## 2019 Vol. 43, No. 3

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2019, 43(3): 031001. doi: 10.1088/1674-1137/43/3/031001
Abstract:
Studies of \begin{document}$e^+e^- \to D^+_s \overline{D}{}^{(*)0}K^-$\end{document} and the \begin{document}$P$\end{document} -wave charmed-strange mesons are performed based on an \begin{document}$e^+e^-$\end{document} collision data sample corresponding to an integrated luminosity of 567 pb−1 collected with the BESIII detector at \begin{document}$\sqrt{s}= 4.600$\end{document} GeV. The processes of \begin{document}$e^+e^-\to D^+_s \overline{D}{}^{*0} K^-$\end{document} and \begin{document}$D^+_s \overline{D}{}^{0} K^-$\end{document} are observed for the first time and are found to be dominated by the modes \begin{document}$D_s^+ D_{s1}(2536)^-$\end{document} and \begin{document}$D_s^+ D^*_{s2}(2573)^-$\end{document} , respectively. The Born cross sections are measured to be \begin{document}$\sigma^{B}(e^+e^-\to D^+_s \overline{D}{}^{*0} K^-) = (10.1\pm2.3\pm0.8)$\end{document} pb and \begin{document}$\sigma^{B}(e^+e^-\to D^+_s \overline{D}{}^{0} K^-) = (19.4\pm2.3\pm1.6)$\end{document} pb, and the products of Born cross section and the decay branching fraction are measured to be \begin{document}$\sigma^{B}(e^+e^-\to D^+_s D_{s1}(2536)^- + c.c.)\cdot$\end{document} \begin{document}${\cal{B}}( D_{s1}(2536)^- \to \overline{D}{}^{*0} K^-) = (7.5 \pm 1.8 \pm 0.7)$\end{document} pb and \begin{document}$\sigma^{B}(e^+e^-\to D^+_s D^*_{s2}(2573)^- + c.c.)\cdot {\cal{B}}( D^*_{s2}(2573)^- \to \overline{D}{}^{0} K^-) =$\end{document} \begin{document}$(19.7 \pm 2.9 \pm 2.0)$\end{document} pb. For the \begin{document}$D_{s1}(2536)^-$\end{document} and \begin{document}$D^*_{s2}(2573)^-$\end{document} mesons, the masses and widths are measured to be \begin{document}$M( D_{s1}(2536)^- ) = (2537.7 \pm 0.5 \pm 3.1)\; {\rm{MeV}}/c^2$\end{document} , \begin{document}$\Gamma( D_{s1}(2536)^- ) = (1.7\pm 1.2 \pm 0.6)$\end{document} MeV, and \begin{document}$M( D^*_{s2}(2573)^- ) =$\end{document} \begin{document}$(2570.7\pm 2.0 \pm 1.7)\; {\rm{MeV}}/c^2,$\end{document} \begin{document}$\Gamma( D^*_{s2}(2573)^- ) = (17.2 \pm 3.6 \pm 1.1)$\end{document} MeV. The spin-parity of the \begin{document}$D^*_{s2}(2573)^-$\end{document} meson is determined to be \begin{document}$J^P=2^{+}$\end{document} . In addition, the processes \begin{document}$e^+e^-\to D^+_s \overline{D}{}^{(*)0} K^-$\end{document} are searched for using the data samples taken at four (two) center-of-mass energies between 4.416 (4.527) and 4.575 GeV, and upper limits at the 90% confidence level on the cross sections are determined.
2019, 43(3): 033001. doi: 10.1088/1674-1137/43/3/033001
Abstract:
This work extends the idea of using a cyclotron-based antineutrino source for purposes of neutrino physics. Long baseline experiments suffer from degeneracies and correlations between \begin{document}$\Theta_{23}$\end{document} , \begin{document}$\delta_{\rm CP}$\end{document} and the mass hierarchy. However, the combination of a superconducting cyclotron and a big liquid scintillator detector like JUNO in a medium baseline experiment, which does not depend on the mass hierarchy, may allow to determine whether the position of the mixing angle \begin{document}$\Theta_{23}$\end{document} is in the lower octant or the upper octant. Such an experiment would improve the precision of the \begin{document}$\Theta_{23}$\end{document} measurement to a degree which depends on the CP-phase.
2019, 43(3): 033101. doi: 10.1088/1674-1137/43/3/033101
Abstract:
In this paper, we introduce leptogenesis via a varying Weinberg operator from a semi-classical perspective. This mechanism is motivated by the breaking of an underlying symmetry which triggers a phase transition that causes the coupling of the Weinberg operator to become dynamical. Consequently, a lepton anti-lepton asymmetry arises from the interference of the Weinberg operator at two different spacetime points. Using the semi-classical approach, we treat the Higgs as a background field and show that a reflection asymmetry between leptons and anti-leptons is generated in the vicinity of the bubble wall. We solve the equations of motion of the lepton and anti-lepton quasiparticles to obtain the final lepton asymmetry.
