Higlights
• A coupled-channel lattice study of the resonance-like structure Zc(3900)
2019, 43(10): 103103. doi: 10.1088/1674-1137/43/10/103103
In this exploratory study, near-threshold scattering of D and $\bar{D}^*$ meson is investigated using lattice QCD with $N_f=2+1+1$ twisted mass fermion configurations. The calculation is performed in the coupled-channel Lüscher finite-size formalism. The study focuses on the channel with $I^G(J^{PC})=1^+(1^{+-})$ where the resonance-like structure $Z_c(3900)$ 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$\sigma$ level.
• Dark matter and LHC phenomenology of a scale-invariant scotogenic model
2019, 43(10): 103102. doi: 10.1088/1674-1137/43/10/103102
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 $Z_2$, 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.
• F(R) gravity in the early Universe: electroweak phase transition and chameleon mechanism
2019, 43(10): 105101. doi: 10.1088/1674-1137/43/10/105101
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.
In Press
More >
• Searching for neutrino-less nouble neta necay of 136Xe with PandaX-II liquid xenon detector
Published: 2019-09-16, doi: 10.1088/1674-1137/43/11/113001
Show Abstract
We report the Neutrino-less Double Beta Decay (NLDBD) search results from PandaX-II dual-phase liquid xenon time projection chamber. The total live time used in this analysis is 403.1 days from June 2016 to August 2018. With NLDBD-optimized event selection criteria, we obtain a fiducial mass of 219 kg of natural xenon. The accumulated xenon exposure is 242 kg·yr, or equivalently 22.2 kg·yr of 136Xe exposure. At the region around 136Xe decay Q-value of 2458 keV, the energy resolution of PandaX-II is 4.2%. We find no evidence of NLDBD in PandaX-II and establish a lower limit for decay half-life of 2.1 $\times 10^{23}$ yr at the 90% confidence level, which corresponds to an effective Majorana neutrino mass $m_{\beta \beta} < (1.4 - 3.7)$ eV. This is the first NLDBD result reported from a dual-phase xenon experiment.
• The contribution of the first forbidden transitions to the nuclear β-decay half-life
Published: 2019-09-16, doi: 10.1088/1674-1137/43/11/114014
Show Abstract
$\beta$-decay half-life is a key quantity for nuclear structure and nucleosynthesis studies. There exist large uncertainties in the contributions of allowed and forbidden transitions to the total $\beta$-decay life, which limits the resolution of the predicted $\beta$-decay half-life. We systematically study the contribution of the first forbidden (FF) transitions to the $\beta^{-}$-decay half-life, and quantify it with a formula based on simple physics considerations. We also propose a new formula for calculation of the $\beta^{-}$-decay half-life that includes the FF contribution. It is shown that the inclusion of the contribution of FF transitions significantly improves the precision of calculations of the $\beta^{-}$-decay half-life. By fitting of the RQRPA results for neutron-rich $Z = 47$, 57 isotopes and $N = 80$, 94 isotones, the formula for the contribution of the FF transitions gives similar results as the RQRPA calculations. However, because of limited experimental data for the branching ratios of unstable nuclei, the fit parameters are not fully constrained. Therefore, the proposed formula for the $\beta^{-}$-decay half-life is more suitable for calculations of half-lives than of the FF contributions. The formula could be used to predict the $\beta^{-}$-decay half-life in nuclear structure studies as well as nucleosynthesis calculations in stars.
• Giant dipole resonance parameters from photoabsorption cross-sections
Published: 2019-09-11, doi: 10.1088/1674-1137/43/11/114102
Show Abstract
The structural effect is believed to have no influence on the decay properties of medium and heavy-mass nuclei at excitation energies above the pairing gap. These properties can be described by statistical properties using so-called photon strength functions for different multipolarities, and directly related to the photoabsorption cross-section ($\sigma_{\rm abs}$). $\sigma_{\rm abs}$ is dominated by the electric giant dipole resonance at $\gamma$ energy $\epsilon_\gamma \leqslant 40$ MeV. In this study, we construct two kinds of systematic giant dipole resonance parameters by fitting the experimental photoabsorption cross-sections. One is based on the microscopic relativistic quasiparticle random phase approximation approach, whereas the other is estimated by the phenomenological models within the Lorentzian representation. Both of them are demonstrated ot efficiently describe the experimental photoabsorption cross-sections available for medium to heavy-mass nuclei, and they can obtain more reliable predictions for the unknown nuclear system.
Current Issued
2019 Vol. 43, No. 10
Published:
Archive