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Nuclear Theory·nucl-th

Friday·June 10, 2016

5 papers—2 primary·3 cross-listed

All5Primary2Cross-lists3
  1. 01

    Statistical analysis of beta decays and the effective value of g_A in the proton-neutron quasiparticle random-phase approximation framework

    Frank F. Deppisch🇬🇧 · Jouni Suhonen🇫🇮

    We perform a Markov Chain Monte Carlo (MCMC) statistical analysis of a number of measured ground-state-to-ground-state single /electron-capture and decays in the nuclear mass range A = 62 - 142. The corresponding experimental comparative half-lives (log ft values) are compared with the theoretical ones obtained by the use of the proton-neutron quasiparticle random-phase approximation (pnQRPA) with G-matrix based effective interactions. The MCMC analysis is performed separately for 47 isobaric triplets and 28 more extended isobaric chains of nuclei to extract values and uncertainties for the effective axial-vector coupling constant g_A in nuclear-structure calculations performed in the pnQRPA framework. As far as available, measured half-lives for two-neutrino double beta-minus decays occurring in the studied isobaric chains are analyzed as well.

    nucl-thhep-exhep-phnucl-exPRC(2016)·46 citations
  3. 03

    Internal X-ray plateau in short GRBs: Signature of supramassive fast-rotating quark stars?

    Ang Li · Bing Zhang · Nai Bo Zhang · He Gao · Bin Qi · Tong Liu

    A supramassive, strongly-magnetized millisecond neutron star (NS) has been proposed to be the candidate central engine of at least some short gamma-ray bursts (SGRBs), based on the "internal plateau" commonly observed in the early X-ray afterglow. While a previous analysis shows a qualitative consistency between this suggestion and the Swift SGRB data, the distribution of observed break time is much narrower than the distribution of the collapse time of supramassive NSs for the several NS equations-of-state (EoSs) investigated. In this paper, we study four recently-constructed "unified" NS EoSs, as well as three developed strange quark star (QS) EoSs within the new confinement density-dependent mass model. All the EoSs chosen here satisfy the recent observational constraints of the two massive pulsars whose masses are precisely measured. We construct sequences of rigidly rotating NS/QS configurations with increasing spinning frequency , from non-rotating () to the Keplerian frequency (), and provide convenient analytical parametrizations of the results. Assuming that the cosmological NS-NS merger systems have the same mass distribution as the Galactic NS-NS systems, we demonstrate that all except the BCPM NS EoS can reproduce the current supramassive NS/QS fraction constraint as derived from the SGRB data. We simultaneously simulate the observed quantities (the break time , the break time luminosity and the total energy in the electromagnetic channel ) of SGRBs, and find that while equally well reproducing other observational constraints, QS EoSs predict a much narrower distribution than that of the NS EoSs, better matching the data. We therefore suggest that the post-merger product of NS-NS mergers might be fast-rotating supramassive QSs rather than NSs.

    ↳ astro-ph.HEastro-ph.SRnucl-thPRD(2016)·104 citations
  4. 04

    Modifying the pion mass in the loosely bound Skyrme model

    Sven Bjarke Gudnason🇨🇳 · Muneto Nitta🇯🇵

    We study the loosely bound Skyrme model with the addition of two different pion mass terms; this is the most general potential of polynomial form up to second order in the trace of the Skyrme field. The two pion mass terms are called the standard pion mass term and the modified pion mass term. We find that the binding energies are not reduced by the introduction of the modified pion mass, but it is analogous to the standard pion mass term with a decrease in the value of the mass parameter of the loosely bound potential (for large values of the latter parameter). We find by increasing the overall pion mass that we can reduce the classical binding energy of the 4-Skyrmion to the 2.7% level and the total binding energy including the contribution from spin/isospin quantization is reduced to the 5.8% level.

    ↳ hep-phnucl-thPRD(2016)·26 citations
  5. 05

    Parametrizations of the quadrupole form factors and Siegert's theorem

    G. Ramalho🇧🇷

    The large limit provides relations that can be used to calculate the quadrupole form factors at low and intermediate under the assumption of the pion cloud dominance. There are two limitations in those parametrizations. First, the parametrization of the Coulomb quadrupole form factor underestimate the low data. Second, when extrapolated for the timelike region, the form factors violate Siegert's theorem by terms of the order . We propose here corrections to the parametrization of the electric quadrupole form factor, which violate Siegert's theorem only by terms of the order . Combining the improved large pion cloud parametrizations with the valence quark contributions based on a covariant quark model for the quadrupole transition form factors, we obtain an extrapolation to the timelike region consistent with Siegert's theorem, and accomplish also a very good description of the data.

    ↳ hep-phhep-latnucl-exnucl-thPRD(2016)·29 citations

Affiliations

first authorsco-authorsvia INSPIRE