Chinese Physics C

2024-1 Contents

2024, 48(1): 1-2.

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Abstract:

Identification of deuterons at BESIII

Wei Wang, Bo Zheng, Jia-Jia Qin, Zhi-Yong Wang

2024, 48(1): 013001. doi: 10.1088/1674-1137/ad061e

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The identification of deuterons with momenta in the range of 0.52−0.72 GeV/c is studied with specific ionization energy loss information using a data sample collected by the BESIII detector at center-of-mass energies between 4.009 and 4.946 GeV. Clean deuteron samples are selected using time of flight information. For all data samples, the deuteron identification efficiencies are higher than 95%, with a maximum difference of

\begin{document}$ (4.9\pm1.0) $\end{document}

% between data and Monte Carlo simulation. This verifies the effectiveness of the deuteron identification method based on specific ionization energy loss and provides valuable information for future studies on processes involving deuterons in the final state at BESIII.

Magnetic and quadrupole moments of the ${\boldsymbol Z_{\boldsymbol c}\bf (4020)^+} $, $ {\boldsymbol Z_{\boldsymbol c}\bf (4050)^+} $, and $ {\boldsymbol Z_{\boldsymbol c}\bf (4600)^{+}} $ states in the diquark-antidiquark picture

Ulaş Özdem

2024, 48(1): 013101. doi: 10.1088/1674-1137/ad0110

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The magnetic and quadrupole moments of the

\begin{document}$ Z_{c}(4020)^+ $\end{document}

,

\begin{document}$ Z_{c}(4050)^+ $\end{document}

, and

\begin{document}$ Z_{c}(4600)^{+} $\end{document}

states are calculated within the QCD light-cone sum rules. The compact diquark-antidiquark interpolating currents and the distribution amplitudes of the on-shell photon are used to extract the magnetic and quadrupole moments of these states. The magnetic moments are acquired as

\begin{document}$\mu_{Z_{c}}^{} = 0.50 ^{+0.22}_{-0.22}\; \mu_{N}^{}$\end{document}

,

\begin{document}$\mu_{Z^{1}_{c}}=1.22 ^{+0.34}_{-0.32}\; \mu_{N}^{}$\end{document}

, and

\begin{document}$\mu_{Z^2_{c}}=2.40 ^{+0.53}_{-0.48}\; \mu_{N}^{}$\end{document}

for the

\begin{document}$ Z_{c}(4020)^+ $\end{document}

,

\begin{document}$ Z_{c}(4050)^+ $\end{document}

, and

\begin{document}$ Z_{c}(4600)^{+} $\end{document}

states, respectively. The magnetic moments evaluated for the

\begin{document}$ Z_{c}4020)^+ $\end{document}

,

\begin{document}$ Z_{c}(4050)^+ $\end{document}

, and

\begin{document}$ Z_{c}(4600)^{+} $\end{document}

states are sufficiently large to be experimentally measurable. The magnetic moment is an excellent platform for studying the internal structure of hadrons governed by the quark-gluon dynamics of QCD because it is the leading-order response of a bound system to a weak external magnetic field. The quadrupole moment results are

\begin{document}$ \mathcal{D}_{Z_c}=(0.20 ^{+0.05}_{-0.04}) \times 10^{-3}\; \rm{fm}^2 $\end{document}

,

\begin{document}$ \mathcal{D}_{Z_c^1}=(0.57 ^{+0.07}_{-0.08}) \times 10^{-3}\; \rm{fm}^2 $\end{document}

, and

\begin{document}$ \mathcal{D}_{Z_c^2}=(0.30 ^{+0.05}_{-0.04}) \times 10^{-3}\; \rm{fm}^2 $\end{document}

for the

\begin{document}$ Z_{c}(4020)^+ $\end{document}

,

\begin{document}$ Z_{c}(4050)^+ $\end{document}

, and

\begin{document}$ Z_{c}(4600)^{+} $\end{document}

states, respectively. We obtain a non-zero, but small, value for the quadrupole moments of the

\begin{document}$ Z_c $\end{document}

states, which indicates a non-spherical charge distribution. The nature and internal structure of these states can be elucidated by comparing future experimental data on the magnetic and quadrupole moments of the

\begin{document}$ Z_{c}(4020)^+ $\end{document}

,

\begin{document}$ Z_{c}(4050)^+ $\end{document}

, and

\begin{document}$ Z_{c}(4600)^{+} $\end{document}

states with the results of the present study.

