Nuclear Theory·nucl-th

Wednesday·December 7, 2016

11 papers—6 primary·5 cross-listed

01
Radiative 3He(2H,g)5Li capture at low deuterium energy
Sergey Dubovichenko🇰🇿 · Nataliya Burkova🇰🇿 · Albert Dzhazairov-Kakhramanov🇰🇿
The results are presented on the total cross sections, astrophysical S-factor, reaction rate of the deuteron radiative capture on 3He at the temperatures from 0.03 up to 3 T9 calculated in the framework of the potential cluster model with the forbidden states coming from the classification of the orbital states by the Young diagrams. Within the used model and exploited Young diagram classification made it possible to reproduce the general features of the available experimental data on the cross section and reconstructed astrophysical S-factor in the energy range from 200 keV up to 1.4 MeV. The parametrization of the obtained reaction rate has been found and been compared with some other actual reactions with light clusters.
nucl-thRuss.Phys.J.(2017)·4 citations
02
Ternary fission within the temperature dependent relativistic mean field approach
M.T. Senthil Kannan · Bharat Kumar · M. Balasubramaniam · B. K. Agrawal · S. K. Patra
For the first time, we apply the temperature dependent relativistic mean field (TRMF) model to study the ternary fission of heavy nucleus using level density approach. The probability of yields of a particular fragment is obtained by evaluating the convolution integrals which employ the excitation energy and the level density parameter for a given temperature calculated within the TRMF formalism. To illustrate, we have considered the ternary fissions in 252Cf, 242Pu and 236U with fixed third fragment A3 = 48Ca, 20O and 16O respectively. The relative yields are studied for the temperatures T = 1, 2 and 3 MeV. For the comparison, the relative yields are also calculated from the single particle energies of the finite range droplet model (FRDM). In general, the larger phase space for the ternary fragmentation is observed indicating that such fragmentations are most probable ones. For T = 2 and 3 MeV, the Sn + Ni + Ca is the most probable combination for the nucleus 252Cf. However, for the nuclei 242Pu and 236U, the maximum fragmentation yields at T = 2 MeV differ from those at T = 3 MeV. For T = 3 MeV, the closed shell (Z = 8) light mass fragments with its corresponding partners has larger yield values. But, at T = 2 MeV Si/P/S are favorable fragments with the corresponding partners. It is noticed that the symmetric binary fragmentation along with the fixed third fragment for 242Pu and 236U are also favored at T = 1 MeV. The temperature dependence of the nuclear shape and the single particle energies are also discussed.
nucl-thPRC(2017)·11 citations
03
SQM2016: Theory Summary
V. Greco🇮🇹
This is an overview of the main theoretical developments presented at SQM2016 held in Berkeley, California (USA) in June 2015.
nucl-thhep-phnucl-exJ.Phys.Conf.Ser.(2017)·3 citations
04
Supernova equations of state including full nuclear ensemble with in-medium effects
Shun Furusawa · Kohsuke Sumiyoshi · Shoichi Yamada · Hideyuki Suzuki
We construct new equations of state for baryons at sub-nuclear densities for the use in core-collapse supernova simulations. The abundance of various nuclei is obtained together with thermodynamic quantities. The formulation is an extension of the previous model, in which we adopted the relativistic mean field theory with the TM1 parameter set for nucleons, the quantum approach for $d$ , $t$ , $h$ and $α$ as well as the liquid drop model for the other nuclei under the nuclear statistical equilibrium. We reformulate the model of the light nuclei other than $d$ , $t$ , $h$ and $α$ based on the quasi-particle description. Furthermore, we modify the model so that the temperature dependences of surface and shell energies of heavy nuclei could be taken into account. The pasta phases for heavy nuclei and the Pauli- and self-energy shifts for $d$ , $t$ , $h$ and $α$ are taken into account in the same way as in the previous model. We find that nuclear composition is considerably affected by the modifications in this work, whereas thermodynamical quantities are not changed much. In particular, the washout of shell effect has a great impact on the mass distribution above $T \sim 1$ MeV. This improvement may have an important effect on the rates of electron captures and coherent neutrino scatterings on nuclei in supernova cores.
