2019 Vol. 43, No. 9

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Novel theoretical constraints for color-octet scalar models
Li Cheng, Otto Eberhardt, Christopher W. Murphy
2019, 43(9): 093101. doi: 10.1088/1674-1137/43/9/093101
We study the theoretical constraints on a model whose scalar sector contains one color octet and one or two color singlet SU(2)L doublets. To ensure unitarity of the theory, we constrain the parameters of the scalar potential for the first time at the next-to-leading order in perturbation theory. Moreover, we derive new conditions guaranteeing the stability of the potential. We employ the HEPfit package to extract viable parameter regions at the electroweak scale and test the stability of the renormalization group evolution up to the multi-TeV region. Furthermore, we set upper limits on the scalar mass splittings. All results are given for both cases with and without a second scalar color singlet.
Properties of the decay ${{H\to\gamma\gamma}} $ using the approximate ${{\alpha_s^4}}$ corrections and the principle of maximum conformality
Qing Yu, Xing-Gang Wu, Sheng-Quan Wang, Xu-Dong Huang, Jian-Ming Shen, Jun Zeng
2019, 43(9): 093102. doi: 10.1088/1674-1137/43/9/093102
The decay channel \begin{document}$ H\to\gamma\gamma $\end{document} is an important channel for probing the properties of the Higgs boson. In this paper, we analyze its decay width by using the perturbative QCD corrections up to the \begin{document}$ \alpha_s^4 $\end{document} order with the help of the principle of maximum conformality (PMC). PMC has been suggested in literature for eliminating the conventional renormalization scheme-and-scale ambiguities. After applying PMC, we observe that an accurate renormalization scale independent decay width \begin{document}$ \Gamma(H\to\gamma\gamma) $\end{document} up to the N4LO level can be achieved. Taking the Higgs mass, \begin{document}$ M_{\rm H} = 125.09\pm $\end{document}\begin{document}$ 0.21\pm0.11 $\end{document} GeV, given by the ATLAS and CMS collaborations, we obtain \begin{document}$ \Gamma(H\to \gamma\gamma)|_{\rm LHC} = 9.364^{+0.076}_{-0.075} $\end{document} KeV.
Neural network study of hidden-charm pentaquark resonances
Halil Mutuk
2019, 43(9): 093103. doi: 10.1088/1674-1137/43/9/093103
Recently, the LHCb experiment announced the observation of hidden-charm pentaquark states \begin{document}$P_c(4312)$\end{document}, \begin{document}$P_c(4440)$\end{document}, and \begin{document}$P_c(4457)$\end{document} near \begin{document}$ \Sigma_c \bar{D}$\end{document} and \begin{document}$ \Sigma_c \bar{D}^\ast$\end{document} thresholds. In this present work, we studied these pentaquarks in the framework of the nonrelativistic quark model with four types of potential. We solved five-body Schrödinger equation by using the artificial neural network method and made predictions of parities for these states, which are not yet determined by experiment. The mass of another possible pentaquark state near the \begin{document}$\bar{D}^\ast \Sigma_c^\ast$\end{document} with \begin{document}$J^P=5/2^-$\end{document} is also calculated.
Study of the ${{s\to d\nu\bar{\nu}}}$ rare hyperon decays in the Standard Model and new physics
Xiao-Hui Hu, Zhen-Xing Zhao
2019, 43(9): 093104. doi: 10.1088/1674-1137/43/9/093104
FCNC processes offer important tools to test the Standard Model (SM) and to search for possible new physics. In this work, we investigate the \begin{document}$s\to d\nu\bar{\nu}$\end{document} rare hyperon decays in SM and beyond. We find that in SM the branching ratios for these rare hyperon decays range from \begin{document}$10^{-14}$\end{document} to \begin{document}$10^{-11}$\end{document} . When all the errors in the form factors are included, we find that the final branching ratios for most decay modes have an uncertainty of about 5% to 10%. After taking into account the contribution from new physics, the generalized SUSY extension of SM and the minimal 331 model, the decay widths for these channels can be enhanced by a factor of \begin{document}$2 \sim 7$\end{document}.
