Cold dark matter (CDM) models predict small-scale structure in excess of observations of the cores and abundance of dwarf galaxies. These problems might be solved, and the virtues of CDM models retained, even without postulating ad hoc dark matter particle or field interactions, if the dark matter is composed of ultralight scalar particles $\left(m\sim {10}^{-22\mathrm{}}\mathrm{eV}\right)$, initially in a (cold) Bose-Einstein condensate, similar to axion dark matter models. The wave properties of the dark matter stabilize gravitational collapse, providing halo cores and sharply suppressing small-scale linear power.

We point out that for solar neutrino oscillations with the mass-squared difference of $\Delta m^2\sim {10}^{-10\mathrm{}}–{10}^{-9\mathrm{}}{\mathrm{eV}}^2$, i.e., in the so-called vacuum oscillation range, the solar matter effects are non-negligible, particularly for the low energy $\mathrm{pp}$ neutrinos. One consequence of this is that the values of the mixing angle $\theta$ and $\pi /2-\theta$ are not equivalent, making it necessary to consider the entire physical range of the mixing angle $0\le \theta \le \pi /2$ when determining the allowed values of the neutrino oscillation parameters.

A new mechanism for electron emission from planar cathodes is described. The theoretical analysis shows that, with an ultrathin wide band-gap semiconductor layer (UTSC) on a metal, the surface barrier is lowered to $\sim 0.1\mathrm{eV}$ due to the creation of a space charge induced by the electrons injected from the metal. The barrier height depends mostly on the UTSC thickness and not on the state of the surface, as in thermionic and field emissions. This mechanism explains the measured stable emission at 300 K and ${10}^{-7\mathrm{}}\mathrm{Torr}$, with a threshold field of only $\sim 50\mathrm{V}/\mu \mathrm{m}$, from these solid-state field-controlled emitters.

The wavelength of the ${}^{57}\mathrm{Fe}$ Mössbauer radiation is measured with a relative uncertainty of 0.19 ppm by using almost exact Bragg backscattering from a reference silicon crystal. Its value is determined as ${\lambda }_{\mathrm{M}}=0.860\mathrm{}25474\left(16\right)\times {10}^{-10\mathrm{}}$ m. The corresponding Mössbauer photon energy is $E_{\mathrm{M}}=14\mathrm{}412.497\left(3\right)$ eV. The wavelength of the ${}^{57}\mathrm{Fe}$ Mössbauer radiation is easily reproducible with an accuracy of at least ${10}^{-11\mathrm{}}{\lambda }_{\mathrm{M}}$ and could be used as a length standard of atomic dimensions.

The phase evolution of light in an optical waveguide structure has for the first time been visualized with subwavelength resolution using a novel heterodyne interferometric photon scanning tunneling microscope. Phase singularities in the optical field of the waveguide have been observed. The phase singularities of charge one appear at locations where the modal field amplitude vanishes, due to the interference of various modes in the waveguide. Excellent agreement of the data with calculations has been obtained.

We report observations of electromagnetic wave-induced 557.7-nm emission in correspondence with a sporadic low-altitude plasma layer (the sporadic- $E$ layer, $E_s$). We show that the structure of 557.7-nm emission seen for some events results from a transformation of transmitted energy by ionization clouds, compiling the patchy type $E_s$, and presents a projection of the sporadic- $E$ layer structure on the emission altitude. This allows us to propose the first method for visualizing a horizontal structure of sporadic- $E$ layers.

Photoelectric charging measurements are presented of dust grains in vacuum for isolated grains and for grains near a photoemissive surface. Isolated grains reach a positive-equilibrium floating potential, dependent upon the work function of the particle, which causes the emitted electrons to be returned. Grains dropped past a photoemitting surface reach a negative floating potential for which the sum of the emitted and collected currents is zero. The particles tested are $90–106\mu \mathrm{m}$ in diameter and are composed of Zn, Cu, graphite, and glass.

The Cryogenic Dark Matter Search (CDMS) employs Ge and Si detectors to search for weakly interacting massive particles (WIMPs) via their elastic-scattering interactions with nuclei while discriminating against interactions of background particles. CDMS data, accounting for the neutron background, give limits on the spin-independent WIMP-nucleon elastic-scattering cross section that exclude unexplored parameter space above $10\mathrm{GeV}/c^2$ WIMP mass and, at $>75\mathrm{}\%$ C.L., the entire $3\sigma$ allowed region for the WIMP signal reported by the DAMA experiment.

Phase-matched relativistic harmonic generation in plasmas is observed for the first time. Third-harmonic light is detected and discriminated spectrally and angularly from the harmonics generated from competing processes. Its angular pattern is a narrow forward-directed cone, which is consistent with phase matching of a high-order transverse mode in a plasma. The signal level is found to be on the same order of magnitude for a circularly polarized pump pulse as for a linearly polarized pump pulse.

The mechanical response of 15 single wall carbon nanotube (SWCNT) ropes under tensile load was measured. For 8 of these ropes strain data were obtained and they broke at strain values of $5.3\%$ or lower. The force-strain data are well fit by a model that assumes the load is carried by the SWCNTs on the perimeter of each rope. This model provides an average breaking strength of SWCNTs on the perimeter of each rope; the 15 values range from 13 to 52 GPa (mean 30 GPa). Based on the same model the 8 average Young's modulus values determined range from 320 to 1470 GPa (mean 1002 GPa).

