Showing papers by "International School for Advanced Studies published in 1989"
TL;DR: In this paper, it was shown that if the energy is not so extreme to cause a gravitational instability and when the scattering angle approaches some critical value from below, the distance starts increasing, thus departing from the usual position-momentum uncertainty relation, and in no instance is the resolution smaller than the string length.
1,392 citations
TL;DR: In this article, the authors studied general properties of the low-energy effective theory for 4D type II superstrings obtained by the compactification on an abstract (2,2) superconformal system.
Abstract: We study general properties of the low-energy effective theory for 4D type II superstrings obtained by the compactification on an abstract (2,2) superconformal system. This is the basic step towards the construction of their moduli space. We give an explicit and general algorithm to convert the effective Lagrangian for the type IIA into that of type IIB superstring defined by the same (2,2) superconformal system (and vice versa). This map converts Kahler manifolds into quaternionic ones (and quaternionic into Kahlerian ones) and has a deep geometrical meaning. The relationship with the theory of normal quaternionic manifolds (and algebras), as well as with Jordan algebras, is outlined. It turns out that only a restricted class of quarternionic geometries is allowed in the string case. We derive a general and explicit formula for the (fully nonlinear) couplings of the vector-multiplets (IIA case) in terms of the basic three-point functions of the underlying superconformal theory. A number of illustrative e...
605 citations
TL;DR: A new robust iterative method based on a convenient adaptation of the conjugate gradient minimization of the energy functional is presented, showing to be rapidly convergent, irrespective of the system under consideration, thus providing an efficient solution to a variety of large-scale electronic structure calculations.
Abstract: A new robust iterative method for electronic structure calculations based on a convenient adaptation of the conjugate gradient minimization of the energy functional is presented. The method is compared with some other techniques using the direct minimization of the density functional and with a more traditional Davidson approach. Numerical results for silicon and carbon are used to compare the different schemes. The new method is shown to be rapidly convergent, irrespective of the system under consideration, thus providing an efficient solution to a variety of large-scale electronic structure calculations.
298 citations
TL;DR: Determination de the structure amorphe par simulation sur ordinateur basee sur une methode de dynamique moleculaire aux premiers principes.
Abstract: An amorphous carbon structure is obtained with a computer simulation based on a first-principles molecular-dynamics method, in which the interatomic potential is constructed directly from the electronic ground state, using density-functional techniques. From our results, which agree well with the limited experimental information available, we analyze the short-range order, particularly the fractions of $s{p}^{2}$ and $s{p}^{3}$ sites, together with the electronic properties.
233 citations
TL;DR: Les densites d'etats electroniques illustrent un comportement metallique and les valeurs calculees pour the conductivite electronique correspondent parfaitement aux donnees experimentales.
Abstract: Etude du silicium liquide selon les premiers principes de la dynamique moleculaire. La description de l'ordre local est en plein accord avec les resultats obtenus par diffraction de RX et de neutrons. La densite de charge electronique met en evidence des liaisons de covalence distinctement identifiables dans le spectre de puissance du systeme. Les densites d'etats electroniques illustrent un comportement metallique et les valeurs calculees pour la conductivite electronique correspondent parfaitement aux donnees experimentales
188 citations
TL;DR: In this paper, the Weyl anomaly is computed for a class of exactly solvable nonlinear (supersymmetric) σ-models describing the string or superstring evolution in nontrivial backgrounds.
184 citations
TL;DR: Second-order propagation equations are derived for covariant and gauge-invariant quantities that characterize density inhomogeneities in an almost-uniform model universe in a transparent way and enable a unified and transparent derivation of a series of results in the literature.
Abstract: In the preceding paper, covariant and gauge-invariant quantities were defined that characterize density inhomogeneities in an almost-uniform model universe in a transparent way. In this paper second-order propagation equations are derived for these quantities in the case of a general perfect fluid,'' and their properties examined. We do not use a harmonic decomposition in our definitions, but when such a decomposition is applied, our results are compatible with those obtained by Bardeen in his harmonically based gauge-invariant analysis. Our second-order equation enables a unified and transparent derivation of a series of results in the literature, without any ambiguity from choice of any particular gauge.
145 citations
TL;DR: An ab initio molecular-dynamics simulation of high-temperature proton diffusion in crystalline silicon finds that the diffusion proceeds via a jumplike mechanism.
Abstract: An ab initio molecular dynamics simulation of high-temperature proton diffusion in crystalline silicon is presented. This is the first time dynamical effects have been included explicitly in the simulation of this system. We find that the diffusion proceeds via a jumplike mechanism. Because of dynamical effects the diffusion path is substantially different from that inferred from static total-energy calculations. The calculated diffusion coefficient and its temperature dependencne are in good agreement with the available experimental data. It is suggested that scattering experiments may distinguish between different diffusion paths.
