Assuming that the fourth family makes an appreciable contribution to B mixing, assuming some mild properties of the (4×4) Cabibbo-Kobayashi-Maskawa matrix, and taking the lattice determination of the pseudoscalar decay constant for B seriously, we arrive at a lower bound on $m_t$, i.e., $m_{t\mathcal{’}}$≳500 GeV. If perturbative unitarity is to be preserved, i.e., $m_{t\mathcal{’}}$∼500 GeV, then our analysis also implies that the top quark is unlikely to be lighter than ≊80 Gev. Experimental consequences for rare B decays, and CP violation in B decays are also discussed.

We report on a measurement of inverse muon decay ${\nu }_{\mu }$+e→${\mu }^{\mathrm{-}}$+${\nu }_e$ at the Fermilab Tevatron. A sample of 1151 inverse-μ-decay events, produced by neutrinos with laboratory energy in the range 15≤$E_{\nu }$≤600 GeV, is extracted. We measure the rate of this reaction with respect to the ${\nu }_{\mu }$-N charged-current interaction to be [0.125±0.009(stat)±0.003(syst)]×${10}^{\mathrm{-}2}$. The measurement supports V—A structure of the weak current, left-handed two-component neutrinos, and a cross section rising linearly with respect to the center-of-mass energy.

We explain ‘‘intermittency’’ in recent data, using a simple model in which pions are emitted from quark-gluon-plasma droplets. We find that droplets with a temperature near the QCD phase transition temperature that emit 10–15 pions, with a droplet volume of 5–10 ${\mathrm{fm}}^3$, reproduce the observations very well.

The problem of signature inversion is studied by using a model of particles coupled to a rotor. We have assumed an axially symmetric equilibrium deformation and taken into account the γ vibration around it. The calculated signature dependence is found inverted in agreement with the experimental data if we adopt a set of moments of inertia which favor the rotation around the shortest axis, but not if we employ the set of the irrotational-flow model.

A new method of fast-timing measurements using β-γ-γ coincidences with ${\mathrm{BaF}}_2$ and plastic detectors has been used to measure a number of lifetimes for low-lying states in ${}_{}{}^{116}{}_{}{}^{}$,118,120Cd in the range of 10–100 ps. The results are discussed in terms of the vibrational and intruder structure of these nuclei.

${\mathrm{H}}^{+}$+He scattering at 0.5 MeV has been investigated using a coincidence technique that completely determines the three-body transverse momentum exchange in single ionization collisions. Three scattering regions could be distinctly recognized that are dominated by proton–helium-nucleus, proton-electron, or electron–helium-nucleus interactions. Calculations and the experimental data show that the coupling between the electronic and nuclear degrees of freedom is required to understand the dynamics for more than 97% of the ionizing collisions.

Theoretical predictions of a new phenomenon arising in photoelectron emission from oriented molecules by circularly polarized light have been experimentally verified for CO. For a special geometry photoelectron-intensity differences occur upon reversal of photon helicity. The measured asymmetries (up to 80%) show good agreement with an ab initio calculation at photon energies between 20 and 40 eV. Theoretically, the new manifestation of circular dichroism is already obtained in the pure electric dipole approximation without inclusion of spin-orbit interaction.

We report frequency locking at Farey fractions of an electrically modulated semiconductor laser within an external cavity. The winding numbers as a function of the ratio of the modulation frequency to inverse resonator round trip time show the hierarchy of a Farey tree and the structure of a devil’s staircase. The dimension of the set complementary to the stairs is determined to be 0.89. This demonstrates that the external-cavity semiconductor laser exhibits the universal properties characteristic for nonlinear systems driven by two competing frequencies.

The long-standing problem of the linear, bi-Maxwellian neutral sheet tearing instability is solved without recourse to an approximation of the orbits or the constant-ψ approximation. We are therefore able to consider regimes beyond the validity of previous theories. As the temperature anisotropy is increased, the growth rate increases and the associated wavelength with the peak growth decreases.

We report the experimental observations of deterministic chaos in a steady-state plasma which is not driven by any extra periodic forces. Two routes to chaos have been found, period-doubling and intermittent chaos. The fine structures in chaos such as periodic windows and bifurcations in windows have also been observed.

