## 2022 Vol. 46, No. 4

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2022, 46(4): 043101. doi: 10.1088/1674-1137/ac3d28
Abstract:
Using the two-fluid Tolman-Oppenheimer-Volkoff equation, the properties of dark matter (DM) admixed neutron stars (DANSs) have been investigated. In contrast to previous studies, we find that an increase in the maximum mass and a decrease in the radius of 1.4 \begin{document}$M_\odot$\end{document} NSs can occur simultaneously in DANSs. This stems from the ability of the equation of state (EOS) for DM to be very soft at low density but very stiff at high density. It is well known that the IU-FSU and XS models are unable to produce a neutron star (NS) with a maximum mass greater than 2.0 \begin{document}$M_\odot$\end{document}. However, by considering the IU-FSU and XS models for DANSs, there are interactions with DM that can produce a maximum mass greater than 2.0 \begin{document}$M_\odot$\end{document} and a radius of 1.4 \begin{document}$M_\odot$\end{document} NSs below 13.7 km. When considering a DANS, the difference between DM with chiral symmetry (DMC) and DM with meson exchange (DMM) becomes obvious when the central energy density of DM is greater than that of nuclear matter (NM). In this case, the DMC model with a DM mass of 1000 MeV can still produce a maximum mass greater than 2.0 \begin{document}$M_\odot$\end{document} and a radius of a 1.4 \begin{document}$M_\odot$\end{document} NS below 13.7 km. Additionally, although the maximum mass of the DANS using the DMM model is greater than 2.0 \begin{document}$M_\odot$\end{document}, the radius of a 1.4 \begin{document}$M_\odot$\end{document} NS can surpass 13.7 km. In the two-fluid system, the maximum mass of a DANS can be larger than 3.0 \begin{document}$M_\odot$\end{document}. Consequently, the dimensionless tidal deformability \begin{document}$\Lambda_{CP}$\end{document} of a DANS with 1.4 \begin{document}$M_\odot$\end{document}, which increases with increasing maximum mass, may be larger than 800 when the radius of the 1.4 \begin{document}$M_\odot$\end{document} DANS is approximately 13.0 km.
2022, 46(4): 043102. doi: 10.1088/1674-1137/ac3d8c
Abstract:
In this work, we generate gauge configurations with \begin{document}$N_f = 2$\end{document} dynamical charm quarks on anisotropic lattices. The mass shift of \begin{document}$1S$\end{document} and \begin{document}$1P$\end{document} charmonia due to the charm quark annihilation effect can be investigated directly in a manner of unitary theory. The distillation method is adopted to treat the charm quark annihilation diagrams at a very precise level. For \begin{document}$1S$\end{document} charmonia, the charm quark annihilation effect barely changes the \begin{document}$J/\psi$\end{document} mass, but lifts the \begin{document}$\eta_c$\end{document} mass by approximately 3–4 MeV. For \begin{document}$1P$\end{document} charmonia, this effect results in positive mass shifts of approximately 1 MeV for \begin{document}$\chi_{c1}$\end{document} and \begin{document}$h_c$\end{document}, but decreases the \begin{document}$\chi_{c2}$\end{document} mass by approximately 3 MeV. We did not obtain a reliable result for the mass shift of \begin{document}$\chi_{c0}$\end{document}. In addition, we observed that the spin averaged mass of the spin-triplet \begin{document}$1P$\end{document} charmonia is in good agreement with \begin{document}$h_c$\end{document}, as expected by the non-relativistic quark model and measured by experiments.
2022, 46(4): 043103. doi: 10.1088/1674-1137/ac3df2
Abstract:
In this study, we consider all P-wave \begin{document}$\Omega_{b}$\end{document} states represented by interpolating currents with a derivative and calculate the corresponding masses and pole residues using the QCD sum rule method. Because of the large uncertainties in our calculation compared with the small difference in the masses of the excited \begin{document}$\Omega_{b}$\end{document} states observed by the LHCb collaboration, it is necessary to study other properties of the P-wave \begin{document}$\Omega_{b}$\end{document} states represented by the interpolating currents investigated in the present work to gain a better understanding of the four excited \begin{document}$\Omega_{b}$\end{document} states observed by the LHCb collaboration.
2022, 46(4): 043104. doi: 10.1088/1674-1137/ac424c
Abstract:
We study the possibility of probing high scale phase transitions that are inaccessible by LIGO. Our study shows that the stochastic gravitational-wave radiation from cosmic strings that are formed after the first-order phase transition can be detected by space-based interferometers when the phase transition temperature is \begin{document}$T_n\sim {\cal{O}}(10^{8-11})$\end{document} GeV.
