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Nuclear Theory·nucl-th

Wednesday·December 27, 2017

20 papers—14 primary·6 cross-listed

All20Primary14Cross-lists6
  1. 15

    Analysis and Monte Carlo Modelling of Multiple Scattering of a Beam of Neutrons or Photons off of the Two Surfaces of a Broad Material Target as a Function of its Thickness

    Eric V. Steinfelds · Keith Andrew

    We consider the scattering of neutrons and photons on solid volume rectangular targets. It is common to treat this problem using the Maxwell Boltzmann Transport Equation and to use underlying symmetries to simplify the calculation. For isotropic scattering centers we can introduce a direct Fredholm integral equation approach to finding the flux. Here we compare a Monte Carlo evaluation of the resulting Fredholm equation to a deterministic iteration method of solution. We include a kernel based method for estimating the overall angular dependence. We find that for simple geometries utilized in studies of radiative dosimetry, of neutron shielding assessments, and indirectly of criticality that we get reasonably rapid convergence of flux and current values.

    ↳ physics.comp-phnucl-th1 citation
  2. 16

    Search For Gravitational Redshifted Absorption Lines In LMXB Serpens X-1

    Hiroki Yoneda · Chris Done · Frits Paerels · Tadayuki Takahashi · Shin Watanabe

    The equation of state for ultra-dense matter can be tested from observations of the ratio of mass to radius of neutron stars. This could be measured precisely from the redshift of a narrow line produced on the surface. X-rays bursts have been intensively searched for such features, but so far without detection. Here instead we search for redshifted lines in the persistent emission, where the accretion flow dominates over the surface emission. We discuss the requirements for narrow lines to be produced, and show that narrow absorption lines from highly ionized iron can potentially be observable in accreting low mass X-ray binaries (low B field) which have either low spin or low inclination so that Doppler broadening is small. This selects Serpens X-1 as the only potential candidate persistent LMXB due to its low inclination. Including surface models in the broad band accretion flow model predicts that the absorption line from He-like iron at 6.7 keV should be redshifted to 5.1 - 5.7 keV (10 - 15 km for ) and have an equivalent width of 0.8 - 8.0 eV for surface temperatures of 7 - 10 10 K. We use the high resolution Chandra grating data to give a firm upper limit of 2 - 3 eV for an absorption line at keV. We discuss possible reasons for this lack of detection (the surface temperature and the geometry of the boundary layer etc.). Future instruments with better sensitivity are required in order to explore the existence of such features.

    ↳ astro-ph.HEnucl-exnucl-thMNRAS(2018)·1 citation
  3. 17

    Exploring Zeptosecond Quantum Equilibration Dynamics: From Deep-Inelastic to Fusion-Fission Outcomes in Ni+Ni Reactions

    E. Williams · K. Sekizawa · D. J. Hinde · C. Simenel · M. Dasgupta · I. P. Carter · K. J. Cook · D. Y. Jeung · S. D. McNeil · C. S. Palshetkar · D. C. Rafferty · K. Ramachandran · A. Wakhle

    Energy dissipative processes play a key role in how quantum many-body systems dynamically evolve towards equilibrium. In closed quantum systems, such processes are attributed to the transfer of energy from collective motion to single-particle degrees of freedom; however, the quantum many-body dynamics of this evolutionary process are poorly understood. To explore energy dissipative phenomena and equilibration dynamics in one such system, an experimental investigation of deep-inelastic and fusion-fission outcomes in the Ni+Ni reaction has been carried out. Experimental outcomes have been compared to theoretical predictions using Time Dependent Hartree Fock and Time Dependent Random Phase Approximation approaches, which respectively incorporate one-body energy dissipation and fluctuations. Excellent quantitative agreement has been found between experiment and calculations, indicating that microscopic models incorporating one-body dissipation and fluctuations provide a potential tool for exploring dissipation in low-energy heavy ion collisions.

    ↳ nucl-exnucl-thquant-phPRL(2018)·56 citations
  4. 18

    On the power divergence in quasi gluon distribution function

    Wei Wang🇨🇳 · Shuai Zhao🇨🇳

    Recent perturbative calculation of quasi gluon distribution function at one-loop level shows the existence of extra linear ultraviolet divergences in the cut-off scheme. We employ the auxiliary field approach, and study the renormalization of gluon operators. The non-local gluon operator can mix with new operators under renormalization, and the linear divergences in quasi distribution function can be into the newly introduced operators. After including the mixing, we find the improved quasi gluon distribution functions contain only logarithmic divergences, and thus can be used to extract the gluon distribution in large momentum effective theory.

    ↳ hep-phhep-latnucl-thJHEP(2018)·59 citations
  5. 19

    New Insights on Low Energy Scattering Amplitudes

    Yu-Fei Wang🇨🇳 · De-Liang Yao🇪🇸 · Han-Qing Zheng🇨🇳

    The - and - wave phase shifts of low-energy pion-nucleon scatterings are analysed using Peking University representation, in which they are decomposed into various terms contributing either from poles or branch cuts. We estimate the left-hand cut contributions with the help of tree-level perturbative amplitudes derived in relativistic baryon chiral perturbation theory up to . It is found that in and channels, contributions from known resonances and cuts are far from enough to saturate experimental phase shift data -- strongly indicating contributions from low lying poles undiscovered before, and we fully explore possible physics behind. On the other side, no serious disagreements are observed in the other channels.

    ↳ hep-phnucl-thEPJC(2018)·26 citations
  6. 20

    Effects of composite pions on the chiral condensate within the PNJL model at finite temperature

    D. Blaschke🇵🇱 · A. Dubinin🇵🇱 · D. Ebert🇩🇪 · A. V. Friesen🇷🇺

    We investigate the effect of composite pions on the behaviour of the chiral condensate at finite temperature within the Polyakov-loop improved NJL model. To this end we treat quark-antiquark correlations in the pion channel (bound states and scattering continuum) within a Beth-Uhlenbeck approach that uses medium-dependent phase shifts. A striking medium effect is the Mott transition which occurs when the binding energy vanishes and the discrete pion bound state merges the continuum. This transition is triggered by the lowering of the continuum edge due to the chiral restoration transition. This in turn also entails a modification of the Polyakov-loop so that the SU(3) center symmetry gets broken at finite temperature and dynamical quarks (and gluons) appear in the system, taking over the role of the dominant degrees of freedom from the pions. At low temperatures our model reproduces the chiral perturbation theory result for the chiral condensate while at high temperatures the PNJL model result is recovered. The new aspect of the current work is a consistent treatment of the chiral restoration transition region within the Beth-Uhlenbeck approach on the basis of mesonic phase shifts for the treatment of the correlations.

    ↳ hep-phnucl-thPhys.Part.Nucl.Lett.(2018)·8 citations

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first authorsco-authorsvia INSPIRE