2023 Vol. 47, No. 2

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2023-2 Contents
2023, 47(2): 1-2.
Observations of the Cabibbo-Suppressed decays ${\boldsymbol \Lambda_{\boldsymbol c}^{\bf +}\to\boldsymbol n\pi^{\bf +}\boldsymbol\pi^{\bf 0}} $, ${\boldsymbol n\pi^{+}\boldsymbol\pi^{\bf -}\boldsymbol\pi^{\bf +} }$ and the Cabibbo-Favored decay ${\boldsymbol \Lambda_{\boldsymbol c}^{\bf +}\to \boldsymbol nK^{\bf -}\boldsymbol\pi^{\bf +}\boldsymbol\pi^{\bf +} }$
M. Ablikim, M. N. Achasov, P. Adlarson, M. Albrecht, R. Aliberti, A. Amoroso, M. R. An, Q. An, Y. Bai, O. Bakina, R. Baldini Ferroli, I. Balossino, Y. Ban, V. Batozskaya, D. Becker, K. Begzsuren, N. Berger, M. Bertani, D. Bettoni, F. Bianchi, E. Bianco, J. Bloms, A. Bortone, I. Boyko, R. A. Briere, A. Brueggemann, H. Cai, X. Cai, A. Calcaterra, G. F. Cao, N. Cao, S. A. Cetin, J. F. Chang, W. L. Chang, G. R. Che, G. Chelkov, C. Chen, Chao Chen, G. Chen, H. S. Chen, M. L. Chen, S. J. Chen, S. M. Chen, T. Chen, X. R. Chen, X. T. Chen, Y. B. Chen, Z. J. Chen, W. S. Cheng, S. K. Choi, X. Chu, G. Cibinetto, F. Cossio, J. J. Cui, H. L. Dai, J. P. Dai, A. Dbeyssi, R. E. de Boer, D. Dedovich, Z. Y. Deng, A. Denig, I. Denysenko, M. Destefanis, F. De Mori, Y. Ding, J. Dong, L. Y. Dong, M. Y. Dong, X. Dong, S. X. Du, Z. H. Duan, P. Egorov, Y. L. Fan, J. Fang, S. S. Fang, W. X. Fang, Y. Fang, R. Farinelli, L. Fava, F. Feldbauer, G. Felici, C. Q. Feng, J. H. Feng, K Fischer, M. Fritsch, C. Fritzsch, C. D. Fu, H. Gao, Y. N.
2023, 47(2): 023001. doi: 10.1088/1674-1137/ac9d29
Using electron-positron annihilation data samples corresponding to an integrated luminosity of 4.5 fb\begin{document}$ ^{-1} $\end{document}, collected by the BESIII detector in the energy region between \begin{document}$ 4599.53\; \,{\rm{MeV}} $\end{document} and \begin{document}$ 4698.82\; \,{\rm{MeV}} $\end{document}, we report the first observations of the Cabibbo-suppressed decays \begin{document}$ \Lambda_c^+\to n\pi^+\pi^0 $\end{document}, \begin{document}$ \Lambda_c^+\to n\pi^+\pi^-\pi^+ $\end{document}, and the Cabibbo-favored decay \begin{document}$ \Lambda_c^+\to nK^-\pi^+\pi^+ $\end{document} with statistical significances of \begin{document}$ 7.9\sigma $\end{document}, \begin{document}$ 7.8\sigma $\end{document}, and \begin{document}$ >10\sigma $\end{document}, respectively. The branching fractions of these decays are measured to be \begin{document}$\mathcal{B}(\Lambda_{c}^{+}\rightarrow n\pi^{+}\pi^{0})=(0.64\pm0.09\pm0.02)$\end{document}%, \begin{document}$\mathcal{B}(\Lambda_{c}^{+}\rightarrow n\pi^{+}\pi^{-}\pi^{+})=(0.45\pm 0.07\pm $\end{document}\begin{document}$ 0.03)$\end{document}%, and \begin{document}$\mathcal{B}(\Lambda_{c}^{+}\rightarrow nK^{-}\pi^{+}\pi^{+})=(1.90\pm0.08\pm0.09)$\end{document}%, where the first uncertainties are statistical and the second are systematic. We find that the branching fraction of the decay \begin{document}$ \Lambda_{c}^{+}\rightarrow n\pi^{+}\pi^{0} $\end{document} is about one order of magnitude higher than that of \begin{document}$ \Lambda_{c}^{+}\rightarrow n\pi^{+} $\end{document}.