116 citations
TL;DR: In this article, the authors showed that the peculiar velocities obtained by subtraction of the general cosmological expansion are best fitted by a flow induced by a 'great attractor' and centred on galactic longitude l = 307° and latitude b = 9° at a distance Rm = 4,350 ± 350 kms−1.
Abstract: THE distances and velocities of 400 elliptical galaxies1, out to redshifts equivalent to recession velocities of ∼6,000 kms−1, suggest that the peculiar velocities obtained by subtraction of the general cosmological expansion are best fitted by a flow induced by a 'great attractor'2, a large mass of 5.4 x 1016 M⊙ and centred on galactic longitude l = 307° and latitude b = 9° at a distance Rm =4,350 ±350 kms−1. A redshift survey of ∼900 galaxies3 shows that the excess galaxy number counts in this direction are due to two substantial concentrations of galaxies at recession velocities v ≈ 3,000 kms∼1 and 4,500 kms−1. Here we show that in roughly the same direction there is also a very rich concentration of galaxy clusters which may have a considerable dynamical influence. The estimated redshift distances of these clusters range from 3,000 to 20,000 km s−1, with a main complex at v ≈ 14,000 km s−1. The barycentre of this concentration lies ∼25° away from the cosmic microwave background dipole4, and ∼10° away from the latest reported position of the Great Attractor5,6.
116 citations
TL;DR: In this article, the authors present an ab initio approach to piezoelectricity, which is given by the stress induced by a homogeneous electric field, treated self-consistently by linear response, thus avoiding both supercells and numerical differentiation.
Abstract: We present a novel ab initio approach to piezoelectricity. The piezoelectric tensor is given by the stress induced by a homogeneous electric field. The perturbation is treated self-consistently by linear response, thus avoiding both supercells and numerical differentiation. We calculate the piezoelectric constants of none III-V semiconductors: as a by-product we also provide the first systematic study of zone-center phonons, internal strain parameters, effective charges, and dielectric constants. Our results agree very well with experiments where available, and allow predictions where they are not.
110 citations
TL;DR: Combining anti-BRS invariance with previously found symmetries of the gauge-fixed Chern-Simons action in three dimensions, the authors obtained a set of transformations that satisfies an unusual kind of supersymmetry algebra.
TL;DR: In this article, a simple and explicit method for the computation of atomic forces in ab initio total energy calculations using a basis of augmented plane waves (APW) and the local density approximation for exchange and correlation is presented.
Abstract: We present a simple and explicit method for the computation of atomic forces in ab initio total-energy calculations using a basis of augmented plane waves (APW) and the local-density approximation for exchange and correlation. The force on an atom is given by integrals over its muffin-tin sphere only, which can be obtained easily in existing implementations of the linear APW method, for example. The extra computational cost of calculating the forces on all the atoms is negligible compared with that of performing one single self-consistency iteration step.
TL;DR: Fusion rules, structure constants and 4-point functions for all the fields in the Neveu-Schwarz, Ramond and twisted sectors of N = 2 minimal models are presented in this article.
Abstract: Fusion rules, structure constants and 4-point functions for all the fields in the Neveu-Schwarz, Ramond and twisted sectors of N = 2 minimal models are presented. It is shown that the additional Zp+2 symmetries of these models are generated by specific chiral N = 2 superfields. The structure of the corresponding N = 2 superparafermionic models is discussed.
TL;DR: On considere l'existence de solutions 2Π-periodiques des systemes hamiltoniens asymptotiquement quadratiques −Jz=H'(z,t) ou J=(0―I/I#0), I=In, la matrice identite de n×n
TL;DR: In this paper, the authors classify all the normal homogeneous Kahler spaces which are allowed in the coupling of vector multiplets to N = 2 SUGRA and construct explicitly the corresponding supergravity models.
Abstract: Motivated by the problem of the moduli space of superconformal theories, we classify all the (normal) homogeneous Kahler spaces which are allowed in the coupling of vector multiplets toN=2 SUGRA. Such homogeneous spaces are in one-to-one correspondence with the homogeneous quaternionic spaces (≠ℍH
n
) found by Alekseevskii. There are two infinite families of homogeneous non-symmetric spaces, each labelled by two integers. We construct explicitly the corresponding supergravity models. They are described by acubic functionF, as in flat-potential models. They are Kahler-Einstein if and only if they are symmetric. We describe in detail the geometry of the relevant manifolds. They are Siegel (bounded) domains of the first type. We discuss the physical relevance of this class of bounded domains for string theory and the moduli geometry. Finally, we introduce theT-algebraic formalism of Vinberg to describe in an efficient way the geometry of these manifolds. The homogeneous spaces allowed inN=2 SUGRA are associated to rank 3T-algebras in exactly the same way as the symmetric spaces are related to Jordan algebras. We characterize theT-algebras allowed inN=2 supergravity. They are those for which theungraded determinant is a polynomial in the matrix entries. The Kahler potential is simply minus the logarithm of this “naive” determinant.
