2023 Vol. 47, No. 9

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2023-9 Contents
2023, 47(9): 1-2.
Search for the doubly heavy baryon ${\boldsymbol\varXi_{\boldsymbol {bc}}^{\bf +}}$ decaying to ${\boldsymbol J/\boldsymbol\psi \boldsymbol\varXi_{\boldsymbol c}^{\bf +}}$
LHCb Collaboration, R. Aaij, A.S.W. Abdelmotteleb, C. Abellan Beteta, F. Abudinén, T. Ackernley, B. Adeva, M. Adinolfi, H. Afsharnia, C. Agapopoulou, C.A. Aidala, S. Aiola, Z. Ajaltouni, S. Akar, K. Akiba, J. Albrecht, F. Alessio, M. Alexander, A. Alfonso Albero, Z. Aliouche, P. Alvarez Cartelle, S. Amato, J.L. Amey, Y. Amhis, L. An, L. Anderlini, M. Andersson, A. Andreianov, M. Andreotti, D. Andreou, D. Ao, F. Archilli, A. Artamonov, M. Artuso, E. Aslanides, M. Atzeni, B. Audurier, S. Bachmann, M. Bachmayer, J.J. Back, A. Bailly-reyre, P. Baladron Rodriguez, V. Balagura, W. Baldini, J. Baptista de Souza Leite, M. Barbetti, R.J. Barlow, S. Barsuk, W. Barter, M. Bartolini, F. Baryshnikov, J.M. Basels, G. Bassi, B. Batsukh, A. Battig, A. Bay, A. Beck, M. Becker, F. Bedeschi, I.B. Bediaga, A. Beiter, V. Belavin, S. Belin, V. Bellee, K. Belous, I. Belov, I. Belyaev, G. Bencivenni, E. Ben-Haim, A. Berezhnoy, R. Bernet, D. Berninghoff, H.C. Bernstein, C. Bertella, A. Bertolin, C. Betancourt, F. Betti, Ia. Bezshyik
2023, 47(9): 093001. doi: 10.1088/1674-1137/ace9c8
A first search for the \begin{document}$ \varXi_{bc}^+ \to J/\psi \varXi_c^+ $\end{document} decay is performed by the LHCb experiment with a data sample of proton-proton collisions, corresponding to an integrated luminosity of 9 fb−1 recorded at centre-of-mass energies of 7, 8, and 13 TeV. Two peaking structures are seen with a local (global) significance of \begin{document}$ 4.3\,(2.8) $\end{document} and \begin{document}$ 4.1\,(2.4) $\end{document} standard deviations at masses of 6571 and 6694 MeV/\begin{document}$c^2$\end{document}, respectively. Upper limits are set on the \begin{document}$\varXi_{bc}^+$\end{document} baryon production cross-section times the branching fraction relative to that of the \begin{document}$B_{c}^{+} \rightarrow J / \psi D_{s}^{+}$\end{document} decay at centre-of-mass energies of 8 and 13 TeV, in the \begin{document}$ \varXi_{bc}^+ $\end{document} and in the \begin{document}$ B_{c}^{+} $\end{document} rapidity and transverse-momentum ranges from 2.0 to 4.5 and 0 to \begin{document}$ 20\;{\rm{GeV}} /{c} $\end{document}, respectively. Upper limits are presented as a function of the \begin{document}$ \varXi_{bc}^+ $\end{document} mass and lifetime.
