Showing papers in "Physical Review D in 1991"

Three exceptions in the calculation of relic abundances

Abstract: The calculation of relic abundances of elementary particles by following their annihilation and freeze-out in the early Universe has become an important and standard tool in discussing particle dark-matter candidates. We find three situations, all occurring in the literature, in which the standard methods of calculating relic abundances fail. The first situation occurs when another particle lies near in mass to the relic particle and shares a quantum number with it. An example is a light squark with neutralino dark matter. The additional particle must be included in the reaction network, since its annihilation can control the relic abundance. The second situation occurs when the relic particle lies near a mass threshold. Previously, annihilation into particles heavier than the relic particle was considered kinematically forbidden, but we show that if the mass difference is \ensuremath{\sim}5-15%, these "forbidden" channels can dominate the cross section and determine the relic abundance. The third situation occurs when the annihilation takes place near a pole in the cross section. Proper treatment of the thermal averaging and the annihilation after freeze-out shows that the dip in relic abundance caused by a pole is not nearly as sharp or deep as previously thought.

HIGING: A Monte Carlo model for multiple jet production in pp, pA, and AA collisions.

Abstract: Combining perturbative-QCD inspired models for multiple jet production with low ${p}_{T}$ multistring phenomenology, we develop a Monte Carlo event generator hijing to study jet and multiparticle production in high energy $\mathrm{pp}$, $\mathrm{pA}$, and $\mathrm{AA}$ collisions. The model includes multiple minijet production, nuclear shadowing of parton distribution functions, and a schematic mechanism of jet interactions in dense matter. Glauber geometry for multiple collisions is used to calculate $\mathrm{pA}$ and $\mathrm{AA}$ collisions. The phenomenological parameters are adjusted to reproduce essential features of $\mathrm{pp}$ multiparticle production data for a wide energy range ($\sqrt{s}=5\ensuremath{-}2000$ GeV). Illustrative tests of the model on $p+A$ and light-ion $B+A$ data at $\sqrt{s}=20$ GeV/nucleon and predictions for Au+Au at energies of the BNL Relativistic Heavy Ion Collider ($\sqrt{s}=200$ GeV/nucleon) are given.

String theory and black holes.

Abstract: An exact conformal field theory describing a black hole in two-dimensional space-time is found as an SL(2,openR)/U(1) gauged Wess-Zumino-Witten model. For k=9/4, the conformal field theory can be regarded as a classical solution of the same system that is probed in the c=1 matrix model. The conformal field theory governing the space-time is regular at the Riemannian singularity, but it appears that generic perturbations blow up there. It is argued that the end point of the Hawking black-hole evaporation is the standard space-time of the c=1 matrix model, which should be regarded as an analog of the extreme Reissner-Nordstr\"om black hole of four-dimensional general relativity. The c=1 model is thus a model of the quantum mechanics of matter interacting with a black hole.

Charged black holes in string theory

Abstract: A family of solutions to low-energy string theory representing static, spherically symmetric charged black holes is described. They are labeled by their mass, charge, and asymptotic value of the scalar dilaton. The presence of the dilaton is found to have important consequences. In particular, the extremal charged "black holes" are found to be geodesically complete spacetimes with no event horizons and no singularities. Implications of these new solutions for black-hole thermodynamics and open questions in general relativity are also discussed.

Implications of precision electroweak experiments for m t , ρ 0 , sin 2 θ W , and grand unification

