Nuclear Theory·nucl-th

Tuesday·January 14, 2020

14 papers—9 primary·5 cross-listed

01
Bayesian inference of the incompressibility, skewness and kurtosis of nuclear matter from empirical pressures in relativistic heavy-ion collisions
Wen-Jie Xie · Bao-An Li
Within the Bayesian statistical framework we infer the incompressibility $K_{0}$ , skewness $J_{0}$ and kurtosis $Z_{0}$ parameters of symmetric nuclear matter (SNM) at its saturation density $ρ_{0}$ using the constraining bands on the pressure in cold SNM in the density range of 1.3 $ρ_{0}$ to 4.5 $ρ_{0}$ from transport model analyses of kaon production and nuclear collective flow in relativistic heavy-ion collisions. As the default option assuming the $K_{0}$ , $J_{0}$ and $Z_{0}$ have Gaussian prior probability distribution functions (PDFs) with the means and variances of $235 \pm 30$ , $- 200 \pm 200$ and $- 146 \pm 1728$ MeV, their posterior most probable values are narrowed down to 192 $_{- 16}^{+ 12}$ MeV, -180 $_{- 110}^{+ 100}$ MeV and 200 $_{- 250}^{+ 250}$ at 68\% confidence level, respectively. The results are largely independent of the prior PDFs of $J_{0}$ and $Z_{0}$ used. However, if one adopts the strong belief that the incompressibility $K_{0}$ has a uniform prior PDF within its absolute boundary of 220-260 MeV as one can find easily in the literature, the posterior most probable values of $K_{0}$ , $J_{0}$ and $Z_{0}$ shift to $K_{0} = 22 0_{- 0}^{+ 6}$ MeV, $J_{0} = - 39 0_{- 70}^{+ 60}$ MeV and $Z_{0} = 60 0_{- 200}^{+ 200}$ MeV, respectively. While the posterior PDFs of the SNM EOS parameters depend somewhat on the prior PDF of $K_{0}$ used, the results from using different prior PDFs are qualitatively consistent. The uncertainties of all three parameters are significantly reduced especially for the $J_{0}$ and $Z_{0}$ parameters compared to their current values.
nucl-thastro-ph.HEastro-ph.SRnucl-exJ.Phys.G(2021)·35 citations
02
Nucleon effective mass in hot dense matter
X. L. Shang · A. Li · Z. Q. Miao · G. F. Burgio · H.-J. Schulze
Nucleon effective masses are studied in the framework of the Brueckner-Hartree-Fock many-body approach at finite temperature. Self-consistent calculations using the Argonne $V_{18}$ interaction including microscopic three-body forces are reported for varying temperature and proton fraction up to several times the nuclear saturation density. Our calculations are based on the exact treatment of the center-of-mass momentum instead of the average-momentum approximation employed in previous works. We discuss in detail the effects of the temperature together with those of the three-body forces, the density, and the isospin asymmetry. We also provide an analytical fit of the effective mass taking these dependencies into account. The temperature effects on the cooling of neutron stars are briefly discussed based on the results for betastable matter.
nucl-thastro-ph.HEastro-ph.SRPRC(2020)·36 citations
03
Box diagram contribution to the axial two-nucleon current
Hermann Krebs🇩🇪 · Evgeny Epelbaum🇩🇪 · Ulf-G. Meißner🇩🇪
Recently, we have worked out the axial two-nucleon current operator to leading one-loop order in chiral effective field theory using the method of unitary transformation. Our final expressions, however, differ from the ones derived by the JLab-Pisa group using time-ordered perturbation theory (Phys. Rev. C 93, no. 1, 015501 (2016) Erratum: [Phys. Rev. C 93, no. 4, 049902 (2016)] Erratum: [Phys. Rev. C 95, no. 5, 059901 (2017)]). In this paper we consider the box diagram contribution to the axial current and demonstrate that the results obtained using the two methods are unitary equivalent at the Fock-space level. We adjust the unitary phases by matching the corresponding two-pion exchange nucleon-nucleon potentials and rederive the box diagram contribution to the axial current operator following the approach of the JLab-Pisa group, thereby reproducing our original result. We provide a detailed information on the calculation including the relevant intermediate steps in order to facilitate a clarification of this disagreement.
