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Nuclear Theory·nucl-th

Wednesday·April 25, 2018

9 papers—6 primary·3 cross-listed

All9Primary6Cross-lists3
  1. 07

    [Submitted on 24 Apr 2018] (cross-list from physics.atom-ph)

    Shielding of an external oscillating electric field inside atoms

    V.V. Flambaum🇦🇺

    According to the Schiff theorem an external electric field vanishes at atomic nucleus in a neutral atom, i.e. it is completely shielded by electrons. This makes a nuclear electric dipole moment (EDM) unobservable. In this paper an extension of the Schiff theorem to an oscillating electric field is considered. Such field can reach the nucleus and interact with the nuclear EDM. The enhancement effect appears if the field is in resonance with atomic or molecular transition. The shielding by electrons strongly affects low-energy nuclear electric dipole transition amplitudes in different nuclear reactions including radiative transitions, radiative nucleon capture, photo or electro-excitation of nuclei and laser-induced or laser-enhanced nuclear reactions.

    Subjects:
    Atomic Physics (physics.atom-ph); High Energy Physics — Phenomenology (hep-ph); Nuclear Theory (nucl-th)
    arXiv:
    1804.08898 [pdf]
    PRA(2018)·9 citations
  2. 08

    [Submitted on 24 Apr 2018] (cross-list from astro-ph.HE)

    On parametrised cold dense matter equation of state inference

    Thomas E. Riley · Geert Raaijmakers · Anna L. Watts

    Constraining the equation of state of cold dense matter in compact stars is a major science goal for observing programmes being conducted using X-ray, radio, and gravitational wave telescopes. We discuss Bayesian hierarchical inference of parametrised dense matter equations of state. In particular we generalise and examine two inference paradigms from the literature: (i) direct posterior equation of state parameter estimation, conditioned on observations of a set of rotating compact stars; and (ii) indirect parameter estimation, via transformation of an intermediary joint posterior distribution of exterior spacetime parameters (such as gravitational masses and coordinate equatorial radii). We conclude that the former paradigm is not only tractable for large-scale analyses, but is principled and flexible from a Bayesian perspective whilst the latter paradigm is not. The thematic problem of Bayesian prior definition emerges as the crux of the difference between these paradigms. The second paradigm should in general only be considered as an ill-defined approach to the problem of utilising archival posterior constraints on exterior spacetime parameters; we advocate for an alternative approach whereby such information is repurposed as an approximative likelihood function. We also discuss why conditioning on a piecewise-polytropic equation of state model - currently standard in the field of dense matter study - can easily violate conditions required for transformation of a probability density distribution between spaces of exterior (spacetime) and interior (source matter) parameters.

    Comments:
    Accepted for publication in MNRAS, 43 pages, 7 figures
    Subjects:
    High Energy Astrophysical Phenomena (astro-ph.HE); General Relativity and Quantum Cosmology (gr-qc); Nuclear Theory (nucl-th)
    arXiv:
    1804.09085 [pdf]
    MNRAS(2018)·48 citations
  3. 09

    [Submitted on 24 Apr 2018] (cross-list from astro-ph.HE)

    A pitfall of piecewise-polytropic equation of state inference

    G. Raaijmakers · T. E. Riley · A. L. Watts

    The only messenger radiation in the Universe which one can use to statistically probe the Equation of State (EOS) of cold dense matter is that originating from the near-field vicinities of compact stars. Constraining gravitational masses and equatorial radii of rotating compact stars is a major goal for current and future telescope missions, with a primary purpose of constraining the EOS. From a Bayesian perspective it is necessary to carefully discuss prior definition; in this context a complicating issue is that in practice there exist pathologies in the general relativistic mapping between spaces of local (interior source matter) and global (exterior spacetime) parameters. In a companion paper, these issues were raised on a theoretical basis. In this study we reproduce a probability transformation procedure from the literature in order to map a joint posterior distribution of Schwarzschild gravitational masses and radii into a joint posterior distribution of EOS parameters. We demonstrate computationally that EOS parameter inferences are sensitive to the choice to define a prior on a joint space of these masses and radii, instead of on a joint space interior source matter parameters. We focus on the piecewise-polytropic EOS model, which is currently standard in the field of astrophysical dense matter study. We discuss the implications of this issue for the field.

    Comments:
    16 pages, 9 figures. Accepted for publication in MNRAS
    Subjects:
    High Energy Astrophysical Phenomena (astro-ph.HE); General Relativity and Quantum Cosmology (gr-qc); Nuclear Theory (nucl-th)
    arXiv:
    1804.09087 [pdf]
    MNRAS(2018)·37 citations

Affiliations

first authorsco-authorsvia INSPIRE