2020 Vol. 44, No. 11

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Mesonic condensation in isospin matter under rotation
Hui Zhang, Defu Hou, Jin-Feng Liao
2020, 44(11): 111001. doi: 10.1088/1674-1137/abae4d
We investigate mesonic condensation in isospin matter under rotation. Using the two-flavor NJL effective model in the presence of global rotation, we demonstrate two important effects of rotation on its phase structure: a rotational suppression of the scalar-channel condensates, in particular, the pion condensation region; and a rotational enhancement of the rho condensation region with vector-channel condensate. A new phase diagram for isospin matter under rotation is mapped out on the \begin{document}$ \omega-\mu_I$\end{document} plane where the three distinct phases, corresponding to the \begin{document}$ \sigma,\; \pi, \;\rho$\end{document} -dominated regions, respectively, are separated by a second-order line at low isospin chemical potential as well as a first-order line at high rotation and are further connected at a tri-critical point.
Unified interpretation of scalegenesis in conformally extended standard models: a dynamical origin of Higgs portal
Hiroyuki Ishida, Shinya Matsuzaki, Ruiwen Ouyang
2020, 44(11): 111002. doi: 10.1088/1674-1137/abb07f
We present a universal interpretation of a class of conformal extended standard models that include Higgs portal interactions as realized in low-energy effective theories. The scale generation mechanism in this class (scalegenesis) arises along the (nearly) conformal/flat direction for breaking scale symmetry, where the electroweak symmetry-breaking structure arises similarly as in the standard model. A dynamical origin for the Higgs portal coupling can provide the discriminator for the low-energy “universality class,” to be probed in forthcoming collider experiments.
Recent progress in multiple chiral doublet bands
Shou-Yu Wang
2020, 44(11): 112001. doi: 10.1088/1674-1137/abaed2
Recent progress regarding multiple chiral doublet bands (\begin{document}$ {\rm{M}}\chi{\rm{D}}$\end{document}) is reviewed from the experimental and theoretical perspectives. In particular, the experimental findings, theoretical predictions, selection rule for electromagnetic transitions, \begin{document}$ {\rm{M}}\chi{\rm{D}}$\end{document} with octupole correlations, and some related topics are highlighted. Based on these discussions, it is of great scientific interest to search for the other \begin{document}$ {\rm{M}}\chi{\rm{D}}$\end{document}, as well as possible chiral wobblers, chirality-parity quartet bands, and chirality-pseudospin triplet (or quartet) bands in the nuclear system.
Probing electroweak dark matter at 14 TeV LHC
Shuai Xu, Si-Bo Zheng
2020, 44(11): 113101. doi: 10.1088/1674-1137/abae4c
Well-motivated electroweak dark matter is often hosted by an extended electroweak sector that also contains new lepton pairs with masses near the weak scale. In this study, we explore such electroweak dark matter by combining dark matter direct detection experiments and high-luminosity LHC probes of new lepton pairs. Using Z- and W-associated electroweak processes with two or three lepton final states, we show that depending on the overall coupling constant, dark matter masses of up to \begin{document}$170-210$\end{document} GeV can be excluded at the \begin{document}$2\sigma$\end{document} level and those up to \begin{document}$175-205$\end{document} GeV can be discovered at the \begin{document}$5\sigma$\end{document} level at the 14 TeV LHC with integrated luminosities of 300 fb\begin{document}$^{-1}$\end{document} and 3000 fb\begin{document}$^{-1}$\end{document}, respectively.
