## 2021 Vol. 45, No. 11

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2021, 45(11): 112001. doi: 10.1088/1674-1137/ac2049
Abstract:
Understanding the thermodynamic phase transition of black holes can provide a deep insight into the fundamental properties of black hole gravity to establish the theory of quantum gravity. We investigate the condition and latent heat of phase transition for non-linear charged AdS black holes using Maxwell's equal-area law. In addition, we analyze the boundary and curve of the two-phase coexistence area in the expanded phase space. We suggest that the phase transition of the non-linear charged AdS black hole with the fixed temperature (\begin{document}$T<T_{\rm c}$\end{document}) is related to the electric potential at the horizon, not only to the location of black hole horizon. Recently, the molecular number density was introduced to study the phase transition and microstructure of black holes. On this basis, we discuss the continuous phase transition of a non-linear charged AdS black hole to reveal the potential microstructure of a black hole by introducing the order parameter and using the scalar curvature.
2021, 45(11): 113101. doi: 10.1088/1674-1137/ac1b9a
Abstract:
The one-loop contributions to the chromomagnetic dipole moment \begin{document}$\hat\mu_t(q^2)$\end{document} and electric dipole moment \begin{document}$\hat d_t(q^2)$\end{document} of the top quark are calculated within the reduced 331 model (RM331) for non-zero \begin{document}$q^2$\end{document}. It is argued that the results are gauge independent and thus represent valid observable quantities. In the RM331, \begin{document}$\hat \mu_t(q^2)$\end{document} receives new contributions from two heavy gauge bosons, namely \begin{document}$Z'$\end{document} and \begin{document}$V^\pm$\end{document}, and one neutral scalar boson \begin{document}$h_2$\end{document}, along with a new contribution from the standard model's Higgs boson via flavor changing neutral currents. The latter, which is also mediated by the \begin{document}$Z'$\end{document} gauge boson and the scalar boson \begin{document}$h_2$\end{document}, can provide a non-vanishing \begin{document}$\hat d_t(q^2)$\end{document} if there is a \begin{document}$CP$\end{document}-violating phase. The analytical results are presented in terms of both Feynman parameter integrals and Passarino-Veltman scalar functions, which are useful to cross-check the numerical results. Both \begin{document}$\hat\mu_t(q^2)$\end{document} and \begin{document}$\hat d_t(q^2)$\end{document} are numerically evaluated for parameter values still allowed by the constraints from experimental data. It is found that the new one-loop contributions of the RM331 to the real (imaginary) part of \begin{document}$\hat \mu_t(q^2)$\end{document} are of the order of \begin{document}$10^{-5}$\end{document} (\begin{document}$10^{-6}$\end{document}), which means at least three orders of magnitude smaller than the standard model prediction but larger than the predictions of other models of new physics. In the RM331, the dominant contribution arises from the \begin{document}$V^\pm$\end{document} gauge boson for \begin{document}$\|q\|$\end{document} in the 30-1000 GeV interval and a mass \begin{document}$m_{V}$\end{document} of the order of a few hundreds of GeV. As for \begin{document}$\hat d_t(q^2)$\end{document}, it receives its largest contribution from \begin{document}$h_2$\end{document} exchange and can reach values of the order of \begin{document}$10^{-19}$\end{document}, i.e., smaller than the contributions predicted by other standard model extensions.
2021, 45(11): 113102. doi: 10.1088/1674-1137/ac1bfd
Abstract:
In this study, we calculate the \begin{document}$t\bar{t}$\end{document} pQCD production cross-section at the NNLO and determine the top-quark pole mass from recent measurements at the LHC at the center-of-mass energy \begin{document}$\sqrt{S}=13$\end{document} TeV to a high precision by applying the principle of maximum conformality (PMC). The PMC provides a systematic method that rigorously eliminates QCD renormalization scale ambiguities by summing the nonconformal \begin{document}$\beta$\end{document} contributions into the QCD coupling constant. The PMC predictions satisfy the requirements of renormalization group invariance, including renormalization scheme independence, and the PMC scales accurately reflect the virtuality of the underlying production subprocesses. By using the PMC, an improved prediction for the \begin{document}$t\bar{t}$\end{document} production cross-section is obtained without scale ambiguities, which in turn provides a precise value for the top-quark pole mass. Moreover, the prediction of PMC calculations that the magnitudes of higher-order PMC predictions are well within the error bars predicted from the known lower-order has been demonstrated for the top-quark pair production. The resulting determination of the top-quark pole mass, \begin{document}$m_t^{\rm{pole}}=172.5\pm1.4$\end{document} GeV, from the LHC measurement at \begin{document}$\sqrt{S}=13$\end{document} TeV agrees with the current world average cited by the Particle Data Group (PDG). The PMC prediction provides an important high-precision test of the consistency of pQCD and the SM at \begin{document}$\sqrt{S}=13$\end{document} TeV with previous LHC measurements at lower CM energies.
