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Nuclear Theory·nucl-th

Wednesday·August 2, 2017

11 papers—6 primary·5 cross-listed

All11Primary6Cross-lists5
  1. 07

    On the importance of viscous dissipation and heat conduction in binary neutron-star mergers

    Mark G. Alford · Luke Bovard · Matthias Hanauske · Luciano Rezzolla · Kai Schwenzer

    Inferring the properties of dense matter is one of the most exciting prospects from the measurement of gravitational waves from neutron star mergers. However, it will require reliable numerical simulations that incorporate viscous dissipation and energy transport if these can play a significant role within the survival time of the post-merger object. We calculate timescales for typical forms of dissipation and find that thermal transport and shear viscosity will not be important unless neutrino trapping occurs, which requires temperatures above about 10 MeV and gradients over lengthscales of 0.1 km or less. On the other hand, if direct-Urca processes remain suppressed, leaving modified-Urca processes to establish flavor equilibrium, then bulk viscous dissipation could provide significant damping to density oscillations observed right after the merger. When comparing with data from a state-of-the-art merger simulation we find that the bulk viscosity takes values close to its resonant maximum in a typical neutron-star merger, motivating a more careful assessment of the role of bulk viscous dissipation in the gravitational-wave signal from merging neutron stars.

    ↳ gr-qcastro-ph.HEnucl-thPRL(2018)·248 citations
  2. 08

    Study of Minor Actinides Transmutation in PWR MOX fuel

    Shengli Chen · Cenxi Yuan · Jingxia Wu · Yaolei Zou

    The management of long-lived radionuclides in spent fuel is a key issue to achieve the closed nuclear fuel cycle and the sustainable development of nuclear energy. Partitioning-Transmutation is supposed to be an efficient method to treat the long-lived radionuclides in spent fuel. Some Minor Actinides (MAs) have very long half-lives among the radionuclides in the spent fuel. Accordingly, the study of MAs transmutation is a significant work for the post-processing of spent fuel. In the present work, the transmutations in Pressurized Water Reactor (PWR) mixed oxide (MOX) fuel are investigated through the Monte Carlo based code RMC. Two kinds of MAs, Np and five MAs (Np, Am, Am, Cm and Cm) are incorporated homogeneously into the MOX fuel assembly. The transmutation of MAs is simulated with different initial MOX concentrations. The results indicate an overall nice efficiency of transmutation in both initial MOX concentrations, especially for the two kinds of MAs primarily generated in the UOX fuel, Np and Am. In addition, the inclusion of Np in MOX has no large influence for other MAs, while the transmutation efficiency of Np is excellent. The transmutation of MAs in MOX fuel depletion is expected to be a new, efficient nuclear spent fuel management method for the future nuclear power generation.

    ↳ physics.app-phnucl-thICONE25-66250, 2017 (Proceedings of the 2…·0 citations
  3. 09

    Squeezing the Efimov effect

    J. H. Sandoval · F. F. Bellotti · M. T. Yamashita · T. Frederico · D. V. Fedorov · A. S. Jensen · N. T. Zinner

    The quantum mechanical three-body problem is a source of continuing interest due to its complexity and not least due to the presence of fascinating solvable cases. The prime example is the Efimov effect where infinitely many bound states of identical bosons can arise at the threshold where the two-body problem has zero binding energy. An important aspect of the Efimov effect is the effect of spatial dimensionality; it has been observed in three dimensional systems, yet it is believed to be impossible in two dimensions. Using modern experimental techniques, it is possible to engineer trap geometry and thus address the intricate nature of quantum few-body physics as function of dimensionality. Here we present a framework for studying the three-body problem as one (continuously) changes the dimensionality of the system all the way from three, through two, and down to a single dimension. This is done by considering the Efimov favorable case of a mass-imbalanced system and with an external confinement provided by a typical experimental case with a (deformed) harmonic trap.

    ↳ cond-mat.quant-gasnucl-thquant-phJ.Phys.B(2018)·18 citations
  4. 10

    Probing the Efimov discrete scaling in atom-molecule collision

    M. A. Shalchi · M. T. Yamashita · M. R. Hadizadeh · E. Garrido · Lauro Tomio · T. Frederico

    The discrete Efimov scaling behavior, well-known in the low-energy spectrum of three-body bound systems for large scattering lengths (unitary limit), is identified in the energy dependence of atom-molecule elastic cross-section in mass imbalanced systems. That happens in the collision of a heavy atom with mass with a weakly-bound dimer formed by the heavy atom and a lighter one with mass . Approaching the heavy-light unitary limit the wave elastic cross-section will present a sequence of zeros/minima at collision energies following closely the Efimov geometrical law. Our results open a new perspective to detect the discrete scaling behavior from low-energy scattering data, which is timely in view of the ongoing experiments with ultra-cold binary mixtures having strong mass asymmetries, such as Lithium and Caesium or Lithium and Ytterbium.

    ↳ physics.atom-phcond-mat.quant-gasnucl-thquant-phPRA(2018)·8 citations
  5. 11

    Kosterlitz-Thouless transition and vortex-antivortex lattice melting in two-dimensional Fermi gases with - or -wave pairing

    Gaoqing Cao · Lianyi He · Xu-Guang Huang

    We present a theoretical study of the finite-temperature Kosterlitz-Thouless (KT) and vortex-antivortex lattice (VAL) melting transitions in two-dimensional Fermi gases with - or -wave pairing. For both pairings, when the interaction is tuned from weak to strong attractions, we observe a quantum phase transition from the Bardeen-Cooper-Schrieffer (BCS) superfluidity to the Bose-Einstein condensation (BEC) of difermions. The KT and VAL transition temperatures increase during this BCS-BEC transition and approach constant values in the deep BEC region. The BCS-BEC transition is characterized by the non-analyticities of the chemical potential, the superfluid order parameter, and the sound velocities as functions of the interaction strength at both zero and finite temperatures; however, the temperature effect tends to weaken the non-analyticities comparing to the zero temperature case. The effect of mismatched Fermi surfaces on the -wave pairing is also studied.

    ↳ cond-mat.quant-gasnucl-thquant-phPRA(2017)·1 citation

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first authorsco-authorsvia INSPIRE