Strong vertices of bottom mesons B and B* and bottomonia ${\Upsilon }$, η_b

Jie Lu, Guo-Liang Yu, Zhi-Gang Wang, Bin Wu

2024, 48(1): 013102. doi: 10.1088/1674-1137/ad061d

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Abstract:
In this study, the strong coupling constants of vertices

\begin{document}$ BB\Upsilon $\end{document}

,

\begin{document}$ BB^{*}\Upsilon $\end{document}

,

\begin{document}$ B^{*}B^{*}\Upsilon $\end{document}

,

\begin{document}$ BB^{*}\eta_{b} $\end{document}

, and

\begin{document}$ B^{*}B^{*}\eta_{b} $\end{document}

are analyzed in the framework of QCD sum rules. All possible off-shell cases and the contributions of vacuum condensate terms including

\begin{document}$ \langle\overline{q}q\rangle $\end{document}

,

\begin{document}$ \langle\overline{q}g_{s}\sigma Gq\rangle $\end{document}

,

\begin{document}$ \langle g_{s}^{2}G^{2}\rangle $\end{document}

,

\begin{document}$ \langle f^{3}G^{3}\rangle $\end{document}

, and

\begin{document}$ \langle\overline{q}q\rangle\langle g_{s}^{2}G^{2}\rangle $\end{document}

are considered. The momentum dependent strong coupling constants are first calculated and then fitted into the analytical function

\begin{document}$ g(Q^{2}) $\end{document}

, which is extrapolated to time-like regions to obtain the final values of strong coupling constants. The final results are

\begin{document}$ g_{BB\Upsilon}=40.67^{+7.55}_{-4.20} $\end{document}

,

\begin{document}$ g_{BB^{*}\Upsilon}=11.58^{+2.19}_{-1.09} $\end{document}

GeV

\begin{document}$ ^{-1} $\end{document}

,

\begin{document}$ g_{B^{*}B^{*}\Upsilon}=57.02^{+5.32}_{-5.31} $\end{document}

,

\begin{document}$ g_{BB^{*}\eta_{b}}=23.39^{+4.74}_{-2.30} $\end{document}

, and

\begin{document}$ g_{B^{*}B^{*}\eta_{b}}=12.49^{+2.12}_{-1.35} $\end{document}

GeV

\begin{document}$ ^{-1} $\end{document}

. These strong coupling constants are important input parameters that reflect the dynamic properties of the interactions among the mesons and quarkonia.

Resonant contribution of the three-body decay process $ {{\bar B}_{s} \rightarrow K^{+}K^{-} P }$ in perturbative QCD

Gang Lü, Chang-Chang Zhang, Yan-Lin Zhao, Li-Ying Zhang

2024, 48(1): 013103. doi: 10.1088/1674-1137/ad0e03

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We investigate CP violation in the decay process

\begin{document}$ \bar B_{s} \rightarrow \phi(\rho,\omega) P \rightarrow K^{+}K^{-}P $\end{document}

by considering the interference effects of

\begin{document}$ \phi\rightarrow K^{+}K^{-} $\end{document}

,

\begin{document}$ \rho\rightarrow K^{+}K^{-} $\end{document}

, and

\begin{document}$ \omega\rightarrow K^{+}K^{-} $\end{document}

within the framework of the perturbative QCD method (P refers to π, K, η, and

\begin{document}$ \eta' $\end{document}

pseudoscalar mesons). We analyze the mixings of

\begin{document}$ \phi-\rho^{0} $\end{document}

,

\begin{document}$ \phi-\omega $\end{document}

, and

\begin{document}$ \omega-\rho^{0} $\end{document}

and provide the amplitudes of the quasi-two-body decay processes. The CP violation for the

\begin{document}$ \bar B_{s} \rightarrow K^{+}K^{-} P $\end{document}

decay process is obvious in the ranges of the three vector meson interferences. Meanwhile, the localized CP violation can be found to compare with the experimental results from the three-body decay process at the LHC in the near future.

