Nuclear Theory·nucl-th

Friday·March 6, 2015

7 papers—4 primary·3 cross-listed

01
Systematic calculations of $α$ -decay half-lives with an improved empirical formula
Z. Y. Wang · Z. M. Niu · Q.Liu · J. Y. Guo
Based on the recent data in NUBASE2012, an improved empirical formula for evaluating the $α$ -decay half-lives is presented, in which the hindrance effect resulted from the change of the ground state spins and parities of parent and daughter nuclei is included, together with a new correction factor for nuclei near the shell closures. The calculated $α$ -decay half-lives are found to be in better agreements with the experimental data, and the corresponding root-mean-square (rms) deviation is reduced to $0.433$ when the experimental $Q$ -values are employed. Furthermore, the $Q$ -values derived from different nuclear mass models are used to predict $α$ -decay half-lives with this improved formula. It is found that the calculated half-lives are very sensitive to the $Q$ -values. Remarkably, when mass predictions are improved with the radial basis function (RBF), the resulting rms deviations can be significantly reduced. With the mass prediction from the latest version of Weizsäcker-Skyrme (WS4) model, the rms deviation of $α$ -decay half-lives with respect to the known data falls to $0.697$ .
nucl-thJ.Phys.G(2015)·32 citations
02
Fission barriers and probabilities of spontaneous fission for elements with Z $\geq$ 100
A. Baran · M. Kowal · P.-G. Reinhard · L.M. Robledo · A. Staszczak · M. Warda
This is a short review of methods and results of calculations of fission barriers and fission half-lives of even-even superheavy nuclei. An approvable agreement of the following approaches is shown and discussed: The macroscopic-microscopic approach based on the stratagem of the shell correction to the liquid drop model and a vantage point of microscopic energy density functionals of Skyrme and Gogny type selfconsistently calculated within Hartree-Fock-Bogoliubov method. Mass parameters are calculated in the Hartree-Fock-Bogoliubov cranking approximation. A short part of the paper is devoted to the nuclear fission dynamics. We also discuss the predictive power of Skyrme functionals applied to key properties of the fission path of $^{266}$ Hs. It applies the standard techniques of error estimates in the framework of a $χ^{2}$ analysis.
nucl-thNPA(2015)·86 citations
03
About consistence between pi N Delta spin-3/2 gauge couplings and electromagnetic gauge invariance
D. Badagnani🇦🇷 · C. Barbero🇦🇷 · A. Mariano🇦🇷
We analyze the consistence between the recently proposed "spin 3/2 gauge" interaction for the Delta resonance with nucleons and pions, and the fundamental electromagnetic gauge invariance in any radiative amplitude. Chiral symmetric pion-derivative pi N Delta couplings can be substituted through a linear transformation to get Delta-derivative ones, which have the property of decoupling the 1/2 field components of the Delta propagator. Nevertheless, the electromagnetic gauge invariance introduced through minimal substitution in all derivatives, can only be fulfilled at a given order n without destroying the spin 3/2 one by dropping n+1 order terms within an effective field theory (EFT) framework with a defined power counting. In addition, we show that the Ward identity for the gamma Delta gamma vertex cannot be fulfilled with a trimmed 3/2 propagator, which should be necessary in order to keep the spin 3/2 gauge symmetry in the radiative case for the gamma Delta gamma amplitude. Finally, it is shown that radiative corrections of the spin 3/2 gauge strong vertexes at one loop, reintroduce the conventional interaction.
nucl-th1 citation
04
Charge symmetry breaking in $Λ$ hypernuclei revisited
Avraham Gal🇮🇱
The large charge symmetry breaking (CSB) implied by the $Λ$ binding energy difference $Δ B_{Λ}^{4} (0_{g.s.}^{+}) \equiv B_{Λ} (_{Λ}^{4}$ He) $-$ $B_{Λ} (_{Λ}^{4}$ H) = 0.35 $\pm$ 0.06 MeV of the $A = 4$ mirror hypernuclei ground states, determined from emulsion studies, has defied theoretical attempts to reproduce it in terms of CSB in hyperon masses and in hyperon-nucleon interactions, including one pion exchange arising from $Λ - Σ^{0}$ mixing. Using a schematic strong-interaction $Λ N \leftrightarrow Σ N$ coupling model developed by Akaishi and collaborators for $s$ -shell $Λ$ hypernuclei, we revisit the evaluation of CSB in the $A = 4$ $Λ$ hypernuclei and extend it to $p$ -shell mirror $Λ$ hypernuclei. The model yields values of $Δ B_{Λ}^{4} (0_{g.s.}^{+}) \sim 0.25$ MeV. Smaller size and mostly negative $p$ -shell binding energy differences are calculated for the $A = 7 - 10$ mirror hypernuclei, in rough agreement with the few available data. CSB is found to reduce by almost 30 keV the 110 keV $_{Λ}^{10}$ B g.s. doublet splitting anticipated from the hyperon-nucleon strong-interaction spin dependence, thereby explaining the persistent experimental failure to observe the $2_{exc}^{-} \to 1_{g.s.}^{-}$ $γ$ -ray transition.
nucl-thhep-phnucl-exPLB(2015)·74 citations
05
Microscopic Study of Vorticities in Relativistic Chiral Fermions