nucl-thhep-phPRC(2020)·13 citations
04
Elastic pion-nucleon scattering in chiral perturbation theory: Explicit $Δ$ (1232) degrees of freedom
Dmitrij Siemens
For the first time, elastic pion-nucleon scattering is analyzed in the framework of chiral perturbation theory up to fourth order with explicit $Δ$ degrees of freedom. The analysis is performed within the heavy-baryon expansion as well as in a covariant approach based on an extended on-mass-shell renormalization scheme. The renormalization of low-energy constants in both chiral approaches is discussed in detail and the explicit expressions to cancel both power-counting breaking as well as decoupling breaking terms are given. The low-energy constants from the $2 π N ˉ N$ interaction as well as additional constants from the $Δ$ sector are reliably constrained by fits to experimental data. The traditional $K$ -matrix unitarization is employed in the near threshold region, whereas a complex mass approach is used to extend the applicability of the theory up to the $Δ$ pole region. Additionally, we estimate a theoretical error based on the truncation of the chiral series as employed in recent analyses of nuclear forces as well as pion-nucleon scattering. The obtained results provide a clear evidence that the explicit inclusion of $Δ$ degrees of freedom is fundamental to describe pion-nucleon physics at threshold. The resulting predictions for the subthreshold and threshold parameters as well as phase shifts are in excellent agreement with the ones determined by the recent Roy-Steiner analysis of pion-nucleon scattering.
nucl-thhep-ph8 citations
05
Charmed and beautiful baryonic systems (hypernuclei) in chiral soliton models
V.B. Kopeliovich🇷🇺 · D.E. Lanskoy🇷🇺
The binding energies of baryonic systems with quantum number charm or beauty and neutron excess (or large isospin) are estimated within the bound state version of the chiral topological soliton model. The procedure of the skyrmion rescaling is applied which is of importance for large enough flavor excitation energies (for heavy flavors). Inclusion of the flavor excitation energies into the minimization of the total mass of the baryonic state naturally leads to its decrease, and this effect increases with increasing flavor mass. Our results concerning the binding energies turned out to be partly negative.
nucl-th1 citation
06
Simulation of the wave neutron-nuclear burning of Th232 enriched with Pu239 for the thermal range of neutron energy
A.O. Kakaev · V.O. Tarasov · S.A. Chernezhenko · V.O. Sova · V.D. Rusov
At the initial stage, the development of wave reactors, which will operate in the mode of wave nuclear burning (WNC), requires the study of the kinetics of the WNC fuel mode when changing both external parameters (flux density of an external neutron source, thermal parameters of heat transfer) and internal parameters (fuel composition, reactor material parameter, delayed neutrons). In order to confirm the possibility of WNC with enrichment, we study its impact on the criterion of WNC for thorium fuel Th232 at different enrichments in Pu239) and its behavior during the "ignition" stage. To confirm the fulfillment of the criterion of slow WNC depending on the neutron energy, we perform a numerical simulation of the thorium fuel WNC mode dynamics, taking into account the delayed neutrons in the thermal and epithermal regions of the neutron energies (0.015-10 eV).
nucl-th0 citations
07
Asymmetry of the neutrino mean free path in partially spin polarized neutron matter within the Skyrme model
E. Bauer🇦🇷 · J. Torres Patiño🇦🇷
The asymmetry in the neutrino mean free path for the absorption reaction $ν + n \to e^{-} + p$ , is evaluated within hot neutron matter under a strong magnetic field. We consider densities in the range $0.05 \leq ρ \leq 0.4$ fm $^{- 3}$ , several temperatures up to 30 MeV and magnetic field strengths from $B = 0$ up to $B = 1 0^{18}$ ~G. Polarized neutron matter is described within the non--relativistic Hartree--Fock model using the LNS Skyrme interaction. The neutrino mean free path has a weak dependence with the temperature and in the strong magnetic field region, it decreases for growing values of it. This contrast with the scattering reaction $ν + n \to ν^{'} + n^{'}$ , where the average mean free path is almost independent of the magnetic field and has a strong dependence with the temperature. We have evaluated the asymmetry from both the absorption and scattering reactions. Our results shows that the total asymmetry depends on the magnetic field intensity, the density and the temperature. For a density of $0.16$ fm $^{- 3}$ and for a magnetic field strength of B= $1 0^{17}$ ~G, the asymmetry in the mean free path is found to be, $\sim 9%$ and $\sim 3.4%$ for temperatures of T $= 15$ and $30$ MeV, respectively. While the same set of asymmetries for B= $1 0^{18}$ ~G, is $\sim 58%$ and $\sim 48%$ .
