## 2019 Vol. 43, No. 10

column

Display Method:          |

2019, 43(10): 103001. doi: 10.1088/1674-1137/43/10/103001
Abstract:
We study the sensitivity of constraining the model independent HZZ coupling based on the effective theory up to dimension-6 operators at a future Higgs factory. Using the current conceptual design parameters of the Circular Electron Positron Collider, we give the experimental limits for the model independent operators given by the total Higgsstrahlung cross-section and the angular distribution of Z boson decays. In particular, we give the very small sensitivity limit for the CP violation parameter \begin{document}$\tilde g$\end{document}, which will be a clear window to test the Standard Model and look for new physics signals.
2019, 43(10): 103101. doi: 10.1088/1674-1137/43/10/103101
Abstract:
Using symmetry properties, we determine the mixing pattern of a class of nonlocal quark bilinear operators containing a straight Wilson line along a spatial direction. We confirm the previous study that mixing among the lowest dimensional operators, which have a mass dimension equal to three, can occur if chiral symmetry is broken in the lattice action. For higher dimensional operators, we find that the dimension-three operators will always mix with dimension-four operators, even if chiral symmetry is preserved. Also, the number of dimension-four operators involved in the mixing is large, and hence it is impractical to remove the mixing by the improvement procedure. Our result is important for determining the Bjorken-x dependence of the parton distribution functions using the quasi-distribution method on a Euclidean lattice. The requirement of using large hadron momentum in this approach makes the control of errors from dimension-four operators even more important.
2019, 43(10): 103102. doi: 10.1088/1674-1137/43/10/103102
Abstract:
We study the phenomenology of a model that addresses the neutrino mass, dark matter, and generation of the electroweak scale in a single framework. Electroweak symmetry breaking is realized via the Coleman-Weinberg mechanism in a classically scale invariant theory, while the neutrino mass is generated radiatively through interactions with dark matter in a typically scotogenic manner. The model introduces a scalar triplet and singlet and a vector-like fermion doublet that carry an odd parity of \begin{document}$Z_2$\end{document}, and an even parity scalar singlet that helps preserve classical scale invariance. We sample over the parameter space by taking into account various experimental constraints from the dark matter relic density and direct detection, direct scalar searches, neutrino mass, and charged lepton flavor violating decays. We then examine by detailed simulations possible signatures at the LHC to find some benchmark points of the free parameters. We find that the future high-luminosity LHC will have a significant potential in detecting new physics signals in the dilepton channel.
2019, 43(10): 103103. doi: 10.1088/1674-1137/43/10/103103
Abstract:
In this exploratory study, near-threshold scattering of D and \begin{document}$\bar{D}^*$\end{document} meson is investigated using lattice QCD with \begin{document}$N_f=2+1+1$\end{document} twisted mass fermion configurations. The calculation is performed in the coupled-channel Lüscher finite-size formalism. The study focuses on the channel with \begin{document}$I^G(J^{PC})=1^+(1^{+-})$\end{document} where the resonance-like structure \begin{document}$Z_c(3900)$\end{document} was discovered. We first identify the two most relevant channels and the lattice study is performed in the two-channel scattering model. Combined with the two-channel Ross-Shaw theory, scattering parameters are extracted from the energy levels by solving the generalized eigenvalue problem. Our results for the scattering length parameters suggest that for the particular lattice parameters that we studied, the best fit parameters do not correspond to the peak in the elastic scattering cross-section near the threshold. Furthermore, in the zero-range Ross-Shaw theory, the scenario of a narrow resonance close to the threshold is disfavored beyond the 3\begin{document}$\sigma$\end{document} level.
2019, 43(10): 103104. doi: 10.1088/1674-1137/43/10/103104
Abstract:
Motivated by the rapid development of heavy flavor physics experiments, we study the tree-dominated nonleptonic \begin{document}$\bar{B}_{u,d,s}^* \to D_{u,d,s}^*V$\end{document} (\begin{document}$V = D^{*-},D_s^{*-},K^{*-},{\rho}^-$\end{document}) decays within the factorization approach. The relevant transition form factors are calculated by employing the covariant light-front quark model. Helicity amplitudes are calculated and analyzed in detail, and a very clear hierarchical structure \begin{document}$|H_{-0}| \approx 2|H_{00}| > |H_{0-}|\approx|H_{–}|>|H_{0+}|\approx|H_{++}|$\end{document} is presented. The branching fractions are computed and discussed. Numerically, the CKM-favored \begin{document}$\bar{B}^*_q\to D^*_q \rho^{-}$\end{document} and \begin{document}$D^*_q D_s^{*-}$\end{document} decays have relatively large branching fractions, \begin{document}$\gtrsim {\cal O}(10^{-8})$\end{document}, and could be observed by LHC and Belle-II experiments in the future.