Dark matter interactions from an extra U(1) gauge symmetry with kinetic mixing and Higgs charge

Lianyou Shan, Zhao-Huan Yu

2024, 48(1): 013104. doi: 10.1088/1674-1137/ad0f88

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We investigate fermionic dark matter interactions with standard model particles from an additional

\begin{document}$ {{U}}(1)_{{X}} $\end{document}

gauge symmetry, assuming kinetic mixing between the

\begin{document}$ {{U}}(1)_{{X}} $\end{document}

and

\begin{document}$ {{U}}(1)_{{Y}} $\end{document}

gauge fields as well as a nonzero

\begin{document}$ {{U}}(1)_{{X}} $\end{document}

charge of the Higgs doublet. To ensure gauge-invariant Yukawa interactions and the cancellation of gauge anomalies, standard model fermions are assigned Y-sequential

\begin{document}$ {{U}}(1)_{{X}} $\end{document}

charges proportional to the Higgs charge. Although the Higgs charge should be small owing to collider constraints, it is useful to decrease the effective cross section of dark matter scattering off nucleons by two orders of magnitude to easily evade direct detection bounds. After performing numerical scans in the parameter space, we find that the introduction of the Higgs charge can also enhance the dark matter relic density by at least two orders of magnitude. In the case where the resonance effect is important for dark matter freeze-out, when the observed relic density and direct detection constraints are tangled, the Higgs charge can expand physical windows to some extent by relieving the tension between the relic density and direct detection.

Jet modification in absence of QGP-medium: the role of multiparton interactions and color reconnection

Prottoy Das, Abhi Modak, Debjani Banerjee, Rathijit Biswas, Supriya Das, Sanjay K. Ghosh, Sibaji Raha, Sidharth Kumar Prasad

2024, 48(1): 013105. doi: 10.1088/1674-1137/ad0b6c

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Recent studies on high-multiplicity events in small collision systems (proton-proton and proton-lead) have drawn considerable research interest toward the possibility of the formation of partonic medium in such systems. One of the important consequences of the formation of dense partonic medium is the quenching of high-momentum final-state particles, resulting in several experimental observations such as suppression in nuclear modification factor

\begin{document}$R_{\rm AA}$\end{document}

, modification of jet shape observable

\begin{document}$ \rho(r) $\end{document}

and jet fragmentation (

\begin{document}$ z^{\rm ch} $\end{document}

) distributions, etc. In this work, we study

\begin{document}$ \rho(r) $\end{document}

and

\begin{document}$ z^{\rm ch} $\end{document}

for inclusive charged-particle jets in proton-proton (pp) collisions at

\begin{document}$ \sqrt{s} $\end{document}

= 13 TeV using the PYTHIA 8 Monash 2013 Monte Carlo simulation. We show that the color reconnection (CR) and multiparton interaction (MPI) mechanisms in PYTHIA 8 can lead to an increased rate of jet production. We also find that the mechanisms of MPI and CR and change in the gluonic contribution in high-multiplicity events result in significant modification of

\begin{document}$ \rho(r) $\end{document}

and

\begin{document}$ z^{\rm ch} $\end{document}

compared to those in minimum bias events for 10

\begin{document}$ < p_{\rm T,\,jet}^{\rm ch}< $\end{document}

20 GeV/c. We notice a direct connection of

\begin{document}$ \langle N_{\rm MPI}\rangle $\end{document}

and gluonic contribution with the amount of modification in

\begin{document}$ \rho(r) $\end{document}

: the larger the number of MPIs and/or gluonic contribution, the larger the amount of modification of

\begin{document}$ \rho(r) $\end{document}

.