2022, 46(4): 043105. doi: 10.1088/1674-1137/ac424f
Abstract:
We present the NLO electroweak radiative corrections to the \begin{document}$e^+e^-\gamma$\end{document} production in γγ collision, which is an ideal channel for calibrating the beam luminosity of a Photon Linear Collider. We analyze the dependence of the total cross section on the beam colliding energy, and then investigate the kinematic distributions of final particles at various initial photon beam polarizations at EW NLO accuracy. The numerical results indicate that the EW relative corrections to the total cross section are non-negligible and become increasingly significant as the increase of the beam colliding energy, even can exceed –10% in the \begin{document}${{J}} = 2$\end{document} γγ collision at \begin{document}$\sqrt{\hat{s}} = 1\; {\rm{TeV}}$\end{document}. Such EW corrections are very important and should be taken into consideration in precision theoretical and experimental studies at high-energy γγ colliders.
2022, 46(4): 043106. doi: 10.1088/1674-1137/ac425a
Abstract:
We consider a model with multi-charged particles, including vector-like fermions, and a charged scalar under a local \begin{document}$U(1)_{\mu - \tau}$\end{document} symmetry. We search for an allowed parameter region explaining muon anomalous magnetic moment (muon \begin{document}$g-2$\end{document}) and \begin{document}$b \to s \ell^+ \ell^-$\end{document} anomalies, satisfying constraints from the lepton flavor violations, Z boson decays, meson anti-meson mixing, and collider experiments. Via numerical analysis, we explore the typical size of the muon \begin{document}$g-2$\end{document} and Wilson coefficients to explain the \begin{document}$b \to s \ell^+ \ell^-$\end{document} anomalies in our model when all other experimental constraints are satisfied. Subsequently, we discuss the collider physics of the multicharged vectorlike fermions, considering a number of benchmark points in the allowed parameter space.
2022, 46(4): 043107. doi: 10.1088/1674-1137/ac4694
Abstract:
We study the mass spectra and decay process of σ and \begin{document}$\pi_0$\end{document} mesons under a strong external magnetic field. To achieve this goal, we deduce the thermodynamic potential in a two-flavor, hot and magnetized Nambu–Jona-Lasinio model. We calculate the energy gap equation through the random phase approximation (RPA). Then we use the Ritus method to calculate the decay triangle diagram and self-energy in the presence of a constant magnetic field B. Our results indicate that the magnetic field has little influence on the mass of \begin{document}$\pi_0$\end{document} at low temperatures. However, for quarks and σ mesons, their mass clearly changes, which reflects the influence of magnetic catalysis (MC). The presence of a magnetic field accelerates the decay of the meson while the presence of a chemical potential will decrease the decay process.
2022, 46(4): 044001. doi: 10.1088/1674-1137/ac3fa4
Abstract:
The reaction cross-sections of 124Xe(n, 2n)123Xe, 126Xe(n, 2n)125Xe, 128Xe(n, 2n)127Xe, 130Xe(n, 2n)129mXe, 132Xe(n, 2n)131mXe, 130Xe(n, p)130I, 131Xe(n, p)131I, and 132Xe(n, p)132I were measured at the 13.5, 13.8, 14.1, 14.4, and 14.8 MeV neutron energies. The monoenergetic neutrons were generated via the 3H(d,n)4He reaction at the China Academy of Engineering Physics using the K-400 Neutron Generator with a solid 3H-Ti target. A high-purity germanium detector was employed to measure the activities of the product. The reactions 93Nb(n, 2n)92mNb and 27Al(n, α)24Na were adopted for neutron flux calibration. The cross sections of the (n, 2n) and (n, p) reactions of the xenon isotopes were obtained within the 13–15 MeV neutron energy range. These cross-sections were then compared with the IAEA-exchange format (EXFOR) database-derived experimental data, together with the evaluation results of the CENDL-3, ENDF/B-VIII.0, JENDL-4.0, RUSFOND, and JEFF-3.3 data libraries, as well as the theoretical excitation function obtained using the TALYS-1.95 code. The cross-sections of the reactions (except for the 124Xe(n, 2n)123Xe and 132Xe(n, p)132I) at 13.5, 13.8, and 14.1 MeV are reported for the first time in this study. The obtained results are beneficial in providing better cross-section constraints for the reactions in the 13–15 MeV region, thus improving the quality of the corresponding database. Meanwhile, these data can also be used for the verification of relevant nuclear reaction model parameters.