Decay constants of Bc(nS) and ${\boldsymbol B_c^*} $ (nS)
Chao Sun, Ru-Hui Ni, Muyang Chen
2023, 47(2): 023101. doi: 10.1088/1674-1137/ac9dea
The decay constants of the low lying S-wave \begin{document}$ B_c $\end{document} mesons, i.e. \begin{document}$ B_c(nS) $\end{document} and \begin{document}$ B^*_c(nS) $\end{document} with \begin{document}$ n\leq 3 $\end{document}, are calculated in the nonrelativistic quark model. The running coupling of the strong interaction is taken into account, and the uncertainties due to varying parameters and losing Lorentz covariance are considered carefully. As a byproduct, the decay constants of the low lying S-wave charmonium and bottomium states are given in the appendixes.
Double-heavy tetraquarks with strangeness in the chiral quark model
Xiaoyun Chen, Fu-Lai Wang, Yue Tan, Youchang Yang
2023, 47(2): 023102. doi: 10.1088/1674-1137/ac9de9
Recently, some progress has been made in the experiments on double-heavy tetraquarks, such as \begin{document}$ T_{cc} $\end{document} reported by the LHCb Collaboration and \begin{document}$ X_{cc\bar{s}\bar{s}} $\end{document} reported by the Belle Collaboration. Coming on the heels of our previous work about \begin{document}$ T_{cc} $\end{document} and \begin{document}$ T_{bb} $\end{document}, we present a study on the bound and resonance states of their companions, \begin{document}$ QQ\bar{q}\bar{s} $\end{document} (\begin{document}$ Q=c,b; q=u, s $\end{document}) tetraquarks with strange flavor in the chiral quark model. Two pictures, meson-meson and diquark-antidiquark ones, and their couplings were considered in our calculations. Isospin violation was neglected herein. Our numerical analysis indicated that the states \begin{document}$ cc\bar{u}\bar{s} $\end{document} with \begin{document}$ \dfrac{1}{2}(1^+) $\end{document} and \begin{document}$ bb\bar{u}\bar{s} $\end{document} with \begin{document}$ \dfrac{1}{2}(1^+) $\end{document} are the most promising stable states against strong interactions. Besides, we found several resonance states for the double-heavy strange tetraquarks with the real scaling method.
Relativistic correction to the dissociation temperature of Bc mesons in a hot medium
Guangyu Li, Baoyi Chen, Yunpeng Liu
2023, 47(2): 023103. doi: 10.1088/1674-1137/ac9fbd
By solving two body Dirac equations with potentials at finite temperature, we calculate the dissociation temperature \begin{document}$ T_d $\end{document} of \begin{document}$ B_c $\end{document} mesons in quark-gluon plasma. It is found that \begin{document}$ T_d $\end{document} becomes higher with the relativistic correction than the \begin{document}$ T_d $\end{document} from the Schrödinger equation. Both the short range interaction and the constant term of the potential at the long-range scale have a contribution to the shift of \begin{document}$ T_d $\end{document}, while the spin interaction is negligible.
Effects from hadronic structure of photon on $ {\boldsymbol B\boldsymbol\to\boldsymbol\phi\boldsymbol\gamma }$ and ${\boldsymbol B_{\boldsymbol s}\boldsymbol\to(\boldsymbol\rho^{\bf 0},\boldsymbol\omega)\gamma }$ decays
Yun Li, Zhi-Tian Zou, Yue-Long Shen, Ying Li
2023, 47(2): 023104. doi: 10.1088/1674-1137/aca38f
Using the perturbative QCD approach, we studied the effects of the hadronic structure of photons on the pure annihilation rediative decays \begin{document}$ B\to\phi\gamma $\end{document} and \begin{document}$ B_s\to(\rho^0,\omega)\gamma $\end{document}. These decays have small branching fractions due to the power suppression by \begin{document}$ \Lambda/m_B $\end{document}, which makes them very sensitive to next-leading power corrections. The quark components and the related two-particle distribution amplitudes of a final state photon are introduced. The branching fractions can be enhanced remarkably by factorizable and nonfactorizable emission diagrams. The branching fraction of \begin{document}$ B\to \phi\gamma $\end{document} increases by approximately 40 times, and those of \begin{document}$ B_s \to \rho^0\gamma $\end{document} and \begin{document}$ B_s \to \omega\gamma $\end{document} are on the order of \begin{document}$ {\cal O}(10^{-10}) $\end{document}. We also note that the ratio of branching fractions of \begin{document}$ B_s \to \rho^0\gamma $\end{document} and \begin{document}$ B_s \to \omega\gamma $\end{document} is very sensitive to the effects of the hadronic structure of photons. All these results can be tested in future.
