We show that black holes are topologically stable under quantum fluctuations but unstable under quantum emission and absorption of gravitons. The probability of emission behaves as exp[-α($M_f$-$M_i$)], where $M_i$ and $M_f$ are the masses associated to the initial and final states, and α is a positive constant of the order of 1. As the black hole loses mass it evolves towards a state corresponding to a black hole of very small mass that cannot be distinguished from a pure graviton state.

We provide a very simple prescription for inserting an arbitrary state into a string amplitude. The corresponding string measure is defined without any additional information whenever the state is Becchi-Rouet-Stora-Tyutin (BRST) invariant, generalizing the usual physical conditions. In particular no world-sheet metric is needed. We recover and interpret in a simple way the b^ prescription of Polchinski and explain geometrically how it secures the decoupling of BRST spurious states.

We study chiral-symmetry breaking in quenched gauge theories with ultraviolet cutoff Λ, to all orders in the gauge coupling. For large Λ/κ, where κ is the chiral-symmetry-breaking scale, we derive Λ/κ∝exp(const/ √(α-${\alpha }_c$) as α→${\alpha }_c$+. This is a gauge-invariant, universal consequence of quenched theories. But we argue that this relation does not define a β function. We also obtain an explicit expression for the self-energy Σ(p) which applies over most of the range κ<p<Λ.

The ratio $\frac{h}{m^{\prime }}$ of Panck's constant to the observable Cooper-pair mass ($\sim 2m_e$) is determined directly using a rotating superconducting ring by measuring the London moment flux $\left(\frac{2m^{\prime }c}{e^{*}}\right)\omega S$, where $S$ is the area bounded by the ring, in units of the flux quantum ($\frac{\mathrm{hc}}{e^{*}}$). The flux in the ring is zero for a set of rotation frequencies which are equally spaced by $\Delta \nu$, and $\frac{h}{m^{\prime }}=2S\Delta \nu$. We have measured $\Delta \nu$ and $S$ with a precision of 5 ppm and an accuracy of 21 ppm. Our result for niobium, ${\left(\frac{m^{\prime }}{2m_e}\right)}_{\mathrm{Nb}}=1.000\mathrm{}084\left(21\right)\mathrm{}$, disagrees with theoretical predictions of 0.999 992.

Based on the equivalence theorem of the on-shell $S$-matrix elements independently of nonlinearly realized Goldstone fields, we clarify the discrepancies raised by the use of the pseudovector derivative and pseudoscalar pion-nucleon couplings in the nucleon-nucleon axion bremsstrahlung process which is often taken as the dominant axion emission mechanism from SN 1987A. In addition, we propose a new method to calculate the axion emission rate from $\mathrm{NN}\to \mathrm{NN}\pi$ data, and compare the result to the theoretical calculation based on the one-pion-exchange approximation.

We prove a theorem stating that a massive Majorana particle (a $\mathrm{CPT}$-self-conjugate particle) with arbitrary spin $J$ can possess only an anapole moment and multipoles of that. We also show that massless Majorana particles, except those of spin ½, do not have any single-photon electromagnetic form factor.

Absorptive parts in QCD-induced charmless $B$ decays allow for a new mechanism of $\mathrm{CP}$ violation. Existing discussions in the literature do not satisfy the $\mathrm{CPT}$ theorem. Solving the problem, we find that, inclusively, a strong cancellation remains between the $b\to \mathrm{su}\overline{u}$ mode $\mathrm{CP}$ rate asymmetries and the purely loop-induced $b\to \mathrm{sd}\overline{d}, \mathrm{ss}\overline{s}, \mathrm{sgg}$ modes. Exclusively, the asymmetries of purely loop-induced modes (such as $B\to K\phi$) are unaffected, but those related to $b\to \mathrm{su}\overline{u}$ (such as $B\to K\pi$) change sign. The discussion for $b\to d$ modes is similar.

Unitarity effects associated with the two-channel system consisting of the states $W_L^{+}{W}_L^{-}$ and $\frac{Z_L^0{Z}_L^0}{\sqrt{2}}$ are investigated using the $K$-matrix technique. In $W_L^{+}{W}_L^{-}$ elastic scattering, we find that for a Higgs-boson mass ($m_H$) of 0.5 TeV the unitarized $s$-wave amplitude is very similar to the Born amplitude modified by the addition of a Higgs-boson width. When $m_H$ reaches 1.4 TeV, which is above the unitarity bound obtained from the Born term, the unitarized amplitude saturates at an absolute value of about $\frac{2}{3}$ of the unitarity limit. The implications of unitarity on $W$-pair production at Superconducting Super Collider energies are also discussed.

We present evidence from the CLEO detector for the charmed strange baryon ${\Xi }_c^0$. It is seen in nonresonant $e^{+}{e}^{-}$ annihilations at $\sqrt{s}$ of 10.5 GeV through its decay to ${\Xi }^{-}{\pi }^{+}$. The measured ${\Xi }_c^0$ mass is 2471 ± 3 ± 4 MeV/${\mathit{c}}^2$.

Corrections to the Fermi matrix element for superallowed transitions due to isospin nonconservation are reexamined. The sources of theoretical uncertainty and the possibility of a previously neglected correction based on the mismatch between the spectator nucleons are investigated. The consequences to the conserved-vector-current hypothesis and the Kobayashi-Maskawa mixing angles are discussed.

The first $\mathrm{Pb}(n, n^{\prime }x)$ data (at 65 MeV) are compared to earlier (61-66 MeV) ($p, p^{\prime }x$) data. The isovector sensitivity of these nucleon probes is used to determine $\frac{M_n}{M_p}\simeq \frac{N}{Z}=1.54\mathrm{}$ for the giant quadrupole resonance (GQR). This result is consistent with other direct GQR measurements, $2_1^{+}$ data connected through core polarization, and several microscopic random-phase-approximation calculations, but in disagreement with a $\frac{{\pi }^{-}}{{\pi }^{+}}$ study which gives $\frac{M_n}{M_p}=3.8\mathrm{}\pm 1.2$.