Search for the rare decays ${\boldsymbol W^{+} \rightarrow \boldsymbol D_s^{+} \gamma}$ and ${\boldsymbol Z \rightarrow \boldsymbol D^0 \gamma}$ at LHCb
LHCb Collaboration, R. Aaij, A.S.W. Abdelmotteleb, C. Abellan Beteta, F. Abudinén, T. Ackernley, B. Adeva, M. Adinolfi, P. Adlarson, H. Afsharnia, C. Agapopoulou, C.A. Aidala, Z. Ajaltouni, S. Akar, K. Akiba, J. Albrecht, F. Alessio, M. Alexander, A. Alfonso Albero, Z. Aliouche, P. Alvarez Cartelle, R. Amalric, S. Amato, J.L. Amey, Y. Amhis, L. An, L. Anderlini, M. Andersson, A. Andreianov, M. Andreotti, D. Andreou, D. Ao, F. Archilli, A. Artamonov, M. Artuso, E. Aslanides, M. Atzeni, B. Audurier, S. Bachmann, M. Bachmayer, J.J. Back, A. Bailly-reyre, P. Baladron Rodriguez, V. Balagura, W. Baldini, J. Baptista de Souza Leite, M. Barbetti, R.J. Barlow, S. Barsuk, W. Barter, M. Bartolini, F. Baryshnikov, J.M. Basels, G. Bassi, B. Batsukh, A. Battig, A. Bay, A. Beck, M. Becker, F. Bedeschi, I.B. Bediaga, A. Beiter, V. Belavin, S. Belin, V. Bellee, K. Belous, I. Belov, I. Belyaev, G. Benane, G. Bencivenni, E. Ben-Haim, A. Berezhnoy, R. Bernet, S. Bernet Andres, D. Berninghoff, H.C. Bernstein, C. Bertella, A. Ber
2023, 47(9): 093002. doi: 10.1088/1674-1137/aceae9
A search for the rare decays \begin{document}$W^{+} \rightarrow D_s^{+} \gamma$\end{document} and \begin{document}$Z \rightarrow D^0 \gamma$\end{document} is performed using proton-proton collision data collected by the LHCb experiment at a centre-of-mass energy of 13\begin{document}$\mathrm{TeV}$\end{document}, corresponding to an integrated luminosity of 2.0\begin{document}$\mathrm{fb}^{-1}$\end{document}. No significant signal is observed for either decay mode and upper limits on their branching fractions are set using \begin{document}$W^{+} \rightarrow \mu^{+} \nu$\end{document} and \begin{document}$Z \rightarrow \mu^{+} \mu^{-}$\end{document} decays as normalization channels. The upper limits are \begin{document}${{{6.5\times 10^{-4}}}}$\end{document} and \begin{document}${{{2.1\times 10^{-3}}}}$\end{document} at 95% confidence level for the \begin{document}$W^{+} \rightarrow D_s^{+} \gamma$\end{document} and \begin{document}$Z \rightarrow D^0 \gamma$\end{document} decay modes, respectively. This is the first reported search for the \begin{document}$Z \rightarrow D^0 \gamma$\end{document} decay, while the upper limit on the \begin{document}$W^{+} \rightarrow D_s^{+} \gamma$\end{document} branching fraction improves upon the previous best limit.
Spin density matrix for ${ \bf\Omega^{-}} $ and its polarization alignment in ${\boldsymbol\psi\bf(3686)\rightarrow \Omega^{-}\bar{\Omega}^{+}}$
Zhe Zhang, Jiao-Jiao Song
2023, 47(9): 093101. doi: 10.1088/1674-1137/ace17e
We investigate the spin density matrix of \begin{document}$ \Omega^{-} $\end{document} in the Cartesian coordinate system of baryon-antibaryon pairs produced in \begin{document}$ e^{+}e^{-} $\end{document} annihilation. Using the helicity formalism of Jacob and Wick, we derive the expression for the spin-3/2 density matrices. Our analysis is based on the angular distribution of the process \begin{document}$e^{+}e^{-}\rightarrow \psi(3686)\rightarrow $\end{document}\begin{document}$ \Omega^{-}\bar{\Omega}^{+}$\end{document} in the BESIII experiment. By decomposing the polarization state of \begin{document}$ \Omega^{-} $\end{document} particles along different coordinate axes, we examine the polarization dependence of the cross-section. Our results demonstrate that \begin{document}$ \Omega^{-} $\end{document} particles exhibit varying degrees of tensor polarization along the x-, y-, and z-axes, as well as weak vector polarization and rank-3 tensor polarization along the y-axis. To the best of our knowledge, this is the first study to calculate the polarization dependence of the cross-section distributions for the annihilation process \begin{document}$ e^+e^-\rightarrow \Omega^-\bar{\Omega}^+ $\end{document}. Our theoretical predictions are in good agreement with the experimental measurements.
