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Ying Zhang

Publications and source records attributed to Ying Zhang.

At least 577 records · Page 32Linked to original sources
arXiv2010

On Temporal Variations of the Multi-TeV Cosmic Ray Anisotropy using the Tibet III Air Shower Array

We analyze the large-scale two-dimensional sidereal anisotropy of multi-TeV cosmic rays by Tibet Air Shower Array, with the data taken from 1999 November to 2008 December. To explore temporal variations of the anisotropy, the data set is divided into nine intervals, each in a time span of about one year. The sidereal anisotropy of magnitude about 0.1% appears fairly stable from year to year over the entire observation period of nine years. This indicates that the anisotropy of TeV Galactic cosmic rays remains insensitive to solar activities since the observation period covers more than a half of the 23rd solar cycle.

astro-ph.HE↗
arXiv2009

Computation of the p6 order chiral Lagrangian coefficients from the underlying theory of QCD

We present results of computing the p6 order low energy constants in the normal part of chiral Lagrangian both for two and three flavor pseudo-scalar mesons. This is a generalization of our previous work on calculating the p4 order coefficients of the chiral Lagrangian in terms of the quark self energy Sigma(p2) approximately from QCD. We show that most of our results are consistent with those we can find in the literature.

hep-ph↗
arXiv2009

Observation of TeV Gamma Rays from the Fermi Bright Galactic Sources with the Tibet Air Shower Array

Using the Tibet-III air shower array, we search for TeV gamma-rays from 27 potential Galactic sources in the early list of bright sources obtained by the Fermi Large Area Telescope at energies above 100 MeV. Among them, we observe 7 sources instead of the expected 0.61 sources at a significance of 2 sigma or more excess. The chance probability from Poisson statistics would be estimated to be 3.8 x 10^-6. If the excess distribution observed by the Tibet-III array has a density gradient toward the Galactic plane, the expected number of sources may be enhanced in chance association. Then, the chance probability rises slightly, to 1.2 x 10^-5, based on a simple Monte Carlo simulation. These low chance probabilities clearly show that the Fermi bright Galactic sources have statistically significant correlations with TeV gamma-ray excesses. We also find that all 7 sources are associated with pulsars, and 6 of them are coincident with sources detected by the Milagro experiment at a significance of 3 sigma or more at the representative energy of 35 TeV. The significance maps observed by the Tibet-III air shower array around the Fermi sources, which are coincident with the Milagro >=3sigma sources, are consistent with the Milagro observations. This is the first result of the northern sky survey of the Fermi bright Galactic sources in the TeV region.

astro-ph.HE↗
arXiv2009

Magnetic moments of $^{33}$Mg in time-odd relativistic mean field approach

The configuration-fixed deformation constrained relativistic mean field approach with time-odd component has been applied to investigate the ground-state properties of $^{33}$Mg with effective interaction PK1. The ground state of $^{33}$Mg has been found to be prolate deformed, $β_2=0.23$, with the odd neutron in $1/2[330]$ orbital and the energy -251.85 MeV which is close to the data -252.06 MeV. The magnetic moment $- 0.9134 μ_\mathrm{N}$ is obtained with the effective electromagnetic current which well reproduces the data $- 0.7456 μ_\mathrm{N}$ self-consistently without introducing any parameter. The energy splittings of time reversal conjugate states, the neutron current, the energy contribution from the nuclear magnetic potential, and the effect of core polarization are discussed in detail.

nucl-th↗
arXiv2009

Solving the Dirac equation with nonlocal potential by Imaginary Time Step method

The Imaginary Time Step (ITS) method is applied to solve the Dirac equation with the nonlocal potential in coordinate space by the ITS evolution for the corresponding Schrödinger-like equation for the upper component. It is demonstrated that the ITS evolution can be equivalently performed for the Schrödinger-like equation with or without localization. The latter algorithm is recommended in the application for the reason of simplicity and efficiency. The feasibility and reliability of this algorithm are also illustrated by taking the nucleus $^{16}$O as an example, where the same results as the shooting method for the Dirac equation with localized effective potentials are obtained.

nucl-th↗
arXiv2009

Large-scale sidereal anisotropy of multi-TeV galactic cosmic rays and the heliosphere