The weak $4_2^{+}$→$2_3^{+}$ transition in ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$ was observed with a branching ratio (0.30±0.08)%, using the ${}_{}{}^{14}{}_{}{}^{}\mathrm{C}(\alpha ,\gamma ){}_{}{}^{18}{}_{}{}^{}\mathrm{O}$ radiative-capture reaction at $E_{\alpha }=1.14\mathrm{}$ MeV. The corresponding $B(E2:4_2^{+}\to 2_3^{+})=5.7\mathrm{}\pm 1.9$ Weisskopf unis appears noncollective, and serves as a crucial test of microscopic models predicting collective band structures and enhanced $E1\mathrm{}$ decays in ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$; it is smaller by a factor of 3-8 than predictions of such models, and cannot be reproduced by the well-established coexistence model for ${}_{}{}^{18}{}_{}{}^{}\mathrm{O}$, suggesting that our understanding of collective motion in light nuclei is incomplete. We review recent suggestions for extending coexistence models.

The photoion-yield spectra $\sigma \left(X^{n+}\right)$ with $n=1-4\mathrm{}$ for seven elements of the lanthanides in the region of the $4d$ giant resonances between 100-200 eV were measured. Dramatic changes in the different $X^{n+}$ signals for increasing $Z$ show the growing influence of the $4f$ subshell in the competition between continuum transitions $4d^{10}\to 4d^9\epsilon f$ and discrete transitions $4d^{10}4f^N\to 4d^{9}4f^{N+1\mathrm{}}$. For the analysis of the spectra the partial photoionization cross sections $\sigma \mathrm{}\left(\mathrm{nl}\right)\mathrm{}$ for the subshells $4d$, $5s$, $5p$, and $4f$ were calculated with the time-dependent local-density approximation.

We confirm in computer experiments the presence of unexpected plateau and cutoff features in high-order harmonic generation accompanying multiphoton ionization. We show the connection between these features and above-threshold ionization.

Quantitative calculations of Auger line shapes of free atoms after particle-impact ionization are presented. It is shown that the line shapes deviate from Lorentzians for all impact energies, due to long-range continuum interactions between the Auger electron and unobserved collision fragments. In particular, even at asymptotically high impact energies, the observed linewidth ${\Gamma }_{\mathrm{FWHM}}$ exceeds the decay width ${\Gamma }_0$ of the initial state by up to 10%; moreover, the line shapes are slightly, but noticeably shifted and asymmetrically distorted with respect to a Lorentzian. The magnitude of these effects was unknown in the past; possible implications for various subfields of physics are discussed.

We show that strong non-Franck-Condon effects can arise from photoionization of molecular Rydberg orbitals which evolve rapidly with internuclear distance and display Cooper minima in their photoelectron spectrum. The non-Franck-Condon mechanism should be most pronounced in excited-state photoionization of diatomic hydrides. The mechanism is illustrated with specific ab initio predictions of ion vibrational distributions for a proposed (3 + 1) one-color or (2 + 1) two-color resonant multiphoton ionization measurement of OH via the $D{}_{}{}^2{}_{}{}^{}\Sigma _{}^{-}{}_{}{}^{}\left(1\mathrm{}{\pi }^{2}5\sigma \right)$ state.

We have studied energy-level statistics of the diamagnetic lithium Rydberg spectrum in a regime of regular classical motion. The distribution of adjacent levels displays the Poisson-type behavior that has been reported in theoretical studies of numerous systems. Long-range correlations in the spectrum can be related simply to the number of underlying manifolds.

Molecular-dynamics simulations were used to study the heat and momentum transport phenomena in very dilute gases flowing through a two-dimensional channel. Aside from pronounced slips in velocity and temperature at the wall, Navier-Stokes equations seem to be valid up to the maximum Knudsen number (Kn), 0.27, studied. It is further shown that the viscosity of a very dilute gas decreases monotonically with the decreasing density. For Kn less than ∼0.05, the slip coefficient, 1.16, calculated from the simulation is in good agreement with theoretical results, ranging from 1.134 to 1.230. However, at higher Kn, the slip coefficient is predicted to depend on the Knudsen number.

We have developed a method to accumulate and store positrons, from a ${}_{}{}^{22}{}_{}{}^{}\mathrm{Na}$ radioactive source, in an electrostatic trap using a tungsten moderator and inelastic collisions with nitrogen molecules. The resulting positron gas is found to cool to room temperature, and to fulfill the criteria for a single-component, positron plasma. The cooling and confinement processes and the potential applications of this many-positron system are discussed.

I study the effects of elastic anisotropy and long-ranged interactions on the fluctuations of solid membranes. Elastic anisotropies prove to be irrelevant in the absence of long-ranged interactions. Long-ranged interactions which fall off with distance $r$ like $r^{-\sigma }$ are relevant only for sufficiently small $\sigma$. In real (two-dimensional) membranes with dipolar interactions ($\sigma =3\mathrm{}$), the Lamé coefficients $\mu$ and $\lambda$ vanish like ${\left[\ln \right(\frac{1}{q}\left)\right]}^{-1\mathrm{}}$, as wave vector $q\to 0$. For larger but still relevant $\sigma \text{'}\mathrm{s}$, $\mu \propto q^{{\eta }_{\perp }}\propto \lambda$ with ${\eta }_{\perp }=2\mathrm{}\sigma -3D$, exactly, for $D$-dimensional membranes.