nucl-thastro-ph.HENPA(2017)·58 citations
05
Self consistent calculation of the nuclear composition in hot and dense stellar matter
Shun Furusawa · Igor Mishustin
We investigate the mass fractions and in-medium properties of heavy nuclei in stellar matter at characteristic densities and temperatures for supernova (SN) explosions. The individual nuclei are described within the compressible liquid-drop model taking into account modifications of bulk, surface and Coulomb energies. The equilibrium properties of nuclei and the full ensemble of heavy nuclei are calculated self-consistently. It is found that heavy nuclei in the ensemble are either compressed or decompressed depending on the isospin asymmetry of the system. The compression or decompression has a little influence on the binding energies, total mass fractions and average mass numbers of heavy nuclei, although the equilibrium densities of individual nuclei themselves are changed appreciably above one hundredth of normal nuclear density. We find that nuclear structure in single nucleus approximation deviates from the actual one obtained in the multi-nucleus description, since the density of free nucleons is different between these two descriptions. This study indicates that a multi-nucleus description is required to realistically account for in-medium effects on the nuclear structure in supernova matter.
nucl-thastro-ph.HEPRC(2017)·14 citations
06
Dipole-dipole dispersion interactions between neutrons
James F. Babb · Renato Higa · Mahir S. Hussein
We investigate the long-range interactions between two neutrons utilizing recent data on the neutron static and dynamic electric and magnetic dipole polarizabilities. The resulting long-range potentials are used to make quantitative comparisons between the collisions of a neutron with a neutron and a neutron with a proton. We also assess the importance of the first pion production threshold and first excited state of the nucleon, the $Δ$ -resonance ( $J^{π}$ = + 3/2, I = 3/2). We found both dynamical effects to be quite relevant for distances r between ~ 50 fm up to ~ $1 0^{3}$ fm in the nn system, the neutron-wall system and in the wall-neutron-wall system, reaching the expected asymptotic limit beyond that. Relevance of our findings to the confinement of ultra cold neutrons inside bottles is discussed.
nucl-thphysics.atom-phEPJA(2017)·4 citations
07
Light Axial Vectors, Nuclear Transitions, and the $^{8}$ Be Anomaly
Jonathan Kozaczuk🇺🇸 · David E. Morrissey🇨🇦 · S. R. Stroberg🇨🇦
New hidden particles could potentially be emitted and discovered in rare nuclear transitions. In this work we investigate the production of hidden vector bosons with primarily axial couplings to light quarks in nuclear transitions, and we apply our results to the recent anomaly seen in $^{8}$ Be decays. The relevant matrix elements for $^{8} Be^{*} (1^{+}) \to^{8} Be (0^{+})$ transitions are calculated using $ab initio$ methods with inter-nucleon forces derived from chiral effective field theory and the in-medium similarity renormalization group. We find that the emission of a light axial vector with mass $m_{X} ≃ 17 MeV$ can account for the anomaly seen in the $1^{+} \to 0^{+}$ isoscalar transition together with the absence of a significant anomaly in the corresponding isovector transition. We also show that such an axial vector can be derived from an anomaly-free ultraviolet-complete theory that is consistent with current experimental data.
↳ hep-phnucl-thPRD(2017)·91 citations
08
Lattice QCD spectroscopy for hadronic CP violation
Jordy de Vries🇳🇱 · Emanuele Mereghetti🇺🇸 · Chien-Yeah Seng🇨🇳 · Andre Walker-Loud🇺🇸
The interpretation of nuclear electric dipole moment (EDM) experiments is clouded by large theoretical uncertainties associated with nonperturbative matrix elements. In various beyond-the-Standard Model scenarios nuclear and diamagnetic atomic EDMs are expected to be dominated by CP-violating pion-nucleon interactions that arise from quark chromo-electric dipole moments. The corresponding CP-violating pion-nucleon coupling strengths are, however, poorly known. In this work we propose a strategy to calculate these couplings by using spectroscopic lattice QCD techniques. Instead of directly calculating the pion-nucleon coupling constants, a challenging task, we use chiral symmetry relations that link the pion-nucleon couplings to nucleon sigma terms and mass splittings that are significantly easier to calculate. In this work, we show that these relations are reliable up to next-to-next-to-leading order in the chiral expansion in both SU(2) and SU(3) chiral perturbation theory. We conclude with a brief discussion about practical details regarding the required lattice QCD calculations and the phenomenological impact of an improved understanding of CP-violating matrix elements.