We develop a model anisotropy best-fitting to the two-dimensional sky-map of multi-TeV galactic cosmic ray (GCR) intensity observed with the Tibet III air shower (AS) array. By incorporating a pair of intensity excesses in the hydrogen deflection plane (HDP) suggested by Gurnett et al., together with the uni-directional and bi-directional flows for reproducing the observed global feature, this model successfully reproduces the observed sky-map including the "skewed" feature of the excess intensity from the heliotail direction, whose physical origin has long remained unknown. These additional excesses are modeled by a pair of the northern and southern Gaussian distributions, each placed ~50 degree away from the heliotail direction. The amplitude of the southern excess is as large as ~0.2 %, more than twice the amplitude of the northern excess. This implies that the Tibet AS experiment discovered for the first time a clear evidence of the significant modulation of GCR intensity in the heliotail and the asymmetric heliosphere.

astro-ph.GA↗
arXiv2009

Z' Boson Mixings with Z-γand Charge Assignments

Based on the general description for Z'-Z-γmixing as derived from the electroweak chiral Lagrangian, we characterize and classify the various new physics models involving the Z' boson that have appeared in the literature into five classes: 1. Models with minimal Z'-Z mass mixing; 2. Models with minimal Z'-Z kinetic mixing; 3. Models with general Z'-Z mixing; 4. Models with Z'-γkinetic and Z'-Z mixing; and 5. Models with Stueckelberg-type mixing. The corresponding mixing matrices are explicitly evaluated for each of these classes. We constrain and classify the Z' boson charges with respect to quark-leptons by anomaly cancellation conditions.

hep-ph↗
arXiv2009

Non-local mean field effect on nuclei near Z=64 sub-shell

Evolutions of single-particle energies and Z=64 sub-shell along the isotonic chain of N=82 are investigated in the density dependent relativistic Hartree-Fock (DDRHF) theory in comparison with other commonly used mean field models such as Skyrme HF, Gogny HFB and density dependent relativistic Hartree model (DDRMF). The pairing is treated in the BCS scheme, except for Gogny HFB. It is pointed out that DDRHF reproduces well characteristic features of experimental $Z$-dependence of both spin orbital and pseudo-spin orbital splittings around the sub-shell closure Z=64. Non-local exchange terms of the isoscalar $σ$ and $ω$ couplings play dominant roles in the enhancements of the spin-orbit splitting of proton 2d states, which is the key ingredient to give the Z=64 sub-shell closure properly. On the other hand, the $π$ and $ρ$ tensor contributions for the spin-orbit splitting cancel each other and the net effect becomes rather small. The enhancement of the sub-shell gaps towards Z=64 is studied by the DDRHF, for which the local terms of the scalar and vector meson couplings are found to be important.

nucl-th↗
arXiv2009

Avoid the Tsunami of the Dirac sea in the Imaginary Time Step method

The discrete single-particle spectra in both the Fermi and Dirac sea have been calculated by the imaginary time step (ITS) method for the Schrödinger-like equation after avoiding the "tsunami" of the Dirac sea, i.e., the diving behavior of the single-particle level into the Dirac sea in the direct application of the ITS method for the Dirac equation. It is found that by the transform from the Dirac equation to the Schrödinger-like equation, the single-particle spectra, which extend from the positive to the negative infinity, can be separately obtained by the ITS evolution in either the Fermi sea or the Dirac sea. Identical results with those in the conventional shooting method have been obtained via the ITS evolution for the equivalent Schrödinger-like equation, which demonstrates the feasibility, practicality and reliability of the present algorithm and dispels the doubts on the ITS method in the relativistic system.

nucl-th↗
arXiv2008

Stueckelberg Mechanism and Chiral Lagrangian for $Z'$ Boson

Traditional Stueckelberg Mechanism is shown equivalent to set up a gauged U(1) chiral Lagrangian and fix special gauge. With this mechanism, the original electro-weak chiral Lagrangian is inlarged by including an extra U(1) symmetry to represent physics for $Z'$ boson. We build up complete list of electro-weak chiral Lagrangian up to order of $p^4$ including $Z'$ and higgs bosons. The most general mixing among neutral gauge bosons is diagonalized completely and the connections among these operators to triple, quartic couplings involving $Z'$ boson and to that in traditional electro-weak chiral Lagrangian are made.

