Showing papers by "International School for Advanced Studies published in 1987"
TL;DR: In this article, an explicitly unitary operator for the light superstring S-matrix above planckian energies was obtained, which is dominated by graviton exchange at large impact parameters and by absorption at small impact parameters.
864 citations
TL;DR: Calculated du spectre d'excitation optique and du coefficient de diffusion des electrons; bon accord avec les valeurs experimentales.
Abstract: The electronic states and dynamical properties of dilute liquid K-KCl solutions are studied by simultaneous integration of the coupled time-dependent Schr\"odinger equation for the excess electrons and classical equations of motion for the ions. Excess electrons are found to spend most of their time in localized F-center states, whose size and shape can fluctuate significantly. Transport is mostly due to jumps between localized states, with a jumping rate \ensuremath{\simeq}3\ifmmode\times\else\texttimes\fi{}${10}^{12}$ ${\mathrm{s}}^{\mathrm{\ensuremath{-}}1}$. The optical excitation spectrum and the electron diffusion coefficient are calculated and found to be in agreement with the experimental data.
143 citations
TL;DR: The equilibrium geometries of selenium clusters Se 3 to Se 8 have been calculated using a parameter-free density functional method, and the most prominent low-energy structures are found using combined molecular dynamics and simulated annealing techniques as mentioned in this paper.
139 citations
01 Jan 1987
122 citations
TL;DR: The nonmelting of Au(111) is contrasted with the gradual melting behavior of Lennard-Jones surfaces.
Abstract: A molecular-dynamics study of the melting behavior of Au(111) (both reconstructed and unreconstructed) has been carried out using a recently developed many-body force scheme. The reconstructed (denser) surface remains stable up to the bulk melting temperature ${T}_{M}$, showing no form of microscopic surface melting. By contrast, the two outermost layers of the unreconstructed surface "melt" \ensuremath{\sim}100 K below ${T}_{M}$. However, no more layers melt as ${T}_{M}$ is approached. The nonmelting of Au(111) is contrasted with the gradual melting behavior of Lennard-Jones surfaces.
86 citations
76 citations
TL;DR: In this paper, the structure and energy of Au(110) were studied by means of a well-tested many-body force model, and molecular dynamics was used to search the lowest energy configuration at T = 0, as well as the mean room temperature configuration.
74 citations
TL;DR: I teoremi astratti vengono applicati per trovare soluzioni periodiche di sistemi dinamici con potenziali sia limitati sia con singolarita as discussed by the authors.
Abstract: Si prova l'esistenza di punti critici di funzionali che non verificano la condizione (PS).I teoremi astratti vengono applicati per trovare soluzioni periodiche di sistemi dinamici con potenziali sia limitati sia con singolarita.
64 citations
TL;DR: The role of the evaluation map in the calculations of global anomalies is discussed in this article, both for field theories and for sigma-models, and it is shown that global anomalies are connected with the differential characters of Cheeger and Simons.
Abstract: In this paper, we examine specifically the role of the evaluation map in sigma-models and strings. We discuss the difference between sigma-models and field theory, as far as anomaly cancellation is concerned. The introduction of the Wess—Zumino terms in different sigma-models is considered. Anomalies in string theory are discussed, with special attention to the conformal anomalies and to the sigma-model anomalies for the imbedded (or immersed) world-sheet of the string. Conformal anomalies in two dimensions are connected to holomorphic and gravitational anomalies. In order to have the cancellation of the sigma-model anomalies of the string, certain topological conditions must be satisfied by the ambient manifold. The role of the evaluation map in the calculations of global anomalies is also discussed, both for field theories and for sigma-models. In particular global anomalies are connected with the differential characters of Cheeger and Simons. We show that the absence of global anomalies in sigma-models is guaranteed by the absence of torsion in suitable homology groups of the target space.
48 citations
46 citations
TL;DR: In this paper, it is shown that the replacement of standard quantum mechanics by QMSL has the only effect of producing an actual reduction of the wave function, which is not the effect of the original quantum mechanics.
Abstract: Quantum mechanics with spontaneous localization (QMSL) is a recently proposed stochastic modification of theN-body Schrodinger equation consistent both with microphysics and macrophysics. QMSL is applied here to the measurement problem. It is shown that the replacement of standard quantum mechanics by QMSL has the only effect of producing an actual reduction of the wave function.
TL;DR: In this paper, the optimal low-temperature surface structure of Au(100), Au(110) and Au(111) was studied by using molecular dynamics as a tool to search, through suitable annealing and quenching cycles, the lowest surface energy states of slabs.
TL;DR: In this paper, the authors used spin density functional theory to describe the interaction between solvated electrons in KCl in the high dilution limit and found that electrons repel each other and localize into separate F-center-like states.
Abstract: Spin density functional theory is used to describe the interaction between solvated electrons in KCl in the high dilution limit. In agreement with recent calculations based on the path integral method our results for antiparallel spin predict a strong tendency to form localized bielectronic complexes. At variance with numerical path integral, our method can efficiently treat the case of parallel spins. For this case we find that electrons repel each other and localize into separate F-center-like states.
TL;DR: In this paper, the Lagrangean is modified with the introduction of an auxiliary field that represents the Hartree potential, leading to the same results as the present version of the theory.