2019, 43(3): 033102. doi: 10.1088/1674-1137/43/3/033102
Abstract:
We evaluate the topological charge density of SU(3) gauge fields on a lattice by calculating the trace of the overlap Dirac matrix employing the symmetric multi-probing (SMP) method in 3 modes. Since the topological charge Q for a given lattice configuration must be an integer number, it is easy to estimate the systematic error (the deviation of Q to the nearest integer). The results demonstrate a high efficiency and accuracy in calculating the trace of the inverse of a large sparse matrix with locality by using the SMP sources when compared to using point sources. We also show the correlation between the errors and probing scheme parameter \begin{document}$r_{\min}$\end{document} , as well as lattice volume \begin{document}$N_{L}$\end{document} and lattice spacing a. It is found that the computational time for calculating the trace by employing the SMP sources is less dependent on \begin{document}$N_{L}$\end{document} than by using point sources. Therefore, the SMP method is very suitable for calculations on large lattices.
2019, 43(3): 033103. doi: 10.1088/1674-1137/43/3/033103
Abstract:
Conserved charge fluctuations can be used to probe the phase structure of strongly interacting nuclear matter in relativistic heavy-ion collisions. To obtain the characteristic signatures of the conserved charge fluctuations for the quantum chromodynamics (QCD) phase transition, we study the susceptibilities of dense quark matter up to eighth order in detail, using an effective QCD-based model. We studied two cases, one with the QCD critical end point (CEP) and one without owing to an additional vector interaction term. The higher order susceptibilities display rich structures near the CEP and show sign changes as well as large fluctuations. These can provide us information about the presence and location of the CEP. Furthermore, we find that the case without the CEP also shows a similar sign change pattern, but with a relatively smaller magnitude compared with the case with the CEP. Finally, we conclude that higher order susceptibilities of conserved charge can be used to probe the QCD phase structures in heavy-ion collisions.
2019, 43(3): 034101. doi: 10.1088/1674-1137/43/3/034101
Abstract:
The effective Lagrangian of a finite volume system should, in principle, depend on the system size. In the framework of the Nambu-Jona-Lasinio (NJL) model, by considering the influence of quark feedback on the effective coupling, we obtain a modified NJL model so that its Lagrangian depends on the volume. Based on the modified NJL model, we study the influence of finite volume on the chiral phase transition at finite temperature, and find that the pseudo-critical temperature of crossover is much lower than that obtained in the normal NJL model. This clearly shows that the volume dependent effective Lagrangian plays an important role in the chiral phase transitions at finite temperature.
2019, 43(3): 034102. doi: 10.1088/1674-1137/43/3/034102
Abstract:
We present the masses of N baryons up to 3300 MeV. The radial and orbital excited states are determined using hypercentral constituent quark model with the first-order correction. The obtained masses are compared with the experimental results and other theoretical predictions. The Regge trajectories are also determined in (n, \begin{document}$M^2$\end{document} ) and (J, \begin{document}$M^2$\end{document} ) planes. Moreover, the magnetic moments with \begin{document}$J^{P}= \displaystyle\frac{1}{2}^{+}, \displaystyle\frac{1}{2}^{-}$\end{document} are calculated. We also calculates the \begin{document}$N\pi$\end{document} decay width of excited nucleons.
2019, 43(3): 034103. doi: 10.1088/1674-1137/43/3/034103
Abstract:
In characterizing the chiral phase-structure of pseudoscalar ( \begin{document}$J^{pc}=0^{-+}$\end{document} ), scalar ( \begin{document}$J^{pc}=0^{++}$\end{document} ), vector ( \begin{document}$J^{pc}=1^{--}$\end{document} ) and axial-vector ( \begin{document}$J^{pc}=1^{++}$\end{document} t) meson states and their dependence on temperature, chemical potential, and magnetic field, we utilize the SU(3) Polyakov linear-sigma model (PLSM) in the mean-field approximation. We first determine the chiral (non)strange quark condensates, \begin{document}$\sigma_l$\end{document} and \begin{document}$\sigma_s$\end{document} , and the corresponding deconfinement order parameters, \begin{document}$\phi$\end{document} and \begin{document}$\phi^*$\end{document} , in thermal and dense (finite chemical potential) medium and finite magnetic field. The temperature and the chemical potential characteristics of nonet meson states normalized to the lowest bosonic Matsubara frequency are analyzed. We note that all normalized meson masses become temperature independent at different critical temperatures. We observe that the chiral and deconfinement phase transitions are shifted to lower quasicritical temperatures with increasing chemical potential and magnetic field. Thus, we conclude that the magnetic field seems to have almost the same effect as the chemical potential, especially on accelerating the phase transition, i.e. inverse magnetic catalysis. We also find that increasing the chemical potential enhances the mass degeneracy of the various meson masses, while increasing the magnetic field seems to reduce the critical chemical potential, at which the chiral phase transition takes place. Our mass spectrum calculations agree well with the recent PDG compilations and PNJL, lattice QCD calculations, and QMD/UrQMD simulations.
