## 2021 Vol. 45, No. 8

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2021, 45(8): 083001. doi: 10.1088/1674-1137/ac061c
Abstract:
This analysis evaluates the possibility of the search for Dark Matter (DM) particles using events with a Z\begin{document}$^{\prime}$\end{document} heavy gauge boson and a large missing transverse momentum at the Large Hadron Collider (LHC). We consider the muonic decay of Z\begin{document}$^{\prime}$\end{document}. The analyzed Monte Carlo samples were the Open simulated files produced by the Compact Muon Solenoid (CMS) collaboration for proton-proton collisions, corresponding to an integrated luminosity of the LHC run-I with 19.7 fb \begin{document}$^{-1}$\end{document} at \begin{document}$\sqrt{s} =$\end{document} 8 TeV. Two scenarios, namely a simplified benchmark scenario, called Dark Higgs, and the effective field theory (EFT) formalism, were used for interpretations. Limits were set on Z\begin{document}$^{\prime}$\end{document}, dark matter masses, and the cutoff scale of the EFT.
2021, 45(8): 083101. doi: 10.1088/1674-1137/ac032f
Abstract:
In this study, we utilize a potentially versatile Bayesian parameter approach to compute the value of the pion charge radius and quantify its uncertainty from several experimental \begin{document}$e^{+}e^{-}$\end{document} datasets for the pion vector form factor. We employ dispersion relations to model the pion vector form factor to extract the radius. Nested model selection is used to determine the order of polynomial appearing in the form factor formulation that can be supported by the data, adapting the computation of Bayes evidence and Bayesian effective complexity based on Occam's razor. Our findings indicate that five out of six used datasets favor the nine-parameter model for radius extraction, and accordingly, we average the radii from the datasets. Despite some inconsistencies with the most updated radius values, our approach may serve as a more intuitive method of addressing parameter estimations in dispersion theory.
2021, 45(8): 083102. doi: 10.1088/1674-1137/ac03ab
Abstract:
A perturbative method of computing the total travel time of both null and lightlike rays in arbitrary static spherically symmetric spacetimes in the weak field limit is proposed. The resultant total time takes a quasi-series form of the impact parameter. The coefficient of this series at a certain order n is shown to be determined by the asymptotic expansion of the metric functions to the order \begin{document}$n+1$\end{document}. For the leading order(s), the time delay, as well as the difference between the time delays of two types of relativistic signals, is shown to take a universal form for all SSS spacetimes. This universal form depends on the mass M and a post-Newtonian parameter \begin{document}$\gamma$\end{document} of the spacetime. The analytical result is numerically verified using the central black hole of galaxy M87 as the gravitational lensing center.
Abstract:
This paper presents the impact of the lepton transverse momentum \begin{document}$p^{l}_{T}$\end{document} threshold on the \begin{document}$W$\end{document} boson charge asymmetry predictions in perturbative QCD for the inclusive \begin{document}$W^{\pm}+X \rightarrow l^{\pm} \nu +X$\end{document} production in proton-proton (\begin{document}$pp$\end{document}) collisions. The predictions are obtained at various low-\begin{document}$p^{l}_{T}$\end{document} thresholds \begin{document}$p^{l}_{T} >$\end{document} 20, 25, 30, and 40 GeV in a fiducial region encompassing both the central and forward detector acceptances in terms of the lepton pseudorapidity \begin{document}$0 \leq \eta_{l} \leq 4.5$\end{document}. The predicted distributions for the lepton charge asymmetry, which is defined by \begin{document}$\eta_{l}$\end{document} (\begin{document}$A_{\eta_{l}}$\end{document}), at the next-to-next-to-leading order (NNLO) accuracy are compared with the CMS and LHCb data at 8 TeV center-of-mass collision energy. The 8 TeV predictions reproduce the data fairly well within the quoted uncertainties. The predictions from the CT14 parton distribution function (PDF) model are in a slightly better agreement with the data over the other PDF sets that are tested. The 13 TeV predictions using various \begin{document}$p^{l}_{T}$\end{document} thresholds are reported for \begin{document}$A_{\eta_{l}}$\end{document} and the charge asymmetries that are defined in terms