Activation cross-sections of titanium isotopes at neutron energies of 13.5–14.8 MeV
Fengqun Zhou, Yueli Song, Yong Li, Xiaojun Sun, Shuqing Yuan
2019, 43(9): 094001. doi: 10.1088/1674-1137/43/9/094001
The cross-sections for 46Ti(n,2n)45Ti, 46Ti(n,p)46m+gSc+47Ti(n,d*)46m+gSc, 46Ti(n,p)46m+gSc, 47Ti(n,p)47Sc+48Ti(n,d*)47Sc, 47Ti(n,p)47Sc, 48Ti(n,p)48Sc+49Ti(n,d*)48Sc,48Ti(n,p)48Sc, and 50Ti(n,α)47Ca reactions were investigated around neutron energies of 13.5–14.8 MeV by means of the activation technique. Fast neutrons were produced by the 3H(d,n)4He reaction. Neutron energies from different directions in the measurements were obtained in advance using the method of cross-section ratios for 90Zr(n,2n)89m+gZr and 93Nb(n,2n)92mNb reactions. The results obtained are analyzed and compared with the experimental data provided by the literature and verified nuclear data in the JEFF-3.3, CENDL-3.1, ENDF/B-VIII.0 libraries, as well as results calculated by Talys-1.9 code.
Tin-accompanied and true ternary fission of 242Pu
M. Zadehrafi, M. R. Pahlavani, M. -R. Ioan
2019, 43(9): 094101. doi: 10.1088/1674-1137/43/9/094101
True ternary fission and Tin-accompanied ternary fission of 242Pu are studied by using the 'Three Cluster Model'. True ternary fission is considered as a formation of heavy fragments in the region \begin{document}$ 28\leqslant Z_1,Z_2,Z_3\leqslant 38 $\end{document} with comparable masses. The possible fission channels are predicted by the potential-energy calculations. Interaction potentials, Q-values and relative yields for all possible fragmentations in equatorial and collinear configurations are calculated and compared. It is found that ternary fission with formation of a double magic nucleus like \begin{document}$ ^{132}{\rm Sn} $\end{document} is more probable than the other fragmentations. Also, the kinetic energies of the fragments for the group \begin{document}$ Z_1 = 32 $\end{document}, \begin{document}$ Z_2 = 32 $\end{document} and \begin{document}$ Z_3 = 30 $\end{document} are calculated for all combinations in the collinear geometry as a sequential decay.
Applicability of 9Be global optical potential to reactions of 7,10,11,12Be
Yong-Li Xu, Yin-Lu Han, Hai-Ying Liang, Zhen-Dong Wu, Hai-Rui Guo, Chong-Hai Cai
2019, 43(9): 094102. doi: 10.1088/1674-1137/43/9/094102
Elastic scattering angular distributions and total reaction cross-sections of 7,10,11,12Be projectiles are predicted by the systematic 9Be global phenomenological optical model potential for target mass numbers ranging from 24 to 209. These predictions provide a detailed analysis by their comparison with the available experimental data. Furthermore, these elastic scattering observables are also predicted for some targets out of the mass number range. The results are in reasonable agreement with the existing experimental data, and they are presented in this study.
