Showing papers by "International School for Advanced Studies published in 1988"
TL;DR: In this paper, upper bounds on all superparticle masses as functions of the top quark mass are derived based on the "naturalness" criterion, which gives an objective criterion to test (or disprove) the idea of low energy supersymmetry, as implemented in supergravity models.
1,126 citations
TL;DR: In this article, a natural way to avoid the introduction by hand of a small mass scale μ in the observable sector of N = 1 supergravity theories is proposed, where all low energy mass parameters arise only from supergravity breaking and SU (2) × U (1) is left unbroken in the limit of exact supersymmetry.
856 citations
TL;DR: The authors showed that superstring collisions at Planckian energies and small deflection angles are calculable through an evaluation and resummation of string loops in flat space-time, leading to a systematic expansion of the collision in classical general relativity and quantum string effects.
Abstract: We argue that superstring collisions at Planckian energies and small deflection angles are calculable through an evaluation and resummation of string loops in flat space-time. This leads to a systematic expansion of the collision in classical general relativity and quantum string effects. Our results explicitly show how unitarity constraints are recovered through loop corrections and how flat metric calculations reveal the generation of nontrivial geometries by energetic particles. Finite-string-size effects can be evaluated in some regimes and are found to modify classical relativity expectations even at impact parameters much larger than the string scale. Conversely, we find that, through the resummation of large genus contributions, intermediate distance physics provides important classical relativity effects even in the hard, fixed angle regime.
517 citations
TL;DR: In this paper, an expression for the total energy of the form V = ½Σ ij φ(r ij ) + Σ i U(ni), where n i = Σiρ(r Ij ) is a generalized atomic coordination.
Abstract: Many well known difficulties associated with the use of two-body forces for the description of metallic systems may be overcome by using an expression for the total energy of the form V = ½Σ ij φ(r ij ) + Σ i U(ni), where n i = Σiρ(r ij ) is a generalized atomic coordination. The three functions φ(r), U(n) and ρ(r) are constructed empirically, by fitting several physical quantities including thermal and surface properties. This simple many-body force scheme can be used in molecular-dynamics simulations with few overheads compared with pair-wise systems. We present our realization for gold and summarize the results of recent structural and dynamical studies of Au surfaces.
386 citations
TL;DR: In this article, a wide variety of theories are discussed in detail: pure Yang-Mills, theories with massive or massless real matter fields, and theories with chiral matter, both for SU( N ) and for the case of a general compact gauge group.
304 citations
204 citations
TL;DR: In this article, a non-linear (supersymmetric) σ-model that describes a string, bosonic or super, both open and closed, in a shock wave background metric with an arbitrary profile was solved.
160 citations
TL;DR: The formation of nontopological solitons in a second-order phase transition in the early universe is discussed, andRatios of dimensionless coupling constants in the Lagrangian determine their abundance and mass.
Abstract: We discuss the formation of nontopological solitons in a second-order phase transition in the early Universe. Ratios of dimensionless coupling constants in the Lagrangean determine their abundance and mass. For a large range of parameters, nontopological solitons can be cosmologically significant, contributing a significant fraction of the present mass density of the Universe.
120 citations
TL;DR: In this article, rotation-curve profiles are used to determine the dark-to-luminous mass ratio within the disk size for 43 spiral galaxies, and it is noted that faint galaxies are halo-dominated and that bright galaxies are diskdominated in the disk regions.
Abstract: Rotation-curve profiles are used to determine the dark-to-luminous mass ratio within the disk size for 43 spiral galaxies. It is noted that faint galaxies are halo-dominated and that bright galaxies are disk-dominated in the disk regions. The luminosity sequence is shown to be a dark-to-luminous sequence. By removing the dark-matter contribution from the velocity at the disk edge, the dispersion affecting the luminosity-kinematics relation is found to decrease in comparison with the conventional Tully-Fisher correlation.
116 citations
TL;DR: In this article, a factorization ansatz for the triplet direction correlation function c (3) is combined with the exact relation between c(3) and the derivative of the pair function c(2) with respect to density.
Abstract: A factorization ansatz for the triplet direction correlation function c (3) is combined with the exact relation between c (3) and the derivative of the pair function c (2) with respect to density to derive a simple and tractable approximation for c (3) in dense, classical fluids. The predictions of this approximation are found to be in good agreement with the results of ‘exact’ molecular dynamics simulations for the ‘soft sphere’ model near freezing. The approximate c (3) is then used to derive an improved integral equation for the pair correlation function which is found to yield satisfactory results. In another application, the third order term in the density functional theory of freezing is systematically evaluated for the first time and is found to lead to significant improvement over the usual second order theory, particularly for soft interatomic repulsions.
106 citations
TL;DR: In this article, an integral formula for the four-massless-particle scattering amplitude at two loops in heterotic string theory has been derived by using the hyperelliptic formalism.