of the differential cross sections in bins of the \begin{document}$W$\end{document} boson rapidity \begin{document}$y_{W}$\end{document} (\begin{document}$A_{y_{W}}$\end{document}) and transverse momentum \begin{document}$p^{W}_{T}$\end{document} (\begin{document}$A_{p^{W}_{T}}$\end{document}). The NNLO predictions for the \begin{document}$A_{\eta_{l}}$\end{document}, \begin{document}$A_{y_{W}}$\end{document}, and \begin{document}$A_{p^{W}_{T}}$\end{document} distributions are assessed to be in close correlation with the \begin{document}$p^{l}_{T}$\end{document} value. The \begin{document}$A_{\eta_{l}}$\end{document} and \begin{document}$A_{y_{W}}$\end{document} distributions are particularly shown to be more correlated at a higher \begin{document}$p^{l}_{T}$\end{document} threshold. The \begin{document}$A_{p^{W}_{T}}$\end{document} distributions are also reported from the merged predictions with improved accuracy by the inclusion of the next-to-next-to-next-to-leading logarithm (N3LL) corrections, i.e., at NNLO+N3LL. The predicted distributions from various \begin{document}$p^{l}_{T}$\end{document} thresholds represent a finer probe in terms of the capability to provide more constraints on the ratio of \begin{document}$u$\end{document} and \begin{document}$d$\end{document} quark distribution functions in the parton momentum fraction range \begin{document}$10^{-4} < x < 1$\end{document}.
2021, 45(8): 083104. doi: 10.1088/1674-1137/ac06ac
Abstract:
Although \begin{document}$J/{\psi}$\end{document} weak decays are rare, they are possible within the standard model of elementary particles. Inspired by the potential prospects of the future intensity frontier, the C parity violating \begin{document}$J/{\psi}$\end{document} \begin{document}${\to}$\end{document} \begin{document}${\pi}{\eta}^{({\prime})}$\end{document}, \begin{document}${\eta}{\eta}^{\prime}$\end{document} decays and the strangeness changing \begin{document}$J/{\psi}$\end{document} \begin{document}${\to}$\end{document} \begin{document}${\pi}K$\end{document}, \begin{document}$K{\eta}^{({\prime})}$\end{document} decays are studied via the perturbative QCD approach. It is determined that the \begin{document}$J/{\psi}$\end{document} \begin{document}${\to}$\end{document} \begin{document}${\eta}{\eta}^{\prime}$\end{document} decays have relatively large branching ratios, approximately on the order of \begin{document}$10^{-11}$\end{document}, which might be within the measurement capability and sensitivity of the future STCF experiment.
2021, 45(8): 083105. doi: 10.1088/1674-1137/ac06ba
Abstract:
Combining the \begin{document}$b\to s\mu^+\mu^-$\end{document} anomaly and dark matter observables, we study the capability of the LHC to test dark matter, \begin{document}$Z^{\prime}$\end{document}, and a vector-like quark. We focus on a local \begin{document}$U(1)_{L_\mu-L_\tau}$\end{document} model with a vector-like \begin{document}$SU(2)_L$\end{document} doublet quark Q and a complex singlet scalar whose lightest component \begin{document}$X_I$\end{document} is a candidate of dark matter. After imposing relevant constraints, we find that the \begin{document}$b\to s\mu^+\mu^-$\end{document} anomaly and the relic abundance of dark matter favor \begin{document}$m_{X_I}< 350$\end{document} GeV and \begin{document}$m_{Z^{\prime}}< 450$\end{document} GeV for \begin{document}$m_Q<$\end{document} 2 TeV and \begin{document}$m_{X_R}<$\end{document} 2 TeV (the heavy partner of \begin{document}$m_{X_I}$\end{document}). Current searches for jets and missing transverse momentum at the LHC sizably reduce the mass ranges of the vector-like quark, and \begin{document}$m_Q$\end{document} is required to be larger than 1.7 TeV. Finally, we discuss the possibility of probing these new particles at the high luminosity LHC via the QCD process \begin{document}$pp \to D\bar{D}$\end{document} followed by\begin{document}$D\to s (b) X_I$\end{document} , \begin{document}$D\to s (b) Z'X_I$\end{document}, and then \begin{document}$Z'\to$\end{document}\begin{document}$\mu^+\mu^-$\end{document}. Taking a benchmark point of \begin{document}$m_Q$\end{document} = 1.93 TeV, \begin{document}$m_{Z^\prime} = 170$\end{document} GeV, and \begin{document}$m_{X_I} =$\end{document} 145 GeV, we perform a detailed Monte Carlo simulation and find that this benchmark point can be accessed at the 14 TeV LHC with an integrated luminosity of 3000 fb\begin{document}$^{-1}$\end{document}.