Abstract: The implications of precision $Z$-pole, $W$-mass, and weak-neutral-current data for SU(2)\ifmmode\times\else\texttimes\fi{}U(1) models are described. Within the minimal model one finds ${{sin}^{2}\stackrel{^}{\ensuremath{\theta}}}_{W}({M}_{Z})=0.2334\ifmmode\pm\else\textpm\fi{}0.0008$ in the modified minimal subtraction scheme or ${{sin}^{2}\ensuremath{\theta}}_{W}\ensuremath{\equiv}1\ensuremath{-}\frac{{M}_{W}^{2}}{{M}_{Z}^{2}}=0.2291\ifmmode\pm\else\textpm\fi{}0.0034$ in the on-shell scheme, where the uncertainties include the ${m}_{t}$ and ${M}_{H}$ dependence. The top-quark mass is predicted to be ${124}_{\ensuremath{-}34\ensuremath{-}15}^{+28+20}$ GeV, where the second uncertainty is from ${M}_{H}$, with ${m}_{t}l174(182)$ GeV at 90 (95)% C.L. For the first time subleading effects and vertex corrections allow a significant separation of ${m}_{t}$ and ${\ensuremath{\rho}}_{0}$ in models with a nonminimal Higgs structure. Allowing arbitrary ${m}_{t}$ and Higgs representations one obtains ${{sin}^{2}\stackrel{^}{\ensuremath{\theta}}}_{W}({M}_{Z})=0.2333\ifmmode\pm\else\textpm\fi{}0.0008$, ${\ensuremath{\rho}}_{0}=0.992\ifmmode\pm\else\textpm\fi{}0.011$, and ${m}_{t}l294(310)$ GeV. The implications of these results for ordinary and supersymmetric grand unified theories are considered. Supersymmetric theories with a grand desert between the supersymmetry and unification scales are in striking agreement with data for ${M}_{\mathrm{SUSY}}$ in the ${M}_{Z}\ensuremath{-}1$ TeV range. Ordinary grand unified theories breaking to the standard model in more than one step are also discussed.

Celestial mechanics, conformal structures, and gravitational waves.

Abstract: Newton's equations for the motion of $N$ nonrelativistic point particles attracting according to the inverse square law may be cast in the form of equations for null geodesics in a ($3N+2$)-dimensional Lorentzian spacetime which is Ricci flat and admits a covariantly constant null vector. Such a spacetime admits a Bargmann structure and corresponds physically to a plane-fronted gravitational wave (generalized pp wave). Bargmann electromagnetism in five dimensions actually comprises the two distinct Galilean electromagnetic theories pointed out by Le Bellac and L\'evy-Leblond. At the quantum level, the $N$-body Schr\"odinger equation may be cast into the form of a massless wave equation. We exploit the conformal symmetries of such spacetimes to discuss some properties of the Newtonian $N$-body problem, in particular, (i) homographic solutions, (ii) the virial theorem, (iii) Kepler's third law, (iv) the Lagrange-Laplace-Runge-Lenz vector arising from three conformal Killing two-tensors, and (v) the motion under time-dependent inverse-square-law forces whose strength varies inversely as time in a manner originally envisaged by Dirac in his theory of a time-dependent gravitational constant $G(t)$. It is found that the problem can be reduced to one with time-independent inverse-square-law forces for a rescaled position vector and a new time variable. This transformation (Vinti and Lynden-Bell) is shown to arise from a particular conformal transformation of spacetime which preserves the Ricci-flat condition originally pointed out by Brinkmann. We also point out (vi) a Ricci-flat metric representing a system of $N$ nonrelativistic gravitational dyons. Our results for a general time-dependent $G(t)$ are also applicable by suitable reinterpretation to the motion of point particles in an expanding universe. Finally we extend these results to the quantum regime.

Thin shells in general relativity and cosmology: The Lightlike limit

Abstract: This paper shows how the structure and dynamics of a thin shell traveling at the speed of light can be obtained from a simple and convenient prescription that is a straightforward extension and continuous limit of the familiar extrinsic-curvature algorithm for subluminal shells. It allows the space-time coordinates to be chosen freely and independently on the two sides of the shell. The prescription is applied to several examples of interest in general relativity and cosmology.

Time in quantum gravity: An hypothesis.