TL;DR: In this article, the authors show that the requirement of modular invariance determines completely the two-loop amplitudes of the heterotic string theory for arbitrary external legs and that the cosmological constant is zero pointwise in moduli space.
TL;DR: Using molecular-dynamics data on a binary-alloy model, the self (incoherent) -part of the density autocorrelation functions of both species in the supercooled liquid and near the glass transition are computed, over an extensive range of wave numbers.
Abstract: Using molecular-dynamics (MD) data on a binary-alloy model, we have computed the self (incoherent) -part of the density autocorrelation functions of both species in the supercooled liquid and near the glass transition, over an extensive range of wave numbers. Standard theoretical models of liquid-state theory fail to reproduce the data, while the Chudley-Elliott jump diffusion model yields reasonable results in the glass range. With a suitable scaling of the time axis, the data for different temperatures can be brought onto a single master curve, which is well fitted by a Kohlrausch (``stretched-exponential'') function with a wave-number-dependent exponent.
TL;DR: In this article, general results about the behaviour of the entropy under dynamical semigroups are derived and an explicit estimate about the Ghirardi-Rimini-Weber model is provided in this light.
Abstract: Some general results about the behaviour of the entropy under dynamical semigroups are derived and an explicit estimate about the Ghirardi-Rimini-Weber model is provided in this light.
TL;DR: In this article, the authors give an explicit formula for the Kahler potential for the chiral multiplets associated to deformation of the kahler class [(1, 1) forms].
TL;DR: In this article, the general form of the limit of the convergence of a sequence of nonlinear variational problems with Dirichlet boundary conditions is studied, and the asymptotic problem is characterized in terms of a limit of suitable nonlinear capacities associated to the domains.
Abstract: We study the general form of the limit, in the sense of Γ-convergence, of a sequence of nonlinear variational problems in varying domains with Dirichlet boundary conditions. The asymptotic problem is characterized in terms of the limit of suitable nonlinear capacities associated to the domains.
TL;DR: In this paper, the non-renormalization theorem is verified at two loops by explicit computation using the hyperelliptic formalism and a set of identities is found which leads to a great simplification of the calculation of the four-particle amplitude.
TL;DR: In this article, a careful reconsideration of the Schwinger model, which takes into account the state space associated to the Wightman functions, is rigorously shown that: physical states have zero charge, bleached states do not exist, only the integer winding number gause transformations are implementable, the vacuum degeneracy is labelled by only one θ angle, with periodicity π rather than 2π, the Goldstone dipole does not exist.
TL;DR: In this article, the authors extend the work of Krichever and Novikov on Virasoro type algebras by constructing Neveu-Schwarz and Ramond type superalgeses on genus-g Riemann surfaces.
TL;DR: In this article, the authors investigated the consequences of modifying and enlarging the class of the considered stochastic processes, by considering the spontaneous occurrence of approximate momentum and of simultaneous position and momentum measurements.
Abstract: Non-Hamiltonian evolution equations have been recently considered for the description of various physical processes. Among these types of equations the class which has been more extensively studied is the one usually referred to as quantum-dynamical semi-group equations (QDS). In particular an equation of the QDS type has been considered as the basis for a model, called quantum mechanics with spontaneous localization (QMSL), which has been shown to exhibit some very interesting features allowing us to overcome most of the conceptual difficulties of standard quantum theory. QMSL assumes a modification of the pure Schrodinger evolution by assuming the occurrence, at random times, of stochastic processes for the wave function corresponding formally to approximate position measurements. In this paper we investigate the consequences of modifying and/or enlarging the class of the considered stochastic processes, by considering the spontaneous occurrence of approximate momentum and of simultaneous position and momentum measurements. It is shown that the considered changes in the elementary processes have unacceptable consequences. In particular they either lead to drastic modifications in the dynamics of microsystems or are completely useless from the point of view of the conceptual advantages that one was trying to get from QMSL. The present work supports therefore the idea that QMSL, as originally formulated, can be taken as the basic scheme for the generalizations which are still necessary in order to make it appropriate for the description of systems of identical particles and to meet relativistic requirements.
TL;DR: In this article, the temperature-dependent zone-boundary surface phonons across the c(2 x 2)..-->..1 x 1 reconstruction phase transition of the clean W(001) surface were studied.
Abstract: We study the temperature-dependent zone-boundary surface phonons across the c(2 x 2)..-->..1 x 1 reconstruction phase transition of the clean W(001) surface. Velocity-velocity correlations and hence the phonon spectral densities are calculated by molecular dynamics for the surface atoms of a finite-thickness (001) slab, with interatomic potentials established in a previous study of the surface statics. Our calculated k = ((1/2, 1) / 2 )(2..pi../a) surface phonon spectra are dominated by three main low-frequency modes. Of these, the longitudinal and the shear horizontal modes are reconstruction related and display critical broadening and softening at the phase transition, while the third, the shear vertical mode, is basically unaffected. The reconstruction phase mode, the shear horizontal, appears to be responsible for the phase fluctuations which destroy long-range order at the transition.