2021, 45(8): 084001. doi: 10.1088/1674-1137/ac0098
Abstract:
Excited states in the odd-A nucleus 71Ga have been studied via the 70Zn(7Li, \begin{document}$\alpha2n$\end{document})71Ga fusion-evaporation reaction with incident beam energies of 30 and 35 MeV. The level scheme is established up to spin \begin{document}$I^{\pi}$\end{document} = (29/2+) and an excitation energy \begin{document}$\sim$\end{document} 6.6 MeV. A previously known sequence built on the 9/2+ state is extended as a novel rotational band originating from the \begin{document}$\nu (g_{9/2}^2)$\end{document} alignment. Furthermore, a negative-parity sequence is also reported. The observed energy levels of 71Ga have been interpreted in the framework of the nuclear shell model (SM).
2021, 45(8): 084002. doi: 10.1088/1674-1137/ac04a0
Abstract:
A multi-nucleon transfer and cluster decay experiment, \begin{document}$^7$\end{document}Li(\begin{document}$^{11}$\end{document}B,\begin{document}$^{14}$\end{document}C\begin{document}$^*\rightarrow\alpha$\end{document}+\begin{document}$^{10}$\end{document}Be)\begin{document}$\alpha$\end{document}, is conducted at an incident beam energy of 55 MeV. This reaction channel has a significantly large Q-value, which favors populating the high lying resonant states in \begin{document}$^{14}$\end{document}C. The decay paths, from these resonances to various states of the final nucleus \begin{document}$^{10}$\end{document}Be, can be selected, owing to the experimentally achieved optimal resolution of the Q-value spectrum. A number of resonant states are reconstructed from the forward emitting \begin{document}$^{10}$\end{document}Be + \begin{document}$\alpha$\end{document} fragments, and their major molecular structures can be detected according to the selective decay paths and relative decay widths. A state at 22.4(2) MeV validates the previously measured and theoretically predicted band head of the positive-parity \begin{document}$\sigma$\end{document}-bond linear-chain molecular band. Two additional resonances at 22.9(2) and 24.2(2) MeV are identified and consistent with the predicted \begin{document}$2^+$\end{document} and \begin{document}$4^+$\end{document} members of the same molecular band, thus providing novel evidences for the existence of the exotic clustering chain structure in neutron-rich carbon isotopes. A few high energy resonances, which also indicate the presence of the \begin{document}$\sigma$\end{document}-bond molecular structure, are observed; however, further studies are still required to clarify their ascription in band systematics.
2021, 45(8): 084101. doi: 10.1088/1674-1137/ac0035
Abstract:
The isoscaling parameters \begin{document}$\alpha_{\rm eval}$\end{document} in the fissioning systems, i.e., those extracted from the Evaluated Nuclear Data Library (ENDF/B-VIII.0) and the Joint Evaluated Fission and Fusion File (JEFF-3.3), show an obvious difference from simple statistic model prediction where only the symmetry energy plays the dominant role. To explain the \begin{document}$\alpha_{\rm eval}$\end{document} as a function of the charge number of the fission fragment, a statistic scission point model is adopted. Our analysis shows that the effects of the shell correction, nuclear shape deformation, and intrinsic temperature of fission fragments are indispensable as well as the symmetry energy. Furthermore, an alternative method for extracting the intrinsic temperatures of fission fragments is proposed based on the isoscaling relationship in fission fragments. The intrinsic temperatures of the light fragments are higher than those of the heavy fragments.