Abstract: A solution to the issue of time in quantum gravity is proposed. The hypothesis that time is not defined at the fundamental level (at the Planck scale) is considered. A natural extension of canonical Heisenberg-picture quantum mechanics is defined. It is shown that this extension is well defined and can be used to describe the "non-Schr\"odinger regime," in which a fundamental time variable is not defined. This conclusion rests on a detailed analysis of which quantities are the physical observables of the theory; a main technical result of the paper is the identification of a class of gauge-invariant observables that can describe the (observable) evolution in the absence of a fundamental definition of time. The choice of the scalar product and the interpretation of the wave function are carefully discussed. The physical interpretation of the extreme "no time" quantum gravitational physics is considered.

Hard-scattering scaling laws for single-spin production asymmetries

Abstract: The extraction of a scaling law of the form (({ital p}{sub {ital T}}{sup 2}+{mu}{sup 2})/{mu}{ital p}{sub {ital T}}){ital A}{sub {ital N}}{congruent}{ital g}({ital x}{sub {ital T}}) (where {ital x}{sub {ital T}}=2{ital p}{sub {ital T}}/ {radical}{ital s} ) from data on a single-spin production asymmetry such as {ital A}{sub {ital N}d}{sigma}({ital pp}{sub {up arrow}}{r arrow}{pi}{sup 0}{ital X}) at large transverse momentum can be used to argue for an underlying hard-scattering'' mechanism. Data from the upcoming Fermilab polarized beam experiment (E-704) can be used to test the scaling hypothesis.

High-energy photons from quark-gluon plasma versus hot hadronic gas

Abstract: Photons in the energy range of about one-half to several GeV have been proposed as a signal of the formation of a quark-gluon plasma in high-energy collisions. To lowest order the thermal emission rate is infrared divergent for massless quarks, but we regulate this divergence using the resummation technique of Braaten and Pisarski. Photons can also be produced in the hadron phase. We find that the dominant contribution comes from the reactions $\ensuremath{\pi}\ensuremath{\pi}\ensuremath{\rightarrow}\ensuremath{\rho}\ensuremath{\gamma}$ and $\ensuremath{\pi}\ensuremath{\rho}\ensuremath{\rightarrow}\ensuremath{\pi}\ensuremath{\gamma}$; the decays $\ensuremath{\omega}\ensuremath{\rightarrow}\ensuremath{\pi}\ensuremath{\gamma}$ and $\ensuremath{\rho}\ensuremath{\rightarrow}\ensuremath{\pi}\ensuremath{\pi}\ensuremath{\gamma}$ are also significant. Comparing the thermal emission rates at a temperature $T=200$ MeV we conclude that the hadron gas shines just as brightly as the quark-gluon plasma.

Particles with small violations of Fermi or Bose statistics.

Abstract: I discuss the statistics of "quons" (pronounced to rhyme with muons), particles whose annihilation and creation operators obey the $q$-deformed commutation relation (the quon algebra or $q$-mutator) which interpolates between fermions and bosons. Topics discussed include representations of the quon algebra, proof of the $\mathrm{TCP}$ theorem and clustering, violation of the usual locality properties, and experimental constraints on violations of the Pauli exclusion principle (i.e., Fermi statistics) and of Bose statistics.

Simplest Z' model.

Abstract: The differences in family-lepton numbers are anomaly-free in the minimal standard model (MSM), and can therefore be gauged. For three generations of quarks and leptons, three models emerge depending on whether (i) ${L}_{e}\ensuremath{-}{L}_{\ensuremath{\mu}}$, (ii) ${L}_{e}\ensuremath{-}{L}_{\ensuremath{\tau}}$, or (iii) ${L}_{\ensuremath{\mu}}\ensuremath{-}{L}_{\ensuremath{\tau}}$ are gauged. These are the simplest models to feature a ${Z}^{\ensuremath{'}}$ boson because no fermions beyond those already present in the MSM are required to cancel gauge anomalies. We analyze the phenomenology of models (i) and (ii) in detail, and present constraints derived from low-energy neutral-current data and CERN LEP data. We find that these ${Z}^{\ensuremath{'}}$ bosons may have a relatively low mass yet still evade present experimental bounds, while remaining detectable in current accelerators. The introduction of neutrino masses into the models is then considered. We discuss how one may incorporate both the reported 17-keV neutrino, and the Mikheyev-Smirnov-Wolfenstein effect solution of the solar-neutrino problem. We then describe how to embed the extra U(1) gauge group into a horizontal SU(2)-symmetry group acting on leptons.