2022, 46(4): 044002. doi: 10.1088/1674-1137/ac4589
Abstract:
The capture cross sections of the 169Tm\begin{document}$(n, \gamma)$\end{document} reaction were measured at the back streaming white neutron beam line (Back-n) of the China Spallation Neutron Source (CSNS) using four C6D6 liquid scintillation detectors. The background subtraction, normalization, and correction were carefully considered in the data analysis to obtain accurate cross sections. For the resonance at 3.9 eV, the R-matrix code SAMMY was used to determine the resonance parameters with the internal normalization method. The average capture cross sections of 169Tm for energy between 30 and 300 keV were extracted relative to the 197Au\begin{document}$(n, \gamma)$\end{document} reaction. The measured cross sections of the 169Tm\begin{document}$(n, \gamma)$\end{document} reaction were reported in logarithmically equidistant energy bins with 20 bins per energy decade with a total uncertainty of 5.4% – 7.0% in this study and described in terms of average resonance parameters using a Hauser-Feshbach calculation with fluctuations. The point-wise cross sections and the average resonance parameters showed fair agreement with the evaluated values of the ENDF/B-VIII.0 library in the energy region studied.
2022, 46(4): 044101. doi: 10.1088/1674-1137/ac3bc9
Abstract:
A systematic study on forward–backward (FB) multiplicity correlations from large systems to small ones through a multi-phase transport model (AMPT) has been performed and the phenomenon that correlation strength increases with centrality can be explained by taking the distribution of events as the superposition of a series of Gaussian distributions. It is also found that correlations in the \begin{document}$\eta -\phi$\end{document} plane can imply the shape of the event. Furthermore, long-range correlations originate from the fluctuations associated with the source information. FB correlations allow us to decouple long-range correlations from short-range correlations, and may provide a chance to investigate the α-clustering structure in initial colliding light nuclei as well. It seems the tetrahedron 16O + 16O collision gives a more uniform and symmetrical fireball, that emits the final particles more isotropically or independently in the longitudinal direction, indicating that the forward–backward multiplicity correlation could be used to identify the pattern of α-clustered 16O in future experiments.
2022, 46(4): 044102. doi: 10.1088/1674-1137/ac3def
Abstract:
The masses of pion and sigma meson modes, along with their dissociation in the quark medium, provide detailed spectral structures of the chiral partners. Collectivity has been observed in pA and pp systems both at LHC and RHIC. In this research, we studied the restoration of chiral symmetry by investigating the finite size effect on the detailed structure of chiral partners in the framework of the Nambu-Jona-Lasinio model. Their diffusion and conduction have been studied using this dissociation mechanism. It is determined that the masses, widths, diffusion coefficients, and conductivities of chiral partners merge at different temperatures in the restoration phase of chiral symmetry. However, merging points are shifted to lower temperatures when finite size effect is introduced into the picture. The strengths of diffusions and conductions are also reduced once the finite size is introduced in the calculations.
2022, 46(4): 044103. doi: 10.1088/1674-1137/ac3e5b
Abstract:
The study of nuclear mass is very important, and the neural network (NN) approach can be used to improve the prediction of nuclear mass for various models. Considering the number of valence nucleons of protons and neutrons separately in the input quantity of the NN model, the root-mean-square deviation of binding energy between data from AME2016 and liquid drop model calculations for 2314 nuclei was reduced from 2.385 MeV to 0.203 MeV. In addition, some defects in the Weizsäcker–Skyrme (WS)-type model were repaired, which well reproduced the two-neutron separation energy of the nucleus synthesized recently by RIKEN RI Beam Factory [Phys. Rev. Lett. 125, (2020) 122501]. The masses of some of the new nuclei appearing in the latest atomic mass evaluation (AME2020) are also well reproduced. However, the results of neural network methods for predicting the description of regions far from known atomic nuclei need to be further improved. This study shows that such a statistical model can be a tool for systematic searching of nuclei beyond existing experimental data.
2022, 46(4): 044104. doi: 10.1088/1674-1137/ac4035
Abstract:
By adopting different neutron and proton density distributions, cluster decay half-lives were investigated using double-folding potentials with constant and nuclear asymmetry dependent sets of nuclear density parameters. Two adopted asymmetry dependent sets of parameters were fitted based on microscopic calculations, and they were calculated based on the neutron skin/halo-type nuclei assumption and by employing experimental rms charge radii. A bulk agreement between theory and experiment was obtained for all sets of parameters using a calculated cluster preformation probability. Few differences were observed between the skin and halo-type assumptions. However, the notable role of the asymmetry parameter was observed in the relatively large differences between the skin and skin-type with zero thickness.
2022, 46(4): 044105. doi: 10.1088/1674-1137/ac42be
Abstract:
A microscopic description of the low-lying positive-parity rotational bands in 20Ne is given within the framework of the symplectic-based proton-neutron shell-model approach provided by the proton-neutron symplectic model (PNSM). For this purpose, a model Hamiltonian is adopted. This includes an algebraic interaction lying in the enveloping algebra of the \begin{document}$Sp(12,R)$\end{document} dynamical group of the PNSM, which introduces both horizontal and vertical mixings of different \begin{document}$SU(3)$\end{document} irreducible representations within the \begin{document}$Sp(12,R)$\end{document} irreducible collective space of 20Ne. A good overall description is obtained for the excitation energies of the ground and first two excited β bands, including the ground state intraband \begin{document}$B(E2)$\end{document} quadrupole collectivity and the known interband \begin{document}$B(E2)$\end{document} transition probabilities between the low-lying collective states, without utilizing an effective charge.