Gauge dependence of the perturbative QCD predictions under the momentum-space subtraction scheme
Jun Zeng, Xing-Gang Wu, Xu-Chang Zheng, Jian-Ming Shen
2020, 44(11): 113102. doi: 10.1088/1674-1137/abae4e
The momentum-space subtraction (MOM) scheme is one of the most frequently used renormalization schemes in perturbative QCD (pQCD) theory. In this paper, we discuss in detail the gauge dependence of the pQCD predictions obtained under the MOM scheme. Conventionally, a renormalization scale ambiguity exists for the fixed-order pQCD predictions; this assigns an arbitrary range and error for the fixed-order pQCD prediction and makes the discussions on the issue of the gauge dependence much more involved. The principle of maximum conformality (PMC) adopts the renormalization group equation to determine the magnitude of the coupling constant; hence, it determines the effective momentum flow of the process, which is independent of the choice of renormalization scale. Thus, no renormalization scale ambiguity exists in PMC predictions. To focus our attention on the MOM scheme's gauge dependence, we first apply the PMC to deal with the pQCD series. As an explicit example, we adopt the Higgs boson decay width \begin{document}$ \Gamma(H\to gg) $\end{document} up to its five-loop QCD contribution, to demonstrate the behavior of the gauge dependence before and after applying the PMC. Interaction vertices are chosen to define five different MOM schemes: mMOM, MOMh, MOMq, MOMg, and MOMgg. Under these MOM schemes, we obtain \begin{document}$ \Gamma(H \to gg)|^{\rm{mMOM}}_{\rm{PMC}} =$\end{document}\begin{document}$332.8{^{+11.6}_{-3.7}}\pm7.3\; \rm{keV}$\end{document}, \begin{document}$ \Gamma(H \to gg)|^{\rm{MOMh}}_{\rm{PMC}} = 332.8{^{+27.5}_{-34.6}}\pm7.3\; \rm{keV} $\end{document}, \begin{document}$ \Gamma(H \to gg)|^{\rm{MOMq}}_{\rm{PMC}} = 332.9{^{+27.4}_{-34.7}}\pm 7.3\; \rm{keV} $\end{document}, \begin{document}$ \Gamma(H \to gg)|^{\rm{MOMg}}_{\rm{PMC}} = 332.7{^{+27.5}_{-34.6}}\pm7.3\; \rm{keV} $\end{document}, and \begin{document}$ \Gamma(H \to gg)|^{\rm{MOMgg}}_{\rm{PMC}} = 337.9{^{+1.2}_{-1.7}}\pm 7.7\; \rm{keV} $\end{document}; here, the central values correspond to the Landau gauge with the gauge parameter \begin{document}$ \xi^{\rm MOM} = 0 $\end{document}, the first errors correspond to \begin{document}$ \xi^{\rm MOM}\in[-1,1] $\end{document}, and the second ones arise through taking \begin{document}$ \Delta \alpha_s^{\overline{\rm MS}}(M_Z) = \pm0.0011 $\end{document}. The uncertainty of the Higgs mass \begin{document}$ \Delta M_H = 0.24\; \rm{GeV} $\end{document} causes an extra error of \begin{document}$ \sim \pm1.7 $\end{document} (or \begin{document}$ \sim\pm1.8 $\end{document}) keV for all the aforementioned MOM schemes. It is found that the Higgs decay width \begin{document}$ \Gamma (H\to gg) $\end{document} depends very weakly on the choice of MOM scheme, which is consistent with renormalization group invariance. It is found that the gauge dependence of \begin{document}$ \Gamma(H\to gg) $\end{document} under the \begin{document}$ \rm{MOMgg} $\end{document} scheme is less than ±1%, which is the smallest gauge dependence among all the aforementioned MOM schemes.
DP(π, K) helicity form factors within light-cone sum rule approach
Hai-Bing Fu, Wei Cheng, Rui-Yu Zhou, Long Zeng
2020, 44(11): 113103. doi: 10.1088/1674-1137/abae4f
In this study, \begin{document}$D\to P(\pi, K)$\end{document} helicity form factors (HFFs) are investigated by applying the QCD light-cone sum rule (LCSR) approach. The calculation accuracy is up to the next-to-leading order (NLO) gluon radiation correction of twist-(2,3) distribution amplitude. The resultant HFFs at a large recoil point are \begin{document}${\cal{P}}_{t,0}^\pi(0) = 0.688^{+0.020}_{-0.024}$\end{document} and \begin{document}${\cal{P}}_{t,0}^K(0)=0.780^{+0.024}_{-0.029}$\end{document}, in which the contributions from the three particles of the leading order (LO) are so small that they can be safely neglected. The maximal contribution of the NLO gluon radiation correction for \begin{document}${\cal{P}}_{t,0}^{\pi,K}(0)$\end{document} is less than 3%. After extrapolating the LCSR predictions for these HFFs to the whole \begin{document}$q^2$\end{document}-region, we obtain the decay widths for semileptonic decay processes \begin{document}$D\to P\ell\nu_\ell$\end{document}, which are consistent with the BES-III collaboration predictions within error limits. After considering the \begin{document}$D^{+}/D^{0}$\end{document}-meson lifetime, we give the branching fractions of \begin{document}$D\to P\ell\nu_\ell$\end{document} with \begin{document}$\ell = e, \mu$\end{document}; our predictions also agree with the BES-III collaboration results within error limits, especially for the \begin{document}$D\to \pi \ell\nu_\ell$\end{document} decay process. Finally, we present the forward-backward asymmetry \begin{document}${\cal{A}}_{\rm{FB}}^\ell(q^2)$\end{document} and lepton convexity parameter \begin{document}${\cal{C}}_F^\ell(q^2)$\end{document}, and further calculate the mean value of these two observations, \begin{document}$\langle{\cal{A}}_{\rm{FB}}^\ell\rangle$\end{document} and \begin{document}$\langle{\cal{C}}_F^\ell\rangle$\end{document}, which may provide a way to test those HFFs in future experiments.