Choice of filters for the detection of gravitational waves from coalescing binaries.

Abstract: Coalescing binaries are one of the most promising candidates for the detection of gravitational waves with the advent of the new generation of laser interferometric gravitational-wave detectors. Signals from coalescing binaries will most probably not stand above the broadband noise of the detector. Their detection is possible by the use of special data analysis techniques such as matched filtering which takes advantage of the fact that the wave form can be fairly well predicted. The wave form of the coalescing binary signal is known very accurately. However, the parameters of the signal are not known priori and the signal needs to be correlated with several filters which are copies of the coalescing binary wave form for different values of the parameters. In this paper we present an algorithm to choose a lattice set of filters by a criterion that every signal of a certain minimal strength is picked up by at least one filter of the set. The wave form is characterized by three parameters: the time of arrival, the mass parameter, and the phase of the signal. We show that it is enough to have just two filters corresponding to the phase of the signal. Determination of the lattice for various values of the mass parameter involves a knowledge of the cross correlation function of two chirp wave forms with different values of the parameters. It is shown that for a considerable range of the mass parameter, the peak value of the correlation function, in a certain approximation, does not depend on the absolute values of the parameters but only on their difference. This leads to a very convenient way of constructing most of the lattice. The maximum possible distance up to which we can see is restricted by the threshold of the detector. There is a further limitation on this distance brought about by the fact that we can use only a finite number of filters. The number of filters which one can use depends on the available computing power. Hence, there is an empirical relation between computing power and the distance up to which we can see. In a restricted sense, the computing power decides the number of detectable events. Numerical experiments indicate that parallel processing is a promising new approach to on-line data analysis.

Quantum mechanics near closed timelike lines

Abstract: The methods of the quantum theory of computation are used to analyze the physics of closed timelike lines. This is dominated, even at the macroscopic level, by quantum mechanics. In classical physics the existence of such lines in a spacetime imposes "paradoxical" constraints on the state of matter in their past and also provides means for knowledge to be created in ways that conflict with the principles of the philosophy of science. In quantum mechanics the first of these pathologies does not occur. The second is mitigated, and may be avoidable without such spacetimes being ruled out. Several novel and distinctive (but nonparadoxical) quantum-mechanical effects occur on and near closed timelike lines, including violations of the correspondence principle and of unitarity. It becomes possible to "clone" quantum systems and to measure the state of a quantum system. A new experimental test of the Everett interpretation against all others becomes possible. Consideration of these and other effects sheds light on the nature of quantum mechanics.

Black-hole evaporation and ultrashort distances.

Abstract: The role played by ultrahigh frequencies or ultrashort distances in the usual derivations of the Hawking effect is discussed and criticized. The question "would a black hole radiate if there were a Planck scale cutoff in the rest frame of the hole?" is posed. Guidance is sought from Unruh's fluid-flow analogue of black-hole radiation, by taking into account the atomic nature of the fluid. Two arguments for black-hole radiation are given which assume a Planck length cutoff. One involves the response of static accelerated detectors outside the horizon, and the other involves conservation of the expectation value of the stress tensor. Neither argument is conclusive, but they do strongly suggest that, in spite of reasonable doubt about the usual derivations of black-hole radiation, a "safe" derivation which avoids our ignorance of ultrashort-distance physics can likely be formulated. Remaining open questions are discussed.

New-Z' phenomenology.