The classical diffusion constant of a point defect in an infinite lattice of binding sites is shown to be expressible as transition-state-theory rates multiplied by dynamical correction factors computed from short-time classical trajectories initiated at the site boundaries. The expression, which results from time differentiating the lattice-discretized mean-square displacement, is valid at any temperature for which the site lattice is well defined. It thus avoids both the time-scale limitations of direct molecular dynamics and the rare-event requirements of standard dynamical-correction methods.

We analyze the nucleation and growth of cohesive tensile cracks using a field-theoretic formulation in which the free energy is written as a functional of the crack separation (offset field). Our results indicate that for certain materials, crack nucleation and growth proceed through the formation and extension of a diffuse ‘‘halo’’ surrounding the classical portion of the crack. This is similar to nonclassical nucleation in magnetic systems. Theoretical considerations and numerical calculations strongly suggest that the diffuse halo can be identified with the fracture ‘‘process zone’’ seen in laboratory studies of advancing cracks.

We report observations of order-disorder phase transitions in metastable cellular patterns of magnetic domains at room temperature. The advance of a front destroys an ordered hexagonal domain lattice and leaves a topologically disordered cellular phase. Front motion is driven by stress in the domain patterns induced by an external bias field. The topological nature of the transitions gives rise to the novel features of particle (cell) nonconservation and irreversibility.

The lattice sites of implanted Li in GaAs single crystals have been determined between 80 and 300 K by measuring channeling and blocking effects of α particles emitted in the decay of implanted radioactive ${}_{}{}^8{}_{}{}^{}\mathrm{Li}$. Below 220 K the tetrahedral interstitial site is preferentially occupied, whereas between 220 and 300 K substitutional and irregular sites are increasingly populated. These site changes are attributed to, respectively, reactions with negatively charged Ga vacancies and defect complexes in recovery stages I and II of GaAs.

The p(2×2) phase of oxygen on a stepped Ru(0001) surface (13±2 atomic rows per terrace, steps parallel to close-packed rows) exhibits long-range order also across the steps and undergoes a continuous order-disorder phase transition. Critical exponents β, γ, and ν were determined by LEED from the temperature dependence of LEED peak intensities and spot profiles of superstructure spots in the range 0.01<‖(T-$T_c$)/$T_c$‖<0.2 both parallel and perpendicular to the step edges. Exponent values are close to those of the 2D-Ising class and equal for both directions.

Single-crystal SM(0001) surfaces have been grown epitaxially on Mo(110). At low temperatures LEED shows a 5×5 surface reconstruction. This new type of valence-transition-induced reconstruction corresponds to a 25% expansion of the interatomic distances in the topmost hexagonal surface layer. At room temperature the 5×5 LEED pattern disappears due to a disordering of the surface. This suggests a very low melting temperature for the surface which may have implications for the understanding of the anomalous melting temperature of Sm metal.

The rate of tunneling of nuclei to classically forbidden small relative separation, in a fully interacting quantum-mechanical many-body system in equilibrium, is rigorously bounded above by a value calculable in terms of the Born-Oppenheimer potential between the nuclei. In the ‘‘cold-fusion’’ problem, the bound can be related to the affinities of helium and deuterium atoms to the metal in question, and shows that the allowed rate of tunneling of deuterons is far too small to be consistent with inferred rates of fusion.

Experimental evidence of relaxation phenomena associated with majority-carrier depletion has been observed for the first time in a high-purity semiconductor. It has been demonstrated in the low-temperature current-voltage (J-V) characteristics of a silicon diode. The material changes from the lifetime to the relaxation regime when the temperature is decreased from 300 to 14 K. A change in the shape of the J-V curve, manifested by increased conductance at low bias, is observed and is in good agreement with recent theoretical modeling of minority-carrier behavior in relaxation semiconductors.

In the standard hierarchical scheme the daughter state at each step results from the fractional quantum Hall effect of the quasiparticles of the parent state. In this paper a new possible approach for understanding the fractional quantum Hall effect is presented. It is proposed that the fractional quantum Hall effect of electrons can be physically understood as a manifestation of the integer quantum Hall effect of composite fermionic objects consisting of electrons bound to an even number of flux quanta.

It is shown that holes on the A and B sublattices of a spin-s antiferromagnet behave as charges ±s coupled to a gauge field $a_{\mu }$(n), n being the local order parameter. This general formalism can be pursued very far in d=1 where the finite-hole-concentration problem is described by massless fermions coupled to the σ model. Many exact results follow: Holes superconduct, destroy the quasi-long-range order, and wipe out the Θ term which distinguishes between integer and half-integer models or describes bond-strength alternation.