hep-ph↗
arXiv2008

A Novel X-Axis Tuning Fork Gyroscope with "8 Vertical Springs-Proofmass" Structure on (111)-Silicon

A novel x-axis tuning fork MEMS gyroscope with "8 vertical springs-proofmass" structure for Coriolis effect detection is presented. Compared with the common single-plane springs, the 8 vertical springs, symmetrically located at the top and bottom sides, more stably suspend the large thick proofmass featuring large capacitance variation and low mechanical noise. A bulk-micromachining technology is applied to obtain the large proofmass and twins-like dual beams. During the fabrication process, the dimensions of the 8 vertical springs are precisely confined by thermal oxide protected limit trenches (LTs) sidewalls and the extreme slowly etched (111)-planes; therefore a small mismatch of less than 30 Hz is achieved before tuning. Initial test shows a sensitivity of 0.15mV/(deg/s) and rate resolution around 0.1deg/s under atmosphere pressure.

cs.OH↗
arXiv2008

Quantum phase transitions in d-wave superconductors

Motivated by the strong, low temperature damping of nodal quasiparticles observed in some cuprate superconductors, we study quantum phase transitions in d_{x^2-y^2} superconductors with a spin-singlet, zero momentum, fermion bilinear order parameter. We present a complete, group-theoretic classification of such transitions into 7 distinct cases (including cases with nematic order) and analyze fluctuations by the renormalization group. We find that only 2, the transitions to d_{x^2-y^2}+is and d_{x^2-y^2} + i d_{xy} pairing, possess stable fixed points with universal damping of nodal quasiparticles; the latter leaves the gapped quasiparticles along (1,0), (0,1) essentially undamped.

cond-mat.str-el↗
arXiv2008

Renormalization group analysis of quantum critical points in d-wave superconductors

We describe a search for renormalization group fixed points which control a second-order quantum phase transition between a d_{x^2-y^2} superconductor and some other superconducting ground state. Only a few candidate fixed points are found. In the finite temperature quantum-critical region of some of these fixed points, the fermion quasiparticle lifetime is very short and the spectral function has an energy width of order k_B T near the Fermi points. Under the same conditions, the thermal conductivity is infinite in the scaling limit. We thus provide simple, explicit, examples of quantum theories in two dimensions for which a purely fermionic quasiparticle description of transport is badly violated.

cond-mat.str-el↗
arXiv2007

Two likelihood-based semiparametric estimation methods for panel count data with covariates

We consider estimation in a particular semiparametric regression model for the mean of a counting process with ``panel count'' data. The basic model assumption is that the conditional mean function of the counting process is of the form $E\{\mathbb{N}(t)|Z\}=\exp(β_0^TZ)Λ_0(t)$ where $Z$ is a vector of covariates and $Λ_0$ is the baseline mean function. The ``panel count'' observation scheme involves observation of the counting process $\mathbb{N}$ for an individual at a random number $K$ of random time points; both the number and the locations of these time points may differ across individuals. We study semiparametric maximum pseudo-likelihood and maximum likelihood estimators of the unknown parameters $(β_0,Λ_0)$ derived on the basis of a nonhomogeneous Poisson process assumption. The pseudo-likelihood estimator is fairly easy to compute, while the maximum likelihood estimator poses more challenges from the computational perspective. We study asymptotic properties of both estimators assuming that the proportional mean model holds, but dropping the Poisson process assumption used to derive the estimators. In particular we establish asymptotic normality for the estimators of the regression parameter $β_0$ under appropriate hypotheses. The results show that our estimation procedures are robust in the sense that the estimators converge to the truth regardless of the underlying counting process.

math.ST↗
arXiv2007

Electroweak Chiral Lagrangian for Left-right Symmetric Models

The complete list of electroweak chiral Lagrangian up to order of p4 for left-right symmetric models with a neutral light higgs is provided. The connection of these operators to left and right gauge boson mixings and masses is made and their contribution to conventional generalized electroweak chiral Lagrangian with a neutral light higgs included in is estimated.

hep-ph↗