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Nuclear Theory·nucl-th

Friday·January 15, 2021

6 papers—4 primary·2 cross-listed

All6Primary4Cross-lists2
  1. 05

    [Submitted on 13 Jan 2021] (cross-list from hep-ph)

    Magnetars and Axion-like Particles: Probes with the Hard X-ray Spectrum

    Jean-François Fortin🇨🇦 · Huai-Ke Guo🇺🇸 · Steven P. Harris🇺🇸 · Elijah Sheridan🇺🇸 · Kuver Sinha🇺🇸

    Quiescent hard X-ray and soft gamma-ray emission from neutron stars constitute a promising frontier to explore axion-like-particles (ALPs). ALP production in the core peaks at energies of a few keV to a few hundreds of keV; subsequently, the ALPs escape and convert to photons in the magnetosphere. The emissivity goes as while the conversion probability is enhanced for large magnetic fields, making magnetars, with their high core temperatures and strong magnetic fields, ideal targets for probing ALPs. We compute the energy spectrum of photons resulting from conversion of ALPs in the magnetosphere and then compare it against hard X-ray data from NuSTAR, INTEGRAL, and XMM-Newton, for a set of eight magnetars for which such data exists. Upper limits are placed on the product of the ALP-nucleon and ALP-photon couplings. For the production in the core, we perform a calculation of the ALP emissivity in degenerate nuclear matter modeled by a relativistic mean field theory. The reduction of the emissivity due to improvements to the one-pion exchange approximation is incorporated, as is the suppression of the emissivity due to proton superfluidity in the neutron star core. A range of core temperatures is considered, corresponding to different models of the steady heat transfer from the core to the stellar surface. For the subsequent conversion, we solve the coupled differential equations mixing ALPs and photons in the magnetosphere. The conversion occurs due to a competition between the dipolar magnetic field and the photon refractive index induced by the external magnetic field. Semi-analytic expressions are provided alongside the full numerical results. We also present an analysis of the uncertainty on the axion limits we derive due to the uncertainties in the magnetar masses, nuclear matter equation of state, and the proton superfluid critical temperature.

    Comments:
    v1: 44 pages, 15 figures. Comments welcome v2: Updated version with uncertainty bands on ALP couplings coming from different choices of the nuclear equation of state, the mass of the magnetar, and the model of proton singlet superfluidity. Calculation of n+p-->n+p+a clarified. Version matches that published in JCAP
    Subjects:
    High Energy Physics — Phenomenology (hep-ph); High Energy Astrophysical Phenomena (astro-ph.HE); Nuclear Theory (nucl-th)
    arXiv:
    2101.05302 [pdf]
    JCAP(2021)·41 citations
  2. 06

    [Submitted on 11 Jan 2021] (cross-list from physics.data-an)

    Multivariate cumulants in flow analyses: The Next Generation

    Ante Bilandzic🇩🇪 · Marcel Lesch🇩🇪 · Cindy Mordasini🇩🇪 · Seyed Farid Taghavi🇩🇪

    We reconcile for the first time the strict mathematical formalism of multivariate cumulants with the usage of cumulants in anisotropic flow analyses in high-energy nuclear collisions. This reconciliation yields to the next generation of estimators to be used in flow analyses. We review all fundamental properties of multivariate cumulants and use them as a foundation to establish two simple necessary conditions to determine whether some multivariate random variable is a multivariate cumulant in the basis they are expressed in. We argue that properties of cumulants are preserved only for the stochastic variables on which the cumulant expansion has been performed directly, and if there are no underlying symmetries due to which some terms in the cumulant expansion are identically zero. We illustrate one possibility of new multivariate cumulants of azimuthal angles by defining them event-by-event and by keeping all non-isotropic terms in the cumulant expansion. Further, we introduce new cumulants of flow amplitudes named Asymmetric Cumulants, which generalize recently introduced Symmetric Cumulants for the case when flow amplitudes are raised to different powers. Finally, we present the new concept of Cumulants of Symmetry Plane Correlations and provide the first realisation for the lowest orders. The new estimators can be used directly to constrain the multivariate probability density function of flow fluctuations, since its functional form can be reconstructed only from its true moments or cumulants. The new definition for cumulants of azimuthal angles enables separation of nonflow and flow contributions, and offers first insights into how the combinatorial background contributes for small multiplicities to flow measurements with correlation techniques. All the presented results are supported by Monte Carlo studies using state-of-the-art models.

    Comments:
    32 pages, 9 figures. Version accepted for publication in PRC
    Subjects:
    Data Analysis, Statistics and Probability (physics.data-an); High Energy Physics — Experiment (hep-ex); Nuclear Theory (nucl-th); Fluid Dynamics (physics.flu-dyn)
    arXiv:
    2101.05619 [pdf]
    PRC(2022)·20 citations

Affiliations

first authorsco-authorsvia INSPIRE