2019, 43(10): 103105. doi: 10.1088/1674-1137/43/10/103105
Abstract:
We consider chiral perturbation theory with an explicit broad σ-meson and study its contribution to the scalar form factors of the pion and the nucleon. Our goal is to learn more about resonance saturation in the scalar sector.
2019, 43(10): 103106. doi: 10.1088/1674-1137/43/10/103106
Abstract:
There are different constructions of the flux of triad in loop quantum gravity, namely the fundamental and alternative flux operators. In parallel to the consistency check on the two versions of operator by the algebraic calculus in the literature, we check their consistency by the graphical calculus. Our calculation based on the original Brink graphical method is obviously simpler than the algebraic calculation. It turns out that our consistency check fixes the regulating factor \begin{document}$\kappa_{\rm reg}$\end{document} of the Ashtekar-Lewandowski volume operator as \begin{document}$\displaystyle\frac{1}{2}$\end{document}, which corrects its previous value in the literature.
2019, 43(10): 104101. doi: 10.1088/1674-1137/43/10/104101
Abstract:
The spallation cross-section data for the long-lived fission products (LLFPs) are scarce but required for the design of accelerator driven systems. In this paper, the isospin dependent quantum molecular dynamics model and the statistical code GEMINI are applied to simulate deuteron-induced spallation in the energy region of GeV/nucleon. By comparing the calculations with the experimental data, the applicability of the model is verified. The model is then applied to simulate the spallation of 90Sr, 93Zr, 107Pd, and 137Cs induced by deuterons at 200, 500 and 1000 MeV/nucleon. The cross-sections of isotopes, the cross-sections of long-lived nuclei, and the reaction energy are presented. Using the above observables, the feasibility of LLFP transmutation by spallation is discussed.
2019, 43(10): 104102. doi: 10.1088/1674-1137/43/10/104102
Abstract:
Excited states of odd-odd nucleus 92Nb and odd-A nucleus 93Nb were populated in the 6Li+ 89Y reaction with an incident energy of 34 MeV. The processes that produce 92,93Nb and can be measured by a combination of light charged particle and gamma ray measurements are discussed. Twenty new transitions are observed and eight new levels are constructed in 92Nb, and in addition two new transitions are added to the level scheme of 93Nb. Using shell model calculations, the low-lying structure of 92Nb is investigated and compared with the experimental results.
2019, 43(10): 104103. doi: 10.1088/1674-1137/43/10/104103
Abstract:
This study investigates the structural properties of super-heavy nuclei with Z = 130 by adopting the relativistic mean-field (RMF) theory within an axially deformed oscillator basis with the NL3 force parameter set. We study the binding energies, quadrupole deformation, nuclear radii, neutron separation energies, and other bulk properties. Moreover, we analyze the favorable decay modes for clear cognitive content of nuclei, such as alpha decay, using different formulae including the Viola-Seaberg, analytical formula of Royer, universal curve formula, and universal decay law. We compare these with the corresponding fission process. The spontaneous fission of super-heavy nuclei is studied with \begin{document}$Z = 130$\end{document} within the mass region \begin{document}$310 \leqslant A\leqslant 340$\end{document}. The results exhibit good agreement with finite range droplet model (FRDM) data. This formalism presents a significant step forward in the study of the structure and decay modes of the isotopes of Z = 130. With this appraisal, we investigate the possible shell/sub-shell closure for super-heavy nuclei adjacent by decay chains of alpha and other radioactive decay particles.
2019, 43(10): 105101. doi: 10.1088/1674-1137/43/10/105101
Abstract:
It is widely believed that the screening mechanism is an essential feature for the modified gravity theory. Although this mechanism has been examined thoroughly in the past decade, their analyses are based on a conventional fluid prescription for the matter-sector configuration. In this paper, we demonstrate a new formulation of the chameleon mechanism in F(R) gravity theory, to shed light on quantum-field theoretical effects on the chameleon mechanism as well as the related scalaron physics, induced by the matter sector. We show a possibility that the chameleon mechanism is absent in the early Universe based on a scale-invariant-extended scenario beyond the standard model of particle physics, in which a realistic electroweak phase transition, yielding the right amount of baryon asymmetry of Universe today, simultaneously breaks the scale invariance in the early Universe. We also briefly discuss the oscillation of the scalaron field and indirect generation of non-tensorial gravitational waves induced by the electroweak phase transition.