Standard model effective field theory from on-shell amplitudes
Teng Ma, Jing Shu, Ming-Lei Xiao
2023, 47(2): 023105. doi: 10.1088/1674-1137/aca200
We present a general method of constructing unfactorizable on-shell amplitudes (amplitude basis) and build up their one-to-one correspondence to the independent and complete operator basis in effective field theory (EFT). We apply our method to the Standard Model EFT and identify the amplitude basis in dimensions 5 and 6, which correspond to the Weinberg operator and operators in the Warsaw basis, except for some linear combinations.
Contributions to the nucleon form factors from bubble and tadpole diagrams
Z. Y. Gao, P. Wang, M. Y. Yang
2023, 47(2): 023106. doi: 10.1088/1674-1137/aca466
The nonlocal chiral effective theory is applied to investigate the electromagnetic and strange form factors of nucleons. The bubble and tadpole diagrams are included in the calculation. With the contributions from bubble and tadpole diagrams, the obtained electromagnetic form factors are close to the results without these contributions as long as the low energy constants \begin{document}$ c_1 $\end{document} and \begin{document}$ c_2 $\end{document} are properly chosen, while the magnitudes of strange form factors become larger. The electromagnetic form factors are in good agreement with the experimental results, while the magnitudes of strange form factors are larger than the lattice data.
Explaining the W boson mass anomaly and dark matter with a U(1) dark sector
Kai-Yu Zhang, Wan-Zhe Feng
2023, 47(2): 023107. doi: 10.1088/1674-1137/aca585
The W boson mass recently reported by the CDF collaboration shows a deviation from the standard model prediction with an excess at the \begin{document}$ 7\sigma $\end{document} level. We investigate two simple extensions of the standard model with an extra \begin{document}$ U(1) $\end{document} dark sector. One is the \begin{document}$ U(1)_x $\end{document} extension, where the \begin{document}$ U(1)_x $\end{document} gauge field mixes with the standard model through gauge kinetic terms. The other is a general \begin{document}$ U(1)_{\mathbf{A} Y+\mathbf{B} q} $\end{document} extension of the standard model. Fitting various experimental constraints, we find that the \begin{document}$ U(1)_x $\end{document}extension with only kinetic mixing can enhance the W boson mass by 10 MeV at most. The\begin{document}$ U(1)_{\mathbf{A} Y+\mathbf{B} q} $\end{document}extension can easily generate a 77 MeV enhancement of the W boson mass and also offer a viable dark matter candidate with a mass ranging from several hundred GeV to TeV, which may be detected by future dark matter direct detection experiments with improved sensitivities.
The cross-section for the ${{\boldsymbol\gamma e}^{\bf -} {\bf\rightarrow} {\boldsymbol Ze}^{\bf -} {\bf\rightarrow}{\boldsymbol l}^{\bf -} {\boldsymbol l}^{\bf +}{\boldsymbol e}^{\bf -} }$ scattering at the LHeC
Bui Thi Ha Giang
2023, 47(2): 023108. doi: 10.1088/1674-1137/aca4c2
A measurement of the Z production cross-section in \begin{document}$ \gamma e^{-} $\end{document} collisions at the Large Hadron-electron Collider (LHeC) is presented for comparison to that at the International Linear Collider (ILC). The total cross-section depends strongly on the polarization of the initial and final \begin{document}$ e^{-} $\end{document} beams and the electron beam energy \begin{document}$ E_{e} $\end{document}; the energy of the proton beam was set to \begin{document}$ E_{p} = 7 $\end{document} TeV. The results show that the total cross-section in \begin{document}$ \gamma e^{-} \rightarrow Z e^{-} \rightarrow l^{-}l^{+}e^{-} $\end{document} at the LHeC is much larger than that at the ILC.