We demonstrate a great simplification in the long-standing problem of measuring optical frequencies in terms of the cesium primary standard. An air-silica microstructure optical fiber broadens the frequency comb of a femtosecond laser to span the optical octave from 1064 to 532 nm, enabling us to measure the 282 THz frequency of an iodine-stabilized Nd:YAG laser directly in terms of the microwave frequency that controls the comb spacing. Additional measurements of established optical frequencies at 633 and 778 nm using the same femtosecond comb confirm the accepted uncertainties for these standards.

The possibility of observing superluminal behavior in the propagation of localized microwaves over distances of tens of wavelengths is experimentally demonstrated. These types of waves, better than the evanescent modes of tunneling, can contribute to answering the question on the luminal limit of the signal velocity.

The variation of a magnetic field as a function of depth beneath the surface of an ${\mathrm{YBa}}_2{\mathrm{Cu}}_3{\mathrm{O}}_{7-\delta }$ thin film in the Meissner state has been measured using low energy muons. The depth of implantation was varied from 20–150 nm by tuning the energy of the implanted muons from 3–30 keV. These are direct measurements of the penetration of a magnetic field beneath a superconducting surface which illustrate the power of low energy muons for near surface studies in superconductivity and magnetism.

In a closed volume of molten sodium an intense single-vortex-like helical flow has been produced by an outside powered propeller. At a flow rate of $0.67{\mathrm{m}}^3/\mathrm{s}$ a slowly growing magnetic field eigenmode was detected. For a slightly lower flow, additional measurements showed a slow decay of this mode. The measured results correspond satisfactorily with numerical predictions for the growth rates and frequencies.

We have directly time resolved the lattice motions associated with the formation of the self-trapped exciton in the quasi-one-dimensional system $\left[\mathrm{Pt}\right(\mathrm{en}{)}_2\left]\right[\mathrm{Pt}\left(\mathrm{en}{)}_2{\mathrm{Br}}_2\right]̇({\mathrm{PF}}_6{)}_4$ ( $\mathrm{en}=\mathrm{ethylene}-\mathrm{diamine}$, ${\mathrm{C}}_2{\mathrm{H}}_8{\mathrm{N}}_2$), using femtosecond impulsive excitation techniques. A strongly damped, low-frequency wave packet modulation at $\sim 110{\mathrm{cm}}^{-1\mathrm{}}$ accompanies the formation of the self-trapped exciton on a $\sim 200\mathrm{fs}$ time scale following excitation of the intervalence charge-transfer transition. Coherent oscillations at the ground state vibrational frequency and its harmonics are also detected.

We present an experimental study of the thermal response to a positive temperature quench in two-phase fluid ${\mathrm{SF}}_6$ in low gravity for temperature ranging from $10.1$ to $0.1$ K from the critical temperature. The temperature was measured simultaneously in the gas, the liquid, and the cell wall by thermistors and the density distribution was observed by interferometry. During the quench the gas temperature considerably exceeded the temperature of the heating walls (overheating up to $23\%$). This striking observation is discussed in the light of the adiabatic heat transfer in this highly compressible fluid while the key role of the localization in low gravity of the gas and liquid phases is revealed.

We describe a general technique that allows for an ideal transfer of quantum correlations between light fields and metastable states of matter. The technique is based on trapping quantum states of photons in coherently driven atomic media, in which the group velocity is adiabatically reduced to zero. We discuss possible applications such as quantum state memories, generation of squeezed atomic states, preparation of entangled atomic ensembles, quantum information processing, and quantum networking.

We present a novel approach to the preparation of neutral (anti-)matter. The scheme is based on recombination of a free electron and an ion, and can be considered as the inverse of pulsed field ionization. We have obtained promising results on rubidium: at low densities already efficiencies of $0.3\%$ were obtained. This is orders of magnitude more than has been achieved in previous recombination studies.

The apparent lack of suitable astrophysical sources for the observed highest energy cosmic rays within $\approx 20\mathrm{Mpc}$ is the “Greisen-Zatsepin-Kuzmin (GZK) paradox.” We constrain representative models of the extragalactic magnetic field structure by Faraday rotation measurements; limits are at the $\mu \mathrm{G}$ level rather than the nG level usually assumed. In such fields, even the highest energy cosmic rays experience large deflections. This allows nearby active galactic nuclei (possibly quiet today) or gamma ray bursts to be the source of ultrahigh energy cosmic rays without contradicting the GZK distance limit.

We propose a mechanism for experimental investigation of relativistic effects in the laser-atom interaction with moderate (nonrelativistic) laser intensities that involves placing the system in a static magnetic field parallel to the laser's magnetic-field component. The resonantly induced relativistic motion of the atomic electron leads to a variety of novel phenomena: a relativistic dephasing leading to a ringlike spatial probability density, a counterintuitive window of relativistically enhanced motion, and a sequence of sawtooth-shaped resonances that may increase the harmonic generation.