2021, 45(11): 113103. doi: 10.1088/1674-1137/ac1c66
Abstract:
Without contamination from the final state interactions, the calculation of the branching ratios of semileptonic decays \begin{document}$\Xi^{(')}_{c}\to\Xi+e^+\nu_e$\end{document} may provide further information about the inner structure of charmed baryons. Moreover, by studying such processes, one can better determine the form factors of \begin{document}$\Xi_c\to\Xi$\end{document} that can be further applied to relevant estimates. In this study, we used the light-front quark model to carry out computations where the three-body vertex functions for \begin{document}$\Xi_c$\end{document} and \begin{document}$\Xi$\end{document} are employed. To fit the new data of the Belle II, we re-adjusted the model parameters to obtain \begin{document}$\beta_{s[sq]} = 1.07$\end{document} GeV, which is 2.9 times larger than \begin{document}$\beta_{s\bar s} = 0.366$\end{document} GeV. This value may imply that the \begin{document}$ss$\end{document} pair in \begin{document}$\Xi$\end{document} constitutes a more compact subsystem. Furthermore, we investigated the non-leptonic decays of \begin{document}$\Xi^{(')}_c\to \Xi$\end{document}, which will be experimentally measured soon. Thus, our model will be tested in terms of consistency with the new data.
2021, 45(11): 113104. doi: 10.1088/1674-1137/ac1e09
Abstract:
In this study, we investigated the cosmological implications of a complex singlet scalar \begin{document}${\cal{S}}$\end{document} with non-trivial \begin{document}$B-L$\end{document} charges in the conformal \begin{document}$U(1)_{B-L}$\end{document} theory. It was found that, in a sizable region of parameter space, \begin{document}${\cal{S}}$\end{document} may disturb the resonant leptogenesis mechanism, which is used to generate baryon asymmetry, and affect the symmetry breaking dynamics in the strong first order phase transition. The stochastic gravitational waves (GWs) produced at the phase transition can be probed in future GW experiments. The GW searches prefer a relatively light \begin{document}${\cal{S}}$\end{document} at the TeV-scale; however, this is difficult to detect directly at future high-energy colliders.
2021, 45(11): 113105. doi: 10.1088/1674-1137/ac1ef9
Abstract:
We apply an equal-velocity quark combination model to study the production of light-flavor hadrons and single-charmed hadrons at midrapidity in the \begin{document}$pp$\end{document} collisions at \begin{document}$\sqrt{s} = 5.02$\end{document} TeV. We find that the experimental data for the \begin{document}$p_{T}$\end{document} spectra of \begin{document}$\Omega$\end{document} and \begin{document}$\phi$\end{document} exhibit the quark number scaling property, which clearly indicates the quark combination mechanism at hadronization. Experimental data for the \begin{document}$p_T$\end{document} spectra of \begin{document}$p$\end{document}, \begin{document}$\Lambda$\end{document}, \begin{document}$\Xi$\end{document}, \begin{document}$\Omega$\end{document}, \begin{document}$\phi$\end{document}, and \begin{document}$K^{*0}$\end{document} are systematically described by the model. The non-monotonic \begin{document}$p_{T}$\end{document} dependence of the \begin{document}$\Omega/\phi$\end{document} ratio is naturally explained, and we find that it is closely related to the shape of the logarithm of the strange quark \begin{document}$p_{T}$\end{document} distribution. Using the \begin{document}$p_{T}$\end{document} spectra of light-flavor quarks obtained from light-flavor hadrons and the \begin{document}$p_T$\end{document} spectrum of charm quarks, which is consistent with perturbative QCD calculations, the experimental data for differential cross-sections of \begin{document}$D^{0,+}$\end{document}, \begin{document}$D_{s}^{+}$\end{document}, and \begin{document}$\Lambda_{c}^{+}$\end{document} as functions of \begin{document}$p_{T}$\end{document} are systematically described. We predict the differential cross-sections of \begin{document}$\Xi_{c}^{0,+}$\end{document} and \begin{document}$\Omega_{c}^{0}$\end{document}. The ratio \begin{document}$\Xi_{c}^{0,+}/D^{0}$\end{document} in our model is approximately 0.16, and \begin{document}$\Omega_{c}^{0}/D^{0}$\end{document} is approximately 0.012, owing to the cascade suppression of strangeness. In addition, the predicted \begin{document}$\Xi_{c}^{0,+}/D^{0}$\end{document} and \begin{document}$\Omega_{c}^{0}/D^{0}$\end{document} ratios exhibit the non-monotonic dependence on \begin{document}$p_{T}$\end{document} in the low \begin{document}$p_{T}$\end{document} range.
