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  • Effects of electric fields on 7Be half-life
    Published: 2021-05-12, doi: 10.1088/1674-1137/abf6c3
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    First-principle calculations based on the density functional theory (DFT) method are adopted to investigate the influence of a strong electric field on the 7Be half-life. Accordingly, electronic structures of Be and BeO are examined in the presence of a homogeneous electric field. The electron density at the nucleus is estimated upon the geometry optimization. Our computations for the Be metal indicate a 0.02% increase in the decay rate of the 7Be nucleus, corresponding to a 0.02% decrease in the 7Be half-life, both at 5.14 V/Å (0.1 a.u.). Furthermore, it is determined that the decay rate of 7Be is not considerably altered up to 3.6 V/Å in the BeO structure. Our results show that the screening energy of the electron can be dependent on the applied electric field strength. Furthermore, we predict variations in the Coulomb potential at the 7Be nucleus due to electric field application.
  • Thermodynamic instability of 3D Einstein-Born-Infeld AdS black holes
    Published: 2021-05-11, doi: 10.1088/1674-1137/abf1dc
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    Super-entropic black holes possess finite-area but noncompact event horizons and violate the reverse isoperimetric inequality. It has been conjectured that such black holes always have negative specific heat at constant volume $ C_{V} $ or negative specific heat at constant pressure $ C_{P} $ whenever $ C_{V}>0 $, making them unstable in extended thermodynamics. In this paper, we describe a test of this instability conjecture with a family of nonlinear electrodynamic black holes, namely 3D Einstein-Born-Infeld (EBI) AdS black holes. Our results show that when nonlinear electrodynamics effects are weak, the instability conjecture is valid. However, the conjecture can be violated in some parameter region when nonlinear electrodynamics effects are strong enough. This observation thus provides a counter example to the instability conjecture, which suggests that super-entropic black holes may be thermodynamically stable.
  • Hydrodynamic description of D meson production in high-energy heavy-ion collisions
    Published: 2021-05-11, doi: 10.1088/1674-1137/abf645
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    The large values and constituent-quark-number scaling of the elliptic flow of low-$ p_T $ D mesons imply that charm quarks, initially produced through hard processes, might be partially thermalized through strong interactions with quark-gluon plasma (QGP) in high-energy heavy-ion collisions. To quantify the degree of thermalization of low-$ p_T $ charm quarks, we compare the $ D^0 $ meson spectra and elliptic flow from a hydrodynamic model to experimental data as well as transport model simulations. We use an effective charm chemical potential at the freeze-out temperature to account for the initial charm quark production from hard processes and assume that they are thermalized in the local comoving frame of the medium before freeze-out. $ D^0 $ mesons are sampled statistically from the freeze-out hyper-surface of the expanding QGP as described by the event-by-event (3+1)D viscous hydrodynamic model CLVisc. Both the hydrodynamic and transport models can describe the elliptic flow of $ D^0 $ mesons at $ p_T<3 $ GeV/c as measured in Au+Au collisions at $ \sqrt{s_{NN}} = 200 $ GeV. Though the experimental data on $ D^0 $ spectra are consistent with the hydrodynamic result at small $ p_T\sim 1 $ GeV/c, they deviate from the hydrodynamic model at high transverse momentum,$ p_T>2 $ GeV/c. The diffusion and parton energy loss mechanisms in the transport model can describe the measured spectra reasonably well within the theoretical uncertainty. Our comparative study indicates that charm quarks only approach local thermal equilibrium at small $ p_T $, even though they acquire sizable elliptic flow comparable to light-quark hadrons at both small and intermediate $ p_T $.