to π^{-} ρ^{0} p$ reaction, the final $π^{-} ρ^{0}$ results from the decay of the $a_{1} (1260)$ resonance which is assumed as a dynamically generated state from the $K^{*} K ˉ$ and $ρ π$ coupled channel interactions. We calculate the total cross section of the $π^{-} p \to a_{1}^{-} (1260) p$ reaction. It is shown that, with the coupling constant of the $a_{1} (1260)$ to $ρ π$ channel obtained from the chiral unitary theory and a cut off parameter $Λ_{ρ} \sim 1.5$ GeV in the form factors, the experimental measurement can be reproduced. Furthermore, the total and differential cross sections of $π^{-} p \to a_{1}^{-} (1260) p \to π^{-} ρ^{0} p$ reaction are evaluated, and it is expected that our model calculations can be tested by future experiments. These reactions are important for the study of the $a_{1} (1260)$ resonance and would provide further clue for the nature of $a_{1} (1260)$ state.
Comments:
5 pages, 5 figures
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph); Nuclear Experiment (nucl-ex)
arXiv:
1609.00442 [pdf]
Commun.Theor.Phys.(2016)·10 citations
05
[Submitted on 2 Sept 2016]
Evidence for a dynamically refracted primary bow in weakly bound $^{9}$ Be rainbow scattering from $^{16}$ O
S. Ohkubo · Y. Hirabayashi
We present for the first time evidence for the existence of a dynamically refracted primary bow for $^{9}$ Be+ $^{16}$ O scattering. This is demonstrated through the use of coupled channel calculations with an extended double folding potential derived from the density-dependent effective two-body force and precise microscopic cluster wave functions for $^{9}$ Be. The calculations reproduce the experimental Airy structure in $^{9}$ Be+ $^{16}$ O scattering well.It is found that coupling of a weakly bound $^{9}$ Be nucleus to excited states plays the role of a booster lens, dynamically enhancing the refraction over the {\it static} refraction due to the Luneburg lens mean field potential between the ground states of $^{9}$ Be and $^{16}$ O.
Comments:
6 pages, 5 figures
Subjects:
Nuclear Theory (nucl-th); Nuclear Experiment (nucl-ex)
arXiv:
1609.00447 [pdf]
PRC(2016)·4 citations
06
[Submitted on 2 Sept 2016]
Consistent description of 12C and 16O using finite range three-body interaction
N. Itagaki
Consistent description of 12C and 16O has been a long standing problem of microscopic alpha cluster models, where the wave function is fully antisymmetrized and the effective interaction is applied not between alpha clusters but between nucleons. When the effective interaction is designed to reproduce the binding energy of 16O (four alpha), the binding energy of 12C (three alpha) becomes underbound by about 10 MeV. In the present study, by taking into account the coupling with the jj-coupling shell model components and utilizing Tohsaki interaction, which is phenomenological but has finite-range three-body interaction terms, we show that consistent understanding of these nuclei can be achieved. The original Tohsaki interaction gives small overbound of about 3 MeV for 16O, and this is improved by slightly modifying three-body Majorana exchange parameter. Also, the coupling with the jj-coupling shell model wave function strongly contributes to the increase of the binding energy of 12C. So far the application of Tohsaki interaction has been limited to 4N nuclei, and here, we add Bartlet and Heisenberg exchange terms in the two-body interaction for the purpose of applying it to neutron-rich systems, and it is applied to 6He.