Search for charm-quark production via dimuons in neutrino telescopes
ChuanLe Sun, Fuyudi Zhang, Fan Hu, Donglian Xu, Jun Gao
2023, 47(2): 023109. doi: 10.1088/1674-1137/aca465
Dimuon events induced by charm-quark productions from neutrino deep inelastic scattering (DIS) processes have been studied in traditional DIS experiments for decades. The recent progress in neutrino telescopes makes it possible to search for such dimuon events at energies far beyond the laboratory scale. In this study, we construct a simulation framework to calculate yields and distributions of dimuon signals in an IceCube-like km3 scale neutrino telescope. Owing to the experimental limitation in the resolution of double-track lateral distance, only dimuons produced outside the detector volume are considered. Detailed information about simulation results for a 10-year exposure is presented. As an earlier paper[Physical Review D 105, 093005 (2022)] and ours report on a similar situation, we use that paper as a baseline to conduct comparisons. We then estimate the impacts of different calculation methods of muon energy losses. Finally, we study the experimental potential of dimuon searches under the hypothesis of single-muon background only. Our results based on a simplified double-track reconstruction indicate a moderate sensitivity, especially with the ORCA configuration. Further developments on both the reconstruction algorithm and possible detector designs are thus required and are under investigation.
Cumulative fission yield measurements with 14.7 MeV neutrons on 238U
Xianlin Yang, Changlin Lan, Yangbo Nie, Liyang Jiang, Yijia Qiu, Yujie Ge, Hongtao Chen, Kai Zhang, Yuting Wei, Jiahao Wang, Gong Jiang, Xichao Ruan, Yi Yang
2023, 47(2): 024001. doi: 10.1088/1674-1137/aca1ab
The fission yield data in the 14 MeV energy neutron induced fission of 238U play an important role in decay heat calculations and generation-IV reactor designs. In order to accurately measure fission product yields (FPYs) of 238U induced by 14 MeV neutrons, the cumulative yields of fission products ranging from 92Sr to 147Nd in the 238U(n, f) reaction with a 14.7 MeV neutron were determined using an off-line γ-ray spectrometric technique. The 14.7 MeV quasi-monoenergetic neutron beam was provided by the K-400 D-T neutron generator at China Academy of Engineering Physics (CAEP). Fission products were measured by a low background high purity germanium gamma spectrometer. The neutron flux was obtained from the 93Nb (n, 2n)92mNb reaction, and the mean neutron energy was calculated using the cross-section ratios for the 90Zr(n, 2n)89Zr and 93Nb(n, 2n)92mNb reactions. With a series of corrections, high precision cumulative yields of 20 fission products were obtained. Our FPYs for the 238U(n, f) reaction at 14.7 MeV were compared with the existing experimental nuclear reaction data and evaluated nuclear data, respectively. The results will be helpful in the design of a generation-IV reactor and the construction of evaluated fission yield databases.
Cross-sections of the 238U (n, γ) 239U reaction in the 3.0–7.0 MeV energy region measured by relative activation method
Chun Wen, Zheng Han, Xiao-Bing Luo
2023, 47(2): 024002. doi: 10.1088/1674-1137/ac9e9b
The reaction cross-sections of 238U (n, γ)239U have been experimentally determined at neutron energies of 6.117 ± 0.119 MeV, 4.626 ± 0.086 MeV, and 3.622 ± 0.348 MeV employing the relative activation approach along with the off-line γ-ray spectroscopy method. The D (d, n)3He reaction was utilized to obtain monoenergetic neutrons of the required energy, and the 197Au (n, γ)198Au reaction cross-sections were adopted as the referential standard to ascertain the neutron capture cross-sections of 238U. Furthermore, the effects of low-energy scattered neutrons, neutron fluence fluctuations, counting of geometric corrections when measuring γ-rays, and neutron and γ-ray self-absorption caused by the sample thickness have been considered and revised in the present work. For a comparison with experimental results, the cross-sections of the 238U (n, γ)239U reaction were calculated theoretically with the original parametric TALYS-1.9 program. The experimental measurements were in contrast to previous experimental results and the evaluation data available for ROSFOND-2010, CENDL-3.2 and ENDF/B-VIII.0.
