共查询到20条相似文献,搜索用时 15 毫秒
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We have searched for hadronic axions which may be produced in the Sun by a bremsstrahlung-like process, and observed in the HPGe detector by an axioelectric effect. A conservative upper limit on the hadronic axion mass of ma?334 eV at 95% C.L. is obtained. Our experimental approach is based on the axion–electron coupling and it does not include the axion–nucleon coupling, which suffers from the large uncertainties related to the estimation of the flavor-singlet axial-vector matrix element. 相似文献
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We consider cosmological consequences of the spontaneous breaking of a global symmetry that is anomalous under technicolor interactions, leading to the emergence of a light axion-like particle. Avoiding overclosure of the universe by such axions yields the upper bound fa?1010 GeV on the symmetry breaking scale, corresponding to keV-scale axions. However, diffuse X-ray background data typically require larger values of fa. The overclosure and X-ray bounds can be reconciled if the axion initial amplitude of oscillations Ai∼fa/10. In this case, a viable axionic dark matter candidate with a mass in the 50–100 eV range emerges. The detection of this type of dark matter may pose a challenge. 相似文献
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The deviation δQW of the weak charge from its standard model prediction due to the mixing of the W boson with the charged bilepton Y as well as of the Z boson with the neutral Z′ and the real part of the non-Hermitian neutral bilepton X in the economical 3–3–1 model is established. Additional contributions to the usual δQW expression in the extra U(1) models and the left–right models are obtained. Our calculations are quite different from previous analyzes in this kind of the 3–3–1 models and give the limit on mass of the Z′ boson, the Z–Z′ and W–Y mixing angles with the more appropriate values: MZ′>564 GeV, −0.018<sinφ<0 and |sinθ|<0.043. 相似文献
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Azimuthal anisotropy in heavy-ion collisions is studied by taking into account the ridges generated by semi-hard scattering of intermediate-momentum partons, which can be sensitive to the initial spatial configuration of the medium in non-central collisions. In a simple treatment of the problem where the recombination of only thermal partons is considered, analytical formulas can be derived that yield results in accord with the data on v2 for pT<1–2 GeV/c. Centrality dependence is described by a geometrical factor. Ridge phenomenology is used to determine the initial slopes of v2 at low pT for both pion and proton. For higher pT, shower partons from high-pT jets must be included, but they are not considered here. 相似文献
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Molecular dynamics is used to study the kinetic stability of a classical fullerene C46 and its non-classical analog with a square. The lifetimes of both clusters till the moments of their isomerization are directly calculated as functions of temperature. The activation energies Ea of isomerization processes are determined from the fits of the results obtained to the Arrhenius law. For the non-classical fullerene, the value of Ea=3.1±0.2 eV is found to be considerably below that for the classical one, Ea=4.5±0.3 eV. In view of rather low kinetic stability of non-classical C46, its experimental registration in a gas phase seems to be problematic. 相似文献
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If light hidden sector photons (γ′s) exist, they could be produced through kinetic mixing with solar photons in the eV energy range. We propose to search for this hypothetical γ′-flux with the Super-Kamiokande and/or upgraded CAST detectors. The proposed experiments are sensitive to the γ–γ′ mixing strength as small as 10−5?χ?10−9 for the γ′ mass region 10−4?mγ′?10−1 eV and, in the case of non-observation, would improve limits recently obtained from photon regeneration laser experiments for this mass region. 相似文献
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To complement existing knowledge of the density matrix γF(x,y) of independent fermions for N particles in one dimension under harmonic confinement, the corresponding matrix γIB(x,y) for impenetrable bosons is given for N=2 and 3 (with the N=4 form available also). For fermions the momentum density is then obtained and illustrated numerically for N=10. The boson momentum density is studied analytically at high momentum p , the coefficients of the p−4 and p−6 terms being tabulated for N=2–5 inclusive. Their dependence on powers of N is exhibited numerically. Finally, the functional relationship between γIB(x,y) and γF(x,y) is formally set out and illustrated. 相似文献
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Fluxmetric and magnetometric demagnetizing factors, Nf and Nm, for cylinders along the axial direction are numerically calculated as functions of material susceptibility χ and the ratio γ of length to diameter. The results have an accuracy better than 0.1% with respect to min(Nf,m,1-Nf,m) and are tabulated in the range of 0.01?γ?500 and -1?χ<∞. Nm along the radial direction is evaluated with a lower accuracy from Nm along the axis and tabulated in the range of 0.01?γ?1 and -1?χ<∞. Some previous results are discussed and several applications are explained based on the new results. 相似文献