Nucleons as modified Ising models
Shu-Man Hu, Yin-Sen Luan, Ji Xu
2023, 47(9): 093102. doi: 10.1088/1674-1137/ace312
In this paper, we propose a map that connects nucleons bound in nuclei and Ising spins in the Ising model. This proposal is based on the fact that the description of states of nucleons and Ising spins could share the same type of observables. We present a nuclear model corresponding to an explicit modified Ising model and qualitatively confirm the correctness of this map with a simulation on a two-dimensional square lattice. This map can help us understand the profound connections between different physical systems.
Phenomenological study of ${{{J/\psi\to\Xi^0(\Lambda \pi^0) {\bar{\Xi}}^0({\bar{\Lambda}} \gamma)}}}$ decays
Peng-Cheng Hong, Rong-Gang Ping, Wei-Min Song, He Li, Xiao-Rong Zhou
2023, 47(9): 093103. doi: 10.1088/1674-1137/ace354
The measurement of decay parameters is one of the important goals of particle physics experiments, and the measurement serves as a probe to search for evidence of CP violation in baryonic decays. The experimental results will aid in advancing existing theoretical research and establishing new experimental objectives. In this study, we formulate the asymmetric parameters that characterize parity violation, and then derive formulas for the measurement of CP violation. The formulae for the joint angular distribution of the full decay chain as well as the polarization observable of \begin{document}$ \Xi ^ 0 $\end{document}, \begin{document}$ \bar { \Xi } ^ 0 $\end{document}, Λ, and \begin{document}$ \bar { \Lambda } $\end{document} are also provided for experiments. Lastly, we evaluated the sensitivity of two asymmetric parameters: \begin{document}$ \alpha _ { \Xi ^ 0 \to \Lambda \pi ^ 0 } $\end{document} (abbreviated as \begin{document}$ \alpha _ { \Xi ^ 0 } $\end{document}) and \begin{document}$\alpha _ { \bar { \Xi } ^ 0 \to \bar { \Lambda } \gamma }$\end{document} (abbreviated as \begin{document}$ \alpha_ {{\bar{\Xi}}^0 } $\end{document}) for future experimental measurements.
Testing type II seesaw leptogenesis at the LHC
Chengcheng Han, Zhanhong Lei, Weihao Liao
2023, 47(9): 093104. doi: 10.1088/1674-1137/ace708
Type II seesaw leptogenesis simultaneously explains the origin of neutrino masses, the baryon asymmetry of our universe, and inflation. The Large Hadron Collider (LHC) provides an opportunity to directly test type II seesaw leptogenesis by looking for the predicted triplet Higgs. In this paper, we perform an analysis of the detection prospect for the triplet Higgs at the LHC through multi-electron channels. We find that due to the contribution of the \begin{document}$pp\to H^{\pm \pm }H^{\mp }$\end{document} process, the sensitivity of multi-electron channels searching for doubly-charged Higgs pair production can be improved. We also investigate the \begin{document}$3e+ {E}^{\rm miss}_{T}$\end{document} signals to probe \begin{document}$pp\to H^{\pm \pm }H^{\mp }$\end{document} production and find that the future high luminosity LHC could probe a triplet Higgs around 1.2 TeV at the \begin{document}$2\sigma$\end{document} level.
J/ψ pair hadroproduction at next-to-leading order in nonrelativistic-QCD at CMS
Li-Ping Sun
2023, 47(9): 093105. doi: 10.1088/1674-1137/ace521
We perform a complete study of \begin{document}$ J/\psi $\end{document} pair hadroproduction at next-to-leading order (NLO) in the nonrelativstic-QCD (NRQCD) framework with the \begin{document}$ c\bar{c} $\end{document} pair either in the \begin{document}$ {}^{3}S_1^{[1]} $\end{document} or \begin{document}$ {}^{1}S_0^{[8]} $\end{document} fock states. It is found that the \begin{document}$ {}^{1}S_0^{[8]} $\end{document}channel contribution at NLO is essential. Our results indicate that for the CMS, the NRQCD predictions cannot describe the experimental data at all, and the total cross section predicted via NRQCD is smaller than the experimental data by an order of magnitude. Therefore, new mechanisms are needed to understand the CMS data for \begin{document}$ J/\psi $\end{document} pair production.