Proposal for a nuclear light source
E. V. Tkalya, P. V. Borisyuk, M. S. Domashenko, Yu. Yu. Lebedinskii
2023, 47(2): 024101. doi: 10.1088/1674-1137/ac9f0a
This study considers a principal possibility of creating a nuclear light source of the vacuum ultra violet (VUV) range based on the \begin{document}$ ^{229} $\end{document}Th nucleus. This nuclear light source can help solve two main problems — excitation of the low-lying \begin{document}$ ^{229m} $\end{document}Th isomer and precision measurement of the nuclear isomeric transition energy. The thorium nuclear light source is based on the nuclei implanted in a thin dielectric film with a large bandgap. While passing an electric current through the sample, the \begin{document}$ ^{229} $\end{document}Th nuclei are excited to the low energy isomeric state \begin{document}$ 3/2^+(8.19\pm0.12 $\end{document} eV) through the process of inelastic scattering of conduction electrons. The subsequent spontaneous decay of \begin{document}$ ^{229m} $\end{document}Th is followed by the emission of γ quanta in the VUV range. The luminosity of the thorium nuclear light source is approximately \begin{document}$ 10^5 $\end{document} photons/s per 1 A of current, per 1 ng of \begin{document}$ ^{229} $\end{document}Th. The suggested scheme to obtain γ radiation from the \begin{document}$ ^{229m} $\end{document}Th isomer can be considered as a type of nuclear analogue of the optical radiation from the usual metal-insulator-semiconductor (MIS) junction.
Neutron skin thickness of 90Zr and symmetry energy constrained by charge exchange spin-dipole excitations
Shi-Hui Cheng, Jing Wen, Li-Gang Cao, Feng-Shou Zhang
2023, 47(2): 024102. doi: 10.1088/1674-1137/aca38e
The charge exchange spin-dipole (SD) excitations of \begin{document}$ ^{90} $\end{document}Zr are studied using the Skyrme Hartee-Fock plus proton-neutron random phase approximation with SAMi-J interactions. The experimental value of the model-independent sum rule obtained from the SD strength distributions of \begin{document}$ ^{90} $\end{document}Zr(p, n)\begin{document}$ ^{90} $\end{document}Nb and \begin{document}$ ^{90} $\end{document}Zr(n, p)\begin{document}$ ^{90} $\end{document}Y is used to deduce the neutron skin thickness. The neutron skin thickness \begin{document}$ \Delta r_{np} $\end{document} of \begin{document}$ ^{90} $\end{document}Zr is extracted as \begin{document}$ 0.083\pm0.032 $\end{document} fm, which is similar to the results of other studies. Based on the correlation analysis of the neutron skin thickness \begin{document}$ \Delta r_{np} $\end{document} and the nuclear symmetry energy J as well as its slope parameter L, a constraint from the extracted \begin{document}$ \Delta r_{np} $\end{document} leads to the limitation of J to \begin{document}$ 29.2 \pm 2.6 $\end{document} MeV and L to \begin{document}$ 53.3 \pm 28.2 $\end{document} MeV.
Universal scaling of kinetic freeze-out parameters across different collision systems at LHC energies
Lian Liu, Zhong-Bao Yin, Liang Zheng
2023, 47(2): 024103. doi: 10.1088/1674-1137/aca38d
In this study, we perform Tsallis Blast-Wave analysis on the transverse momentum spectra of identified hadrons produced in a wide range of collision systems at the Large Hadron Collider (LHC) including pp, pPb, XeXe, and PbPb collisions. The kinetic freeze-out properties varying with event multiplicity are investigated across these systems. We find that the extracted kinetic freeze-out temperature, radial flow velocity, and non-extensive parameter exhibit a universal scaling behavior for these systems with very different geometric sizes, especially when the independent baryon Tsallis non-extensive parameter is considered. This universality may indicate the existence of a unified partonic evolution stage in different collision systems at the LHC energies.