nucl-thPRC(2020)·5 citations
08
The Mass of Short-Range Correlated Nucleon
Rong Wang · Xurong Chen · Taofeng Wang
The nucleon properties and structure should be modified by short-range correlations (SRC) among nucleons. By analyzing SRC ratio data, we extract the mass of nucleon in the SRC pair and the expected number of pn-SRC pairs in deuterium, under the assumption that the SRC nucleon mass is universal in different nuclei. The nucleon mass of a two-nucleon SRC pair is $m_{SRC} = 852 \pm 18$ MeV, and the number of pn-SRC pairs in deuterium is $n_{SRC}^{d} = 0.021 \pm 0.005$ . The mass deficit of the strongly overlapping nucleon can be explained by the trace anomaly contribution to the mass in QCD or alternatively by the vacuum energy in the MIT bag model.
nucl-thhep-phnucl-exCPC(2021)·6 citations
09
Effect of Nucleon Dressing on the Triton Binding Energy
B. Blankleider🇦🇺 · S. S. Kumar🇦🇺 · A. N. Kvinikhidze🇬🇪
The effect of nucleon dressing by pions, on the binding energy of three nucleons interacting via two-body forces, is calculated for the first time within a conventional nuclear physics approach. It is found that the dressing increases the binding energy of the triton by an amount approximately in the range from 0.3 MeV to 0.9 MeV, depending on the model used for dressing. This suggests that nucleon dressing may help explain the underestimation of the triton binding energy in previous calculations using only two-nucleon forces.
nucl-thhep-phFew Body Syst.(2021)·0 citations
10
Mean Field Quarks on the Light Front
Christopher Leon🇺🇸 · Misak Sargsian🇺🇸
We present a new approach for the calculation of the valence quark distributions in the nucleon based on the scenario in which the spectrum of the valence quarks at x>0.05 is generated through three main mechanisms: interaction of valence quarks with the mean field generated by the residual nucleon system, two and three quark short range interactions through gluon exchanges. In the current report we present the first phase of the project in which we develop a non-perturbative model for valence quark interaction in the mean field of the nucleonic interior to describe their distribution in the moderate x region (0.05 < x < 0.4). The short range quark-quark interaction effects in our approach generate the high x tail of valence quark distributions. The presented non-perturbative model is based on the picture in which three relativistic valence quarks occupy the nucleon core at distances of $\leq 0.5$ Fm while interacting in the mean field generated by the residual nucleon system. The calculations are based on the assumption of the a factorization of the internal interaction of short-range three valence quarks with the long-range interaction of these quarks with the residual system. The theoretical approach is based on effective light-front diagrammatic approach which allows us to introduce the valence quark and residual system wave functions in a consistent way The parameters of these wave functions are fixed by the position of the peak of the xf_q(x) distribution of valence quarks at Q_0 corresponding to the charm-quark mass. With few parameters we achieved a very reasonable description of the up and down valence quark distributions in the moderate x region (x < 0.4), where one expects the mean field dynamics to dominate. The model, however, systematically underestimates the high $x$ region where enhanced contributions from partonic short-range correlations are expected.
↳ hep-phhep-exnucl-exnucl-thPoS(2020)·4 citations
11
Nuclear effects in high-energy neutrino interactions
Spencer R. Klein🇺🇸 · Sally A. Robertson🇺🇸 · Ramona Vogt🇺🇸
Neutrino telescopes like IceCube, KM3NeT and Baikal-GVD offer physicists the opportunity to study neutrinos with energies far beyond the reach of terrestrial accelerators. These neutrinos are used to study high-energy neutrino interactions and to probe the Earth through absorption tomography. Current studies of TeV neutrinos use cross sections which are calculated for free nucleons with targets which are assumed to contain equal numbers of protons and neutrons. Here we consider modifications of high-energy neutrino interactions due to two nuclear effects: modifications of the parton densities in the nucleus, referred to here as shadowing, and the effect of non-isoscalar targets, with unequal numbers of neutrons and protons. Both these effects depend on the interaction medium. Because shadowing is larger for heavier nuclei, such as iron, found in the Earth's core, it introduces a zenith-angle dependent change in the absorption cross section. These modifications increase the cross sections by 1-2\% at energies below 100 TeV (antishadowing), and reduce it by 3-4\% at higher energies (shadowing). Nuclear effects also alter the inelasticity distribution of neutrino interactions in water/ice by increasing the number of low inelasticity interactions, with a larger effect for $ν$ than $ν ˉ$ . These effects are particularly large in the energy range below a few TeV. These effects could alter the cross sections inferred from events with tracks originating within the active detector volume as well as the ratio $ν / ν ˉ$ inferred from inelasticity measurements. The uncertainties in these nuclear effects are larger than the uncertainties on the free-proton cross sections and will thus limit the systematic precision of future high-precision measurements at neutrino telescopes.
