It is shown that grand unification of the minimal supersymmetric standard model does not lead to a prediction for the scale of the superpartner masses, even if the inputs α, ${\sin }^2$θ, and ${\mathrm{\alpha }}_{\mathit{s}}$ are known exactly.

In contrast to the conventional belief that the gauge-boson-propagator renormalizations to every m-loop order contribute to ${\sin }^2$${\mathit{FTHETA}}_{\mathit{W}}$ at all scales (μ) below the grand unification mass (${\mathit{M}}_{\mathit{U}}$), for the first time we prove that all higher-order multiloop (m≥2) corrections are absent for μ=${\mathit{M}}_{\mathit{I}}$-${\mathit{M}}_{\mathit{U}}$ in a class of grand unified theories where the Pati-Salam intermediate gauge symmetry breaks at the highest intermediate scale (${\mathit{M}}_{\mathit{I}}$). This theorem holds also with supersymmetry and in string-inspired models.

The Z-boson pair signal from strong WW scattering, WW→ZZ, is significantly enhanced by a contribution from gluon-gluon fusion, gg→ZZ, if W-boson and t-quark masses are both generated by electroweak symmetry-breaking condensates formed by quanta heavier than 1 TeV. By measuring the two components of the signal it will be possible to probe for different origins of the W-boson and t-quark masses.

A hadron spectrum calculation with two light dynamical quark flavors was carried out with the Kogut-Susskind quark action at β=5.7 on lattices of spatial size $8^3$, ${12}^3$, and ${20}^3$ for ${\mathit{m}}_{\mathit{q}}$=0.01 and 0.02 in lattice units, with emphasis given to a systematic study of the finite-lattice-size effect. It is found that hadron masses on a ${16}^3$ spatial lattice at this β still suffer from a significant finite-lattice effect at least for ${\mathit{m}}_{\mathit{q}}$=0.01, showing the importance of a quantitative control over the finite-size effect in comparing simulation results with the experimental hadron masses even for a fairly large lattice. A comparison is also made to the analytic prediction for the finite-size effect from chiral perturbation theory.

In tachyon-free string theories the ratio of the densities of bosonic and fermionic states must approach unity with increasing energy. This observation of Kutasov and Seiberg is considered in the context of a potential stringy description of the hadron spectrum. The densities of the meson and baryon states are approximately equal up to a mass of about 1.7 GeV/${\mathit{c}}^2$, above which the density of baryon states appears greater. In a stringy picture of hadrons, this result implies the existence of a large number of as yet unseen meson states above 1.7 GeV/${\mathit{c}}^2$. These are likely to be exotic, consisting of at least two quarks and two antiquarks, and to be accompanied at still higher masses by exotic baryons as well.

With 4.36×${10}^6$ events, spin precession in a magnetic field has been used to measure the magnetic moment of the ${\mathrm{\Xi }}^{\mathrm{-}}$ hyperon as -0.6505±0.0025 nuclear magnetons.

Saturation properties of nuclear matter are determined within a Dirac-Brueckner approach. Relativistic covariance is implemented by constructing the complete representation of the nucleon-nucleon amplitude in the Dirac space. As a dynamical model the relativistic one-boson-exchange model is used, including also the negative-energy-state components. A consistent treatment is discussed of nucleon propagation in the nuclear medium. The compressibility obtained for symmetric matter is rather low as compared to other calculations and more in agreement with the value suggested by astrophysical studies.

The interference structure function ${\mathit{f}}_{01}$, the transverse structure function ${\mathit{f}}_{11}$, and the longitudinal structure function ${\mathit{f}}_{00}$ have been determined in a ${}_{}{}^2{}_{}{}^{}\mathrm{H}$(e,e’p) experiment at a four-momentum transfer ${\mathit{Q}}^2$=0.21 (GeV/c${)}^2$. The ${\mathit{f}}_{00}$ and ${\mathit{f}}_{11}$ data are in agreement both with a nonrelativistic calculation that includes the effects of final-state interaction (FSI), meson-exchange currents, and isobar configurations, and with a relativistic calculation that only includes FSI effects. The ${\mathit{f}}_{01}$ data demonstrate the relevance of a relativistic approach even at this low value of the momentum transfer.

We explain why the measured parity-violating asymmetries for ${\mathit{p}}_{1/2}$ compound-nuclear resonances tend to have a common sign. We show that the asymmetry is a sum of two terms: a’ average term dominated by admixtures of distant levels and a term that fluctuates from resonance to resonance dominated by admixtures of nearby compound-nuclear states. The average asymmetry involves single-particle transition amplitudes of the parity-violating interaction, while the fluctuating asymmetry retains a statistical character. Our theoretical estimate of the average asymmetry agrees with a value extracted from experimental data.

Single-photon ionization of ${\mathrm{C}}_{60}$ and ${\mathrm{C}}_{70}$ has been studied using synchrotron radiation in an energy range from the ionization potential (7.54±0.04 eV for ${\mathrm{C}}_{60}$ 7.3±0.2 eV for ${\mathrm{C}}_{70}$) up to 35 eV. The photoion yield is dominated by a strong resonance at about 20 eV with a FWHM of ∼10 eV. We interpret this as being due to autoionization via the giant plasmon resonance recently predicted in the RPA approximation. ${\mathrm{C}}_{60}$ and ${\mathrm{C}}_{70}$ offer the unique possibility for a quantitative comparison of this collective excitation in the free molecule with that observed in the solid phase by electron-energy-loss spectroscopy at about 28 eV.