2019, 43(3): 034104. doi: 10.1088/1674-1137/43/3/034104
Abstract:
We revisit hidden-charm pentaquark states \begin{document}$P_c(4380)$\end{document} and \begin{document}$P_c(4450)$\end{document} using the method of QCD sum rules by requiring the pole contribution to be greater than or equal to 30% in order to better that the one-pole parametrization is valid. We find two mixing currents, and our results suggest that \begin{document}$P_c(4380)$\end{document} and \begin{document}$P_c(4450)$\end{document} can be identified as hidden-charm pentaquark states having \begin{document}$J^P=3/2^-$\end{document} and \begin{document}$5/2^+$\end{document} , respectively. However, there still exist other possible spin-parity assignments, such as \begin{document}$J^P=3/2^+$\end{document} and \begin{document}$J^P=5/2^-$\end{document} , which must be clarified in further theoretical and experimental studies.
2019, 43(3): 035101. doi: 10.1088/1674-1137/43/3/035101
Abstract:
An extended Nambu-Jona-Lasinio (eNJL) model with nucleons as the degrees of freedom is used to investigate properties of nuclear matter and neutron stars (NSs), including the binding energy and symmetry energy of the nuclear matter, the core-crust transition density, and mass-radius relation of NSs. The fourth-order symmetry energy at saturation density is also investigated. When the bulk properties of nuclear matter at saturation density are used to determine the model parameters, the double solutions of parameters are obtained for a given nuclear incompressibility. It is shown that the isovector-vector interaction has a significant influence on the nuclear matter and NS properties, and the sign of isovector-vector coupling constant is critical in the determination of the trend of the symmetry energy and equation of state. The effects of the other model parameters and symmetry energy slope at saturation density are discussed.
2019, 43(3): 035102. doi: 10.1088/1674-1137/43/3/035102
Abstract:
In this study, we consider charged massive scalar fields around a Kerr–Sen spacetime. The radial and angular parts of the covariant Klein–Gordon equation are solved in terms of the confluent Heun function. From the exact radial solution, we obtain the Hawking radiation spectrum and discuss its resonant frequencies. The massless case of the resonant frequencies is also examined.
2019, 43(3): 035103. doi: 10.1088/1674-1137/43/3/035103
Abstract:
The dependence of implications from observations on cosmological models is an intractable problem not only in cosmology, but also in astrophysics. Gaussian processes (GPs), a powerful nonlinear interpolating tool without assuming a model or parametrization, have been widely used to directly reconstruct functions from observational data (e.g., expansion rate and distance measurements) for cosmography. However, the fidelity of this reconstructing method has never been checked. In this study, we test the fidelity of GPs for cosmography by mocking observational data sets comprising different number of events with various uncertainty levels. These factors are of great importance for the fidelity of reconstruction. That is, for the expansion rate measurements, GPs are valid for reconstructing the functions of the Hubble parameter versus redshift when the number of observed events is as many as 256 and the uncertainty of the data is ~ 3%. Moreover, the distance-redshift relation reconstructed from the observations of the upcoming Dark Energy Survey type Ia supernovae is credible.
2019, 43(3): 035104. doi: 10.1088/1674-1137/43/3/035104
Abstract:
In this study, the scattering of fermions by a class of Bardeen black holes is investigated. After obtaining the scattering modes by solving the Dirac equation in this geometry, we use the partial wave method to derive an analytical expression for the phase shifts that enter into the definitions of partial amplitudes that define the scattering cross sections and induced polarization. It is shown that, similar to Schwarzschild and Reissner-Nordström black holes, the phenomena of glory and spiral scattering are present.
2019, 43(3): 035105. doi: 10.1088/1674-1137/43/3/035105
Abstract:
We provide a comprehensive survey of possible applications of the matrix method for black hole quasinormal modes. The proposed algorithm can generally be applied to various background metrics, and in particular, it accommodates both analytic and numerical forms of the tortoise coordinates, as well as black hole spacetimes. We give a detailed account of different types of black hole metrics, master equations, and the corresponding boundary conditions. Besides, we argue that the method can readily be applied to cases where the master equation is a system of coupled equations. By adjusting the number of interpolation points, the present method provides a desirable degree of precision, in reasonable balance with its efficiency. The method is flexible and can easily be adopted to various distinct physical scenarios.