The Λ-type P-wave bottom baryon states via the QCD sum rules
Qi Xin, Zhi-Gang Wang, Fei Lü
2023, 47(9): 093106. doi: 10.1088/1674-1137/ace81f
Our study focuses on the Λ-type P-wave bottom baryon states with spin-parity \begin{document}$J^P={1}/{2}^-$\end{document}, \begin{document}${3}/{2}^-$\end{document}. We introduce an explicit P-wave between the two light quarks in the interpolating currents (these light quarks are antisymmetric in the flavor space, thus giving rise to the designation of Λ-type baryon) to investigate the \begin{document}$\Lambda_b$\end{document} and \begin{document}$\Xi_b$\end{document} states within the framework of the full QCD sum rules. The predicted masses show that \begin{document}$\Xi_b(6087)$\end{document} and \begin{document}$\Xi_b(6095/6100)$\end{document} could be the P-wave bottom-strange baryon states with spin-parity \begin{document}$J^P={1}/{2}^-$\end{document} and \begin{document}${3}/{2}^-$\end{document}, respectively; meanwhile, \begin{document}$\Lambda_b(5912)$\end{document} and \begin{document}$\Lambda_b(5920)$\end{document} could be the P-wave bottom baryon states with spin-parity \begin{document}$J^P={1}/{2}^-$\end{document} and \begin{document}${3}/{2}^-$\end{document}, respectively. Moreover, \begin{document}$\Lambda_b(5920)$\end{document} and \begin{document}$\Xi_b(6095/6100)$\end{document} may have two remarkable under-structures or Fock components at least.
Measurement of the (n, 2n) reaction cross-sections of iodine and cesium induced by D-T neutrons with covariance analysis
Changlin Lan, Yuxing Niu, Yuting Wei, Fangxiao Lu, Xianlin Yang, Ruirui Xu, Yue Zhang, Yujie Ge, Jiahao Wang, Gong Jiang
2023, 47(9): 094001. doi: 10.1088/1674-1137/ace313
The cross-sections of the 127I (n, 2n) 126I and 133Cs (n, 2n) 132Cs reactions at neutron energies of 13.83 ± 0.05, 14.33 ± 0.10, and 14.79 ± 0.10 MeV were measured relative to the 93Nb (n, 2n) 92mNb reaction using the activation technique in combination with off-line γ-ray spectrometry. A neutron beam was generated from the T (d, n) 4He reaction using the K-400 neutron generator at the China Academy of Engineering Physics. Considering the correlations between different attributes, detailed uncertainty propagation was performed using covariance analysis, and the cross-sections were reported with their uncertainties and correlation matrix. The uncertainty of the measurement cross-sections ranged from 4.84 to 5.90%, which is lower than previous experimental data. Furthermore, the theoretical excitation functions of the 127I (n, 2n) 126I and 133Cs (n, 2n) 132Cs reactions were calculated using the TALYS-1.95 and EMPIRE-3.2.3 codes. Then, the experimentally determined cross-sections were analyzed by comparing them with literature data available in the EXFOR database and evaluated nuclear data in the ENDF/B-VIII.0, JEFF-3.3, JENDL-5, BROND-3.1, CENDL-3.2, and TENDL-2021 databases. Compared with the values previously reported in the 13.8-14.8 MeV energy region, the precision of the results obtained in this study was greatly improved. The current experimental results with thorough uncertainties and covariance information are critical for verifying the reliability of the theoretical model and improving the quality of the nuclear database.