Abstract: We show that {ital L}{sub 1}={ital L}{sub {ital e}}{minus}{ital L}{sub {mu}}, {ital L}{sub 2}={ital L}{sub {ital e}}{minus}{ital L}{sub {tau}}, and {ital L}{sub 3}={ital L}{sub {mu}}{minus}{ital L}{sub {tau}} (where {ital L}{sub {ital e},{mu},{tau}} are the family lepton numbers) are anomaly-free and can thus be gauged. Three simple theories featuring a flavor-conserving second {ital Z} boson ({ital Z}{sub 1,2,3}{sup {prime}}) result. Bounds on the {ital Z}{sub {ital i}}{sup {prime}} coupling constant ({ital g}{sub {ital i}}{sup {prime}}) and mass are derived. The mass of {ital Z}{sub 1}{sup {prime}} has a lower bound of 60--150 GeV at 90% confidence level for reasonable values of {ital g}{sub 1}{sup {prime}}. The mass of {ital Z}{sub 2}{sup {prime}} has a best-fit value of about 60 GeV. The physics of these bosons in the KEK TRISTAN and CERN LEP window of 63--87 GeV is discussed. Constraints on {ital Z}{sub 3}{sup {prime}} interactions are derived from ({ital g}{minus}2){sub {mu}}.

General-relativistic celestial mechanics. I. Method and definition of reference systems.

Abstract: We present a new formalism for treating the general-relativistic celestial mechanics of systems of $N$ arbitrarily composed and shaped, weakly self-gravitating, rotating, deformable bodies. This formalism is aimed at yielding a complete description, at the first post-Newtonian approximation level, of (i) the global dynamics of such $N$-body systems ("external problem"), (ii) the local gravitational structure of each body ("internal problem"), and, (iii) the way the external and the internal problems fit together ("theory of reference systems"). This formalism uses in a complementary manner $N+1$ coordinate charts (or "reference systems"): one "global" chart for describing the overall dynamics of the $N$ bodies, and $N$ "local" charts adapted to the separate description of the structure and environment of each body. The main tool which allows us to develop, in an elegant manner, a constructive theory of these $N+1$ reference systems is a systematic use of a particular "exponential" parametrization of the metric tensor which has the effect of linearizing both the field equations, and the transformation laws under a change of reference system. This linearity allows a treatment of the first post-Newtonian relativistic celestial mechanics which is, from a structural point of view, nearly as simple and transparent as its Newtonian analogue. Our scheme differs from previous attempts in several other respects: the structure of the stress-energy tensor is left completely open; the spatial coordinate grid (in each system) is fixed by algebraic conditions while a convenient "gauge" flexibility is left open in the time coordinate [at the order $\ensuremath{\delta}t=O({c}^{\ensuremath{-}4})$]; the gravitational field locally generated by each body is skeletonized by particular relativistic multipole moments recently introduced by Blanchet and Damour, while the external gravitational field experienced by each body is expanded in terms of a particular new set of relativistic tidal moments. In this first paper we lay the foundations of our formalism, with special emphasis on the definition and properties of the $N$ local reference systems, and on the general structure and transformation properties of the gravitational field. As an illustration of our approach we treat in detail the simple case where each body can, in some approximation, be considered as generating a spherically symmetric gravitational field. This "monopole truncation" leads us to a new (and, in our opinion, improved) derivation of the Lorentz-Droste-Einstein-Infeld-Hoffmann equations of motion. The detailed treatment of the relativistic motion of bodies endowed with arbitrary multipole structure will be the subject of subsequent publications.

Properties of P-wave mesons with one heavy quark.

Abstract: We present the results of a quark model study of $L=1$ mesons with one heavy quark. We give the masses of these states as predicted by the relativized quark model and the decay properties as calculated using both the pseudoscalar emission model and the flux-tube-breaking model. We examine the idealized limit of one infinitely massive quark and one light quark and discuss our results in this context as a guide to what can be learned from the study of these states. We find that, even for $B$ mesons, the tensor interactions play an important role in the spectroscopy and the ${m}_{Q}\ensuremath{\rightarrow}\ensuremath{\infty}$ has not yet been reached. We conclude that further experimental study of the decay properties of the ${D}_{1}$ mesons is important to the understanding of the $^{3}P_{1}\ensuremath{-}^{1}P_{1}$ mixing mechanism.