Revisiting nonfactorizable contributions to factorization-forbidden decays of B mesons to charmonium
Ya-Qian Li, Meng-Kun Jia, Rui Zhou
2020, 44(11): 113104. doi: 10.1088/1674-1137/abae50
Motivated by the large rates of \begin{document}$B\rightarrow (\chi_{c0}, \chi_{c2}, h_c)K$\end{document} decays observed by the \begin{document}$BABAR$\end{document} and Belle collaborations, we investigate the nonfactorizable contributions to these factorization-forbidden decays, which can occur through a gluon exchange between the \begin{document}$c\bar c$\end{document} system and the spectator quark. Our numerical results demonstrate that the spectator contributions are capable of producing a large branching ratio consistent with the experiments. As a by-product, we also study the Cabibbo-suppressed decays, such as \begin{document}$B\rightarrow (\chi_{c0}, \chi_{c2}, h_c)\pi$\end{document} and the U-spin-related \begin{document}$B_s$\end{document} decay, which have so far received less theoretical and experimental attention. The calculated branching ratios reach the order of \begin{document}$10^{-6}$\end{document}, which is within the scope of the Belle-II and LHCb experiments. Further, the \begin{document}$CP$\end{document}-asymmetry parameters are also calculated for these decays. The obtained results are compared with the available experimental data and numbers from other predictions. We also investigate the sources of theoretical uncertainties in our calculation.
Dark matter search at colliders and neutrino floor
Qing-Hong Cao, An-Kang Wei, Qian-Fei Xiang
2020, 44(11): 113105. doi: 10.1088/1674-1137/abae53
The sensitivity of the direct detection of dark matter (DM) approaches the so-called neutrino floor, below which it is difficult to disentangle the DM candidate from the neutrino background. In this work, we consider the scenario that no DM signals are reported in various DM direct detection experiments and explore whether collider searches could probe DM below the neutrino floor. We adopt several simplified models in which the DM candidate couples to electroweak gauge bosons or leptons in the standard model only through high-dimensional operators. After including the RGE running effect, we investigate the constraints of direct detection, indirect detection, and collider searches. The collider search can probe light DM below the neutrino floor. Particularly, for the effective interaction of \begin{document}$ \bar{\chi}\chi B_{\mu\nu}B^{\mu\nu}$\end{document}, current data from the mono-photon channel at the 13 TeV LHC has already covered the entire parameter space of the neutrino floor.
Tetraquark candidates in LHCb's di-J/ψ mass spectrum
Zhi-Gang Wang
2020, 44(11): 113106. doi: 10.1088/1674-1137/abb080
In this article, we study the first radial excited states of the scalar, axialvector, vector, and tensor diquark-antidiquark-type \begin{document}$cc\bar{c}\bar{c}$\end{document} tetraquark states with the QCD sum rules and obtain the masses and pole residues; then, we use the Regge trajectories to obtain the masses of the second radial excited states. The predicted masses support assigning the broad structure from 6.2 to 6.8 GeV in the di- \begin{document}$J/\psi$\end{document} mass spectrum to be the first radial excited state of the scalar, axialvector, vector, or tensor \begin{document}$cc\bar{c}\bar{c}$\end{document} tetraquark state, as well as assigning the narrow structure at about 6.9 GeV in the di- \begin{document}$J/\psi$\end{document} mass spectrum to be the second radial excited state of the scalar or axialvector \begin{document}$cc\bar{c}\bar{c}$\end{document} tetraquark state.