Reactions induced by 30 MeV ³He beam on ⁹Be : cluster transfer reactions

B. A. Urazbekov, T. Issatayev, S. M. Lukyanov, A. Azhibekov, A. S. Denikin, K. Mendibayev, D. M. Janseitov, Yu E. Penionzhkevich, K. A. Kuterbekov, T. K. Zholdybayev

2024, 48(1): 014001. doi: 10.1088/1674-1137/ad0376

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An experiment was conducted for studying the cluster structure of

\begin{document}$ ^9 $\end{document}

Be induced by

\begin{document}$ ^3 $\end{document}

He ions at an energy of 30 MeV. As results of the nuclear reaction ³He + ⁹Be, the differential cross sections for the exit channels – elastic, inelastic, α + ⁸Be, ⁶He + ⁶Be, ⁶Li + ⁶Li, and ⁷Be + ⁵He – were measured. Elastic and inelastic scattering data were treated within both the optical model and coupled channel method. A new set of optical potentials was considered for the elastic scattering. The deformation parameter

\begin{document}$ \delta_2 $\end{document}

was established for the transition

\begin{document}$ 3/2\rightarrow5/2 $\end{document}

. Cluster transfer reactions were analyzed via the coupled reaction channel method. The nuclear reactions with the exit channels ⁶He + ⁶Be, ⁶Li + ⁶Li, and ⁷Be + ⁵He were complemented by two-step transfer mechanisms. The contribution of each reaction mechanism were shown and compared with the findings of other authors.

Elastic scattering and total reaction cross sections of ⁶Li examined via a microscopic continuum discretized coupled-channels model

Wendi Chen, Danyang Pang, Hairui Guo, Tao Ye, Weili Sun, Yangjun Ying

2024, 48(1): 014101. doi: 10.1088/1674-1137/ad0453

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We present a systematic study of ⁶Li elastic scattering and total reaction cross sections at incident energies around the Coulomb barrier within the continuum discretized coupled-channels (CDCC) framework, where ⁶Li is treated in an α+d two-body model. Collisions with ²⁷Al, ⁶⁴Zn, ¹³⁸Ba, and ²⁰⁸Pa are analyzed. The microscopic optical potentials (MOP) based on Skyrme nucleon-nucleon interaction for α and d are adopted in CDCC calculations and satisfactory agreement with the experimental data is obtained without any adjustment on MOPs. For comparison, α and d global phenomenological optical potentials (GOP) are also used in CDCC analysis and a reduction of no less than 50% on the surface imaginary part of deuteron GOP is required for describing the data. In all cases, the ⁶Li breakup effect is significant and provides repulsive correction to the folding model potential. The reduction on the surface imaginary part of GOP of deuteron reveals a strong suppression of the reaction probability of deuteron as a component of ⁶Li when compared with that of a free deuteron. Further investigation is performed by considering the d breakup process equivalently within the dynamic polarization potential approach, and the results show that d behaves in a manner similar to a tightly bound nucleus in ⁶Li induced reactions.

Microscopic shell-model description of irrotational-flow dynamics in ¹⁰²Pd

H. G. Ganev

2024, 48(1): 014102. doi: 10.1088/1674-1137/ad021e

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The structure of the low-lying collective excitations in

\begin{document}$ ^{102} $\end{document}

Pd is examined within the recently proposed microscopic shell-model version of the Bohr-Mottelson (BM) collective model. A good description of the excitation energies of the lowest ground, γ, and β bands, as well as the staggering function between the collective states of the γ band and some other energy-dependent quantities, is obtained. The low-energy intraband and interband quadrupole dynamics is reasonably well described within the present proton-neutron sympletic based shell-model approach without the use of an effective charge and compared with the predictions of nuclear structure models. The obtained results of the present study shed light on the question of the existence of irrotational-flow type quadrupole dynamics, which lies on the ground of the original BM model of quantized vibrations and surface-wave rotations in atomic nuclei.

Bethe-Heitler lepton pair production in the deuteron breakup reaction

Mengchu Cai, Tianbo Liu, Bo-Qiang Ma

2024, 48(1): 014103. doi: 10.1088/1674-1137/ad0375

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We study the lepton pair production via the Bethe-Heitler mechanism in the deuteron breakup reaction. The complete seven-fold differential cross section is calculated with final state interactions taken into account. The deuteron bound state is described by a relativistic covariant deuteron-nucleon vertex. The numerical results indicate that the differential cross section is highly dependent on the lepton's azimuthal angle in regions of small polar angles and exhibits sharp peaks in the distribution over the invariant mass of the generated lepton pair or the two nucleons in the final state. We demonstrate that such a nearly singular feature originates from the collinearity between the produced lepton or antilepton and the incident photon, and it is physically regularized by the lepton mass in our calculation. The final state interaction between the knocked-out nucleon and recoil nucleon redistributes the differential cross section over the missing momentum, with a significant enhancement at a large missing momentum and a suppression in the intermediate region. With a further decomposition of the final state interaction contribution, It is found that the on-shell term dominates the near quasi-elastic region, while the off-shell term dominates the other end. Additionally, we examine the contribution from the interference between the proton amplitude and neutron amplitude, which, as expected, is found negligible even if the proton-neutron rescattering is included. The results of this study can serve as inputs for the analysis and background estimation of multiple exclusive measurements at Jefferson Lab and future electron-ion colliders.