↳ hep-phastro-ph.HEnucl-exnucl-thPRC(2020)·23 citations
12
Unified equations of state for cold non-accreting neutron stars with Brussels-Montreal functionals. II. Pasta phases in semi-classical approximation
J. M. Pearson · N. Chamel · A. Y. Potekhin
We generalize our earlier work on neutron stars (arXiv:1903.04981), which assumed spherical Wigner-Seitz cells in the inner crust, to admit the possibility of pasta phases, i.e., non-spherical cell shapes. Full fourth-order extended Thomas-Fermi calculations using the density functional BSk24 are performed for cylindrical and plate-like cells. Unlike in our spherical-cell calculations, we do not include shell and pairing corrections, but there are grounds for expecting these corrections for pasta to be significantly smaller. It is therefore meaningful to compare the ETF pasta results with the full spherical-cell results, i.e., with shell and pairing corrections included. However, in view of the many previous studies in which shell and pairing corrections were omitted entirely, it is of interest to compare our pasta results with the ETF part of the corresponding spherical calculations. Making this latter comparison we find that as the density increases the cell shapes pass through the usual sequence sphere $\to$ cylinder $\to$ plate before the transition to the homogeneous core. The filling fractions found at the phase transitions are in close agreement with expectations based on the liquid-drop model. On the other hand, when we compare with the full spherical-cell results, we find the sequence to be sphere $\to$ cylinder $\to$ sphere $\to$ cylinder $\to$ plate. In neither case do any "inverted", i.e., bubble-like, configurations appear. We provide accurate fitting formulas to all our essential numerical results for each of the three phases, designed especially for the density range where the nonspherical shapes are expected, which enable one to capture not only the general behavior of the fitted functions, but also the differences between them in different phases.
↳ astro-ph.HEnucl-thPRC(2020)·56 citations
13
On QCD strings beyond non-interacting model
A. S. Bakry🇨🇳 · M. A. Deliyergiyev🇵🇱 · A. A. Galal🇪🇬 · M. Khalil William🇪🇬
We investigate the implications of Nambu-Goto (NG), Lüscher-Weisz (LW) and Polyakov-Kleinert (PK) string actions for the Casimir energy of the QCD flux-tube at one and two loop order at finite temperature. We perform our numerical study on the 4-dim pure SU(3) Yang-Mills lattice gauge theory at finite temperature $β = 6.0$ . The static quark-antiquark potential is calculated using link-integrated Polyakov loop correlators. At a high temperature-close to the critical point- We find that the rigidity and self-interactions effects of the QCD string to become detectable. The remarkable feature of this model is that it retrieves a correct dependency of the renormalized string tension on the temperature. Good fit to static potential data at source separations $R \geq 0.5$ fm is obtained when including additional two-boundary terms of (LW) action. On the other-hand, at a lower temperature-near the QCD plateau- We detect signatures of two boundary terms of the Lüscher-Weisz (LW) string action. The (LW) string with boundary action is yielding a static potential which is in a good agreement with the lattice data, however, for color source separation as short as $R = 0.3$ fm.
↳ hep-lathep-phhep-thnucl-th6 citations
14
Probing impact-parameter dependent nuclear parton densities from double parton scatterings in heavy-ion collisions
Hua-Sheng Shao🇫🇷
We propose a new method to determine the spatially or impact-parameter dependent nuclear parton distribution functions (nPDFs) using the double parton scattering (DPS) processes in high-energy heavy-ion (proton-nucleus and nucleus-nucleus) collisions. We derive a simple generic DPS formula in nuclear collisions by accommodating both the nuclear collision geometry and the spatially dependent nuclear modification effect, under the assumption that the impact-parameter dependence of nPDFs is only related to the nuclear thickness function. While the geometric effect is widely adopted, the impact of the spatially dependent nuclear modification on DPS cross sections has been overlooked so far, which can, however, be significant when the initial nuclear modification is large. In turn, the DPS cross sections in heavy-ion collisions can provide useful information on the spatial dependence of nPDFs. They can be, in general, obtained in minimum-bias nuclear collisions, featuring the virtue of independence of Glauber modeling.
↳ hep-phhep-exnucl-exnucl-thPRD(2020)·25 citations

Affiliations

first authorsco-authorsvia INSPIRE