Energy loss of a heavy quark in the quark-gluon plasma.

Abstract: The energy loss {ital dE}/{ital dx} for a heavy quark propagating through a quark-gluon plasma is calculated to leading order in the QCD coupling constant. Simple formulas for {ital dE}/{ital dx} are obtained in the regions {ital E}{much lt}{ital M}{sub {ital Q}}{sup 2}/{ital T} and {ital E}{much gt}{ital M}{sub {ital Q}}{sup 2}/{ital T}, where {ital M}{sub {ital Q}} is the mass of the heavy quark and {ital T} is the temperature. The crossover energy between the two regions is determined to be approximately 1.8{ital M}{sub {ital Q}}{sup 2}/{ital T}. Under conditions relevant to ultrarelativistic heavy-ion collisions, charm quarks and bottom quarks lie on opposite sides of the crossover energy and therefore experience significantly different energy losses.

Rare decays of the top quark in the standard and two-Higgs-doublet models.

Abstract: The decays $t\ensuremath{\rightarrow}\mathrm{cV}$, where $V=\ensuremath{\gamma}, g, or Z$, and $t\ensuremath{\rightarrow}\mathrm{cH}$ are calculated, keeping all masses, in the standard model (SM) for all possible values of the top-quark mass that are consistent with present data. We find that the branching fractions for these processes are small, the largest being $B(t\ensuremath{\rightarrow}cH)\ensuremath{\sim}{10}^{\ensuremath{-}7}$ and $B(t\ensuremath{\rightarrow}cg)\ensuremath{\sim}{10}^{\ensuremath{-}10}$. Our calculations are then extended to include the possible contributions of charged Higgs bosons to the transitions $t\ensuremath{\rightarrow}\mathrm{cV}$ in the context of general two-Higgs-doublet models. These new contributions can enhance the SM branching fractions by as much as 3-4 orders of magnitude, e.g., $B(t\ensuremath{\rightarrow}cg)\ensuremath{\sim}{10}^{\ensuremath{-}7}\ensuremath{-}{10}^{\ensuremath{-}6}$, for various values of the parameters. General expressions for flavor-changing neutral-current decays of heavy quarks including all masses and momenta, in the SM and in the two-Higgs-doublet models, are also given.

Left-right-symmetric electroweak models with triplet Higgs field

Abstract: We examine the predictions of the conventional SU(2${)}_{\mathit{L}}$\ensuremath{\bigotimes}SU(2${)}_{\mathit{R}}$\ensuremath{\bigotimes}U(1${)}_{\mathit{B}\mathrm{\ensuremath{-}}\mathit{L}}$ left-right-symmetric model in the case where the minimal Higgs sector (containing one bidoublet, one L-triplet, and one R-triplet Higgs field) and the standard lepton representations (incorporating right-handed partners for the observed neutrinos) are adopted. We show that a complete analysis of spontaneous symmetry breaking for the Higgs sector leads to a highly restrictive range of possibilities for global minima that are simultaneously consistent with all experimental observations (such as lepton masses, ${\mathit{K}}_{\mathit{L}}$-${\mathit{K}}_{\mathit{S}}$ mixing, etc.). As a result, the possible phenomenologies for the gauge and Higgs bosons of the model are very limited. For instance, we demonstrate that in the absence of explicit CP violation in the Higgs potential, spontaneous CP violation does not arise and the fermion couplings exhibit ``manifest'' left-right symmetry. Further, we find no entirely natural solutions other than ones in which all of the extra (non-standard-model) gauge and Higgs bosons associated with the left-right-symmetric extension are extremely heavy (typically, more massive than ${10}^{7}$ GeV). Only by ``fine-tuning'' certain parameters of the Higgs potential is it possible to bring these extra particles down to an observable mass scale. Alternatively, symmetries can be introduced to eliminate the terms in the Higgs potential associated with these parameters, but only at the sacrifice of introducing undesirable consequences for fermion masses. Many of the pitfalls and problems are illustrated using a simplified model. Overall, we emphasize the necessity of performing a complete minimization of the Higgs sector before extracting phenomenology.