2021, 45(8): 084102. doi: 10.1088/1674-1137/ac0097
Abstract:
A systematic analysis on experimental data of the half-lives of nuclear double-\begin{document}$\beta$\end{document} decays with two neutrinos (\begin{document}$2\nu\beta\beta$\end{document}) is performed based on the analytical formula proposed by Primakoff and Rosen. We improve the formula by considering the shell effects and refining the energy dependence of the phase-space factor. This improved formula can closely describe all available experimental half-lives of \begin{document}$2\nu\beta^{-}\beta^{-}$\end{document} decays, both for ground-state transitions and transitions from ground states of parent nuclei to the first \begin{document}$0^{+}$\end{document} excited states of daughter nuclei. The calculated half-lives agree with the experimental data of ground-state transitions of all known eleven nuclei with an average factor of 2.3. Further predictions are provided for \begin{document}$2\nu\beta\beta$\end{document}-decay candidates with decay energies above 0.5 MeV. We compare different theoretical predictions and emphasize the importance of experimental measurements on the half-lives of double-\begin{document}$\beta$\end{document} transitions between the ground state of \begin{document}$^{48}$\end{document}Ca, \begin{document}$^{76}$\end{document}Ge, and \begin{document}$^{136}$\end{document}Xe and the first \begin{document}$0^{+}$\end{document} excited states of their corresponding daughter nuclei, which will be very useful for understanding the underlying mechanisms of double-\begin{document}$\beta$\end{document} decays and for further studying the shell effects on nuclear transition matrix elements.
2021, 45(8): 084103. doi: 10.1088/1674-1137/ac009a
Abstract:
The isospin effects of projectile fragmentation at intermediate energies are investigated using an isospin-dependent Boltzmann-Langevin model. The collisions of mass-symmetric reactions including 58Fe, 58Ni + 58Fe, and 58Ni at intermediate energies, in the 30 to 100 MeV/A range, are studied for different symmetry energies. Yield ratios of the isotopic, isobaric, and isotonic pairs of fragments from the intermediate-mass region using three symmetry energies are extracted as functions of the N/Z ratio of the composite systems in the entrance channel and the incident energies. It is found that the yield ratios are sensitive to symmetry energies, especially for neutron-rich systems, and the calculations using soft symmetry energy are closer to the experimental data. The isospin effect is stronger for the soft symmetry energy, owing to the competition of the repulsive Coulomb force and the symmetry energy attractive force on the proton. For the first time, the splits are presented, revealing a transition from the isospin equilibrium at lower energies to translucency at intermediate energies. The results show a degree of transparency in that intermediate mass fragments undergo a transition from dependence on the composite systems in the entrance channel to reliance on the projectile and target nuclei.
2021, 45(8): 084104. doi: 10.1088/1674-1137/ac012b
Abstract:
A rovibrational model, including anharmonic, centrifugal, and Coriolis corrections, is used to calculate π, K, N, and Ʃ orbital and radial resonances. The four orbital excitations of the π meson correspond to the b(1235), π2(1670), b3(2030), and π4(2250) resonances. Its first four radial excitations correspond to the π(1300), π(1800), π(2070), and π(2360) resonances. The orbital excitations of the K meson are interpreted as the K1(1270), K2(1770), K3(2320), and K4(2500) resonances; its radial excitations correspond to the K(1460) and K(1830) resonances. The N orbital excitations are identified with the N(1520), N(1680), N(2190), N(2220), and N(2600) resonances. The first four radial excitations of the N family correspond to the N(1440), N(1880), N(2100), and N(2300) resonances. The orbital excitations of the Ʃ baryon are associated with the Ʃ(1670), Ʃ(1915), Ʃ(2100), and Ʃ(2250) resonances, whereas its radial excitations are identified with the Ʃ(1660), Ʃ(1770), and Ʃ(1880) resonances. The proposed rovibrational model calculations show a good agreement with the corresponding experimental values and allow for the prediction of hadron resonances, thereby proving to be useful for the interpretation of excited hadron spectra.