Investigation of the relationship between mirror proton radii and neutron-skin thickness
Meng-Qi Ding, Ping Su, De-Qing Fang, Si-Min Wang
2023, 47(9): 094101. doi: 10.1088/1674-1137/ace680
Through systematic investigations using the axially deformed solutions of the Skyrme-Hartree-Fock-Bogoliubov equations with 132 sets of Skyrme interaction parameters, it is confirmed that the neutron-skin thickness (\begin{document}$ S_{n} $\end{document}) of a neutron-rich nucleus is proportional to the difference between the proton radii of mirror nuclei (\begin{document}$ R_{p}^{\rm mir} $\end{document}). This indicates that \begin{document}$ S_{n} $\end{document} may be deduced from \begin{document}$ R_{p}^{\rm mir} $\end{document}. Compared with the results of the Skyrme-Hartree-Fock model, pairing effects are found to enhance the correlation for most mirror pairs, whereas deformation effects may weaken the correlation. Furthermore, the correlation between \begin{document}$ S_{n} $\end{document} and \begin{document}$ R_{p}^{\rm mir} $\end{document} is studied for isotones with \begin{document}$ N=20 $\end{document} and \begin{document}$ N=28 $\end{document}, which reveals a stronger linear correlation with increasing \begin{document}$ |N-Z| $\end{document}. This result demonstrates that it is possible to extract the neutron-skin thickness of an unstable nucleus from the proton radii difference of the mirror nuclei of its isotones.
Multi-skyrmion states in the Skyrme model with a false vacuum potential
Jun-Shuai Wang, Yong-Liang Ma
2023, 47(9): 094102. doi: 10.1088/1674-1137/ace9c7
We study multi-skyrmion states using the Skyrme model with a false vacuum potential up to baryon number \begin{document}$ B=8 $\end{document} using the product ansatz. It is found that both the false and true vacuum potentials can result in a cluster structure for the multi-skyrmion states. We also analyze the effect of explicit chiral breaking on the masses and contour surfaces of the baryon number density of the multi-skyrmion states.
Systematic calculations of cluster radioactivity half-lives with a screened electrostatic barrier
Xiao Liu, Jie-Dong Jiang, Lin-Jing Qi, Yang-Yang Xu, Xi-Jun Wu, Xiao-Hua Li
2023, 47(9): 094103. doi: 10.1088/1674-1137/ace351
In this study, based on Wentzel-Kramers-Brillouin theory, we systematically investigate the cluster radioactivity half-lives of 22 nuclei ranging from \begin{document}$ ^{221} {{\rm{Fr}}}$\end{document} to \begin{document}$^{242} {{\rm{Cm }}}$\end{document} using a phenomenological model that considers the screened electrostatic effect of the Coulomb potential. In this model, there are two adjustable parameters, t and g, which are related to the screened electrostatic barrier and the strength of the spectroscopic factor, respectively. The calculated results indicate that this model can effectively reproduce the experimental data, with a corresponding root-mean-square deviation of 0.660. In addition, we extend this model to predict the half-lives of possible cluster radioactive candidates whose cluster radioactivities are energetically allowed or observed but not yet quantified in the evaluated nuclear properties table NUBASE2020. The predicted results are consistent with those obtained using other theoretical models and/or empirical formulas, including the universal decay law proposed by Qi et al. [Phys. Rev. C 80, 044326 (2009)], a semi-empirical model for both α decay and cluster radioactivity proposed by Santhosh et al. [J. Phys. G 35, 085102 (2008)], and a unified formula for the half-lives of α decay and cluster radioactivity proposed by Ni et al. [Phys. Rev. C 78, 044310 (2008)].