Role of a high ground-state centrifugal barrier in the breakup of the 31Ne nucleus
B. Mukeru
2023, 47(2): 024104. doi: 10.1088/1674-1137/ac9e4b
An analysis of the breakup of the \begin{document}$ ^{31}{\rm Ne} $\end{document} weakly-bound neutron-halo system on a lead target is presented, considering the \begin{document}$ 2p_{3/2} $\end{document} and \begin{document}$ 1f_{7/2} $\end{document} ground-state configurations. It is shown that a high centrifugal barrier almost wipes out the breakup channel, thus assimilating the breakup of a weakly-bound system to that of a tightly-bound system, and also reduces the range of the monopole nuclear potential. Consequently, a high centrifugal barrier prevents the suppression of the Coulomb-nuclear interference (CNI) peak by weakening couplings to the breakup channel and reducing the range of the monopole nuclear potential, two main factors that would otherwise suppress such a peak. The present study also identifies couplings to the breakup channel and a long-ranged monopole nuclear potential as the main factors that lead to the suppression of the CNI peak. A low centrifugal barrier together with a Coulomb barrier would also effectively prevent the suppression of the CNI peak in proton-halos as reported in the case of the \begin{document}$ ^8{\rm B} $\end{document} proton-halo.
Signals of α clusters in 16O+16O collisions at the LHC from relativistic hydrodynamic simulations
Chi Ding, Long-Gang Pang, Song Zhang, Yu-Gang Ma
2023, 47(2): 024105. doi: 10.1088/1674-1137/ac9fb8
In relativistic heavy ion collisions, the fluctuations of initial entropy density convert to the correlations of final state hadrons in momentum space through the collective expansion of strongly interacting QCD matter. Using a (3+1)D viscous hydrodynamic program, CLVisc, we consider whether the nuclear structure, which provides initial state fluctuations as well as correlations, can affect the final state of heavy ion collisions, and whether one can find signals of α cluster structures in oxygen using final state observables in \begin{document}$ ^{16}\text{O}+{}^{16}\text{O} $\end{document} collisions at the CERN Large Hadron Collider. For the initial nucleon distributions in oxygen nuclei, we compare three different configurations, a tetrahedral structure with four-α clusters, the deformed Woods-Saxon distribution, and a spherical symmetric Woods-Saxon distribution. Our results show that the charged multiplicity as a function of centrality and the elliptic flow at the most central collisions using the four-α structure differs from those with the Woods-Saxon and deformed Woods-Saxon distributions, which may help to identify α clustering structures in oxygen nuclei.
Effects of the formation time of parton shower on jet quenching in heavy-ion collisions
Mengxue Zhang, Yang He, Shanshan Cao, Li Yi
2023, 47(2): 024106. doi: 10.1088/1674-1137/aca4c1
Jet quenching has successfully served as a hard probe to study the properties of Quark-Gluon Plasma (QGP). As a multi-particle system, jets require time to develop from a highly virtual parton to a group of partons close to mass shells. In this study, we present a systematical analysis on the effects of this formation time on jet quenching in relativistic nuclear collisions. Jets from initial hard scatterings were simulated with Pythia, and their interactions with QGP were described using a Linear Boltzmann Transport (LBT) model that incorporates both elastic and inelastic scatterings between jet partons and the thermal medium. Three different estimations of the jet formation time were implemented and compared, including instantaneous formation, formation from single splitting, and formation from sequential splittings, before which no jet-medium interaction was assumed. We found that deferring the jet-medium interaction with a longer formation time not only affects the overall magnitude of the nuclear modification factor of jets but also its dependence on the jet transverse momentum.
Interactions between heavy quarks and tilted QGP fireballs in 200 A GeV Au+Au collisions
Ze-Fang Jiang, Shanshan Cao, Wen-Jing Xing, Xiaowen Li, Ben-Wei Zhang
2023, 47(2): 024107. doi: 10.1088/1674-1137/aca64f
Heavy quark observables are applied to probe the initial energy density distribution with violation of longitudinal boost invariance produced in relativistic heavy-ion collisions. Using an improved Langevin model coupled to a (3+1)-dimensional viscous hydrodynamic model, we study the nuclear modification factor (\begin{document}$R_{AA}$\end{document}) and directed flow (\begin{document}$ v_1 $\end{document}) and elliptic flow (\begin{document}$ v_2 $\end{document}) coefficients of heavy mesons and their decayed electrons at an RHIC energy. We find that the counter-clockwise tilt of nuclear matter in the reaction plane results in a positive (negative) heavy flavor \begin{document}$ v_1 $\end{document} in the backward (forward) rapidity region, whose magnitude increases with the heavy quark transverse momentum. The difference in the heavy flavor \begin{document}$R_{AA}$\end{document} between different angular regions is also proposed as a complementary tool to characterize the asymmetry of the medium profile. Our model results are consistent with currently available data at the RHIC and provide predictions that can be tested by future measurements.