2021, 45(8): 084105. doi: 10.1088/1674-1137/ac032a
Abstract:
We present a preliminary study of charge exchange heavy ion induced reactions based on the constrained molecular dynamics (CoMD) model. The purpose is to test the capability of the model in predicting the occurrence of single charge exchange (SCE) and double charge exchange (DCE) exit channels for three different entrance channels at the same laboratory incident energy. The nuclear reaction dynamics and nuclear interaction within the CoMD approach are the only ingredients that have given, at this stage, promising results for SCE and DCE cross section calculations. The obtained results suggest an upgrade and possible future employment of the model for studies relating to the production of exotic nuclei through charge exchange reactions or DCE reactions and their connection with neutrinoless double beta decay.
2021, 45(8): 084106. doi: 10.1088/1674-1137/ac05a0
Abstract:
A scheme to solve the Hamiltonian in the interacting boson-fermion model in terms of the SU(3) coupling basis is introduced, through which the effects of an odd particle on shape phase transitions (SPTs) in odd-A nuclei are examined by comparing the critical behaviors of some selected quantities in odd-even and even-even systems. The results indicate that the spherical to prolate (U(5)-SU(3)) SPT and spherical to \begin{document}$\gamma$\end{document}-soft (U(5)-O(6)) SPT may clearly occur in the odd-even system with the SPT signatures revealed by various quantities including the excitation energies, energy ratio, \begin{document}$B(E2)$\end{document} ratio, quadrupole moments, and one-particle-transfer spectroscopic intensities. In particular, the results indicate that the spherical to prolate SPT in the odd-even system can even be strengthened by the effects of the odd particle with the large fluctuations of the quadrupole deformations appearing near the critical point.
2021, 45(8): 084107. doi: 10.1088/1674-1137/ac05a1
Abstract:
The dynamics of high-energy proton-induced spallation reactions on target nuclides of 56Fe, 58Ni, 107Ag, 112Cd, 184W, 181Ta, 197Au, and 208Pb are investigated with the quantum molecular dynamics transport model motivated by the China initiative Accelerator Driven System (CiADS) in Huizhou and the China Spallation Neutron Source (CSNS) in Dongguan. The production mechanism of light nuclides and fission fragments is thoroughly analyzed, and the results obtained thereby are compared with available experimental data. The statistical code GEMINI is employed in conjunction with a transport model for describing the decay of primary fragments. For the treatment of cluster emission during the preequilibrium stage, a surface coalescence model is implemented into the model. It is found that the available data in terms of total fragment yields are well reproduced in the combined approach for spallation reactions both on the heavy and light targets. The energetic light nuclides (deuteron, triton, helium isotopes etc) mainly created during the preequilibrium stage are treated within the framework of surface coalescence, whereas their evaporation is described in the conventional manner by the GEMINI code. With this combined approach, a good overall description of light clusters and neutron emission is obtained, and some discrepancies with the experimental data are discussed. Possible production of radioactive isotopes in the spallation reactions is also analyzed, i.e., the 6,8He energy spectra.
2021, 45(8): 084108. doi: 10.1088/1674-1137/ac06aa
Abstract:
Proton capture reactions on Mg isotopes are significant in the Mg-Al cycle in stellar H-burning. In particular, the resonance strengths and branching ratios of low-energy resonances in 25Mg(\begin{document}$p,\gamma$\end{document})26Al reactions determine the production of 26Al, which is one of the most important long-lived radioactive nuclei in nuclear astrophysics. In this article, we report our first experiment using the intense proton beam of approximately 2 mA provided by the JUNA accelerator ground laboratory and a new technique that can minimize the composition change of targets under intense beam irradiation. The resonance strengths and branching ratios of E = 214, 304, and 326 keV resonances in the reactions of 24Mg(\begin{document}$p,\gamma$\end{document})25Al, 25Mg(\begin{document}$p,\gamma$\end{document})26Al, and 26Mg(\begin{document}$p,\gamma$\end{document})27Al, respectively, were measured with high accuracy. The success of this experiment provides a good calibration for the nuclear astrophysical experiment at the Jinping underground laboratory.