Prospects for the detection rate of very-high-energy γ-ray emissions from short γ-ray bursts with the HADAR experiment
Qi-Ling Chen, Pei-Jin Hu, Jing-Jing Su, Ming-Ming Kang, Yi-Qing Guo, Tian-Lu Chen, Dan-Zeng Luo-Bu, Yu-fan Fan, You-Liang Feng, Qi Gao, Quan-Bu Gou, Hong-Bo Hu, Hai-Jin Li, Cheng Liu, Mao-Yuan Liu, Wei Liu, Xiang-Li Qian, Bing-Qiang Qiao, Hui-Ying Sun, Xu Wang, Zhen Wang, Guang-Guang Xin, Yu-Hua Yao, Qiang Yuan, Yi Zhang, Bing Zhao
2023, 47(9): 095001. doi: 10.1088/1674-1137/ace3ac
The observation of short gamma ray bursts (SGRBs) in the TeV energy range plays an important role in understanding the radiation mechanism and probing potential new physics, such as Lorentz invariance violation (LIV). However, no SGRBs have been observed in this energy range owing to the short duration of SGRBs and the weakness of current experiments. New experiments with new technology are required to detect the very high energy (VHE) emission of SGRBs. In this study, we simulate the VHE γ-ray emissions from SGRBs and calculate the annual detection rate with the High Altitude Detection of Astronomical Radiation (HADAR) experiment. First, a set of pseudo-SGRB samples is generated and checked using the observations of the Fermi-GBM, Fermi-LAT, and Swift-BAT measurements. The annual detection rate is calculated from these SGRB samples based on the performance of the HADAR instrument. As a result, the HADAR experiment can detect 0.5 SGRBs per year if the spectral break-off of γ-rays caused by the internal absorption and Klein-Nishina (KN) effect is larger than 100 GeV. For a GRB090510-like GRB in HADAR's view, it should be possible to detect approximately 2000 photons considering the internal absorption and KN effect. With a time delay assumption due to LIV effects, a simulated light curve of GRB090510 has evident energy dependence. We hope that the HADAR experiment can perform SGRB observations and test our calculations in the future.
Freeze-in dark matter in EDGES 21-cm signal
Shengyu Wu, Shuai Xu, Sibo Zheng
2023, 47(9): 095101. doi: 10.1088/1674-1137/ace17f
The first measurement of the temperature of the hydrogen 21-cm signal reported by EDGES strongly favors the Coulomb-like interaction between freeze-in dark matter and baryon fluid. We investigate such dark matter in both the one- and two-component context with the light force carrier(s) essential for the Coulomb-like interaction being other than photons. Using a conversion of cross sections used by relevant experiments and Boltzmann equations to encode the effects of the dark matter-baryon interaction, we show that both cases are robustly excluded by the stringent stellar cooling bounds in the sub-GeV dark matter mass range. The exclusion of the one-component case applies to simplified freeze-in dark matter with the light force carrier as dark photons, gauged \begin{document}$ B-L $\end{document}, \begin{document}$ L_{e}-L_{\mu} $\end{document},\begin{document}$ L_{e}-L_{\tau} $\end{document}, or axion-like particles, whereas the exclusion of the two-component case applies to simplified freeze-in dark matter with the two light force carriers as two axion-like particles coupled to standard model quarks and leptons.
Two non-perturbative α' or loop corrected string cosmological solutions
Li Song, Deyou Chen
2023, 47(9): 095102. doi: 10.1088/1674-1137/acddd5
In this paper, we present two non-perturbative string cosmological solutions without curvature singularities for the bosonic gravi-dilaton system. These solutions are general in that they can straightforwardly match the perturbative solution to arbitrarily high orders in the perturbative region. The first solution includes non-perturbative \begin{document}$ \alpha' $\end{document} corrections based on Hohm-Zwiebach action. We then use the simple phenomenological map between the \begin{document}$ \alpha^{\prime} $\end{document} and loop corrected theories in string cosmology to construct a non-perturbative loop corrected non-singular solution. Both solutions are non-singular everywhere. Therefore, the pre- and post-big-bangs are smoothly connected by these solutions.