Strangeness S = −2 baryon-baryon interactions and femtoscopic correlation functions in covariant chiral effective field theory
Zhi-Wei Liu, Kai-Wen Li, Li-Sheng Geng
2023, 47(2): 024108. doi: 10.1088/1674-1137/ac988a
We study the baryon-baryon interactions with strangeness \begin{document}$ S = -2 $\end{document} and corresponding momentum correlation functions in leading order covariant chiral effective field theory. The relevant low energy constants are determined by fitting to the latest HAL QCD simulations, taking into account all the coupled channels. Extrapolating the so-obtained strong interactions to the physical point and considering both quantum statistical effects and the Coulomb interaction, we calculate the \begin{document}$ \Lambda\Lambda $\end{document} and \begin{document}$ \Xi^-p $\end{document} correlation functions with a spherical Gaussian source and compare them with recent experimental data. We find a good agreement between our predictions and the experimental measurements by using the source radius determined in proton-proton correlations, which demonstrates the consistency between theory, experiment, and lattice QCD simulations. Moreover, we predict the \begin{document}$ \Sigma^+\Sigma^+ $\end{document}, \begin{document}$ \Sigma^+\Lambda $\end{document}, and \begin{document}$ \Sigma^+\Sigma^- $\end{document} interactions and corresponding momentum correlation functions. We further investigate the influence of the source shape and size of the hadron pair on the correlation functions studied and show that the current data are not very sensitive to the source shape. Future experimental measurements of the predicted momentum correlation functions will provide a non-trivial test of not only SU(3) flavor symmetry and its breaking but also the baryon-baryon interactions derived in covariant chiral effective field theory.
${ \boldsymbol f(\bar{\boldsymbol R}, \boldsymbol L(\boldsymbol X))} $-gravity in the context of dark energy with power law expansion and energy conditions
Goutam Manna, Arijit Panda, Aninda Karmakar, Saibal Ray, Md. Rabiul Islam
2023, 47(2): 025101. doi: 10.1088/1674-1137/ac9fbe
The objective of this work is to generate a general formalism of \begin{document}$ f(\bar{R}, L(X))- $\end{document}gravity in the context of dark energy under the framework of K-essence emergent geometry with the Dirac-Born-Infeld (DBI) variety of action, where \begin{document}$ \bar{R} $\end{document} is the familiar Ricci scalar, \begin{document}$ L(X) $\end{document} is the DBI type non-canonical Lagrangian with \begin{document}$ X={1\over 2}g^{\mu\nu}\nabla_{\mu}\phi\nabla_{\nu}\phi $\end{document}, and ϕ is the K-essence scalar field. The emergent gravity metric (\begin{document}$ {\bar{G}}_{\mu\nu} $\end{document}) and the well known gravitational metric (\begin{document}$ g_{\mu\nu} $\end{document}) are not conformally equivalent. We have constructed a modified field equation using the metric formalism in \begin{document}$ f(\bar{R}, L(X)) $\end{document}-gravity incorporating the corresponding Friedmann equations into the framework of the background gravitational metric, which is of Friedmann-Lemaître-Robertson-Walker (FLRW) type. The solution of the modified Friedmann equations have been deduced for the specific choice of \begin{document}$ f(\bar{R}, L(X)) $\end{document}, which is of Starobinsky-type, using the power law expansion method. The consistency of the model with the accelerating phase of the universe has been shown when we restrict ourselves to consider the value of the dark energy density as \begin{document}$\dot\phi^{2}=8/9=0.888 < 1$\end{document}, which indicates that the present universe is dark-energy dominated. Graphical plots for the energy density (ρ), pressure (p), and equation of state parameter (\begin{document}$ {\omega} $\end{document}) with respect to (w.r.t.) time (t) based on parametric values are interestingly consistent with the dark energy domination theory, and hence the accelerating features. We also highlight the corresponding energy conditions and constraints of the \begin{document}$ f(\bar{R}, L(X)) $\end{document} theory with a basic example.