Uncertainties of critical temperatures based on higher-order fluctuations of the largest fragment charge

Erxi Xiao, Xin Lei, Yingge Huang, Yujie Feng, Long Zhu, Jun Su

2024, 48(1): 014104. doi: 10.1088/1674-1137/ad021d

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The new signature of liquid-gas phase transition has been well indicated by the higher-order fluctuations of the largest fragment charge, but the uncertainties of critical temperatures based on this signature have not been revealed. This study extracts the critical temperatures of liquid-gas phase transition in nuclear reactions and investigates their uncertainties. Utilizing the isospin-dependent quantum molecular dynamics model in conjunction with the statistical model GEMINI enables us to describe the dynamical path from the initial to the final state. An isotope thermometer and a quantum fluctuation thermometer are employed to extract the nuclear temperature. The higher-order fluctuations of the largest fragment charge and critical temperatures are studied in ¹²⁴Sn + ¹²⁰Sn collisions ranging from 400 to 1000 MeV/nucleon and ¹²⁴Sn + ^AZ collisions at 600 MeV/nucleon. Observations revealed that the pseudo-critical point is robustly indicated by the higher-order fluctuations of the largest fragment charge. The critical temperatures extracted by the isotope thermometer are relatively consistent, with an uncertainty of 15%, while those obtained by the quantum fluctuation thermometer are heavily influenced by the incident energy and mass number of target nuclei. The excitation energy

\begin{document}$ E^{*} $\end{document}

and bound charge

\begin{document}$Z_{\rm bound}$\end{document}

are used for event-sorting. These two ensembles represent the statistical properties of the initial and final states of the system, respectively. The initial-final correlations of statistical properties might lead to two phenomena. First, the size distribution of the largest fragment at the pseudo-critical point based on the

\begin{document}$Z_{\rm bound}$\end{document}

ensemble is wide, while that based on

\begin{document}$ E^{*} $\end{document}

ensemble exhibits bimodality, which is a typical characteristic in the liquid-gas coexistence of a finite system. Second, the temperature at the pseudo-critical point based on the

\begin{document}$Z_{\rm bound}$\end{document}

ensemble is higher than that based on the

\begin{document}$ E^{*} $\end{document}

ensemble. Furthermore, the projectile-like system exhibits a significant dynamical effect in its evolution path from the initial to final state, closely associated with the fluctuation of critical temperature.

Theoretical predictions on cluster radioactivity of superheavy nuclei with Z = 119, 120

Jiejie Liu, Zhen Wang, Hantao Zhang, Zhongzhou Ren

2024, 48(1): 014105. doi: 10.1088/1674-1137/ad0827

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In this study, we investigate the cluster radioactivity (CR) of new superheavy elements with

\begin{document}$ Z=119 $\end{document}

and 120 based on two successful theoretical methods with modified parameters: the density-dependent cluster model (DDCM) and unified decay formula (UDF). First, we employ the DDCM and UDF to accurately reproduce the experimental half-lives of cluster emissions, which demonstrates the high reliability of our theoretical methods. Then, we systematically predict the probable cluster modes of ^293-311119 and ^293-302120 as well as their corresponding decay energies and half-lives. The half-lives of cluster decay derived from the DDCM are consistent with those from the UDF. Therefore, our results reveal that the cluster emission of ⁸Be, emitted from the

\begin{document}$ Z= $\end{document}

119 and 120 isotopic chains, exhibits the minimum half-life for cluster emission, and hence, ⁸Be emission is considered the most probable cluster decay mode. Moreover, we explore the competition between α decay and CR and find that α decay may be the dominant decay mode against CR. Furthermore, the good linear relationship between the decay energy and the number of α particles within the emitted cluster is extended to the range of superheavy nuclei (SHN). We anticipate that our theoretical predictions for CR will provide valuable references for the experimental synthesis of new SHN.