2021, 45(8): 084109. doi: 10.1088/1674-1137/ac06ab
Abstract:
In our previous studies [Phys. Rev. C 97, 044619 (2018); Phys. Rev. C 103, 044610 (2021)], a universal odd-even staggering (OES) has been observed in extensive cross sections of isotopes not far from stability, measured for different fragmentation and spallation reactions. Four OES relations have been proposed on the basis of this OES universality. However, it is still unclear whether this OES universality and OES relations are applicable to many isotopes near the drip-lines. Here, the OES in recent experimental cross sections of very neutron-rich nuclei approaching the drip-line (from \begin{document}$^{76}$\end{document}Ge,\begin{document}$^{82}$\end{document}Se+\begin{document}$^{9}$\end{document}Be) is quantitatively investigated, to further validate the OES universality and OES relations. The OES magnitudes in these experimental data approaching the neutron drip-line generally agree with those evaluated previously, mainly from experimental data near stability. New OES evaluations derived from these experimental data are also recommended for more exotic nuclei near the neutron drip-line, which extends the conclusions of our previous OES studies. In addition, the OES relation calculations are consistent with these experimental data of very neutron-rich nuclides according to their comparisons in this work. Finally, comparisons with additional experimental data (from \begin{document}$^{238}$\end{document}U+\begin{document}$^{9}$\end{document}Be) also support that new OES evaluations and OES relation calculations can be applied for exotic nuclei near the neutron drip-line.
2021, 45(8): 084110. doi: 10.1088/1674-1137/ac0329
Abstract:
The chiral phase transition and equation of state are studied within a novel self-consistent mean-field approximation of the two-flavor Nambu-Jona-Lasinio model. In this newly developed model, modifications to the chemical μ and chiral chemical \begin{document}$\mu_5$\end{document} potentials are naturally included by introducing vector and axial-vector channels from Fierz-transformed Lagrangian to the standard Lagrangian. In the proper-time scheme, the chiral phase transition is a crossover in the \begin{document}$T-\mu$\end{document} plane. However, when \begin{document}$\mu_5$\end{document} is incorporated, our study demonstrates that a first order phase transition may emerge. Furthermore, the chiral imbalance will soften the equation of state of quark matter. The mass-radius relationship and tidal deformability of quark stars are calculated. The maximum mass and radius decrease as \begin{document}$\mu_5$\end{document} increases. Our study also indicates that the vector and axial-vector channels exhibit an opposite influence on the equation of state.
2021, 45(8): 085001. doi: 10.1088/1674-1137/ac0099
Abstract:
Extensive Air Showers (EAS) induced by cosmic ray particles of very low energies, owing to the significantly steep cosmic ray energy spectrum, dominate the secondary particle flux measured by single detectors and small shower arrays. Such arrays connected in extended networks can be used to determine potentially interesting spatial correlations between showers, which may shed new light on the nature of ultra high-energy cosmic rays. The quantitative interpretation of showers recorded by small local arrays requires a methodology that differs from that used by ordinary large EAS arrays operating in the "knee" region and above. We present "small EAS generator," a semi-analytical method for integrating cosmic ray spectra over energies of interest and summing over the mass spectra of primary nuclei in arbitrary detector configurations. Furthermore, we provide results on the EAS electron and muon fluxes and particle density spectra.
2021, 45(8): 085002. doi: 10.1088/1674-1137/ac041b
Abstract:
The first Water Cherenkov detector of the LHAASO experiment (WCDA-1) has been operating since April 2019. The data for the first year have been analyzed to test its performance by observing the Crab Nebula as a standard candle. The WCDA-1 achieves a sensitivity of 65 mCU per year, with a statistical threshold of 5 \begin{document}$\sigma$\end{document}. To accomplish this, a 97.7% cosmic-ray background rejection rate around 1 TeV and 99.8% around 6 TeV with an approximate photon acceptance of 50% is achieved after applying an algorithm to separate gamma-induced showers. The angular resolution is measured using the Crab Nebula as a point source to be approximately 0.45° at 1 TeV and better than 0.2° above 6 TeV, with a pointing accuracy better than 0.05°. These values all match the design specifications. The energy resolution is found to be 33% for gamma rays around 6 TeV. The spectral energy distribution of the Crab Nebula in the range from 500 GeV to 15.8 TeV is measured and found to be in agreement with the results from other TeV gamma ray observatories.