2022, 46(4): 044106. doi: 10.1088/1674-1137/ac45ef
Abstract:
Considering the preformation probability of the two emitted protons in the parent nucleus, we extend the Coulomb and proximity potential model (CPPM) to systematically study two-proton (2p) radioactivity half-lives of the nuclei close to proton drip line. The proximity potential chosen is Prox. 81 proposed by Blocki et al. in 1981. Furthermore, we apply this model to predict the half-lives of possible 2p radioactive candidates whose 2p radioactivity is energetically allowed or observed but not yet quantified in the evaluated nuclear properties table NUBASE2016. The predicted results are in good agreement with those from other theoretical models and empirical formulas, namely the effective liquid drop model (ELDM), generalized liquid drop model (GLDM), Gamow-like model, Sreeja formula and Liu formula.
2022, 46(4): 045101. doi: 10.1088/1674-1137/ac3d29
Abstract:
This study explores the scalar and Dirac quasinormal modes pertaining to a class of black hole solutions in the scalar-tensor-Gauss-Bonnet theory. The black hole metrics in question are novel analytic solutions recently derived in the extended version of the theory, which effectively follows at the level of the action of string theory. Owing to the existence of a nonlinear electromagnetic field, the black hole solution possesses a nonvanishing magnetic charge. In particular, the metric is capable of describing black holes with distinct characteristics by assuming different values of the ADM mass and the magnetic charge. This study investigates the scalar and Dirac perturbations in these black hole spacetimes; in particular, we focus on two different types of solutions, based on distinct horizon structures. The properties of the complex frequencies of the obtained dissipative oscillations are investigated, and the stability of the metric is subsequently addressed. We also elaborate on the possible implications of this study.
2022, 46(4): 045102. doi: 10.1088/1674-1137/ac3d2b
Abstract:
We propose a two-component dark matter explanation to the EDGES 21 cm anomalous signal. The heavier dark matter component is long-lived, and its decay is primarily responsible for the relic abundance of the lighter dark matter, which is millicharged. To evade the constraints from CMB, underground dark matter direct detection, and XQC experiments, the lifetime of the heavier dark matter has to be larger than \begin{document}$0.1\, \tau_U$\end{document}, where \begin{document}$\tau_U$\end{document} is the age of the universe. Our model provides a viable realization of the millicharged dark matter model to explain the EDGES 21 cm signal, since the minimal model in which the relic density is generated via thermal freeze-out has been ruled out by various constraints.
2022, 46(4): 045103. doi: 10.1088/1674-1137/ac42bd
Abstract:
It is well known that a primordial black hole (PBH) can be generated in the inflation process of the early universe, especially when the inflation field has a number of non-trivial features that could break the slow-roll condition. In this study, we investigate a toy model of inflation with bumpy potential, which has one or several bumps. We determined that the potential with multi-bump can generate power spectra with multi-peaks in small-scale region, which can in turn predict the generation of primordial black holes in various mass ranges. We also consider the two possibilities of PBH formation by spherical and elliptical collapses. Finally, we discuss the scalar-induced gravitational waves (SIGWs) generated by linear scalar perturbations at second-order.
2022, 46(4): 045104. doi: 10.1088/1674-1137/ac46bb
Abstract:
The main aim of this study is to explore the existence and salient features of spherically symmetric relativistic quark stars in the background of massive Brans-Dicke gravity. The exact solutions to the modified Einstein field equations are derived for specific forms of coupling and scalar field functions using the equation of state relating to the strange quark matter that stimulates the phenomenological MIT-Bag model as a free Fermi gas of quarks. We use a well-behaved function along with the Karmarkar condition for class-one embedding as well as junction conditions to determine the unknown metric tensors. The radii of strange compact stars viz., PSR J1416-2230, PSR J1903+327, 4U 1820-30, CenX-3, and EXO1785-248, are predicted via their observed mass for different values of the massive Brans-Dicke parameters. We explore the influences of the mass of scalar field \begin{document}$m_{\phi}$\end{document}, coupling parameter \begin{document}$\omega_{\rm BD}$\end{document}, and bag constant \begin{document}${\cal{B}}$\end{document} on state determinants and perform several tests on the viability and stability of the constructed stellar model. Conclusively, we find that our stellar system is physically viable and stable as it satisfies all the energy conditions and necessary stability criteria under the influence of a gravitational scalar field.