2021, 45(11): 113106. doi: 10.1088/1674-1137/ac21b8
Abstract:
We calculate the \begin{document}$D\to P$\end{document} transition form factors within the framework of the light-cone QCD sum rules (LCSR) with the D-meson light-cone distribution amplitudes (LCDAs). The next-to-leading power (NLP) corrections to the vacuum-to-D-meson correlation function are considered, and the NLP corrections from the high-twist D-meson LCDAs and the SU(3) breaking effect from a strange quark mass are investigated. Adopting the exponential model of the D-meson LCDAs, the SU(3) flavor symmetry breaking effects are predicted as \begin{document}$R_{SU(3)}^{+,0}=1.12$\end{document} and \begin{document}$R_{SU(3)}^{T}=1.39$\end{document}, respectively, confirming the results obtained from LCSR with pion LCDA. The numerical predictions of the form factors show that the contribution from two-particle higher-twist contributions is of great importance and the uncertainties are dominated by the inverse moment of \begin{document}$\phi_D^+(\omega, \mu)$\end{document}. With the obtained form factors, the predicted Cabibbo-Kobayashi-Maskawa (CKM) matrix elements are \begin{document}$|V_{cd}|=0.151\,{}^{+0.091}_{-0.043} \big |_{\rm th.}\,{}^{+0.017}_{-0.02} \big |_{\rm exp.}$\end{document} and \begin{document}$|V_{cs}|=0.89\,{}^{+0.467}_{-0.234} \big |_{\rm th.}\,{}^{+0.008}_{-0.008} \big |_{\rm exp.}$\end{document}.
2021, 45(11): 113107. doi: 10.1088/1674-1137/ac224b
Abstract:
The strong coupling constants are basic quantities that carry information on the strong interactions among the baryon and meson multiplets as well as information on the nature and internal structures of the involved hadrons. These parameters are introduced in the transition matrix elements of various decays as main inputs and play key roles in analyses of experimental data including various hadrons. We derive the strong coupling constants among the doubly heavy spin-\begin{document}$3/2$\end{document} baryons, \begin{document}$\Xi^*_{QQ'}$\end{document} and \begin{document}$\Omega^*_{QQ'}$\end{document}, and light pseudoscalar mesons, π, K, and η, using the light-cone QCD. The values obtained for these constants under study may be used to construct the strong potentials among the doubly heavy spin-3/2 baryons and light pseudoscalar mesons.
2021, 45(11): 114101. doi: 10.1088/1674-1137/ac1c67
Abstract:
The matrix elements along the reduction chain Sp(12,R) \begin{document}$\supset$\end{document} SU(1,1) \begin{document}$\otimes$\end{document} SO(6) \begin{document}$\supset$\end{document} U(1) \begin{document}$\otimes$\end{document} SU\begin{document}$_{pn}$\end{document}(3) \begin{document}$\otimes$\end{document} SO(2) \begin{document}$\supset$\end{document} SO(3) of the proton-neutron symplectic model (PNSM) are considered. Closed analytical expressions are obtained for the matrix elements of the basic building blocks of the PNSM and the Sp(12,R) symplectic generators, allowing the computation of matrix elements of other physical operators as well. The computational technique developed in the present study generally provides us with the required algebraic tool for performing realistic symplectic-based shell-model calculations of nuclear collective excitations. Utilizing two simple examples, we illustrate the application of the theory.
