[en] A 10%Ca-substitution in 124 leads to an increase of the Tc from 80K to 90K. Nevertheless, room temperature x-ray and neutron diffraction measurements do not show a contraction of the apical bond in Ca-124, like in the case of 123. The dependence of the bondlengths of 124 and Ca-124 as a function of temperature between 3000-100K has been determined with x-ray single crystal structure refinement of several crystals. The results of one crystal show that the Ca-substitution causes at lower temperatures a contraction of the apical bond, and the decrease of the orthorhombicity.This indicates that in all members of the Y-Ba-Cu-O family the contraction of the apical bond is associated with the increase of the positive carrier concentration and increase of the Tc:This is achieved in 123 with variation of the nonstoichiometry of the single chains, in 124 with pressure, and in Ca-124 with the thermal compression at low temperatures. In addition, Ca-124 shows a structural phase transition at 150K, the assumed spin gap opening temperature. The bondlength changes accompanying this transition have been measured. (author)

[en] An earlier calculation of the energy surface for X-point tilts if the CuO6 octahedra in La_2-x(Sr, Ba)_xCuO₄ revealed an eight well potential surface. This surface indicated an extremely anharmonic situation and seemed to provide an explanation of a number of observed phenomena in this system, especially the coincidence of a drop in Tc with the occurrence of the low temperature tetragonal phase. We review experimental developments since that time, which indicate new complications. We also reconsider the zone boundary chain-buckling mode of the chain oxygen atoms in YBa₂Cu₃O₇, for which our earlier calculation indicated a very flat (slightly double well) energy surface that would provide very little restoring force to this motion. We have studied the coupling of the chain buckling motion to the carriers by evaluating the shifts of bands near the Fermi energy. These deformation potentials themselves are not large (∼ 0.1-0.2 eV/A) and non-linear coupling is minor out to displacements of 0.25 A. (author)

[en] The superconducting state in the high Tc oxides can be fully understood by strong electron coupling to low frequency phonon modes. The major features of this state and the parameters are described. (author)

[en] The Chou-Yang model is applied to the identical/sup -/rho elastic data from the SPS hyperon beam experiments under the assumption that hyperons have approximately equal form factors. Three different expressions for the proton electric form factor are used. All cases yield similar results in good agreement with experiment. The model predicts a dip in dσ/dt around - t≅1 (GeV/c)/sup 2/ at present energies

[en] The authors study the production of heavy bound sttes of squarks at the SSC and analyse their decays into longitudinal W's and Z's. In some situations a squarkonium state can be detected through its decay into a pair of W's

[en] The authors explore general properties of matter coupled supergravities with antisymmetric tensor fields embedded in linear multiplets. The four-dimensional supersymmetric version of the Green-Schwarz mechanism leads to the introduction of super Chern-Simons form multiplets whose general component expressions are derived. The use of superconformal techniques allows us to discuss several topics relevant to superstring effective actions and in particular to give simple forms for the string-loop corrections to the Kahler potential and the U(1) anomaly cancelling term present in certain superstring compactifications

[en] The authors give explicit formulas for the decays of the neutralinos and charginos of the minimal model of supersymmetry into other neutralinos and charginos plus a W, Z, or Higgs boson. The important features of these decays are illustrated and their phenomenological implications discussed. In general, this class of two-body decays is dominant for the heaviest charginos and neutralinos

[en] The way to evaluate multi-parton cross-sections systematically is discussed. In the leading-double-log approximation in QCD, the successive emission of soft gluons is at successively smaller angles. The angular ordering, however, is violated in the next-to-leading order

[en] The authors examine the possibility of finding charged Higgs bosons (H^+-) at the SSC. The charged Higgs boson is produced with a top quark via a gluon + bottom quark interaction (g + b → H + t[. For the two Higgs doublet models, H^+- decays predominantly into t+b. Since the background from QCD processes will be very severe for this decay mode, the authors studied the H^+- → tau + ν decay mode. Even for this mode, background from the processes rhorho → W +t+ spectators → iota + ν/sub iota/ +t+ spectators will be very high. In the two Higgs doublet models, it is very difficult to extract the charged Higgs signal for reasonable values of the ratio of the two vacuum expectation values (tan β = v₁v₂

[en] The authors examined the production of t quarks at the SSC when the t quarks have mass 100 < M/sub t/ < 200 GeV and found a clean lepton trigger. The trigger is a single high rho/sub T/ charged lepton accompanied by missing transverse energy. The large rho/sub T/ cuts on the leptons ensure that the decay products of the recoiling t-bar lie in a hemisphere roughly opposite the charged lepton. Application of simple jet algorithms to this hadronic hemisphere suggests that this technique can measure the t-quark mass to O