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Nuclear Theory·nucl-th

Thursday·March 21, 2019

8 papers—3 primary·5 cross-listed

All8Primary3Cross-lists5
  1. 01

    [Submitted on 19 Mar 2019]

    Thermodynamics of Neutrons in a Magnetic Field and its Implications for Neutron Stars

    E. J. Ferrer🇺🇸 · A. Hackebill🇺🇸

    We investigate the effects of a magnetic field on the thermodynamics of a neutron system at finite density and temperature. Our main motivation is to deepen the understanding of the physics of a class of neutron stars known as magnetars, which exhibit extremely strong magnetic fields. Taking into account two facts, (i) the existence of a pressure anisotropy in the presence of a magnetic field and (ii) that the quantum field theory contribution to the pressure is non-negligible, we show that the maximum value that the inner magnetic field of a star can reach while being in agreement with the magnetohydrostatic equilibrium between the gravitational and matter pressures becomes G, an order of magnitude smaller than the previous value obtained through the scalar virial theorem; that the magnetic field has a negligible effect on the neutron system's equation of state; that the system's magnetic susceptibility increases with the temperature; and that the specific heat does not significantly change with the magnetic field in the range of temperatures characteristic of protoneutron stars.

    Subjects:
    Nuclear Theory (nucl-th); High Energy Astrophysical Phenomena (astro-ph.HE); High Energy Physics — Phenomenology (hep-ph)
    arXiv:
    1903.08224 [pdf]
    PRC(2019)·45 citations
  2. 02

    [Submitted on 20 Mar 2019]

    Thermal quasiparticle random-phase approximation calculations of stellar electron capture rates with the Skyrme effective interaction

    Alan A. Dzhioev · A. I. Vdovin · Ch. Stoyanov

    A microscopic thermodynamically consistent approach is applied to compute electron capture (EC) rates and cross sections on nuclei in hot stellar environments. The cross section calculations are based on the Donnelly-Walecka multipole expansion method for treatment of semi-leptonic processes in nuclei. To take into account thermal effects, we express the electron capture cross section in terms of temperature- and momentum-dependent spectral functions for respective multipole charge-changing operators. The spectral functions are computed by employing the self-consistent thermal quasiparticle RPA (TQRPA) with the Skyrme effective interaction. Three different Skyrme parametrizations (SkM, SGII and SLy4) are used to investigate thermal effects on EC for Fe and Ni. For Fe, the impact of thermally unblocked GT transitions on EC is discussed and the results are compared with those from shell-model calculations. In particular, it is shown that for some temperature and density regimes the TQRPA rates exceed the shell-model rates due to violation of the Brink-Axel hypothesis within the TQRPA. For neutron-rich Ni the full momentum-dependence of multipole transition operators is considered and it is found that not only thermally unblocked allowed transitions but also thermally unblocked first-forbidden and transitions favour EC.

    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    1903.08418 [pdf]
    PRC(2019)·16 citations
  3. 03

    [Submitted on 20 Mar 2019]

    Microscopically based energy density functionals for nuclei using the density matrix expansion

    R. Navarro Pérez · N. Schunck

    While ab initio many-body techniques have been able to successfully describe the properties of light and intermediate mass nuclei based on chiral effective field theory interactions, neutron-rich nuclei still remain out of reach for these methods. Conversely, energy density functional approaches can be used to calculate properties of heavy nuclei but rely mostly on phenomenological interactions. A usable form of the nuclear energy density functional that is rooted in the modern theory of nuclear forces was presented recently. The first component of this new set of functionals corresponds to the direct part (Hartree term) of the expectation value of local chiral potentials on a Slater determinant. The exchange term, which is a functional of the non-local density, is transformed into a local functional by applying the density matrix expansion. In order to reduce the computational cost due to the direct implementation of non-separable, local interactions in the Hartree term, we use an approximation to represent the regularized Yukawa functions in terms of a sum of (separable) Gaussian functions. These proceedings analyze the accuracy of such an approximation in terms of the number of Gaussian functions and look for an optimal value that gives an acceptable level of accuracy while maintaining the computational memory requirements in a many-body calculation as low as possible.

    Comments:
    7 pages, 2 figures, conference proceedings of the 42nd Symposium on Nuclear Physics held in Cocoyoc, Morelos, Mexico. January 2019
    Subjects:
    Nuclear Theory (nucl-th)
    arXiv:
    1903.08537 [pdf]
    J.Phys.Conf.Ser.(2019)·4 citations

Affiliations

first authorsco-authorsvia INSPIRE