We consider radiation caused by the collective electromagnetic field of one beam deflecting particles of the other. We find the number of photons for a single collision is ${\mathit{dN}}_{\gamma }$≊${\mathit{N}}_0$ ${\mathit{dE}}_{\gamma }$/${\mathit{E}}_{\gamma }$ in the energy range ${\mathit{E}}_{\gamma }$<${\mathit{E}}_{\mathit{c}}$=4ħc${\gamma }^2$<l, where l is the length of the bunch. At the Superconducting Super Collider, for example, ${\mathit{N}}_0$=50 and ${\mathit{E}}_{\mathit{c}}$=6 keV. Specific features of this radiation can be used for a fast control over collisions and for measuring beam parameters. A background due to synchrotron radiation in the magnetic field of a collider is estimated.

A formulation to characterize stimulated emission of synchrotron radiation is presented, based on simplification of a theory developed by Sokolov and Ternov. It is shown that optical gain may be obtained up to gyration harmonics of the order of the critical harmonic number for spontaneous radiation 3${\gamma }^3$, where γ is the relativistic energy factor. Synchrotron-radiation lasers (SRL’s) in the infrared and visible portions of the spectrum are shown to be feasible, provided beams with high energy definition are used. SRL gain can exceed free-electron-laser gain for similar beams.

The broadband radiation emitted from a NaZ pinch is used to photoionize Ne to the He-like ground state and radiation from the Na 1${\mathit{s}}^2$-1s2p ${}_{}{}^1{}_{}{}^{}$${\mathit{P}}_1$ transition is used to resonantly photoexcite the Ne 1${\mathit{s}}^{2\mathrm{-}}$1s4p ${}_{}{}^1{}_{}{}^{}$${\mathit{P}}_1$ transition. Time-resolved and time-integrated spectral measurements of the Ne K-shell emission demonstrate the first population inversion driven by a Z pinch. This is the first experiment in any medium to demonstrate a soft-x-ray inversion pumped solely by resonant photoexcitation.

A high-resolution x-ray study of the nematic–to–smectic ${\mathit{A}}_1$ phase transition of 8OPCBOB gives a critical exponent for the susceptibility γ=1.39±0.08, and for the parallel correlation length ${\nu }_{\mathrm{\parallel }}$=0.71±0.04. These values, as well as the known exponent of the heat capacity, agree with the predictions from the 3D-XY model. The different critical behavior of the perpendicular correlation length (${\nu }_{\mathrm{\perp }}$=0.56±0.05) is shown to be related to the quartic term in ${\mathit{q}}_{\mathrm{\perp }}$ present in the structure factor. Our analysis resolves a long-standing puzzle about the critical behavior of this phase transition.

Optical study of point disclinations in the two-dimensional director field of freely suspended smectic-C liquid-crystal films shows that these defects exhibit Brownian spontanous positional fluctuations.

Implantation of a heavy marker in the near-surface region of crystalline and amorphous ${\mathrm{Ni}}_3$B has allowed us to study locally the macroscopic atomic transport induced in metallic alloys by high-energy heavy-ion irradiation. The modifications of the marker profile were backscattering monitored by Rutherford backscattering experiments. No effect was observed in crystalline ${\mathrm{Ni}}_3$B a huge shift of the marker peak maximum towards the sample surface as well as a surprising decrease of the peak width and of th peak integral were evidenced in amorphous ${\mathrm{Ni}}_3$B. These features can be accounted for by the plastic-deformation phenomenon observed so far in amorphous materials.

Domain growth in a two-dimensional quenched binary alloy which undergoes an order-disorder transition is studied. We have used Monte Carlo simulation of a nearest-neighbor antiferromagentic Ising model. The novelty is that the dynamics is introduced via a single vacancy that moves by jumping to nearest as well as next nearest neighbors. The excess energy decay and the scaling of the structure factor have been studied. An algebraic behavior R(t)∝${\mathit{t}}^{\mathit{x}}$ with x=0.77±0.03 is found. This dynamics can be used to accelerate equilibrium Monte Carlo simulations.

On slightly miscut Si(001) surfaces, straight steps are predicted to be unstable against the formation of long-wavelength undulations. These undulations lower the energy, by, in effect, reducing the size of the stress domains; they are thus analogous to the spontaneous step formation proposed by Alerhand et al. However, step undulations are expected to be kinetically favored, and therefore to preempt spontaneous step formation. Moreover, they lead to an unexpected distinct thermodynamic phase in the surface phase diagram at small angles.

Using low-energy electron microscopy we have found a new phase transition on the Si(001) surface at miscut angles smaller than ∼0.1°. The surface phase separates into facets with ∼300 Å terrace width, and regions with much larger, wavy terraces. This wavy phase is stabilized by a reduction of surface-stress-induced strain energy. A theoretical study by Tersoff and Pehlke compares favorably with our observations.

Using the Car-Parrinello method we have investigated theoretically the properties of ${\mathrm{K}}_6$${\mathrm{C}}_{60}$ and ${\mathrm{Rb}}_6$${\mathrm{C}}_{60}$ crystals. Our results are in very good agreement with available experimental data. We find an interesting pattern of relaxations both in the ${\mathrm{C}}_{60}$ fullerene cage and in the position of the K ions with respect to an ideal configuration. The relaxation energy gain is ≊1 eV and is due in comparable amounts to the ${\mathrm{C}}_{60}$ and the K’s. These energy gains are achieved by relatively small ionic dispalcements. Analysis of the electronic charge density reveals non-rigid-band effects. Similarities and differences with graphite intercalation compounds are discussed.