Semilocal cosmic strings.

Abstract: We show that the presence of global symmetries in a Lagrangian can lead to U(1) flux-tube solutions even when the vacuum manifold is simply connected. We provide a model in which these flux tubes, called semilocal'' strings, occur and explicitly prove the existence of stable string solutions by Bogomol'nyi's method. The formation of semilocal strings in the early Universe and the evolution of the network is discussed. We also show that semilocal magnetic monopoles cannot exist.

Energy loss of a heavy fermion in a hot QED plasma.

Abstract: The energy loss $\frac{\mathrm{dE}}{\mathrm{dx}}$ for a heavy lepton propagating through a high-temperature QED plasma is calculated to leading order in the QED coupling constant. The screening effects of the plasma are computed consistently using a resummation of perturbation theory in the small-momentum-transfer region. At large momentum transfer, recoil effects are properly taken into account. Our complete leading-order calculation differs significantly from previous calculations.

Top-quark-mass prediction from supersymmetric grand unified theories.

Abstract: We consider a supersymmetric grand-unified-theory (GUT) framework motivated by SO(10) or E{sub 6} unification in which the parameter tan{beta}(=={ital v}{sub 2}/{ital v}{sub 1}) of the minimal supersymmetric standard model is constrained by the condition that the Yukawa couplings {ital h}{sub {ital t}},{ital h}{sub {ital b}}, and {ital h}{sub {tau}} are all equal at the GUT scale. With {alpha}{sub {ital s}}({ital M}{sub {ital Z}})=0.106{plus minus}0.006, the estimate for the {ital b}-quark mass, which depends on tan{beta}, lies in the observed'' range {ital m}{sub {ital b}}({ital m}{sub {ital b}})=4.25{plus minus}0.10 GeV, provided that the top-quark mass is 142{sub {minus}49}{sup +26} GeV.

Real-time, directional measurement of 8B solar neutrinos in the Kamiokande II detector.

Abstract: The method of $^{8}\mathrm{B}$ solar-neutrino measurement by means of the reaction ${\ensuremath{ u}}_{e}e\ensuremath{\rightarrow}{\ensuremath{ u}}_{e}e$ in the Kamiokande II detector is described in detail. A data sample of 1040 live detector days in the time period January 1987 through April 1990 yields a clear directional correlation of the solar-neutrino-induced electron events with respect to the Sun and a measurement of the differential electron energy distribution. The measured flux of $^{8}\mathrm{B}$ solar neutrinos from the subsamples of 450 days at electron energy threshold ${E}_{e}\ensuremath{\ge}9.3$ MeV, and 590 days at ${E}_{e}\ensuremath{\ge}7.5$ MeV relative to calculations of the $^{8}\mathrm{B}$ flux based on the standard solar model are 0.46\ifmmode\pm\else\textpm\fi{}0.05(stat)\ifmmode\pm\else\textpm\fi{}0.06(syst) times the prediction of Bahcall and Ulrich, and 0.70\ifmmode\pm\else\textpm\fi{}0.08(stat)\ifmmode\pm\else\textpm\fi{}0.09(syst) times the prediction of Turck-Chi\`eze et al. The shape of the recoil electron energy distribution is consistent with that expected from the product of the known shape of the neutrino flux from $^{8}\mathrm{B}$ $\ensuremath{\beta}$ decay and the cross section for ${\ensuremath{ u}}_{e}e\ensuremath{\rightarrow}{\ensuremath{ u}}_{e}e$ scattering. Within the statistical error, there is no evidence in the solar-neutrino signal for a significant time variation.