Weak deflection angle and shadow cast by the charged-Kiselev black hole with cloud of strings in plasma
Farruh Atamurotov, Ibrar Hussain, Ghulam Mustafa, Ali Övgün
2023, 47(2): 025102. doi: 10.1088/1674-1137/ac9fbb
In this study, the gravitational deflection angle of photons in the weak field limit (or the weak deflection angle) and shadow cast by the electrically charged and spherically symmetric static Kiselev black hole (BH) in the string cloud background are investigated. The influences of the BH charge Q, quintessence parameter γ, and string cloud parameter a on the weak deflection angle are studied using the Gauss-Bonnet theorem, in addition to studying the influences on the radius of photon spheres and size of the BH shadow in the spacetime geometry of the charged-Kiselev BH in string clouds. Moreover, we study the effects of plasma (uniform and non-uniform) on the weak deflection angle and shadow cast by the charged-Kiselev BH surrounded by the clouds of strings. In the presence of a uniform/nonuniform plasma medium, an increase in the string cloud parameter a increases the deflection angle α. In contrast, a decrease in the BH charge Q decreases the deflection angle. Further, we observe that an increase in the BH charge Q causes a decrease in the size of the shadow of the BH. We notice that, with an increase in the values of the parameters γ and a, the size of the BH shadow increases, and therefore, the intensity of the gravitational field around the charged-Kiselev BH in string clouds increases. Thus, the gravitational field of the charged-Kiselev BH in the string cloud background is stronger than the field produced by the pure Reissner-Nordstrom BH. Moreover, we use the data released by the Event Horizon Telescope (EHT) collaboration, for the supermassive BHs M87* and Sgr A*, to obtain constraints on the values of the parameters γ and a.
Singularities of regular black holes and the monodromy method for asymptotic quasinormal modes
Chen Lan, Yi-Fan Wang
2023, 47(2): 025103. doi: 10.1088/1674-1137/aca07c
We use the monodromy method to investigate the asymptotic quasinormal modes of regular black holes based on the explicit Stokes portraits. We find that, for regular black holes with spherical symmetry and a single shape function, the analytical forms of the asymptotic frequency spectrum are not universal and do not depend on the multipole number but on the presence of complex singularities and the trajectory of asymptotic solutions along the Stokes lines.
Black hole shadow in f(R) gravity with nonlinear electrodynamics
Jiaojiao Sun, Yunqi Liu, Wei-Liang Qian, Songbai Chen, Ruihong Yue
2023, 47(2): 025104. doi: 10.1088/1674-1137/aca4bc
By analyzing the propagation of discontinuity in nonlinear electrodynamics, we numerically investigate the related black hole shadows of recently derived rotating black hole solutions in \begin{document}$f(R) $\end{document} gravity. In this context, the geodesic motion of the relevant perturbations is governed by an effective geometry, which is closely related to the underlying spacetime metric. We derive the effective geometry, and the latter is used to determine the trajectory of the propagation vector of an arbitrary finite discontinuity in the electrodynamic perturbations, namely, the photon. Subsequently, the image of the black hole is evaluated using the ray-tracing technique. Moreover, we discuss the physical relevance of metric parameters, such as the nonlinear coupling, spin, and charge, by studying their impact on the resultant black hole shadows.
Effect of nonlinear electrodynamics on shadows of slowly rotating black holes
Jiuyang Tang, Yunqi Liu, Wei-Liang Qian, Ruihong Yue
2023, 47(2): 025105. doi: 10.1088/1674-1137/ac9fba
In this study, we investigate the effect of nonlinear electrodynamics on the shadows of charged, slowly rotating black holes with the presence of a cosmological constant. Rather than the null geodesic of the background black hole spacetime, the trajectory of a photon, as a perturbation of the nonlinear electrodynamic field, is governed by an effective metric. The latter can be derived by analyzing the propagation of a discontinuity of the electromagnetic waveform. Subsequently, the image of the black hole and its shadow can be evaluated using the backward ray-tracing technique. We explore the properties of the resultant black hole shadows of two different scenarios of nonlinear electrodynamics, namely, the logarithmic and exponential forms. In particular, the effects of nonlinear electrodynamics on the optical image are investigated, as well as the image's dependence on other metric parameters, such as the black hole spin and charge. The resulting black hole image and shadow display rich features that potentially lead to observational implications.