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We calculate the strange star properties in the framework of the Field Correlator Method. We find that for gluon condensate values G2 in the range 0.006–0.007 GeV4, which give a critical temperature Tc∼170 MeV at μc=0, the sequences of strange stars are compatible with some of the semi-empirical mass–radius relations and data obtained from astrophysical observations. 相似文献
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The phase stability and electronic structure of YCu were studied by self-consistent full-potential linearized augmented plane wave method (FP_LAPW) on the basis of the density functional theory (DFT). The calculated equilibrium volumes are 41.963 and 173.21 Å3 for B2 and B27 structures respectively, which are in good agreement with the experimental values. The total energy of the B27 phase is about 0.03 eV lower than that of the B2 phase. The formation energies are −1.173 and −1.204 eV for B2 and B27 structures respectively. The density of state at the Fermi energy, N(EF), is 1.08 states/eV for B2 phase and 0.92 states/eV for B27 phase, respectively. These results indicate that the B27 phase is the thermodynamic ground state equilibrium phase of YCu at low temperatures, as observed experimentally. However, our calculations also predict that a pressure-induced B27 to B2 phase transition exists in YCu. 相似文献
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Hong Li Jie Liu Jun-Qing Xia Lei Sun Zu-Hui Fan Charling Tao Andre Tilquin Xinmin Zhang 《Physics letters. [Part B]》2009
In this Letter, we study the cosmological implications of the 100 square degree Weak Lensing survey (the CFHTLS-Wide, RCS, VIRMOS-DESCART and GaBoDS surveys). We combine these weak lensing data with the cosmic microwave background (CMB) measurements from the WMAP5, BOOMERanG, CBI, VSA, ACBAR, the SDSS LRG matter power spectrum and the Type Ia Supernoave (SNIa) data with the “Union” compilation (307 sample), using the Markov Chain Monte Carlo method to determine the cosmological parameters, such as the equation-of-state (EoS) of dark energy w , the density fluctuation amplitude σ8, the total neutrino mass ∑mν and the parameters associated with the power spectrum of the primordial fluctuations. Our results show that the ΛCDM model remains a good fit to all of these data. In a flat universe, we obtain a tight limit on the constant EoS of dark energy, w=−0.97±0.041 (1σ ). For the dynamical dark energy model with time evolving EoS parameterized as wde(a)=w0+wa(1−a), we find that the best-fit values are w0=−1.064 and wa=0.375, implying the mildly preference of Quintom model whose EoS gets across the cosmological constant boundary during evolution. Regarding the total neutrino mass limit, we obtain the upper limit, ∑mν<0.471 eV (95% C.L.) within the framework of the flat ΛCDM model. Due to the obvious degeneracies between the neutrino mass and the EoS of dark energy model, this upper limit will be relaxed by a factor of 2 in the framework of dynamical dark energy models. Assuming that the primordial fluctuations are adiabatic with a power law spectrum, within the ΛCDM model, we find that the upper limit on the ratio of the tensor to scalar is r<0.35 (95% C.L.) and the inflationary models with the slope ns?1 are excluded at more than 2σ confidence level. In this Letter we pay particular attention to the contribution from the weak lensing data and find that the current weak lensing data do improve the constraints on matter density Ωm, σ8, ∑mν, and the EoS of dark energy. 相似文献
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We calculate low scale gravity effects on the cross section for neutrino–nucleon scattering at center of mass energies up to the Greisen–Zatsepin–Kuzmin (GZK) scale, in the eikonal approximation. We compare the cases of an infinitely thin brane embedded in n=5 compactified extra-dimensions, and of a brane with a physical tension MS=1 TeV and MS=10 TeV. The extra dimensional Planck scale MD is set at 103 GeV and 2×103 GeV. We also compare our calculations with neutral current standard model calculations in the same energy range, and compare the thin brane eikonal cross section to its saddle point approximation. New physics effects enhance the cross section by orders of magnitude on average. They are quite sensitive to MS and MD choices, though much less sensitive to n. 相似文献
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A family of spherically symmetric solutions with horizon in the model with m -component anisotropic fluid is presented. The metrics are defined on a manifold that contains a product of n−1 Ricci-flat “internal” spaces. The equation of state for any s -th component is defined by a vector Us belonging to Rn+1. The solutions are governed by moduli functions Hs obeying non-linear differential equations with certain boundary conditions imposed. A simulation of black brane solutions in the model with antisymmetric forms is considered. An example of solution imitating M2–M5 configuration (in D=11 supergravity) corresponding to Lie algebra A2 is presented. 相似文献