Yield ratio of hypertriton to light nuclei in heavy-ion collisions from ${ \sqrt{{ s}_{{NN}}}}$ = 4.9 GeV to 2.76 TeV
Tian-Hao Shao, Jin-Hui Chen, Che Ming Ko, Kai-Jia Sun, Zhang-Bu Xu
2020, 44(11): 114001. doi: 10.1088/1674-1137/abadf0
We argue that the difference in the yield ratio \begin{document}${{{S}}_{\rm{3}}} = \dfrac{{{{{N}}_{_\Lambda ^3{\rm{H}}}}/{{{N}}_\Lambda }}}{{{{{N}}_{^3{\rm{He}}}}/{{{N}}_{{p}}}}}$\end{document} measured in Au+Au collisions at \begin{document}$\rm \sqrt{s_{NN}}$\end{document} = 200 GeV and in Pb-Pb collisions at \begin{document}$\rm \sqrt{s_{NN}}$\end{document} = 2.76 TeV is mainly owing to the different treatment of the weak decay contribution to the proton yield in the Au+Au collisions at \begin{document}$\rm \sqrt{s_{NN}}$\end{document} = 200 GeV. We then use the coalescence model to extract from measured \begin{document}$\rm S_3$\end{document} the information about the \begin{document}$\Lambda$\end{document} and nucleon density fluctuations at the kinetic freeze-out of heavy-ion collisions. We also show, using available experimental data, that the yield ratio \begin{document}${{{S}}_{\rm{2}}} = \dfrac{{{{{N}}_{_\Lambda ^3{\rm{H}}}}}}{{{{{N}}_\Lambda }{{{N}}_{{d}}}}}$\end{document} is a more promising observable than \begin{document}$\rm S_3$\end{document} for probing the local baryon-strangeness correlation in the produced medium.
Cross-sections for ${{(n,2n)},\, {(n,\alpha)},\, {(n,p)},\, {(n,d)}} $, and ${{(n,t)}} $ reactions on molybdenum isotopes in the neutron energy range of 13 to 15 MeV
Junhua Luo, Li Jiang
2020, 44(11): 114002. doi: 10.1088/1674-1137/abaded
Given the insufficient cross-sectional data regarding the 14-MeV-neutron experiment of molybdenum, the vital fusion reactor structural material, and the significant heterogeneities among the reported values, this study examined the (n,2n), (n,α), (n,p), (n,d), and (n,t) reaction cross sections in molybdenum isotopes based on the neutrons produced via a T(d,n)4He reaction carried out in the Pd-300 Neutron Generator at the China Academy of Engineering Physics (CAEP). A high-resolution gamma-ray spectrometer, which was equipped with a coaxial high-purity germanium detector, was used to measure the product nuclear gamma activities. In addition, 27Al(n,α)24Na and 93Nb(n,2n)92mNb reactions were utilized as the neutron fluence standards. The experimental 92Mo(n,2n)91Mo, 94Mo(n,2n)93mMo, 100Mo(n,2n)99Mo, 98Mo(n,α)95Zr, 100Mo(n,α)97Zr, 92Mo(n,p)92mNb, 96Mo(n,p)96Nb, 97Mo(n,p)97Nb, 98Mo(n,p)98mNb, 92Mo(n,d)91mNb, and 92Mo(n,t)90Nb reaction cross sections were acquired within the 13–15 MeV neutron energy range. Thereafter, we compared and analyzed these obtained cross sections based on the existing IAEA-EXFOR database-derived experimental data, together with evaluation results corresponding to ENDF/B-VIII.0, JEFF-3.3, BROND-3.1, and CENDL-3.1 and the theoretical outcomes acquired through TALYS-1.95 and EMPIRE-3.2.3 (nuclear-reaction modeling tools).
Decay properties of the Zc(3900) through the Fierz rearrangement
Hua-Xing Chen
2020, 44(11): 114003. doi: 10.1088/1674-1137/abae4b
We systematically construct all the tetraquark currents/operators of \begin{document}$J^{PC} = 1^{+-}$\end{document} with the quark configurations \begin{document}$[cq][\bar c \bar q]$\end{document}, \begin{document}$[\bar c q][\bar q c]$\end{document}, and \begin{document}$[\bar c c][\bar q q]$\end{document} (\begin{document}$q=u/d$\end{document}), and derive their relations through the Fierz rearrangement of the Dirac and color indices. Using the transformations of \begin{document}$[qc][\bar q \bar c] \to [\bar c c][\bar q q]$\end{document} and \begin{document}$[\bar c q][\bar q c]$\end{document}, we study decay properties of the \begin{document}$Z_c(3900)$\end{document} as a compact tetraquark state; while using the transformation of \begin{document}$[\bar c q][\bar q c] \to [\bar c c][\bar q q]$\end{document}, we study its decay properties as a hadronic molecular state.