TL;DR: A system of gravity and free massless scalar fields minimally coupled to gravity in a 7-dimensional background which is a direct product of a 4-dimensional Minkowski space and a 3-dimensional homogeneously deformed three-sphere is studied.
Abstract: We study a system of gravity and free massless scalar fields minimally coupled to gravity in a 7-dimensional background which is a direct product of a 4-dimensional Minkowski space and a 3-dimensional homogeneously deformed three-sphere. Compactification is caused by the vacuum energy of scalar fields. The effective potential as a function of two parameters (scale and deformation) is calculated numerically after dimensional regularization. We find the effective potential decreases rapidly toward negative infinity in both prolate and oblate directions. The classical curvature, however, can balance the quantum effect and yields three extrema. In addition to the round S/sup 3/ solution in the quantum-corrected field equations, we find two deformed ones. One of the deformed solutions corresponds to the local minimum of the total potential. The round three-sphere solution, however, corresponds to the local maximum of that. More scalar fields can enlarge the scale of the internal space but not affect the shape. This serves as an example of gauge symmetry breaking by deformation of the internal space in multidimensional theories. The stability of these background solutions is discussed but not established conclusively. A discussion of four different analytic-continuation procedures is presented in one of the appendixes.
TL;DR: In this article, the contribution from the Z0-boson decays into neutralino pairs to the Z 0-total width, the Neutrino-counting cross section σ(e+e−→γ+missing energy), and events with very characteristics missing energy signatures, arising from the decays of heavier neutralinos are investigated.
TL;DR: In this paper, a Coulomb gas representation for the Ramond sectors of the N = 1 supersymmetric models is constructed, and the fusion rules and the 4-point functions are calculated explicitly by this method.
TL;DR: In this article, the longitudinal phonon spectrum and the associated Raman strength of (100) InAs GaSb superlattices are calculated along the growth direction, showing new modes localized at the interface.
TL;DR: In this article, the mechanism for generating radiative breaking of the gauge symmetry at an intermediate mass scale is analyzed in E 6 superstring-inspired models, which can be induced by large vacuum expectation values, which are developed along a flat direction of the scalar potential.
TL;DR: In this article, the problem of distinguishing between the standard model and the supersymmetric Higgs bosons is considered in the context of °Z decays, and it is shown that for some choices of the parameters, the branching ratio for Z° → H°γ is strongly enhanced by the exchange of super-ymmetric fermions as virtual particles.
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TL;DR: In this paper, the simplest synchrotron-self-Compton (SSC) model is applied to all blazars that have been observed in the X-ray region and have known VLBI sizes, and the minimum kinematic Doppler factor for each source is derived All high polarization quasars (HPQs) but only half of the 30 BL Lac objects in the sample require relativistic enhancement of radiation due to beaming effects.
Abstract: Relativistic beaming of radiation is generally invoked to explain the extreme properties of blazars The simplest synchrotron-self-Compton (SSC) model is applied to all blazars that have been observed in the X-ray region and have known VLBI sizes, and the minimum kinematic Doppler factor for each source is derived All high polarization quasars (HPQs), but only half of the 30 BL Lac objects in the sample require relativistic enhancement of radiation due to beaming effects The different Doppler factor distributions for the two classes of sources argue against the hypothesis that BL Lacs could be low-luminosity HPQs whose strong emission lines are swamped out by the boosted nonthermal continuum Thus HPQs and BL Lacs could be intrinsically different in their physical structure
TL;DR: In this article, conditions ensuring the strong flow-invariance property for a compact set M, with respect to the differential system x′ = ƒ(t, x), are considered.
TL;DR: In this article, the results of interband magneto-optical measurements of GaAs quantum wells are compared with the calculated transition energies and amplitudes in a six-band envelope function approach.
TL;DR: In this paper, a brief review of the first stage of spinors associated with higher-dimensional geometries and the physical relevance of Cartan's simple (pure) spinors is presented.
TL;DR: In this paper, it was argued that due to the existence of a previously unnoticed topological term, three dimensional gravity on ℝ 3 with asymptotically flat boundary conditions can be consistently quantized for any value of the topological mass.
01 Jan 1987
TL;DR: In this article, a discussion on some recent advances in the existence of periodic solutions of some second order dynamical systems with singular potentials is presented, and a discussion of the relation between these solutions and singular potential solutions is discussed.
Abstract: The paper contains a discussion on some recent advances in the existence of periodic solutions of some second order dynamical systems with singular potentials.
TL;DR: In this paper, it was shown that there exists at least one T-periodic solution of (V) under suitable assumptions on v,Y,(t, 0), this solution is not identically zero.
TL;DR: In this paper, the neutrino oscillations in matter are assumed to be responsible for the observed reduction in the capture rate for the 37 Cl detector, and the expression of the probability that a solar v e reaches the Earth as a v e is given in the case of three generations.
TL;DR: In this paper, the curvatures of superdiffS1/S1 and superdiff S1/super S1 were calculated using super-Toeplitz operator techniques, and the critical dimension D = 10 was discovered as a result of vanishing curvature of the product bundle over the super-flag manifold.