The familiar nucleosynthesis constraint on the number of neutrino species, ${\mathit{N}}_{\nu }$≤3.4, applies to massless neutrino species. An MeV-mass neutrino can have even greater impact, and we show that primordial nucleosynthesis excludes a τ-neutrino mass from 0.3 to 25 MeV (Dirac) and 0.5 to 25 MeV (Majorana) provided that its lifetime ${\mathrm{\tau }}_{\nu }$≳1 sec, and from 0.3 to 30 MeV (Dirac) and 0.5 to 32 MeV (Majorana) for ${\mathrm{\tau }}_{\nu }$≳${10}^3$ sec. A modest improvement in the laboratory mass limit—from 35 to 25 MeV—would imply that the τ-neutrino mass must be less than 0.5 MeV (provided ${\mathrm{\tau }}_{\nu }$≳1 sec).

We investigate the possibility of observing CP violation in the process ${\mathit{K}}^{+}$→${\mathrm{\pi }}^{+}$ll¯. We find that, from the point of view of probing the Cabbibo-Kobayashi-Maskawa (CKM) mechanism, the measurement of two-spin correlations of the outgoing leptons is the best recourse. For this purpose, we define a T-violating asymmetry ${\mathit{A}}_{\mathrm{CPV}}$, which is the coefficient of the coefficient of the correlation p${\mathrm{^}}_{\mathit{l}}$⋅s×s¯ in the differential decay rate. In the standard model we estimate ${\mathit{A}}_{\mathrm{CPV}}$∼1.9×${10}^{\mathrm{-}2}$ for the muon mode, using the currently allowed CKM parameters and a top-quark mass of 200 GeV/${\mathit{c}}^2$.

Isospin relations are used to eliminate hadronic uncertainties in various CP asymmetries in ${\mathit{B}}^0$ decays via b→uu¯s, e.g., ${\mathit{B}}^0$→${\mathrm{\pi }}^0$${\mathit{K}}_{\mathit{S}}$. A clean measurement of the angle α of the unitarity triangle is thus made possible. The magnitudes of the tree and the penguin amplitudes can be measured.

We construct a particle physics scenario which avoids the cosmological mass-density constraint on a Dirac-type neutrino in the mass range 100 eV–1 MeV by letting it decay primarily to three light Dirac neutrino final states. The nucleosynthesis constraints on the extra number of neutrinos (i.e., δ${\mathit{N}}_{\nu }$≤0.3) is saturated in this case. Identifying the recently reported 17-keV neutrino with ${\nu }_{\mathrm{\tau }}$, we predict its lifetime to be ${10}^8$≤${\mathrm{\tau }}_{\nu \mathrm{\tau }}$≤${10}^{13}$ sec. A hierarchy in the Dirac neutrino masses where ${\mathit{m}}_{\nu \mathrm{\tau }}$≃17 keV and ${\mathit{m}}_{\nu \mathit{e}}$≪${\mathit{m}}_{\nu \mathrm{\mu }}$≃${10}^{\mathrm{-}3}$ eV (so that the solar neutrino puzzle is resolved by the Mikheyev-Smirnov-Wolfenstein mechanism) can naturally be realized in an extension of the standard model.

An SU(2${)}_{\mathit{L}}$⊗U(1${)}_{\mathit{Y}}$ model containing exotic charged leptons can allow sizeable leptonic flavor violations (LFV) and hence rare Z decays into leptons of different flavors. The rates as well as CP-violating asymmetries are constrained using available limits on LFV and data from the CERN ${\mathit{e}}^{+}$${\mathit{e}}^{\mathrm{-}}$ collider LEP on Z→${\mathit{l}}_{\mathit{i}}$${\mathit{l}}_{\mathit{i}}$,${\mathit{l}}_{\mathit{i}}$=e,μ,τ. Sizeable CP-violating rate asymmetries are theoretically possible in the model and are allowed by the former data. In contrast, the measured leptonic Z widths severely constrain these asymmetries. As a result, an experimental observation of the CP asymmetries in the model seems unlikely with less than ${10}^9$ Z’s.

We study the chiral-odd spin structure functions of the nucleon, ${\mathit{h}}_1$(x) and ${\mathit{h}}_2$(x), their physical significance, sum rules, and model estimates. We show that they can be measured in the Drell-Yan process with polarized beams at order ${\mathit{Q}}^0$ and ${\mathit{Q}}^{\mathrm{-}1}$, respectively.

Using the analogy of the deuteron, spin-flavor symmetry, statistics, etc., it is argued that the one-pion exchange potential is likely to bind a few states composed of two ground-state mesons. The best S-wave candidates have masses, quantum numbers, and decay widths similar to those observed for the experimentally best established non-qq¯ candidates θ/${\mathit{f}}_0$(1720), G/${\mathit{f}}_0$(1590), ${\mathit{A}}_{\mathit{X}}$/${\mathit{f}}_2$(1520), and E/${\mathit{f}}_1$(1420). Possible P-wave states are the η(1410) and η(1490). Also the threshold enhancements seen in J/ψ→γρρ, γωω, γ${\mathit{K}}^{\mathrm{*}}$K¯ ${}_{}{}^{\mathrm{*}}{}_{}{}^{}$ and in γγ→ρρ are likely to be involved.

A search for neutrinos of mass 10–40 keV has been made by studying the internal-bremsstrahlung spectrum of ${}_{}{}^{71}{}_{}{}^{}\mathrm{Ge}$. We find evidence for a 17.2-keV neutrino with a mixing ratio of 1.6%.

