Nuclear Theory·nucl-th

Monday·May 2, 2016

5 papers—4 primary·1 cross-listed

01
[Submitted on 28 Apr 2016]
Statistical Hauser-Feshbach theory with width fluctuation correction including direct reaction channels for neutron induced reaction at low energies
T. Kawano · R. Capote · S. Hilaire
A model to calculate particle-induced reaction cross sections with statistical Hauser-Feshbach theory including direct reactions is given. The energy average of scattering matrix from the coupled-channels optical model is diagonalized by the transformation proposed by Engelbrecht and Weidenmüller. The ensemble average of $S$ -matrix elements in the diagonalized channel space is approximated by a model of Moldauer [Phys.Rev.C {\bf 12}, 744 (1975)] using newly parametrized channel degree-of-freedom $ν_{a}$ to better describe the Gaussian Orthogonal Ensemble (GOE) reference calculations. Moldauer approximation is confirmed by a Monte Carlo study using randomly generated $S$ -matrix, as well as the GOE three-fold integration formula. The method proposed is applied to the $^{238}$ U(n,n') cross section calculation in the fast energy range, showing an enhancement in the inelastic scattering cross sections.
Subjects:
Nuclear Theory (nucl-th)
arXiv:
1604.08635 [pdf]
PRC(2016)·67 citations
02
[Submitted on 29 Apr 2016]
Probing QED Vacuum with Heavy Ions
Johann Rafelski🇺🇸 · Johannes Kirsch🇩🇪 · Berndt Müller🇺🇸 · Joachim Reinhardt🇩🇪 · Walter Greiner🇩🇪
We recall how nearly half a century ago the proposal was made to explore the structure of the quantum vacuum using slow heavy-ion collisions. Pursuing this topic we review the foundational concept of spontaneous vacuum decay accompanied by observable positron emission in heavy-ion collisions and describe the related theoretical developments in strong fields QED.
Comments:
40 pages, Presented by JR at the International Symposium on"New Horizons in Fundamental Physics: From Neutrons Nuclei via Superheavy Elements and Supercritical Fields to Neutron Stars and Cosmic Rays," held to honor Walter Greiner on his 80th birthday at Makutsi Safari Farm, South Africa, November 23-29, 2015
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph); Atomic Physics (physics.atom-ph)
arXiv:
1604.08690 [pdf]
FIAS Interdisc.Sci.Ser.(2017)·21 citations
03
[Submitted on 29 Apr 2016]
Interplay between Symmetry Energy and Excluded Volume Corrections under the Direct Urca Cooling Constraint in Neutron Stars
David E. Alvarez-Castillo🇲🇽 · David Blaschke🇷🇺
Both the symmetry energy part and excluded volume corrections to the equation of state play an important role for the neutron star interior structure and composition, namely for the profile of the baryon density and the proton fraction. While the symmetry energy uniquely determines the proton fraction, excluded volume effects control the maximum density values inside neutron stars. Observations of cooling neutron stars indicate that the fast direct Urca cooling is not operative for the typical, low mass stars, pointing at proton fractions that lie below the threshold for the onset of direct Urca cooling process. This in turn, restricts the density range admissible in neutron star interiors and may require an excluded volume correction. In this contribution we discuss the interplay between fast cooling, symmetry energy and excluded volume corrections to the equation of state that would be required to fulfil the direct Urca cooling constraint.
Comments:
10 pages, 5 figures, Proceedings of the Conference "The Modern Physics of Compact Stars 2015", 30 September 2015 - 3 October 2015, Yerevan, Armenia
Subjects:
Nuclear Theory (nucl-th); High Energy Astrophysical Phenomena (astro-ph.HE); High Energy Physics — Phenomenology (hep-ph)
arXiv:
1604.08923 [pdf]
PoS(2016)·5 citations
04
[Submitted on 29 Apr 2016]
Early Time Dynamics of Gluon Fields in High Energy Nuclear Collisions
Joseph I. Kapusta🇺🇸 · Guangyao Chen🇺🇸 · Rainer J. Fries🇺🇸 · Yang Li🇺🇸
Nuclei colliding at very high energy create a strong, quasi-classical gluon field during the initial phase of their interaction. We present an analytic calculation of the initial space-time evolution of this field in the limit of very high energies using a formal recursive solution of the Yang-Mills equations. We provide analytic expressions for the initial chromo-electric and chromo-magnetic fields and for their energy-momentum tensor. In particular, we discuss event-averaged results for energy density and energy flow as well as for longitudinal and transverse pressure of this system. Our results are generally applicable if $τ < 1/ Q_{s}$ . The transverse energy flow of the gluon field exhibits hydrodynamic-like contributions that follow transverse gradients of the energy density. In addition, a rapidity-odd energy flow also emerges from the non-abelian analog of Gauss' Law and generates non-vanishing angular momentum of the field. We will discuss the space-time picture that emerges from our analysis and its implications for observables in heavy ion collisions.
Comments:
4 pages, 2 figures. To appear in the Proceedings of Quark Matter 2015
Subjects:
Nuclear Theory (nucl-th); High Energy Physics — Phenomenology (hep-ph)
arXiv:
1604.08942 [pdf]
NPA(2016)·2 citations
05
[Submitted on 29 Apr 2016] (cross-list from hep-ph)
Properties of Mesons in a Strong Magnetic Field
Rui Zhang🇨🇳 · Wei-jie Fu🇩🇪 · Yu-xin Liu🇨🇳
By extending the $Φ$ -derivable approach in Nambu-Jona-Lasinio model to finite magnetic field we calculate the properties of pion, $σ$ and $ρ$ mesons in a magnetic field at finite temperature in not only the quark-antiquark bound state scheme but also the pion-pion scattering resonant state scenario. Our calculation results manifest that the masses of $π^{0}$ and $σ$ meson can be nearly degenerate at the pseudo-critical temperature which increases with increasing the magnetic field strength, and the $π^{\pm}$ mass ascends suddenly at almost the same critical temperature. While the $ρ$ mesons' masses decrease with the temperature but increase with the magnetic field strength. We also check the Gell-Mann-Oakes-Renner relation and find that the relation can be violated obviously with increasing the temperature, and the effect of the magnetic field becomes pronounced around the critical temperature. With different criteria, we analyze the effect of the magnetic field on the chiral phase transition and find that the pseudo-critical temperature of the chiral phase cross, $T_{c}^{χ}$ , is always enhanced by the magnetic field. Moreover our calculations indicate that the $ρ$ mesons will get melted as the chiral symmetry has not yet been restored, but the $σ$ meson does not disassociate even at very high temperature. Particularly, it is the first to show that there does not exist vector meson condensate in the QCD vacuum in the pion-pion scattering scheme.
Comments:
15 pages, 14 figures, 2 tables. To appear in EPJC
Subjects:
High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
arXiv:
1604.08888 [pdf]
EPJC(2016)·72 citations

Affiliations

first authorsco-authorsvia INSPIRE

Statistical Hauser-Feshbach theory with width fluctuation correction including direct reaction channels for neutron induced reaction at low energies

Probing QED Vacuum with Heavy Ions

Interplay between Symmetry Energy and Excluded Volume Corrections under the Direct Urca Cooling Constraint in Neutron Stars

Early Time Dynamics of Gluon Fields in High Energy Nuclear Collisions

Properties of Mesons in a Strong Magnetic Field

Affiliations