Further monopole effects in neutron-rich Sb isotopes

Han-Kui Wang, Yu-Le Sun, Bo-Wen Jiang, Fan-Fei Zeng, Min-Liang Liu

2024, 48(1): 014106. doi: 10.1088/1674-1137/ad0b6b

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The level spectra of neutron-rich Sb isotopes have been investigated within a shell-model space containing cross-shell excitations and the intruder orbit

\begin{document}$ i_{13/2} $\end{document}

. High-spin levels (27/2

\begin{document}$ ^- $\end{document}

) and (29/2

\begin{document}$ ^- $\end{document}

) in

\begin{document}$ ^{135} $\end{document}

Sb are taken over by the monopole effect induced by orbit

\begin{document}$ i_{13/2} $\end{document}

. The ground state and excited levels in

\begin{document}$ ^{136} $\end{document}

Sb are well improved by considering the monopole correction between neutron orbits

\begin{document}$ f_{7/2} $\end{document}

and

\begin{document}$ h_{9/2} $\end{document}

. The energy shrinking of the first excited state 5/2

\begin{document}$ ^+ $\end{document}

in

\begin{document}$ ^{135,137} $\end{document}

Sb isotopes is explained by the

\begin{document}$ \pi d_{5/2} $\end{document}

shift due to the attractive

\begin{document}$ \pi d_{5/2} \nu f_{7/2} $\end{document}

monopole interaction when increasingly more neutrons occupy orbit

\begin{document}$ f_{7/2} $\end{document}

. The ground state of

\begin{document}$ ^{139} $\end{document}

Sb is predicted as 5/2

\begin{document}$ ^+ $\end{document}

owing to the shrinking of the 5/2

\begin{document}$ ^+ $\end{document}

states in Sb isotopes that causes ground state inversion when N = 88. Further monopole effects extend the applicable range of the present Hamiltonian to nuclei with more neutrons above the N = 82 shell. This Hamiltonian will be public, and researchers are encouraged to contact the authors.

Evolution of N = 20, 28, 50 shell closures in the 20 ≤ Z ≤ 30 region in deformed relativistic Hartree-Bogoliubov theory in continuum

Ru-You Zheng, Xiang-Xiang Sun, Guo-fang Shen, Li-Sheng Geng

2024, 48(1): 014107. doi: 10.1088/1674-1137/ad0bf2

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Magicity, or shell closure, plays an important role in our understanding of complex nuclear phenomena. In this work, we employ one of the state-of-the-art density functional theories, the deformed relativistic Hartree-Bogoliubov theory in continuum (DRHBc) with the density functional PC-PK1, to investigate the evolution of the

\begin{document}$ N=20,28,50 $\end{document}

shell closures in the

\begin{document}$ 20 \leqslant Z \leqslant 30 $\end{document}

region. We show how these three conventional shell closures evolve from the proton drip line to the neutron drip line by studying the charge radii, two-neutron separation energies, two-neutron gaps, quadrupole deformations, and single-particle levels. In particular, we find that in the

\begin{document}$ 21 \leqslant Z \leqslant 27 $\end{document}

region, the

\begin{document}$ N=50 $\end{document}

shell closure disappears or becomes quenched, mainly due to the deformation effects. Similarly, both experimental data and theoretical predictions indicate that the

\begin{document}$ N=28 $\end{document}

shell closure disappears in the Mn isotopic chain, mainly due to the deformation effects. The DRHBc theory predicts the existence of the

\begin{document}$ N=20 $\end{document}

shell closure in the Ca, Sc, and Ti isotopic chains, but the existing data for the Ti isotopes suggest the contrary, and therefore further research is needed.

Gauss-Bonnet solution with a cloud of strings in de Sitter and anti-de Sitter space

Wenxi Zhai, Xiangdong Zhang

2024, 48(1): 015101. doi: 10.1088/1674-1137/ad010d

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In this study, we investigate exact spherically symmetric Gauss-Bonnet black hole solutions surrounded by a cloud of string fluid with the cosmological constant in

\begin{document}$ D>4 $\end{document}

dimensions. Both charged and uncharged cases are considered. We focus on the de Sitter solutions in the main text and provide the anti-de Sitter solutions in the appendix. We analyze the features of event horizons and thermodynamic properties of the black hole solutions. The mass, Hawking temperature, thermal stability, and phase transitions are discussed. Moreover, the equation of state and critical phenomena associated with these solutions are explored.