Parity-nonconserving longitudinal analyzing powers were measured for 23 p-wave neutron resonances in ${}_{}{}^{232}{}_{}{}^{}\mathrm{Th}$. Seven resonances show effects of greater than 2σ statistical significance (95% confidence)—the largest sample yet measured in a single nucleus. All seven analyzing powers have positive sign. Strong sign correlations are not a feature of the conventional statistical model of parity mixing between compound nuclear states. The results suggest that the mechanism of parity violation in resonance reactions is more complicated than previously assumed.

In one of the first measurements of its type, the nuclear response function ${\mathit{R}}_{\mathit{L}\mathit{T}}$ has been determined in the ${}_{}{}^{16}{}_{}{}^{}\mathrm{O}$(e,e’p${)}^{15}$N reaction in quasielastic kinematics for the ground state (1/$2^{\mathrm{-}}$) and the first excited state (6.32 MeV, 3/$2^{\mathrm{-}}$). Extracted momentum distributions for these two states exhibit asymmetric behavior. Spectroscopic factors show significant depletion of strength, consistent with previous results. ${\mathit{R}}_{\mathit{L}\mathit{T}}$ agrees better with relativistic distorted-wave impulse-approximation calculations in magnitude than does the total cross section.

Exclusive p-p correlations from the ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$${+}^{58}$Ni reaction at 850 MeV incident energy have been measured. The enhancement in the p-p correlation function observed for small values of Δp with a gate on ${\mathit{v}}_{\mathrm{rel}}$ is satisfactorily explained by stochastic proton emission followed by the p-p final-state interaction. A strong dependence of the p-p correlation function on the relative angle between the two-proton c.m. and the fragment velocities has been found. Also a dependence of the p-p correlation function on the Δp orientation with respect to the plane defined by the two-proton c.m. and the fragment velocities has been observed. This latter behavior has been attributed to angular momentum effects.

The first measurement of photoelectron spectra emitted in the photoionization of a single-charged-ion beam by synchrotron radiation is reported. A ${\mathrm{Ca}}^{+}$-ion beam is resonantly photoionized by the monochromatized photon beam of the SU6 undulator of the SuperACO Storage Ring at 33.20 eV photon energy. The values observed for the kinetic energy and for the intensity of the photoelectron line are in good agreement with the predicted values. The success of this feasibility experiment opens up wide opportunities for similar photoionization and Auger studies on multiply charged ions.

The effect of transient gain in photodetection of light is studied. By treating the photoelectron multiplication as a classical, stochastic process, a generalization of the quantum Mandel formula is given. To illustrate the theory developed, the detection of sub-Poisson light from single-atom resonance fluorescence is studied. It is shown that the results may substantially differ from those predicted from the Burgess variance theorem. In particular, a reduction of noise of the photoelectric counts can be achieved even if the value of the gain rate is increased.

We present experiments and computer simulations of slow drainage in a two-dimensional porous medium. The effect of gravity is systematically varied by tilting the system from the horizontal position. The width σ of the front between the fluids is found to scale with the dimensionless Bond number Bo (ratio between gravitational and capillary forces) as σ∼${\mathrm{Bo}}^{\mathrm{-}0.57}$, as predicted by theory. The external perimeter of the invaded structure is shown to be fractal with the fractal dimension ${\mathit{D}}_{\mathit{e}}$≃1.34 for length scales smaller than the front width.

Magnetically confined columns of electrons are excellent experimental realizations of extended two-dimensional vortices in an inviscid fluid. Here, we consider two nearly identical vortices orbiting around one another inside a cylindrical wall. The vortices merge symmetrically, in a time which varies from less than 1 to about ${10}^4$ orbit periods as the vortex separation is increased by 30%. We have obtained images of the vorticity distribution during this merger process, and observe filamentary tails and mixing. These experimental results are consistent with analytic models and numerical simulations.

The inverse scattering transform for the periodic Korteweg–de Vries equation is used to analyze surface-wave data obtained in the Adriatic Sea and a robust solition spectrum is found. While the solitons are not observable in the data due to the presence of energetic radiation modes, a new nonlinear filtering technique renders the solitons visible. Numerical simulations support the existence of solitons in the measurements and suggest that, as a wave train propagates into shallow water, the solitons grow at the expense of the radiation.

Measurements of the correlation function below the electrohydrodynamic instability in a thin layer of a nematic liquid crystal reveal fluctuating convection patches. Their amplitude A¯, correlation length ξ, and correlation time τ can be desribed by a stochastic mean-field model. The amplitude agrees with the expected fluctuations due to thermal noise.

Excess energies are calculated for cylindrical Coulomb crystals at very low temperature and various densities as an approximation of a cooled ion beam in a storage ring or of cold trapped ions. Even for the large six-shell structures it is found that the plane hexagonal lattice on the surface is still dominating–with an excess (Madelung) energy of -0.892 28–over the expected infinite bcc structure. The results of molecular-dynamics computer simulations are compared with results of a classical shell model which takes into account the constant intershell distances and hexagonal surface occupation.

We have measured the sticking probability of atomic hydrogen on a superfluid ${}_{}{}^4{}_{}{}^{}\mathrm{He}$ surface for atom energies between 100 μK and 1 mK. The sticking probability shows little variation with energy over this interval, and is close to the value 0.2. The studies were carried out using a magnetic trap that produced a density of 8×${10}^{13}$ ${\mathrm{cm}}^{\mathrm{-}3}$ at a temperature of 100 μK.

Electronic wave functions in disordered systems are studied within the Anderson model of localization. At the critical disorder in 3D we diagonalize very large (103 823×103 823) secular matrices by means of the Lanczos algorithm. On all length scales the obtained strong spatial fluctuations of the amplitude of the eigenstates display a multifractal character, reflected in the set of generalized fractal dimensions and the singularity spectrum of the fractal measure. An analysis of 1D systems shows multifractality too, in contrast to previous claims.