2021, 45(11): 114102. doi: 10.1088/1674-1137/ac1d9c
Abstract:
A strong background field drastically changes the vacuum structure and proper basis of a system in both classical and quantum mechanics, e.g., the Landau levels in a background magnetic field. This is true even for a rotating system. In such a system, the usual set of plane-wave states would no longer be suitable as a starting point of perturbation. Alternatively and straightforwardly, in a rapidly and globally rotating system, it is better to reformulate the perturbation computation in principle. In this study, we completed the first step for the spin-1 field, which includes solving the Proca equation in the presence of a background rotation and completing its canonical quantization. We show that because of the symmetry, the eigen states are actually the same as those of Maxwell equations in cylindrical coordinates. The propagator as well as the near-central approximation were obtained by assuming that the vorticity areas are very small in the relativistic QGP.
2021, 45(11): 114103. doi: 10.1088/1674-1137/ac1fe1
Abstract:
The elastic-scattering angular distributions and total reaction cross sections of \begin{document}$^{9,10,11,13,14}{\rm{C}}$\end{document} projectiles were predicted using the obtained \begin{document}$^{12}{\rm{C}}$\end{document} and \begin{document}$^{9}{\rm{Be}}$\end{document} global optical model potentials, respectively. The predictions were analyzed in detail by comparison with the available experimental data. The results indicate that the \begin{document}$^{12}{\rm{C}}$\end{document} and \begin{document}$^{9}{\rm{Be}}$\end{document} global optical model potentials provide a satisfactory description of the elastic scattering data for the reactions induced by the \begin{document}$^{9,10,11,13}{\rm{C}}$\end{document}. For the neutron-rich carbon isotope \begin{document}$^{14}{\rm{C}}$\end{document}, the elastic scattering can be well described by changing the real part radius parameter of the \begin{document}$^{12}{\rm{C}}$\end{document} global optical model potential. Possible physical explanations for the observed differences are further discussed.
2021, 45(11): 114104. doi: 10.1088/1674-1137/ac2298
Abstract:
The scission point model is improved by considering the excitation-dependent liquid drop model to calculate mass distributions for neutron-induced actinide nuclei fission. Excitation energy effects influence the deformations of light and heavy fragments. The improved scission point model shows a significant advance with regard to accuracy for calculating pre-neutron-emission mass distributions of neutron-induced typical actinide fission with incident-neutron-energies up to 99.5 MeV. The theoretical frame assures that the improved scission point model is suitable for evaluating the fission fragment mass distributions, which will provide guidance for studying fission physics and designing nuclear fission engineering and nuclear transmutation systems.
2021, 45(11): 115101. doi: 10.1088/1674-1137/ac1c65
Abstract:
Supernova remnants are supposed to be the most possible sources of cosmic rays. However, alternative sources of cosmic rays, such as an active galactic nucleus, gamma-ray bursts, and pulsars, have not be excluded. In this study, we investigate the possibility of cosmic rays being generated by pulsars. The pulsar is simply described as a rotational magnetic dipole, the so-called Hertzian magnetic dipole, an exact solution of the d'Alembert equations. In the rotational magnetic dipole field, charged particles experience an accelerated electric field with their radiation reaction. The particles, which are initially static out of the light cylinder radius, can be accelerated up to a high energy.
2021, 45(11): 115102. doi: 10.1088/1674-1137/ac1e83
Abstract:
Recently, a de-Sitter epoch has been found in the new model of loop quantum cosmology, which is governed by the scalar constraint with both Euclidean and Lorentz terms. The singularity free bounce in the new LQC model and the emergent cosmology constant strongly suggest that the effective stress-energy tensor induced by quantum corrections must violate the standard energy conditions. In this study, we perform an explicit calculation to analyze the behaviors of specific representative energy conditions, i.e., average null, strong, and dominant energy conditions. We reveal that the average null energy condition is violated at all times, while the dominant energy condition is violated only at a period around the bounce point. The strong energy condition is violated not only at a period around the bounce point but also in the whole period from the bounce point to the classical phase corresponding to the de Sitter period. Our results will shed some light on the construction of a wormhole and time machine, which usually require exotic matter to violate energy conditions.