35,279 research outputs found

    Empirical pseudopotential calculations of Cd1-xMnxTe

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    Empirical pseudopotential calculations for the entire range of alloy concentrations of cubic Cd(1-x)Mn(x)Te are presented. The atomic form factors have been deduced empirically by fitting the band structure to spectroscopic data available from the literature. The pseudopotential band structures indicate optical bowing may occur in the alloy Cd(1-x)Mn(x)Te and have been used to determine the effective masses of the electron and light, and heavy holes, which for CdTe are in agreement with accepted values. The effective masses for Cd(1-x)Mn(x)Te are given for the first time, acid are expressed as first- and second-order polynomials in x. The implications of these results for spectroscopic experiments are discussed. © 1996 American Institute of Physics

    Modelling the shear-tension coupling of woven engineering fabrics

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    An approach to incorporate the coupling between the shear compliance and in-plane tension of woven engineering fabrics, in finite-element-based numerical simulations, is described. The method involves the use of multiple input curves that are selectively fed into a hypoelastic constitutive model that has been developed previously for engineering fabrics. The selection process is controlled by the current value of the in-plane strain along the two fibre directions using a simple algorithm. Model parameters are determined from actual experimental data, measured using the Biaxial Bias Extension test. An iterative process involving finite element simulations of the experimental test is used to normalise the test data for use in the code. Finally, the effectiveness of the method is evaluated and shown to provide qualitatively good predictions

    A Method to Determine Vcb|V_{cb}| at the Weak Scale in Top Decays at the LHC

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    Until now, the Cabibbo Kobayashi Maskawa matrix element, Vcb|V_{cb}|, has always been measured in BB decays, i.e.~at an energy scale qbmb2q_b\sim \frac{m_b}{2}, far below the weak scale. We consider here the possibility of measuring it close to the weak scale, at qWmWq_W\sim m_W, in top decays at the Large Hadron Collider (LHC). Our proposed method would use data from the LHC experiments in hadronic top decays tbWbbct\rightarrow bW\rightarrow b\overline{b} c, tagged by the semileptonic decay of the associated top. We estimate the uncertainty of such a measurement, as a function of present and potential future experimental jet flavour-tagging performances, and conclude that first measurements using the data collected during 2016 - 2018 could yield a fractional error on \Vcb\ of order 7\% per experiment. We also give projected performances at higher luminosities, which could yield sensitivity to any Standard Model running of \Vcb\ below the weak scale, if present.Comment: 15 pages, 1 figures. Changes for V3: removed earlier Fig. 1, associated text and citations, added one new citatio

    Fully Constrained Majorana Neutrino Mass Matrices Using Σ(72×3)\Sigma(72\times 3)

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    In 2002, two neutrino mixing ansatze having trimaximally-mixed middle (ν2\nu_2) columns, namely tri-chi-maximal mixing (TχM\text{T}\chi\text{M}) and tri-phi-maximal mixing (TϕM\text{T}\phi\text{M}), were proposed. In 2012, it was shown that TχM\text{T}\chi\text{M} with χ=±π16\chi=\pm \frac{\pi}{16} as well as TϕM\text{T}\phi\text{M} with ϕ=±π16\phi = \pm \frac{\pi}{16} leads to the solution, sin2θ13=23sin2π16\sin^2 \theta_{13} = \frac{2}{3} \sin^2 \frac{\pi}{16}, consistent with the latest measurements of the reactor mixing angle, θ13\theta_{13}. To obtain TχM(χ=±π16)\text{T}\chi\text{M}_{(\chi=\pm \frac{\pi}{16})} and TϕM(ϕ=±π16)\text{T}\phi\text{M}_{(\phi=\pm \frac{\pi}{16})}, the type~I see-saw framework with fully constrained Majorana neutrino mass matrices was utilised. These mass matrices also resulted in the neutrino mass ratios, m1:m2:m3=(2+2)1+2(2+2):1:(2+2)1+2(2+2)m_1:m_2:m_3=\frac{\left(2+\sqrt{2}\right)}{1+\sqrt{2(2+\sqrt{2})}}:1:\frac{\left(2+\sqrt{2}\right)}{-1+\sqrt{2(2+\sqrt{2})}}. In this paper we construct a flavour model based on the discrete group Σ(72×3)\Sigma(72\times 3) and obtain the aforementioned results. A Majorana neutrino mass matrix (a symmetric 3×33\times 3 matrix with 6 complex degrees of freedom) is conveniently mapped into a flavon field transforming as the complex 6 dimensional representation of Σ(72×3)\Sigma(72\times 3). Specific vacuum alignments of the flavons are used to arrive at the desired mass matrices.Comment: 20 pages, 1 figure. arXiv admin note: substantial text overlap with arXiv:1402.085

    Deviations from Tribimaximal Neutrino Mixing using a Model with Δ(27)\Delta(27) Symmetry

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    We present a model of neutrino mixing based on the flavour group Δ(27)\Delta(27) in order to account for the observation of a non-zero reactor mixing angle (θ13\theta_{13}). The model provides a common flavour structure for the charged-lepton and the neutrino sectors, giving their mass matrices a `circulant-plus-diagonal' form. Mass matrices of this form readily lead to mixing patterns with realistic deviations from tribimaximal mixing, including non-zero θ13\theta_{13}. With the parameters constrained by existing measurements, our model predicts an inverted neutrino mass hierarchy. We obtain two distinct sets of solutions in which the atmospheric mixing angle lies in the first and the second octants. The first (second) octant solution predicts the lightest neutrino mass, m329 meVm_3 \sim 29~\text{meV} (m365 meVm_3 \sim 65~\text{meV}) and the CPCP phase, δCPπ4\delta_{CP} \sim -\frac{\pi}{4} (δCPπ2\delta_{CP} \sim \frac{\pi}{2}), offering the possibility of large observable CPCP violating effects in future experiments.Comment: 9 pages, 3 figure

    The structural dependence of the effective mass and Luttinger parameters in semiconductor quantum wells

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    A detailed comparison of the empirical pseudopotential method with single and multiple band calculations based on the envelope function and effective mass approximations are presented. It is shown that, in order to give agreement with the more rigorous microscopic approach of the pseudopotential method, structural dependent effective masses and Luttinger parameters must be invoked. The CdTe/Cd(1 – x)Mn(x)Te system has been employed as an example, and the first pseudopotential calculations of quantum wells and superlattices in this material are presented. It is shown that the electron, light- and heavy-hole effective masses tend towards twice their bulk values in the limit of narrow quantum wells. © 1997 American Institute of Physics

    The physics of B factories

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