Strange quark mass (ms) dependent model of anisotropic strange quark star
A. Hakim, K.B. Goswami, P.K. Chattopadhyay
2023, 47(9): 095103. doi: 10.1088/1674-1137/acddd6
This article presents the configuration of strange quark stars in hydrostatic equilibrium considering the Vaidya-Tikekar metric ansatz. The interior of such stars comprises strange quark matter (henceforth SQM), whose equation of state (\begin{document}$henceforth~EoS$\end{document}) is described by the MIT EoS \begin{document}$p=\dfrac{1}{3}(\rho-4B)$\end{document}, where B is the difference between perturbative and non-perturbative vacuum. We have included the mass of the strange quark \begin{document}$(m_s)$\end{document} into the EoS and studied its effect on the overall properties of the strange quark star in this work. It is observed that the maximum mass reaches its highest value when \begin{document}$m_s=0$\end{document}. We have evaluated the range of the maximum mass of the strange quark star by solving the TOV equation for \begin{document}$57.55 < B < 91.54~\rm MeV/fm^3$\end{document} necessary for stable strange quark matter at a zero external pressure condition with respect to neutrons. Maximum mass lies within the range of \begin{document}$2.01$\end{document} to \begin{document}$1.60~M_{\odot}$\end{document} when B ranges from \begin{document}$57.55$\end{document} to \begin{document}$91.54~\rm MeV/fm^3$\end{document} and \begin{document}$m_s=0$\end{document}. It is noted that the maximum mass decreases with an increase in \begin{document}$m_s$\end{document}. Our model is found suitable for describing the mass of pulsars such as PSR J1614-2230 and Vela X-1 and the secondary objects in the GW170817 event. The model is also useful in predicting the radius of the recently observed pulsars PSR J0030+0451, PSR J0740+6620, and PSR J0952-0607 and the secondary objects in the GW170817 and GW190814 events. Our model is found to be stable with respect to all stability criteria of the stellar configurations and is also stable with respect to small perturbations.
Thin-shell gravastar model in f(Q, T) gravity
Sneha Pradhan, Debasmita Mohanty, P.K. Sahoo
2023, 47(9): 095104. doi: 10.1088/1674-1137/ace311
In the last few decades, gravastars have been proposed as an alternative to black holes. The stability of a gravastar has been examined in many modified theories of gravity along with Einstein's GR. The \begin{document}$ f(Q, T) $\end{document} gravity, a successfully modified theory of gravity for describing the current accelerated expansion of the universe, has been used in this study to examine gravastar in different aspects. According to Mazur and Mottola [Proc. Natl. Acad. Sci. 101, 9545 (2004); Gravitational condensate stars: An alternative to black holes, I12-011, (2002)], a gravastar has three regions with three different equations of state. In this study, we examined the interior of a gravastar by considering \begin{document}$ p=-\rho $\end{document} EoS to describe the dark sector for the interior region. The next region is a thin shell of ultrarelativistic stiff fluid, in which we investigated several physical properties, including proper length, energy, entropy, and surface energy density. Additionally, we examined the surface redshift and speed of sound to check the potential stability of our proposed thin-shell gravastar model. Furthermore, we used the entropy maximization technique to verify the stability of the gravastar model. A gravastar's outer region is a complete vacuum described by exterior Schwarzschild geometry. Finally, we presented a stable gravastar model, which is singularity-free and devoid of any incompleteness in classical black hole theory.
Restricted phase space thermodynamics of charged AdS black holes in conformal gravity
Xiangqing Kong, Zhiqiang Zhang, Liu Zhao
2023, 47(9): 095105. doi: 10.1088/1674-1137/ace9c2
The thermodynamics of charged spherically symmetric AdS black holes in conformal gravity is revisited using the recently proposed restricted phase space (RPS) formalism. This formalism avoids all the bizarreness arising in the extended phase space formalism for this model. It is found that the charged AdS black holes in this model may belong to a new universality class that is different from all previously studied cases under the RPS formalism. Besides the distinguished isocharge \begin{document}$ T-S $\end{document} and isothermal \begin{document}$ \Phi-Q_e $\end{document} behaviors, the absence of the Hawking-Page transition is another notable feature. However, in the high temperature limit, the thermodynamic behavior of the present model becomes exactly the same as that of the Einstein gravity and black hole scan models, which adds further evidence for the universality of the recently reported correspondence between high temperature AdS black holes and low temperature quantum phonon gases in nonmetallic crystals.