TL;DR: In this paper, a detailed discussion of the Ramond sector of the superconformal minimal models (m.m.) in terms of the Coulomb gas representation is given, where the basic elements of this construction, vertices and screening operators, are written in the critical Ising variables (order-disorder parameter fields, free Majorana fermion) and of a free dimensionless field.
TL;DR: In this article, the Sugawara construction for a Kac-Moody algebra defined over a generic Riemann surface was carried out using the formalism developed by Krichever and Novikov.
TL;DR: In this paper, the authors reanalyze the constraints on the minimal N = 1 supergravity extension of the standard model arising from the requirement of a correct spontaneous breakdown of the electroweak symmetry.
Abstract: We reanalyze the constraints on the minimalN=1 supergravity extension of the standard model arising from the requirement of a correct spontaneous breakdown of the electroweak symmetry. Driven by recent experimental results, we devote special attention to the case of a top quark much heavier than the conventional choice of 40 GeV, used in previous analyses. Our results are stated in a space of phenomenologically meaningful parameters, providing a direct comparison between the constraints fromSU(2)×U(1) breaking and the predictions for supersymmetric particle production. Moreover, an upper bound for the ratio of the two Higgs vacuum expectation values is given, for any value of the top quark mass.
01 Jan 1988
TL;DR: In this article, the authors show how the existence of a preferred inner product in the representation space of a simple algebra is related to that of an involutive antiautomorphism of the algebra.
Abstract: Our approach to spinors is based on Clifford algebras and their representations. It is convenient to present first the relevant notions in the general context of associative algebras. In particular, we show how the existence of a preferred inner product in the representation space of a simple algebra is related to that of an involutive antiautomorphism of the algebra.
TL;DR: In this article, a scalar massless noninteracting quantum field theory on an arbitrary gravitational shock wave background is exactly solved S -matrix and expectation values of the energy-momentum tensor are computed for an arbitrary polarized sourceless gravitational wave and for a homogeneous infinite planar shell shock wave, all performed in any number of space-time dimensions.
TL;DR: A lattice theory of surface melting based on minimization of the free energy with respect to two spatially varying order parameters---density and ``crystallinity'' is developed and surface melting is found to be continuous without any singularities below ${T}_{M}$ in the surface free energy.
Abstract: We have developed a lattice theory of surface melting based on minimization of the free energy with respect to two spatially varying order parameters---density and ``crystallinity.'' The partition function is evaluated using mean-field and free-volume approximations on a lattice. Direct application is made to (100) and (110) Lennard-Jones crystal surfaces. It is shown that on the coexistence line and very close to the triple-point temperature ${T}_{M}$ a quasiliquid layer forms on the crystal-gas interface. The thickness of the layer grows asymptotically as (${T}_{M}$-T${)}^{\mathrm{\ensuremath{-}}1/3}$, in good agreement with the recent experiments on Ar films. A change from long- to short-range interparticle attraction reduces the growth behavior to logarithmic, while a switch of the potential tail from attractive to repulsive can block altogether the growth of the quasiliquid layer. It is further shown that in cases where no in-plane disorder can arise no surface melting occurs and the crystal-vapor interface can even be overheated. Within the present mean-field approximation, surface melting is found to be continuous without any singularities below ${T}_{M}$ in the surface free energy, which is explicitly calculated. The decay of the ``crystallinity'' order parameter at the quasi-liquid-gas interface is predicted to be a ``stretched exponential'' in the long-range case and power law in the short-range case.
TL;DR: In this article, the authors discuss general problems of superstring-inspired models, such as compactification, first problems for model building, and problems with supersymmetry breaking, and a minimal model is described.
Abstract: The author discusses general problems of superstring - inspired models. These include some results on compactification, first problems for model building, and problems with supersymmetry breaking. A minimal model is described. This description focuses on generalities of the model, radiative breaking of the gauge symmetry, the particle spectrum, Gauginos and Higgs particles, and exotic color triplets (D-particles).
TL;DR: On considere la resolubilite du probleme aux valeurs limites periodique non lineaire: x''+h(x)=p(+), x(T)-x(0)=x'(T), x'(0) = 0 (T>0) ou h:R\R continue et p:[0,T]→R integrable de Lebesgue as discussed by the authors
Abstract: On considere la resolubilite du probleme aux valeurs limites periodique non lineaire: x''+h(x)=p(+), x(T)-x(0)=x'(T)-x'(0)=0 (T>0) ou h:R\R continue et p:[0,T]→R integrable de Lebesgue