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1609.00466 [pdf]
PRC(2016)·30 citations
07
[Submitted on 2 Sept 2016]
Nuclear matter properties from local chiral interactions with $Δ$ isobar intermediate states
Domenico Logoteta · Ignazio Bombaci · Alejandro Kievsky
Using two-nucleon and three-nucleon interactions derived in the framework of chiral perturbation theory (ChPT) with and without the explicit $Δ$ isobar contributions, we calculate the energy per particle of symmetric nuclear matter and pure neutron matter in the framework of the microscopic Brueckner-Hartree-Fock approach. In particular, we present for the first time nuclear matter calculations using the new fully local in coordinate-space two-nucleon interaction at the next-to-next-to-next-to-leading-order (N3LO) of ChPT with $Δ$ isobar intermediate states (N3LO $Δ$ ) recently developed by Piarulli et al. [arXiv:1606:06335]. We find that using this N3LO $Δ$ potential, supplemented with a local N2LO three-nucleon interaction with explicit $Δ$ isobar degrees of freedom, it is possible to obtain a satisfactory saturation point of symmetric nuclear matter. For this combination of two- and three-nucleon interactions we also calculate the nuclear symmetry energy and we compare our results with the empirical constraints on this quantity obtained using the excitation energies to isobaric analog states in nuclei and using experimental data on the neutron skin thickness of heavy nuclei, finding a very good agreement with these empirical constraints in all the considered nucleonic density range. In addition, we find that the explicit inclusion of $Δ$ isobars diminishes the strength of the three-nucleon interactions needed the get a good saturation point of symmetric nuclear matter. We also compare the results of our calculations with those obtained by other research groups using chiral nuclear interactions with different many-body methods, finding in many cases a very satisfactory agreement.
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1609.00649 [pdf]
PRC(2016)·52 citations
08
[Submitted on 1 Sept 2016] (cross-list from nucl-ex)
Search for Tetraneutron by Pion Double Charge Exchange Reaction at J-PARC
Hiroyuki Fujioka🇯🇵 · Tomokazu Fukuda🇯🇵 · Toru Harada🇯🇵 · Emiko Hiyama🇯🇵 · Kenta Itahashi🇯🇵 · Shunsuke Kanatsuki🇯🇵 · Tomofumi Nagae🇯🇵 · Takuya Nanamura🇯🇵 · Takahiro Nishi🇯🇵
Tetraneutron ( $^{4} n$ ) has come back in the limelight, because of recent observation of a candidate resonant state at RIBF. We propose to investigate the pion double charge exchange (DCX) reaction, i.e. $^{4} He (π^{-}, π^{+})$ , as an alternative way to populate tetraneutron. An intense $π^{-}$ beam with the kinetic energy of ~850 MeV, much higher than that in past experiments at LAMPF and TRIUMF, will open up a possibility to improve the experimental sensitivity of the formation cross section, which will be much smaller than hitherto known DCX cross sections such as $^{9} Be (π^{-}, π^{+})^{9} He (g . s .)$ .
Comments:
4 pages, 1 figure; proceedings of the 14th International Conference on Meson-Nucleon Physics and the Structure of the Nucleon (MENU2016), Kyoto, Japan, 25-30 July 2016
Subjects:
Nuclear Experiment (nucl-ex); Nuclear Theory (nucl-th)
arXiv:
1609.00079 [pdf]
JPS Conf.Proc.(2017)·2 citations
09
[Submitted on 2 Sept 2016] (cross-list from hep-ph)
Analytical On-shell Calculation of Low Energy Higher Order Scattering
Barry R. Holstein🇺🇸
We demonstrate that the use of analytical on-shell methods involving calculation of the discontinuity across the t-channel cut associated with the exchange of a pair of massless particles (photons or gravitons) can be used to evaluate one-loop contributions to electromagnetic and gravitational scattering, with and without polarizability, reproducing via simple algebraic manipulations, results obtained previously, generally using Feynman diagram techniques. In the gravitational case the use of factorization permits a straightforward and algebraic calculation of higher order scattering without consideration of ghost contributions or of triple-graviton couplings, which made previous evaluations considerably more arduous.
Comments:
16 pages
Subjects:
High Energy Physics — Phenomenology (hep-ph); General Relativity and Quantum Cosmology (gr-qc); High Energy Physics — Theory (hep-th); Nuclear Theory (nucl-th)
arXiv:
1609.00714 [pdf]
J.Phys.G(2017)·21 citations

Affiliations

first authorsco-authorsvia INSPIRE