Heavy flavor quenching and flow: the roles of initial condition, pre-equilibrium evolution, and in-medium interaction
Shu-Qing Li, Wen-Jing Xing, Feng-Lei Liu, Shanshan Cao, Guang-You Qin
2020, 44(11): 114101. doi: 10.1088/1674-1137/abadee
Within an advanced Langevin-hydrodynamics framework coupled to a hybrid fragmentation-coalescence hadronization model, we study heavy flavor quenching and flow in relativistic heavy-ion collisions. We investigate how the initial heavy quark spectrum, the in-medium energy loss and hadronization mechanisms of heavy quarks, the evolution profile of the pre-equilibrium stage, the medium flow, and the temperature dependence of heavy quark diffusion coefficients influence the suppression and elliptic flow of heavy mesons at the RHIC and the LHC. Our results show that the different modeling of initial conditions, pre-equilibrium evolution, and in-medium interactions can individually yield uncertainties of approximately 10-40% in D meson suppression and flow at a low transverse momentum. We also find that proper combinations of collisional versus radiative energy loss, coalescence versus fragmentation in hadronization, and the inclusion of medium flow are the most important factors for describing the suppression and elliptic flow of heavy mesons.
Cross-section measurements for 58,60,61Ni(n, α)55,57,58Fe reactions in the 4.50 – 5.50 MeV neutron energy region
Haoyu Jiang, Zengqi Cui, Yiwei Hu, Jie Liu, Jinxiang Chen, Guohui Zhang, Yu. M. Gledenov, E. Sansarbayar, G. Khuukhenkhuu, L. Krupa, I. Chuprakov
2020, 44(11): 114102. doi: 10.1088/1674-1137/abadf2
The cross sections at 5 energy points of the 58Ni(n, α)55Fe reaction were measured in the 4.50 MeV ≤ En ≤ 5.50 MeV region while those for the 60Ni(n, α)57Fe and 61Ni(n, α)58Fe reactions were measured at En = 5.00 and 5.50 MeV using the 4.5 MV Van de Graaff accelerator at Peking University. A gridded twin ionization chamber (GIC) was used as the detector, and enriched 58Ni, 60Ni, and 61Ni foil samples were prepared and mounted at the sample changer of the GIC. Three highly enriched 238U3O8 samples inside the GIC were used to determine the relative and absolute neutron fluxes. The neutron energy spectra were obtained through unfolding the pulse height spectra measured by the EJ-309 liquid scintillator. The interference from the low-energy neutrons and impurities in the samples has been corrected. The present data of the 60Ni(n, α)57Fe reaction are the first measurement results below 6.0 MeV, and those of the 61Ni(n, α)58Fe reactions are the first measurement results in the MeV region. The present results have been compared with existing measurements, evaluations, and TALYS-1.9 calculations.
Orientation dichroism effect of proton scattering on deformed nuclei
Li Ou, Zhi-Gang Xiao
2020, 44(11): 114103. doi: 10.1088/1674-1137/abadf1
Proton-induced scattering of 238U nuclei, with spheroidal deformations at beam energies above 100 MeV, is simulated using an improved quantum molecular dynamics model. The angular distribution of the deflected protons is highly sensitive to the orientation of the symmetrical long axis of the target nuclei with respect to the beam direction. As a result, in reverse kinematic reactions, an orientation dichroism effect is predicted, implying that the absorption rate of the 238U beam by a proton target discerns between the parallel and perpendicular orientations of the deformed 238U nuclei.
Radiative decays of f1(1285) as the ${ { K}^*\bar { K}}$ molecular state
Ju-Jun Xie, Gang Li, Xiao-Hai Liu
2020, 44(11): 114104. doi: 10.1088/1674-1137/abae51
With \begin{document}$f_1(1285)$\end{document} as a dynamically generated resonance from \begin{document}$ K^*\bar K$\end{document} interactions, we estimate the rates of the radiative transitions of the \begin{document}$f_1(1285)$\end{document} meson to the vector mesons \begin{document}$\rho^0$\end{document}, \begin{document}$\omega$\end{document} and \begin{document}$\phi$\end{document}. These radiative decays proceed via the kaon loop diagrams. The calculated results are in a fair agreement with experimental measurements. Some predictions can be tested experimentally; their analysis will be valuable for decoding the strong coupling of the \begin{document}$f_1(1285)$\end{document} state to the \begin{document}$\bar{K}K^*$\end{document} channel.