Response functions of hot and dense matter in the Nambu-Jona-Lasino model
Chengfu Mu, Ziyue Wang, Lianyi He
2019, 43(9): 094103. doi: 10.1088/1674-1137/43/9/094103
We investigate current-current correlation functions, or the so-called response functions of a two-flavor Nambu-Jona-Lasino model at finite temperature and density. The linear response is investigated introducing the conjugated gauge fields as external sources within the functional path integral approach. The response functions can be obtained by expanding the generational functional in powers of the external sources. We derive the response functions parallel to two well-established approximations for equilibrium thermodynamics, namely mean-field theory and a beyond-mean-field theory, taking into account mesonic contributions. Response functions based on the mean-field theory recover the so-called quasiparticle random phase approximation. We calculate the dynamical structure factors for the density responses in various channels within the random phase approximation, showing that the dynamical structure factors in the baryon axial vector and isospin axial vector channels can be used to reveal the quark mass gap and the Mott dissociation of mesons, respectively. Noting that the mesonic contributions are not taken into account in the random phase approximation, we also derive the response functions parallel to the beyond-mean-field theory. We show that the mesonic fluctuations naturally give rise to three kinds of famous diagrammatic contributions: the Aslamazov-Lakin contribution, the self-energy or density-of-state contribution, and the Maki-Thompson contribution. Unlike the equilibrium case, in evaluating the fluctuation contributions, we need to carefully treat the linear terms in external sources and the induced perturbations. In the chiral symmetry breaking phase, we find an additional chiral order parameter induced contribution, which ensures that the temporal component of the response functions in the static and long-wavelength limit recovers the correct charge susceptibility defined using the equilibrium thermodynamic quantities. These contributions from mesonic fluctuations are expected to have significant effects on the transport properties of hot and dense matter around the chiral phase transition or crossover, where the mesonic degrees of freedom are still important.
Energy staggering parameters in nuclear magnetic rotational bands
Wu-Ji Sun, Jian Li
2019, 43(9): 094104. doi: 10.1088/1674-1137/43/9/094104
This study presents the systematics of energy staggering for magnetic rotational bands with \begin{document}$ M1 $\end{document} and \begin{document}$ E2 $\end{document} transition properties, which are strictly consistent with the features of good candidates of magnetic rotational bands in the \begin{document}$ A\sim80 $\end{document}, 110, 130, and 190 mass regions. The regularities exhibited by these bands with respect to the staggering parameter, which increases with increasing spin, are in agreement with the semiclassical description of shears mechanism. Moreover, the abnormal behaviour in the backbend regions or close to band termination has also been discussed. Taking the magnetic dipole bands with same configuration in three \begin{document}$ N = 58 $\end{document} isotones, i.e., \begin{document}$ ^{103} {\rm Rh}$\end{document}, \begin{document}$ ^{105} {\rm Ag}$\end{document}, and \begin{document}$ ^{107} {\rm In}$\end{document}, as examples, the transition from chiral to magnetic rotation with the proton number approaching \begin{document}$ Z = 50 $\end{document} is presented. Moreover, the self-consistent tilted axis and principle axis cranking relativistic mean-field theories are applied to investigate the rotational mechanism in the dipole band of \begin{document}$ ^{105} {\rm Ag}$\end{document}.
Classical model for diffusion and thermalization of heavy quarks in a hot medium: memory and out-of-equilibrium effects
Marco Ruggieri, Marco Frasca, Santosh Kumar Das
2019, 43(9): 094105. doi: 10.1088/1674-1137/43/9/094105
We consider a simple model for the diffusion of heavy quarks in a hot bath, modeling the latter by an ensemble of oscillators distributed according to either a thermal distribution or to an out-of-equilibrium distribution with a saturation scale. In this model it is easy to introduce memory effects by changing the distribution of oscillators: we model them by introducing a Gaussian distribution, \begin{document}$ {\rm d}N/{\rm d}\omega $\end{document}, which can be deformed continuously from a \begin{document}$ \delta- $\end{document}function, giving a Markov dissipation, to a broad kernel with memory. Deriving the equation of motion of the heavy quark in the bath, we remark how dissipation comes out naturally as an effect of the back-reaction of the oscillators on the bath. Moreover, the exact solution of this equation allows to define the thermalization time as the time necessary to remove any memory of the initial conditions. We find that the broadening of the dissipative kernel, while keeping the coupling fixed, lowers the thermalization time. We also derive the fluctuation-dissipation theorem for the bath, and use it to estimate the kinematic regime in which momentum diffusion of the heavy quark dominates over drift. We find that diffusion is more important as long as \begin{document}$ K_0/{\cal E} $\end{document} is small, where \begin{document}$ K_0 $\end{document} and \begin{document}$ {\cal E} $\end{document} denote the initial energy of the heavy quark and the average energy of the bath, respectively.