TL;DR: The liquid state of carbon at low pressure is investigated in terms of density of states and conductivity calculations, showing that the system is a metal, in agreement with experiments reported last year.
Abstract: The liquid state of carbon at low pressure is investigated wtih a first-principles molecular dynamics simulation. Its controversial electronic properties are elucidated in terms of density of states and conductivity calculations, showing that the system is a metal, in agreement with experiments reported last year. Furthermore, an accurate analysis of the atomic structure indicates that the liquid is composed of two-fold, three-fold, and four-fold coordinated atoms, which display different bonding properties.
TL;DR: In this paper, the area of the parameter space that gives rise to a massive, stable neutralino χ, with a cosmologically significant relic density, is described, and the effect of the lightest Higgs exchange on the elastic neutralino-nucleus cross section is shown.
TL;DR: In this paper, the Ray-Singer torsion is used to partition topological theories with classical action Tr B ∧ F. Their partition function is shown to be an integral integral over the moduli space of flat connections with measure determined by the Ray Singer Torsion.
TL;DR: In this article, a class of correlation functions for the 2-d N = 2 Wess-Zumino models with superpotential φ′ and generic Kahler potential were derived.
TL;DR: In this paper, an ab initio molecular dynamics study of the ground state, finite temperature, dynamical and electronic properties of Na20 and Na10K10 microclusters is presented.
Abstract: We present an ab initio molecular dynamics study of the ground state, finite temperature, dynamical and electronic properties of Na20 and Na10K10 microclusters. For Na20 the lowest-energy structure has several bulklike features. The vibrational spectrum at 200 K is compared to that of the liquid. From our results we derive a rationale for the so far unexplained dependence of the mass spectrum on the nozzle temperature and compositional abundance of the mixed clusters. The implications of our calculations on the validity of the shell model are discussed in detail.
TL;DR: In this article, it was shown that there exists a renormalization group flow from p th to (p - l )th model in the l th level SU (2) coset series, for p large.
TL;DR: The analysis of the tricritical 3-state Potts model perturbed by the energy density field e =o (1 7 1 7 ) and the S -matrices of the (conjectured) field theory is presented in this paper.
TL;DR: In this paper, a priori estimates for solutions and subsolutions are given for one-sided obstacle problems and for generalized Dirichlet problems, and the Wiener criterion for generalized solutions.
Abstract: Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 Part I. Notation and preliminary results . . . . . . . . . . . . . . . . . 60 1. Capacity notions . . . . . . . . . . . . . . . . . . . . . . . . 60 2. The Sobolev spaces . . . . . . . . . . . . . . . . . . . . . . . 61 3. The Kato spaces . . . . . . . . . . . . . . . . . . . . . . . . 63 4. The operator L . . . . . . . . . . . . . . . . . . . . . . . . . 64 5. A priori estimates for solutions and subsolutions . . . . . . . 65 6. Hkdominated quasi uniform convergence . . . . . . . . . . . 66 7. The Wiener moduli . . . . . . . . . . . . . . . . . . . . . . . 68 8. Potential estimates for one-sided obstacle problems . . . . . . 71 Part II. Variational solutions . . . . . . . . . . . . . . . . . . . . . . . 73 1. Statement of the main results . . . . . . . . . . . . . . . . . . 73 2. Oscillation and energy estimates . . . . . . . . . . . . . . . . 75 3. Proof of the Wiener criterion . . . . . . . . . . . . . . . . . . 89 Part III. Generalized solutions . . . . . . . . . . . . . . . . . . . . . . 91 1. Dominated generalized solutions . . . . . . . . . . . . . . . . 91 2. Wiener criterion for generalized solutions . . . . . . . . . . . 99 3. Generalized Dirichlet problems . . . . . . . . . . . . . . . . . 103 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106
TL;DR: In this paper, the Virasoro minimal models on the hyperelliptic surfaces are mapped into specific models on a branched sphere by a generalized Coulomb gas representation, and the partition functions of the models on Z 2-surfaces (g⩾1) are constructed in terms of the correlation functions of fields from the twisted sector of the Branched Sphere models.
TL;DR: In this paper, the static properties (surface tension, density profile, structure and correlations) of a model liquid metal surface were studied, in conjunction with a many-body force scheme (the "glue" model) optimized to describe gold.
TL;DR: In this paper, a class of non-linear covariant gauges containing only one gauge parameter is characterized by requiring that the gauge-fixing action, in addition to the BRS symmetry, is invariant under a second global symmetry which commutes with BRS, and which leads to a Ward identity which is the analogue of the equation of motion of the antighost in the case of the linear gauges and which ensures the stability of the model under radiative corrections.
01 Mar 1989
TL;DR: In this article, the existence of solutions to the Cauchy problem for the differential inclusion problem when A is cyclically monotone and upper semicontinuous is proved.
Abstract: We prove existence of solutions to the Cauchy problem for the differential inclusion x E A(x) , when A is cyclically monotone and upper semicontinuous.