Pion parton distribution function in light-front holographic QCD
Lei Chang, Khépani Raya, Xiaobin Wang
2020, 44(11): 114105. doi: 10.1088/1674-1137/abae52
The valence-quark distribution function of the pion has been of interest for decades; particularly, the profile it should adopt when \begin{document}$x\to1$\end{document} (the large-x behavior) has been the subject of a long-standing debate. In the light-front holographic QCD (LFHQCD) approach, this behavior is controlled by the so-called reparametrization function, \begin{document}$w_\tau(x)$\end{document}, which is not fully determined from first principles. We show that, owing to the flexibility of \begin{document}$w_\tau(x)$\end{document}, the large-x profile \begin{document}$u^{\pi}(x)\sim (1-x)^{2}$\end{document} can be contained within the LFHQCD formalism. This is in contrast to a previous LFHQCD study (Guy F. de Teramond et al., Phys. Rev. Lett., 120(18), 2018) in which \begin{document}$u^{\pi}(x)\sim (1-x)^{1}$\end{document} was found instead. Given our observations, augmented by perturbative QCD and recent lattice QCD results, we state that the large-x exponent of “2” cannot be excluded.
Near-threshold K*(892)+ meson production in the interaction of π mesons with nuclei
E. Ya. Paryev
2020, 44(11): 114106. doi: 10.1088/1674-1137/abae55
We study the inclusive production of strange vector \begin{document}$K^*(892)^+$\end{document} mesons in \begin{document}${\pi^-}A$\end{document} reactions at near-threshold laboratory incident pion momenta of 1.4–2.0 GeV/c via a nuclear spectral function approach. The approach accounts for incoherent primary \begin{document}$\pi^-$\end{document} meson–proton \begin{document}${\pi^-}p \to {K^*(892)^+}\Sigma^-$\end{document} production processes as well as the influence of the scalar \begin{document}$K^*(892)^+$\end{document}–nucleus potential (or the \begin{document}$K^*(892)^+$\end{document} in-medium mass shift) on these processes. We calculate the absolute differential and total cross sections for the production of \begin{document}$K^*(892)^+$\end{document} mesons from carbon and tungsten nuclei at laboratory angles of 0\begin{document}$^{\circ}$\end{document}–45\begin{document}$^{\circ}$\end{document} and at the aforementioned momenta in five scenarios for the aforenoted shift. We show that the \begin{document}$K^*(892)^+$\end{document} momentum distributions and their excitation functions (absolute and relative) possess a high sensitivity to changes in the in-medium \begin{document}$K^*(892)^+$\end{document}mass shift in the low-momentum region of 0.1–0.6 GeV/c. Therefore, the measurement of such observables in a dedicated experiment at the GSI pion beam facility in the near-threshold momentum domain will allow us to get valuable information on the \begin{document}$K^*(892)^+$\end{document} in-medium properties.
Prediction of moment of inertia of rotating nuclei
Mohd Kh. M. Abu El Sheikh, A. A. Okhunov, H. Abu Kassim, M. U. Khandaker
2020, 44(11): 114107. doi: 10.1088/1674-1137/abb0dd
In this study, the mathematical expression formulated by Bohr for the moment of inertia of even-even nuclei based on the hydrodynamical model is modified. The modification pertains to the kinetic energy of the surface oscillations, including the second and third terms of the R-expansion as well as the first term, which had already been modified by Bohr. Therefore, this work can be considered a continuation and support of Bohr's hydrodynamic model. The procedure yields a Bohr formula to be multiplied by a factor that depends on the deformation parameter. Bohr's (modified) formula is examined by applying it on axially symmetric even-even nuclei with atomic masses ranging between 150 and 190 as well as on some triaxial symmetry nuclei. In this paper, the modification of Bohr's formula is discussed, including information about the stability of this modification and the second and third terms of the R-expansion in Bohr's formula. The results of the calculation are compared with the experimental data and Bohr's results recorded earlier. The results obtained are in good agreement with experimental data, with a ratio of approximately 0.7, and are better than those of the unmodified ones.