Dimuon production in proton-copper collisions at sqrt s =38.8 GeV.

Abstract: Experimental results on the production of dimuons by 800-GeV protons incident on a copper target are presented. The results include measurements of both the continuum of dimuons and the dimuon decays of the three lowest-mass $\ensuremath{\Upsilon}$ $S$ states. A description of the apparatus, data acquisition, and analysis techniques is included. A comparison of the results with data taken at lower incident energies indicates a scaling behavior of the continuum dimuon yields.

Heavy-quark bound states in lattice QCD

Abstract: We present a new technique for analyzing heavy-quark bound states in lattice QCD. The method is based upon a nonrelativistic reformulation of the heavy-quark dynamics that is systematically developed starting from the Dirac theory. It is far superior to traditional relativistic techniques, as we illustrate in a numerical study of the $\ensuremath{\Upsilon}$ and $\ensuremath{\psi}$ meson families.

Confining phase of superstrings and axionic strings.

Abstract: In the four-dimensional effective field theory of the heterotic superstring compactified on a C.alabi- Yau manifold, we find a new class of spacetime string instantons in the gravity sector that involves graviton, dilaton, and Kalb-Ramond (axion) fields. The instantons satisfy generalized (anti)self-duality equations, and saturate a Bogomolnyi bound provided by the underlying supersymmetry. The instantons lead to several intriguing nonperturbative phenomena to low-energy string theory. A mass gap is generated to the Kalb-Ramond gauge fields, and results in the confinement of superstrings into Kalb-Ramond domain walls below the compactification scale. More interestingly, they provide a new example of the nonperturbative breakdown of the superpotential nonrenormalization theorem. Together with the world-sheet string instantons, this implies that all would-be Peccei-Quinn symmetries that arise in four-dimensional string theories are completely broken around the string compactification scale. Being self-dual, the instantons provide precisely two gravitino zero modes, thus might induce dynamical supersymmetry breaking. We also point out an underlying analogy with the invisible-axionic domain walls bounded by axionic strings.

Quark- and gluon-jet emission from primordial black holes. II. The emission over the black-hole lifetime.

Abstract: The emission produced over the lifetime of black holes with masses less than ${M}_{*}\ensuremath{\simeq}4\ensuremath{-}6\ifmmode\times\else\texttimes\fi{}{10}^{14}$ g is investigated by convolving the Hawking emission formulas with a Monte Carlo QCD jet code. Such emission may be astrophysically important if, for example, holes form from initial density perturbations in the early Universe. The quark and gluon decay products contribute significantly to the ${M}_{*}$ emission and dominate the lifetime emission from holes with initial masses less than about ${10}^{14}$ g. The ${M}_{*}$ emission shows little sensitivity to the uncertainties in particle-physics models around 100-300 MeV and above 100 GeV. A more precise determination of the mass of a primordial black hole which just expires today is also given as a function of the cosmological matter density and Hubble constant.

Fractal structure in the scalar lambda ( phi2-1)2 theory.

Abstract: Head-on collisions of kink and antikink solitons are investigated numerically in the classical one-dimensional {lambda}({phi}{sup 2}{minus}1){sup 2} model. It is shown that whether a kink-antikink interaction settles to a bound state or a two-soliton solution depends fractally'' on the impact velocity. We discuss the results using the framework of perturbation theory which helps to clarify the nature of the fractal structure in terms of resonances with the internal shape mode oscillations. We also review the technique of collective coordinates used to reduce the infinite-dimensional system to one with just two degrees of freedom. Although we do not expect exact agreement by using such a simplification, we show that the reduced system bears a striking qualitative resemblance to the full infinite-dimensional system, reproducing the fractal structure. The maximum Lyapunov exponents are computed for the bound-state oscillations and found to be {similar to}0.3 for both the full and reduced systems, demonstrating the chaotic nature of the bound state.