A Model of Low-lying States in Strongly Interacting Electroweak Symmetry-Breaking Sector

It is proposed that, in a strongly-interacting electroweak sector, besides the Goldstone bosons, the coexistence of a scalar state ($H$) and vector resonances such as $A_1$ [$I^G(J^P)=1^-(1^+$)], $V$ [$1^+(1^-)$] and $\omega_H^{}$ [$0^-(1^-)$] is required by the proper Regge behavior of the forward scattering amplitudes. This is a consequence of the following well-motivated assumptions: (a). Adler-Weisberger-type sum rules and the superconvergence relations for scattering amplitudes hold in this strongly interacting sector; (b). the sum rules at $t=0$ are saturated by a minimal set of low-lying states with appropriate quantum numbers. It therefore suggests that a complete description should include all these resonances. These states may lead to distinctive experimental signatures at future colliders.Comment: revised version, to appear in Modern Physics Letters A; file also available via anonymous ftp at ftp://ucdhep.ucdavis.edu/han/sews/lowlying.p

Co-doped Ceria: Tendency towards ferromagnetism driven by oxygen vacancies

We perform an electronic structure study for cerium oxide homogeneously-doped with cobalt impurities, focusing on the role played by oxygen vacancies and structural relaxation. By means of full-potential ab-initio methods, we explore the possibility of ferromagnetism as observed in recent experiments. Our results indicate that oxygen vacancies seem to be crucial for the appearance of a ferromagnetic alignment among Co impurities, obtaining an increasing tendency towards ferromagnetism with growing vacancy concentration. The estimated couplings cannot explain though, the experimentally observed room-temperature ferromagnetism. In this systematic study, we draw relevant conclusions regarding the location of the oxygen vacancies and the magnetic couplings involved. In particular, we find that oxygen vacancies tend to nucleate in the neighborhood of Co impurities and we get a remarkably strong ferromagnetic coupling between Co atoms and the Ce^{3+} neighboring ions. The calculated magnetic moments per cell depend on the degree of reduction which could explain the wide spread in the magnetization values observed in the experiments

Cosmological Constant in LQG Vertex Amplitude

A new q-deformation of the Euclidean EPRL/FK vertex amplitude is proposed by using the evaluation of the Vassiliev invariant associated with a 4-simplex graph (related to two copies of quantum SU(2) group at different roots of unity) embedded in a 3-sphere. We show that the large-j asymptotics of the q-deformed vertex amplitude gives the Regge action with a cosmological constant. In the end we also discuss its relation with a Chern-Simons theory on the boundary of 4-simplex.Comment: 6 pages, 5 figures, result and presentation improve

Impurity states in d-wave superconductors with a competing antiferromagnetic interaction

Impurity states in d-wave superconductors with a competing antiferromagnetic (AF) order are investigated by solving the Bogoliubov-de Gennes equations. The potential scattering (PS) model with moderate strength and the Anderson impurity (AI) model with on-site hybridization are employed to describe the weak impurities. In zero external field, the impurity-induced AF order is rather weak and both models are able to give rise to impurity resonant states with close energy and similar profile of the local density of states. In the mixed state, the effect of magnetic-field-induced AF order on the impurity quasiparticle excitation is also examined. We find that the response of the impurity state to the presence of a local AF order is quite different for the two impurity models when a superconducting vortex is pinned by the impurity. For the PS model, the impurity resonance is subtly dependent on the sign and strength of the scattering potential, while for the AI model in the strong hybridization regime, the low-lying resonance is pinned near the Fermi level within the small gap opened by the AF order and is insensitive to the strength of the coupling between the impurity spin and the conduction electron. Based on our numerical results, we think that the two models give rise to different behaviors of the impurity resonances for both the nickel and zinc impurities in the magnetic field and the prospective scanning tunneling microscopic observation might give a clue to the dominant mechanism of the impurity states in the high-T c cuprates.published_or_final_versio

Heavy Grazing Significantly Reduced the Temporal Stability of Aboveground Biomass

The stability of a plant community is the embodiment of the dynamic balance achieved by the interaction between populations in the form of competition or mutual benefit. Temporal stability refers to the ratio of the average value to the variance of the biomass of the population or community. For grassland ecosystems, the stability of the grassland plant community is the basis for its survival and functional performance, and is the key factor affecting its structure and function. In order to study the impact of grazing on the temporal stability of aboveground biomass of desert steppe, this study used a completely randomized block design to study the relationship between the temporal stability of Stipa breviflora desert steppe vegetation communities and functional groups under different grazing intensities and their influencing factors, and then explored the relationship between temporal stability and species richness and species asynchrony. The results showed that heavy grazing significantly reduced temporal stability, species richness and species asynchrony of grassland communities. In terms of plant functional groups, grazing significantly reduced the stability of shrubs, semi-shrubs and perennial miscellaneous grasses. There were significant positive correlations between species richness and species asynchrony and community stability. Therefore, understanding changes in community asynchrony, richness and functional group stability is of great significance to further understanding of the temporal stability of desert grassland plant communities

Left-right loading dependence of shock response of (111)//(112) Cu bicrystals: Deformation and spallation

We investigate with molecular dynamics the dynamic response of Cu bicrystals with a special asymmetric grain boundary (GB), (111)//(112)〈110〉, and its dependence on the loading directions. Shock loading is applied along the GB normal either from the left or right to the GB. Due to the structure asymmetry, the bicrystals demonstrate overall strong left-right loading dependence of its shock response, including compression wave features, compression and tensile plasticity, damage characteristics (e.g., spall strength), effective wave speeds and structure changes, except that spallation remains dominated by the GB damage regardless of the loading directions. The presence or absence of transient microtwinning also depends on the loading directions

Deformation and spallation of shocked Cu bicrystals with Σ3 coherent and symmetric incoherent twin boundaries

We perform molecular dynamics simulations of Cu bicrystals with two important grain boundaries (GBs), Σ3 coherent twin boundaries (CTB), and symmetric incoherent twin boundaries (SITB) under planar shock wave loading. It is revealed that the shock response (deformation and spallation) of the Cu bicrystals strongly depends on the GB characteristics. At the shock compression stage, elastic shock wave can readily trigger GB plasticity at SITB but not at CTB. The SITB can induce considerable wave attenuation such as the elastic precursor decay via activating GB dislocations. For example, our simulations of a Cu multilayer structure with 53 SITBs (∼1.5-μm thick) demonstrate a ∼80% elastic shock decay. At the tension stage, spallation tends to occur at CTB but not at SITB due to the high mobility of SITB. The SITB region transforms into a threefold twin via a sequential partial dislocation slip mechanism, while CTB preserves its integrity before spallation. In addition, deformation twinning is a mechanism for inducing surface step during shock tension stage. The drastically different shock response of CTB and SITB could in principle be exploited for, or benefit, interface engineering and materials design