Modified astrophysical S-factor of 12C+12C fusion reaction at sub-barrier energies
Y. J. Li, X. Fang, B. Bucher, K. A. Li, L. H. Ru, X. D. Tang
2020, 44(11): 115001. doi: 10.1088/1674-1137/abae56
The 12C+12C fusion reaction plays a crucial role in stellar evolution and explosions. Its main open reaction channels include \begin{document}$\alpha$\end{document}, p, n, and 8Be. Despite more than a half century of efforts, large differences remain among the experimental data of this reaction measured using various techniques. In this work, we analyze the existing data using a statistical model. Our calculation shows the following: 1) the relative systematic uncertainties of the predicted branching ratios decrease as the predicted ratios increase; 2) the total modified astrophysical S-factors (S* factors) of the p and \begin{document}$\alpha$\end{document} channels can be obtained by summing the S* factors of their corresponding ground-state transitions and the characteristic \begin{document}$\gamma$\end{document} rays, while taking into account the contributions of the missing channels to the latter. After applying corrections based on branching ratios predicted by the statistical model, an agreement is achieved among the different data sets at Ecm > 4 MeV, while some discrepancies remain at lower energies, suggesting the need for better measurements in the near future. We find that the S* factor recently obtained from an indirect measurement is inconsistent with the direct measurement value at energies below 2.6 MeV. We recommend upper and lower limits for the 12C+12C S* factor based on the existing models. A new 12C+12C reaction rate is also recommended.
Horizon thermodynamics in ${f(R,R^{\mu\nu}R_{\mu\nu}})$ theory
Haiyuan Feng, Rong-Jia Yang
2020, 44(11): 115101. doi: 10.1088/1674-1137/abadef
We investigate whether the new horizon first law still holds in \begin{document}$f(R,R^{\mu\nu}R_{\mu\nu})$\end{document} theory. For this complicated theory, we first determine the entropy of a black hole by using the Wald method, and then derive the energy of the black hole by using the new horizon first law, the degenerate Legendre transformation, and the gravitational field equations. For application, we consider the quadratic-curvature gravity, and first calculate the entropy and energy of a static spherically symmetric black hole, which are in agreement with the results obtained in the literature for a Schwarzschild-(A)dS black hole.
Cosmic acceleration caused by the extra-dimensional evolution in a generalized Randall-Sundrum model
Guang-Zhen Kang, De-Sheng Zhang, Chao Shi, Long Du, Dan Shan, Hong-Shi Zong
2020, 44(11): 115102. doi: 10.1088/1674-1137/abadec
We investigate an \begin{document}$(n+1) $\end{document}-dimensional generalized Randall-Sundrum model with an anisotropic metric which has three different scale factors. One obtains a positive effective cosmological constant \begin{document}$\Omega_{\rm eff}\sim10^{-124}$\end{document}(in Planck units), which only needs a solution \begin{document}$ kr\simeq50-80$\end{document} without fine tuning. Both the visible and hidden brane tensions are positive, which renders the two branes stable. Then, we find that the Hubble parameter is close to a constant in a large region near its minimum, thus causing the acceleration of the universe. Meanwhile, the scale of extra dimensions is smaller than the observed scale but greater than the Planck length. This may suggest that the observed present acceleration of the universe is caused by the extra-dimensional evolution.
Null geodesics, quasinormal modes, and thermodynamic phase transition for charged black holes in asymptotically flat and dS spacetimes
Shao-Wen Wei, Yu-Xiao Liu
2020, 44(11): 115103. doi: 10.1088/1674-1137/abae54
A numerical study has indicated that there exists a relation between the quasinormal modes and the Davies point for a black hole. In this paper, we analytically study this relation for charged Reissner-Nordström black holes in asymptotically flat and de Sitter (dS) spacetimes in the eikonal limit, under which the quasinormal modes can be obtained from the null geodesics using the angular velocity \begin{document}$\Omega$\end{document} and the Lyapunov exponent \begin{document}$\lambda$\end{document} of the photon sphere. Both in asymptotically flat and dS spacetimes, we observe spiral-like shapes in the complex quasinormal mode plane. However, the starting point of the shapes does not coincide with the Davies point. Nevertheless, we find a new relation in which the Davies point exactly meets the maximum temperature T in the T-\begin{document}$\Omega$\end{document} and T-\begin{document}$\lambda$\end{document} planes. In a higher-dimensional asymptotically flat spacetime, although there is no spiral-like shape, such a relation still holds. Therefore, we provide a new relation between black hole thermodynamics and dynamics in the eikonal limit. Applying this relation, we can test the thermodynamic property of a black hole using the quasinormal modes.