Holographic Schwinger effect in spinning black hole backgrounds

Yi-Ze Cai, Zi-Qiang Zhang

2024, 48(1): 015102. doi: 10.1088/1674-1137/ad061f

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We perform a potential analysis for the holographic Schwinger effect in spinning Myers-Perry black holes. We compute the potential between the produced pair by evaluating the classical action of a string attached on a probe D3-brane at an intermediate position in the AdS bulk. We find that increasing the angular momentum reduces the potential barrier, thus enhancing the Schwinger effect, consistent with previous findings obtained via the local Lorentz transformation. In particular, these effects are more visible for the particle pair lying in the transversal plane compared with that along the longitudinal orientation. In addition, we discuss how the Schwinger effect changes with the shear viscosity to entropy density ratio at strong coupling under the influence of angular momentum.

Thermal analysis and Joule-Thomson expansion of black hole exhibiting metric-affine gravity

Muhammad Yasir, Tiecheng Xia, Faisal Javed, G. Mustafa

2024, 48(1): 015103. doi: 10.1088/1674-1137/ad0962

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This study examines a recently hypothesized black hole, which is a perfect solution of metric-affine gravity with a positive cosmological constant, and its thermodynamic features as well as the Joule-Thomson expansion. We develop some thermodynamical quantities, such as volume, Gibbs free energy, and heat capacity, using the entropy and Hawking temperature. We also examine the first law of thermodynamics and thermal fluctuations, which might eliminate certain black hole instabilities. In this regard, a phase transition from unstable to stable is conceivable when the first law order corrections are present. In addition, we study the efficiency of this system as a heat engine and the effect of metric-affine gravity for the physical parameters

\begin{document}$ q_e $\end{document}

,

\begin{document}$ q_m $\end{document}

,

\begin{document}$\kappa_{s}$\end{document}

,

\begin{document}$\kappa_{d}$\end{document}

, and

\begin{document}$ \kappa_{\mathrm{sh}} $\end{document}

. Further, we study the Joule-Thomson coefficient and inversion temperature, and observe the isenthalpic curves in the

\begin{document}$ T_i -P_i $\end{document}

plane. In metric-affine gravity, a comparison is made between a van der Waals fluid and a black hole to study their similarities and differences.

Strong gravitational lensing of blazar gamma-radiation and intergalactic magnetic fields

Yu. N. Eroshenko

2024, 48(1): 015104. doi: 10.1088/1674-1137/ad0b6a

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The influence of intergalactic magnetic fields on the strong gravitational lensing of blazar secondary gamma radiation is discussed. Currently, two cases of strong gravitational lensing of blazar gamma-radiation are known, where radiation is deflected by galaxies on the line of sight between the blazars and Earth. The magnetic field can affect the movements of electron-positron pairs generated by primary radiation, thereby changing the directions of secondary gamma radiation. It modifies the equation of the gravitational lens and leads to the dependence of the observed signal in the secondary gamma radiation on the energy of photons and magnetic field. Accordingly, it is possible, in principle, to estimate the intergalactic magnetic fields from the time delay of signals, from the angular position of images (for future high-resolution gamma-ray telescopes) or from the shape of the observed energy spectrum. This method is demonstrated by the example of the blazar B0218+357. In this case, however, it is not possible to obtain useful constraints due to the large distances to the blazar and lens galaxy. The result is only a lower limit on the magnetic field

\begin{document}$ B>2\times10^{-17} $\end{document}

G, which is weaker than other existing constraints. However, future discoveries of lensed blazars may provide more favorable opportunities for measuring the magnetic fields, especially with the help of a new generation of gamma-ray telescopes such as e-ASTROGAM, GECAM, and SVOM as well as future gamma-ray telescopes with a high angular resolution,

\begin{document}$ \sim0.1''$\end{document}

.

2024 Vol. 48, No. 1