↳ hep-lathep-phnucl-thPLB(2017)·46 citations
09
The stability of relativistic stars and the role of the adiabatic index
Ch.C. Moustakidis
We study the stability of three analytical solutions of the Einstein's field equations for spheres of fluid. These solutions are suitable to describe compact objects including white dwarfs, neutron stars and supermassive stars and they have been extensively employed in the literature. We re-examine the range of stability of the Tolman VII solution, we focus on the stability of the Buchdahl solution which is under contradiction in the literature and we examine the stability of the Nariai IV solution. We found that all the mentioned solutions are stable in an extensive range of the compactness parameter. We also concentrate on the effect of the adiabatic index on the instability condition. We found that the critical adiabatic index, depends linearly on the ratio of central pressure over central energy density $P_{c} / E_{c}$ , up to high values of the compactness. Finally, we examine the possibility to impose constraints, via the adiabatic index, on realistic equations of state in order to ensure stable configurations of compact objects.
↳ gr-qcastro-ph.HEastro-ph.SRnucl-thGen.Rel.Grav.(2017)·216 citations
10
Mixing of charged and neutral Bose condensates at nonzero temperature and magnetic field
Alexander Haber🇬🇧 · Andreas Schmitt🇬🇧
It is expected that in the interior of compact stars a proton superconductor coexists with and couples to a neutron superfluid. Starting from a field-theoretical model for two complex scalar fields - one of which is electrically charged - we derive a Ginzburg-Landau potential which includes entrainment between the two fluids and temperature effects from thermal excitations of the two scalar fields and the gauge field. The Ginzburg-Landau description is then used for an analysis of the phase structure in the presence of an external magnetic field. In particular, we study the effect of the superfluid on the flux tube phase by computing the various critical magnetic fields and deriving an approximation for the flux tube interaction. As a result, we point out differences to the naive expectations from an isolated superconductor, for instance the existence of a first-order flux tube onset, resulting in a more complicated phase structure in the region between type-I and type-II superconductivity.
↳ astro-ph.HEhep-phnucl-thEPJ Web Conf.(2017)·7 citations
11
Evidence of effective axial U(1) symmetry restoration at high temperature QCD
A. Tomiya🇨🇳 · G. Cossu🇬🇧 · S. Aoki🇯🇵 · H. Fukaya🇯🇵 · S. Hashimoto🇯🇵 · T. Kaneko🇯🇵 · J. Noaki🇯🇵
We study the axial U(1) symmetry at finite temperature in two-flavor lattice QCD. Employing the Mobius domain-wall fermions, we generate gauge configurations slightly above the critical temperature Tc with different lattice sizes L = 2-4 fm. Our action allows frequent topology tunneling while keeping good chiral symmetry close enough to that of overlap fermions. This allows us to recover full chiral symmetry by an overlap/domain-wall reweighting. Above the phase transition, a strong suppression of the low-lying modes is observed in both of overlap and domain-wall Dirac spectra. We, however, find a sizable violation of the Ginsparg-Wilson relation in the Mobius domain-wall Dirac eigenmodes, which dominates the signals of the axial U(1) symmetry breaking near the chiral limit. We also find that the use of overlap fermion only in the valence sector is dangerous since it suffers from the artifacts due to partial quenching. Reweighting the Mobius domain-wall fermion determinant to that of the overlap fermion, we observe the axial U(1) breaking to vanish in the chiral limit, which is stable against the changes of the lattice volume and lattice spacing.
↳ hep-lathep-phhep-thnucl-thPRD(2017)·144 citations

Affiliations

first authorsco-authorsvia INSPIRE