Anisotropic evolution of 4-brane in a 6D generalized Randall-Sundrum model
Guang-Zhen Kang, De-Sheng Zhang, Long Du, Jun Xu, Hong-Shi Zong
2019, 43(9): 095101. doi: 10.1088/1674-1137/43/9/095101
We investigate a 6D generalized Randall-Sundrum brane world scenario with a bulk cosmological constant. Each stress-energy tensor \begin{document}$ T_{ab}^{i} $\end{document} on the brane is shown to be similar to a constant vacuum energy. This is consistent with the Randall-Sundrum model, in which each 3-brane Lagrangian yielded a constant vacuum energy. By adopting an anisotropic metric ansatz, we obtain the 5D Friedmann-Robertson-Walker field equations. In a slightly later period, the expansion of the universe is proportional to the square root of time, \begin{document}$ t^{\frac{1}{2}} $\end{document}, which is similar to the period of the radiation-dominated regime. Moreover, we investigate the case with two \begin{document}$ a(t) $\end{document} and two \begin{document}$ b(t) $\end{document}. In a large range of \begin{document}$ t $\end{document}, we obtain the 3D effective cosmological constant \begin{document}$ \Lambda_{\rm eff} = -2\Omega/3>0 $\end{document}, which is independent of the integral constant. Here, the scale factor is an exponential expansion, which is consistent with our present observation of the universe. Our results demonstrate that it is possible to construct a model that solves the dark energy problem, while guaranteeing a positive brane tension.
On the possibility to determine neutrino mass hierarchy via supernova neutrinos with short-time characteristics
Junji Jia, Yaoguang Wang, Shun Zhou
2019, 43(9): 095102. doi: 10.1088/1674-1137/43/9/095102
In this paper, we investigate whether it is possible to determine the neutrino mass hierarchy via a high-statistics and real-time observation of supernova neutrinos with short-time characteristics. The essential idea is to utilize distinct times-of-flight for different neutrino mass eigenstates from a core-collapse supernova to the Earth, which may significantly change the time distribution of neutrino events in the future huge water-Cherenkov and liquid-scintillator detectors. For illustration, we consider two different scenarios. The first case is the neutronization burst of \begin{document}$ \nu^{}_e$\end{document} emitted in the first tens of milliseconds of a core-collapse supernova, while the second case is the black hole formation during the accretion phase for which neutrino signals are expected to be abruptly terminated. In the latter scenario, it turns out only when the supernova is at a distance of a few Mpc and the fiducial mass of the detector is at the level of gigaton, might we be able to discriminate between normal and inverted neutrino mass hierarchies. In the former scenario, the probability for such a discrimination is even less due to a poor statistics.
Perturbative modes and black hole entropy in f (Ricci) gravity
Chuanyi Wang, Liu Zhao
2019, 43(9): 095103. doi: 10.1088/1674-1137/43/9/095103
f (Ricci) gravity is a special kind of higher curvature gravity whose bulk Lagrangian density is the trace of a matrix-valued function of the Ricci tensor. It is shown that under some mild constraints, f (Ricci) gravity admits Einstein manifolds as exact vacuum solutions, and can be ghost-free and tachyon-free around maximally symmetric Einstein vacua. It is also shown that the entropy for spherically symmetric black holes in f (Ricci) gravity calculated via the Wald method and the boundary Noether charge approach are in good agreement.
W-hairs of the black holes in three-dimensional spacetime
Jing-Bo Wang
2019, 43(9): 095104. doi: 10.1088/1674-1137/43/9/095104
In a previous publication, we claimed that a black hole can be considered as a topological insulator. A direct consequence of this claim is that their symmetries should be related. In this paper, we give a representation of the near-horizon symmetry algebra of the BTZ black hole using the W1+∞ symmetry algebra of the topological insulator in three-dimensional spacetime. Based on the W1+∞ algebra, we count the number of the microstates of the BTZ black holes and obtain the Bekenstein-Hawking entropy.