Kiyoumars A. Sohrabi🇨🇭
It is usually believed that unlike the external magnetic field which one can set directly, vorticity is a property of the flow of particles, which is indirectly controlled by external fields and initial conditions. Using the curved-space technics it is shown that the influence of the vorticity on the relativistic chiral fermions can indeed be controlled directly.
↳ hep-phcond-mat.str-elhep-thnucl-thJHEP(2015)·3 citations
06
Phases of SU(3) Gauge Theories with Fundamental Quarks via Dirac Spectral Density
Andrei Alexandru🇺🇸 · Ivan Horváth🇺🇸
We propose that, in SU(3) gauge theories with fundamental quarks, confinement can be inferred from spectral density of the Dirac operator. This stems from the proposition that its possible behaviors are exhausted by three distinct types (Fig.1). The monotonic cases are standard and entail confinement with valence chiral symmetry breaking (A) or the lack of both (C,C'). The bimodal (anomalous) option (B) was frequently regarded as an artifact (lattice or other) in previous studies, but we show for the first time that it persists in the continuum limit, and conclude that it informs of a non-confining phase with broken valence chiral symmetry. This generalization rests on the following. $(α)$ We show that bimodality in $N_{f}$ =0 theory past deconfinement temperature $T_{c}$ is stable with respect to removal of both infrared and ultraviolet cutoffs, indicating that anomalous phase is not an artifact. $(β)$ We demonstrate that transition to bimodality in $N_{f}$ =0 is simultaneous with the loss of confinement: anomalous phase occurs for $T_{c} < T < T_{c h}$ , where $T_{c h}$ is the valence chiral restoration temperature. $(γ)$ Evidence is presented for thermal anomalous phase in $N_{f}$ =2+1 QCD at physical quark masses, whose onset too coincides with the conventional "crossover $T_{c}$ ''. We conclude that the anomalous regime $T_{c} < T < T_{c h}$ is very likely a feature of nature's strong interactions. $(δ)$ Our past studies of zero-temperature $N_{f}$ =12 theories revealed that bimodality also arises via purely light-quark effects. As a result, we expect to encounter anomalous phase on generic paths to valence chiral restoration. We predict its existence also for $N_{f}$ massless flavors ( $T = 0$ ) in the range $N_{f}^{c} < N_{f} < N_{f}^{c h}$ , where $N_{f}^{c}$ could be quite low. Conventional arguments would associate $N_{f}^{c h}$ with the onset of conformal window.
↳ hep-lathep-phhep-thnucl-thPRD(2015)·36 citations
07
Quantum Monte Carlo calculations of the thermal conductivity of neutron star crusts
Sajad Abbar (UNM) · Joe Carlson (LANL) · Huaiyu Duan (UNM) · Sanjay Reddy (UW)
We use the quantum Monte Carlo (QMC) techniques to calculate the static structure function $S (q)$ of a one-component ion lattice and use it to calculate the thermal conductivity $κ$ of high-density solid matter expected in the neutron star crust. By making detailed comparisons with the results for the thermal conductivity obtained using standard techniques based on the one-phonon approximation (OPA) valid at low temperature, and the multi-phonon harmonic approximation expected to be valid over a wide range of temperatures, we asses the temperature regime where $S (q)$ from QMC can be used directly to calculate $κ$ . We also compare the QMC results to those obtained using classical Monte Carlo to quantitatively asses the magnitude of the quantum corrections. We find that quantum effects became relevant for the calculation of $κ$ at temperature $T ≲ 0.3 Ω_{P}$ , where $Ω_{P}$ is the ion plasma frequency. At $T ≃ 0.1 Ω_{P}$ the quantum effects suppress $κ$ by about $30%$ . The comparison with the results of the OPA indicates that dynamical information beyond the static structure is needed when $T ≲ 0.1 Ω_{P}$ . These quantitative comparisons help to establish QMC as a viable technique to calculate $κ$ at moderate temperatures in the range $T = 0.1 - 1 Ω_{P}$ of relevance to the study of accreting neutron stars. This finding is especially important because QMC is the only viable technique so far for calculating $κ$ in multi-component systems at low-temperatures.
↳ astro-ph.HEcond-mat.othernucl-thPRC(2015)·6 citations

Affiliations

first authorsco-authorsvia INSPIRE

Systematic calculations of α-decay half-lives with an improved empirical formula

Fission barriers and probabilities of spontaneous fission for elements with Z≥100

About consistence between pi N Delta spin-3/2 gauge couplings and electromagnetic gauge invariance

Charge symmetry breaking in Λ hypernuclei revisited

Microscopic Study of Vorticities in Relativistic Chiral Fermions

Phases of SU(3) Gauge Theories with Fundamental Quarks via Dirac Spectral Density

Quantum Monte Carlo calculations of the thermal conductivity of neutron star crusts

Affiliations

Systematic calculations of $α$ -decay half-lives with an improved empirical formula

Fission barriers and probabilities of spontaneous fission for elements with Z $\geq$ 100

Charge symmetry breaking in $Λ$ hypernuclei revisited