2019, 43(10): 105102. doi: 10.1088/1674-1137/43/10/105102
Abstract:
Neutrinos produced from \begin{document}$\gamma$\end{document}-ray bursts (GRBs) carry significant physical information. The electron density in the GRBs outflow is very large. In this study, we calculate the matter effect on neutrinos when they propagate through such a dense region. The average survival probability and the flavor ratio of neutrinos are determined. The ratio of resonant neutrino energy from different spherical shells provides the information of power index N for the power-law distribution of electrons in the hot fireball model. Electron density in the magnetic jet model is sufficiently lower than in the hot fireball model. The matter effect on neutrinos can be used to distinguish these two models. The coherent effect of strongly lensed PeV neutrinos is also discussed. The average survival probability of strongly-lensed electron neutrinos in the normal and inverted hierarchical cases are presented. The results show that this coherent effect can be used to determine the hierarchical mass of neutrinos.
2019, 43(10): 105103. doi: 10.1088/1674-1137/43/10/105103
Abstract:
Based on the cosmological principle and quantum Yang-Mills gravity in the super-macroscopic limit, we obtain an exact recession velocity and cosmic redshift z, as measured in an inertial frame \begin{document}$F\equiv F(t,x,y,z).$\end{document} For a matter-dominated universe, we have the effective cosmic metric tensor \begin{document}$G_{\mu\nu}(t) = (B^2(t),-A^2(t), -A^2(t),-A^2(t)),$\end{document} \begin{document}$\ A\propto B\propto t^{1/2}$\end{document}, where \begin{document}$t$\end{document} has the operational meaning of time in \begin{document}$F$\end{document} frame. We assume a cosmic action \begin{document}$S\equiv S_{\rm cos}$\end{document} involving \begin{document}$G_{\mu\nu}(t)$\end{document} and derive the ‘Okubo equation’ of motion, \begin{document}$G^{\mu\nu}(t)\partial_\mu S \partial_\nu S - m^2 = 0$\end{document}, for a distant galaxy with mass \begin{document}$m$\end{document}. This cosmic equation predicts an exact recession velocity, \begin{document}$\dot{r} = rH/[1/2 +\sqrt{1/4+r^2H^2/C_o^2} ]<C_o$\end{document}, where \begin{document}$H = \dot{A}(t)/A(t)$\end{document} and \begin{document}$C_o = B/A$\end{document}, as observed in the inertial frame \begin{document}$F$\end{document}. For small velocities, we have the usual Hubble's law \begin{document}$\dot{r} \approx rH$\end{document} for recession velocities. Following the formulation of the accelerated Wu-Doppler effect, we investigate cosmic redshifts z as measured in \begin{document}$F$\end{document}. It is natural to assume the massless Okubo equation, \begin{document}$G^{\mu\nu}(t)\partial_\mu \psi_e \partial_\nu \psi_e = 0$\end{document}, for light emitted from accelerated distant galaxies. Based on the principle of limiting continuation of physical laws, we obtain a transformation for covariant wave 4-vectors between and inertial and an accelerated frame, and predict a relationship for the exact recession velocity and cosmic redshift, \begin{document}$z = [(1+V_r)/(1-V_r^2)^{1/2}] - 1$\end{document}, where \begin{document}$V_r = \dot{r}/C_o<1$\end{document}, as observed in the inertial frame \begin{document}$F$\end{document}. These predictions of the cosmic model are consistent with experiments for small velocities and should be further tested.
2019, 43(10): 105104. doi: 10.1088/1674-1137/43/10/105104
Abstract:
As a charged fermion drops into a BTZ black hole, the laws of thermodynamics and the weak cosmic censorship conjecture are investigated in both the normal and extended phase space, where the cosmological parameter and renormalization length are regarded as extensive quantities. In the normal phase space, the first and second law of thermodynamics, and the weak cosmic censorship are found to be valid. In the extended phase space, although the first law and weak cosmic censorship conjecture remain valid, the second law is dependent on the variation of the renormalization energy dK. Moreover, in the extended phase space, the configurations of extremal and near-extremal black holes are not changed, as they are stable, while in the normal phase space, the extremal and near-extremal black holes evolve into non-extremal black holes.