2021, 45(8): 085101. doi: 10.1088/1674-1137/ac0419
Abstract:
In this study, we investigate the Hawking radiation in higher dimensional Reissner-Nordström black holes as received by an observer located at infinity. The frequency-dependent transmission rates, which deform the thermal radiation emitted in the vicinity of the black hole horizon, are evaluated numerically. In addition to those in four-dimensional spacetime, the calculations are extended to higher dimensional Reissner-Nordström metrics, and the results are observed to be sensitive to the spacetime dimension to an extent. Generally, we observe that the transmission coefficient practically vanishes when the frequency of the emitted particle approaches zero. It increases with frequency and eventually saturates to a certain value. For four-dimensional spacetime, the above result is demonstrated to be mostly independent of the metric's parameter and the orbital quantum number of the particle, when the location of the event horizon, \begin{document}$r_h$\end{document}, and the product of the charges of the black hole and the particle qQ are known. However, for higher-dimensional scenarios, the convergence becomes more gradual. Moreover, the difference between states with different orbital quantum numbers is observed to be more significant. As the magnitude of the product of charges qQ becomes more significant, the transmission coefficient exceeds 1. In other words, the resultant spectral flux is amplified, which results in an accelerated process of black hole evaporation. The relationship of the calculated outgoing transmission coefficient with existing results on the greybody factor is discussed.
2021, 45(8): 085102. doi: 10.1088/1674-1137/ac041a
Abstract:
This study addresses the formation of anisotropic compact star models in the background of \begin{document}$f(T,{\cal{T}})$\end{document} gravity (where T and \begin{document}${\cal{T}}$\end{document} represent the torsion and trace of the energy momentum tensor, respectively). \begin{document}$f(T,{\cal{T}})$\end{document} gravity is an extension of the \begin{document}$f(T)$\end{document} theory, and it allows a general non-minimal coupling between T and \begin{document}${\cal{T}}$\end{document}. In this setup, we apply Krori and Barua's solution to the static spacetime with the components \begin{document}$\xi=B r^2+c$\end{document} and \begin{document}$\Psi=A r^2$\end{document}. To develop viable solutions, we select a well-known model \begin{document}$f(T,{\cal{T}})= \alpha T^m+\beta {\cal{T}}+\phi$\end{document} (where α and β are coupling parameters, and ϕ indicates the cosmological constant). We adopt the conventional matching of interior and exterior space time to evaluate the unknowns, which are employed in the stellar configuration. We present a comprehensive discussion on the stellar properties to elaborate the anisotropic nature of compact stars corresponding to well-known models: \begin{document}$PSR J1416-2230$\end{document}, \begin{document}$4U 1608-52$\end{document}, \begin{document}$Cen X-3$\end{document}, \begin{document}$EXO 1785-248$\end{document} , and \begin{document}$SMC X-1$\end{document}. Via physical analysis, it is observed that the solution of compact spheres satisfy the acceptability criteria, and its models behave optimally and depict stability and consistency, in accordance with \begin{document}$f(T,{\cal{T}})$\end{document} gravity.
2021, 45(8): 085103. doi: 10.1088/1674-1137/ac06bb
Abstract:
We calculate photon sphere \begin{document}$r_{ph}$\end{document} and critical curve \begin{document}$b_c$\end{document} for a quantum corrected Schwarzschild black hole, finding that they violate universal inequalities proved for asymptotically flat black holes that satisfy the null energy condition in the framework of Einstein gravity. This violation seems to be a common phenomenon when considering quantum modification of Einstein gravity. Furthermore, we study the shadows, lensing rings, and photon rings in the quantum corrected Schwarzschild black hole. The violation leads to a larger bright lensing ring in the observational appearance of the thin disk emission near the black hole compared with the classical Schwarzschild black hole. Our analysis may provide observational evidence for the quantum effect of general relativity.
2021, 45(8): 089001. doi: 10.1088/1674-1137/ac009b
Abstract: