June 1995 arXiv papers — page 11

Claude LeBrun

Using Seiberg-Witten theory, it is shown that any Kaehler metric of constant negative scalar curvature on a compact 4-manifold M minimizes the L^2-norm of scalar curvature among Riemannian metrics compatible with a fixed decomposition H^2(M)=(H^+) + (H^-). This implies, for example, that any such metric on a minimal ruled surface must be locally symmetric.

Barbara Drossel

I determine the scaling behavior of the free energy barriers encountered by a flux line in moving through a three-dimensional random potential. A combination of numerical simulations and analytic arguments suggest that these barriers scale with the length of the line in the same way as the fluctuation in the free energy.

B. L. Altshuler, L. B. Ioffe, A. J. Millis

We analyze pairing in two dimensional spin liquids. We argue that interplane pairing enhanced by magnetic correlations is the most plausible explanation of the spin gap phenomenon observed in underdoped cuprates. The details of the pairing theory depend on the in-plane antiferromagnetic correlations. We consider two models: $2p_F$ correlations induced by a s

P. Sitko, L. Jacak

Within the Hartree-Fock approximation the ground state of the composite fermion metal is found. We observe that the single-particle energy spectrum is dominated by the logarithmic interaction exchange term which leads to an infinite jump of the single-particle energy at the Fermi momentum. It is shown that the Hartree-Fock result brings no corrections to the

N. Provatas, T. Ala-Nissila, M. Grant, K. R. Elder

We introduce a model of two coupled reaction-diffusion equations to describe the dynamics and propagation of flame fronts in random media. The model incorporates heat diffusion, its dissipation, and its production through coupling to the background reactant density. We first show analytically and numerically that there is a finite critical value of the backg

G J Chaitin

This material was presented in a series of lectures at the Santa Fe Institute, the Los Alamos National Laboratory, and the University of New Mexico, during a one-month visit to the Santa Fe Institute, April 1995.

R. Schack, C. M. Caves

Using the method of symbolic dynamics, we show that a large class of classical chaotic maps exhibit exponential hypersensitivity to perturbation, i.e., a rapid increase with time of the information needed to describe the perturbed time evolution of the Liouville density, the information attaining values that are exponentially larger than the entropy increase

Darren J Wilkinson, Michael Goldstein

A methodology is developed for the adjustment of the covariance matrices underlying a multivariate constant time series dynamic linear model. The covariance matrices are embedded in a distribution-free inner-product space of matrix objects which facilitates such adjustment. This approach helps to make the analysis simple, tractable and robust. To illustrate

James R. Graham, Michael C. Liu

We present near--infrared observations of the ultraluminous high-redshift (z=2.286) IRAS source FSC 10214+4724 obtained in 0.''4 seeing at the W. M. Keck telescope. These observations show that FSC 10214+4724 consists of a highly symmetric circular arc centered on a second weaker source. The arc has an angular extent of about 140 degrees and is proba

Patrick B. Hall, Erica Ellingson, Richard F. Green, Howard Yee

We report the results of a search for X-ray emission from quasar host clusters at moderate redshift using the {\sl ROSAT} HRI. We detect no emission from the host clusters of 3C~263 (z=0.646) and PKS~2352-34 (z=0.706) to 3$σ$\ limits of 3.26 and 2.86 $\times$10$^{44}$\ ergs~s$^{-1}$ respectively (H$_o$=50, q$_o$=1/2) for clusters with r$_{core}$=125~kpc and

Barbara Ryden

Because the transformation from distance to redshift is nonlinear, maps in redshift space become increasingly distorted as the redshift z becomes greater. As noted by Alcock \& Paczyński (1979), observed redshift distortions can be used to estimate the deceleration parameter $q_0$. If $q_0$ is greater than -1, voids in redshift space will be elongated along

Sidney van den Bergh

It is found that the ages of the most metal-poor Galactic globular clusters are probably around 18 Gyr. On the other hand a Hubble parameter of 82 +/- 8 km/sec/Mpc (in conjunction with the standard Einstein-de Sitter model with an Omega =1 and Lambda =0) yields and age of the Universe of about 8 Gyr. Some possible reasons for this discrepancy are explored.

Alejandro Gonzalez

The strenth of the tidal shear produced by the large-scale density field acting on primordial density perturbations is calculated in power law models. It is shown that the large-scale tidal field could, strongly affect the morphology, orientation and angular momentum aquisition of density peaks possibly playing a role in the formation of early-type galaxies.

D. Montes, E. De Castro, M. J. Fernandez-Figueroa, M. Cornide

We present new spectroscopic observations in the Ca~{\sc ii} H \& K line region for a sample of 28 chromospherically active binary systems (RS$~$CVn and BY$~$Dra classes), with different activity levels. By using the spectral subtraction technique (subtraction of a synthesized stellar spectrum constructed from reference stars of similar spectral type and lum

H. Ardavan, J. E. Ffowcs Williams

The generally familiar notion that the conservation of energy requires the intensity of the radiation generated by a localized finite-duration source to decay like the inverse square of the distance from the source is not necessarily true. In this paper, we identify physically tenable sources of acoustic and electromagnetic radiations the amplitudes of whose

Steven B. Bradlow

Unstable holomorphic bundles can be described algebraically by Harder-Narasimhan filtrations. In this note we show how such filtrations correspond to the existence of special metrics defined by Hermitian-Einstein inequalities.

Darren J Wilkinson, Michael Goldstein

We examine the problem of covariance belief revision using a geometric approach. We exhibit an inner-product space where covariance matrices live naturally --- a space of random real symmetric matrices. The inner-product on this space captures aspects of our beliefs about the relationship between covariance matrices of interest to us, providing a structure r

H1 Collaboration

We present a QCD analysis of the proton structure function $F_2$ measured by the H1 experiment at HERA, combined with data from previous fixed target experiments. The gluon density is extracted from the scaling violations of $F_2$ in the range $2\cdot 10^{-4}<x<3\cdot 10^{-2}$ and compared with an approximate solution of the QCD evolution equations. The gluo

R. D. Ball, S. Forte

We compute the proton structure function F_2^p at small x and large Q^2 at next-to-leading order in alpha_s(Q^2), including summations of all leading and subleading logarithms of Q^2 and 1/x in a way consistent with momentum conservation. We perform a detailed comparison to the 1993 HERA data, and show that they may be used to determine alpha_s(M_Z^2)=0.120

A. P. Balachandran, L. Chandar, Arshad Momen

It is well-known that gauge fields defined on manifolds with spatial boundaries support states localized at the boundary. In this talk, we show how similar states arise in canonical gravity abd discuss their physical relevance using their analogy to quantum Hall effect.

B. G. Sidharth

In this note it is shown that for a mono-energetic collection of Bosons, at a certain (non-zero) momentum or temperature, there is condensation while there is another momentum or temperature at which there is infinite dilution and below which the gas exhibits anomalous Fermionic behaviour.

C. Gomez, E. Lopez

A connection between the conifold locus of the type II string on the $W\:P_{11226}^4$ Calabi-Yau manifold and the geometry of the quantum moduli of $N = 2$ $SU(2)$ super Yang-Mills is presented. This relation is obtained from the anomalous behaviour of the $SU(2)$ super Yang-Mills special coordinates under $S$-duality transformation in $Sl(2;Z) / Γ_2$.

I. M. Dremin

Recent developments in studies of multiparticle correlations in high energy particle collisions are reviewed. Both experimental data and theoretical results in quantum chromodynamics are discussed. Application of the developed methods to the coherent, squeezed and correlated states of photons is considered. Some speculations concerning possible coherent and

O. Buryak, A. Doroshkevich

Geometrical model of structure of the universe is examined to obtain analytical expression for the two points nonlinear correlation function. According to the model the objects (galaxies) are concentrated into two types of structure elements - filaments and sheets. We considered the filaments ( similar to galaxy filaments ) simply as straight lines and the s

V. V. Usov, D. B. Melrose

Modifications to polar-gap models for pulsars are discussed for the case where the surface magnetic field, $B_§$, of the neutron star is strong. For $B\ga4\times10^8\rm\,T$, the curvature $γ$-quanta emitted tangentially to the curved force lines of the magnetic field are captured near the threshold of bound pair creation and are channelled along the magnetic

Lisa C. Jeffrey, Frances C. Kirwan

Suppose $(M,ω)$ is a compact symplectic manifold acted on by a compact Lie group $K$ in a Hamiltonian fashion, with moment map $μ: M \to \Lie(K)^*$ and Marsden-Weinstein reduction $M_{red} = μ^{-1}(0)/K$. In this paper, we assume that $M$ has a $K$-invariant Kähler structure. In an earlier paper, we proved a formula (the residue formula) for $η_0 e^{ω_0}[M_{

Frank Tzschichholz

Using a two dimensional lattice model we investigate the crack growth under the influence of remote tensile forces as well as due to an internally applied pressure (hydraulic fracturing). For homogeneous elastic properties we present numerical finite-size scalings for the breaking stresses and pressures in terms of crack lengths and lattice sizes. Continuum

Saburo Higuchi, Ivan K. Kostov

We derive a minimal set of Feynman rules for the loop amplitudes in unitary models of closed strings, whose target space is a simply laced (extended) Dynkin diagram. The string field Feynman graphs are composed of propagators, vertices (including tadpoles) of all topologies, and leg factors for the macroscopic loops. A vertex of given topology factorizes int

Andrei Linde, Arthur Mezhlumian

We discuss various models of inflationary universe with $Ω\not = 1$. A homogeneous universe with $Ω> 1$ may appear due to creation of the universe &#34;from nothing&#34; in the theories where the effective potential becomes very steep at large $ϕ$, or in the theories where the inflaton field $ϕ$ nonminimally couples to gravity. Inflation with $Ω< 1$ generall

Doron Zeilberger

The Bordelaise philosophy, or rather a juvenile version of it, is used to enumerate self avoiding walks in a $[0,1] \times (- \infty, \infty)$.

L. D. FADDEEV, O. TIRKKONEN

The quantum theory of the Liouville model with imaginary field is considered using the quantum inverse scattering method. An integrable structure with nontrivial spectral parameter dependence is developed for lattice Liouville theory by scaling the $L$-matrix of lattice sine-Gordon theory. This $L$-matrix yields Bethe Ansatz equations for Liouville theory, b

H. Arodz, L. Hadasz

Excitation of a vortex in the Abelian Higgs model is investigated with the help of a polynomial approximation. The excitation can be regarded as a longitudinal component of the vector field trapped by the vortex. The energy and profile of the excitation are found. Back-reaction of the excitation on the vortex is calculated in the small $κ$ limit. It turns ou

R. H. Dalitz, Gary R. Goldstein

We have analyzed the available data on $p\bar{p}\,\rightarrow\, t\, \bar{t}$ followed by the decays ($t\rightarrow bW^{+},\: \bar{t}\rightarrow \bar{b}W^{-}$) which lead to $e^{\pm}μ^{\mp}2 \mathrm{jets}$ or $l^{\pm}4 \mathrm{jets}$ configurations, using a likelihood method we proposed earlier. The outcome is compared with the recent CDF analysis. In an appe

Michael I. Eides, Howard Grotch

Two corrections to the Lamb shift, induced by the polarization operator insertions in the external photon lines are calculated.

A. Buonanno, G. Cella, G. Curci

We define the energy-momentum tensor on lattice for the $λϕ^4$ and for the nonlinear $σ$-model Symanzik tree-improved actions, using Ward identities or an explicit matching procedure. The resulting operators give the correct one loop scale anomaly, and in the case of the sigma model they can have applications in Monte Carlo simulations.

A. Buonanno, G. Cella

We study a generalization of Swendsen-Wang algorithm suited for Potts models with next-next-neighborhood interactions. Using the embedding technique proposed by Wolff we test it on the Symanzik improved bidimensional non-linear $σ$ model. For some long range observables we find a little slowing down exponent ($z \simeq 0.3$) that we interpret as an effect of

Atul Bahel, Jun Pan, Mushti V. Ramakrishna

Tight-binding molecular dynamics simulated annealing technique is employed to search for the ground state geometries of silicon clusters containing 11-17 atoms. These studies revealed that layer formation is the dominant growth pattern in all these clusters. Fullerene-like precursor structures consisting of fused pentagon rings are also observed. The atoms i

Jun Pan, Atul Bahel, Mushti V. Ramakrishna

The ground state structures of small silicon clusters are determined through exhaustive tight-binding molecular dynamics simulation studies. These simulations revealed that \Si{11} is an icosahedron with one missing cap, \Si{12} is a complete icosahedron, \Si{13} is a surface capped icosahedron, \Si{14} is a 4-4-4 layer structure with two caps, \Si{15} is a

Antonietta Tomasulo, Mushti V. Ramakrishna

The band gaps and spectral shifts of CdS, CdSe, CdTe, AlP, GaP, GaAs, and InP semiconductor clusters are calculated from band structure calculations using accurate local and non-local empirical pseudopotentials. The effect of spin-orbit coupling on the band structures is included in the calculations when they are important. The complete set of pseudopotentia

Richard Pogge, Michael De Robertis

Narrow-band emission-line and continuum images obtained in subarcsecond seeing conditions are presented for the Seyfert~2 galaxy, Markarian 573. Images in the emission-lines of [\oi], [\oii], [\oiii], [\sii], and \halpha+[\nii] are used to measure the structure and excitation in the extended emission regions surrounding the active nucleus. The biconical regi

S. Bardelli, E. Zucca, A. Malizia, G. Zamorani

We present the results of a pointed ROSAT PSPC observation of the cluster A3558 which is part of the core of the Shapley Concentration. The X-ray brightness distribution can be fitted as the sum of an elliptical King law, with a major core radius of about 0.20 Mpc and an axial ratio 0.72, and a Gaussian central source associated with the cD galaxy. Among the

Toshio Tsuchiya, Naoteru Gouda, Tetsuro Konishi

Though one dimensional self-gravitating $N$-body systems have been studied for three decade, the nature of relaxation was still unclear. There were inconsistent results about relaxation time; some initial state relaxed in the time scale $T\sim N\,t_c$, but another state did not relax even after $T\sim N^2\,t_c$, where $t_c$ is the crossing time. The water-ba

Stephen Sawin

The Jones polynomial and the Kauffman bracket are constructed, and their relation with knot and link theory is described. The quantum groups and tangle functor formalisms for understanding these invariants and their descendents are given. The quantum group $U_q(sl_2)$, which gives rise to the Jones polynomial, is constructed explicitly. The $3$-manifold inva

R. W. Robinett

The proposal to perform polarized proton-proton collisions at collider energies at RHIC is reviewed. After a brief reminder of the desirability of high energy spin physics measurements, we discuss the machine parameters and detector features which are taken to define a program of spin physics at RHIC. Some of the many physics processes which can provide info

K. Moulopoulos, F. Cyrot-Lackmann

Scattering of electrons due to fractons can result in a resistivity that {\it decreases} with temperature. Such a behavior also appears in real quasicrystals. If this is then attributed to fracton scattering, fracton-superconductivity would be theoretically possible. By fitting with the scattering result the experimental resistivity data for the AlPdMn quasi

S. Frixione, P. Nason, G. Ridolfi

We compute pseudorapidity and transverse momentum distributions for charm and bottom production at HERA. We examine the effect of next-to-leading order QCD corrections, the effect of possible intrinsic transverse momenta of the incoming partons, and of fragmentation. We compare our results with full Monte Carlo simulation using HERWIG. The importance of the

A. Hoferichter, V. K. Mitrjushkin, M. Müller--Preussker

The chiral limit $~κ\simeq κ_c(β)~$ in lattice gauge theories with Wilson fermions and problems related to near--to--zero (&#39;exceptional&#39;) eigenvalues of the fermionic matrix are studied. For this purpose we employ compact lattice QED in the confinement phase. A new estimator $~\mpr_π~$ for the calculation of the pseudoscalar mass $~m_π~$ is proposed

A. M. Egorov, G. G. Likhachev, A. I. Studenikin

A review of the neutrino conversion and oscillations among the two neutrino species (active and sterile) induced by strong twisting magnetic field is presented and implications to neutrinos in neutron star, supernova, the Sun and interstellar galactic media are discussed. The ``cross-boundary effect&#34; (CBE) (i.e., a possible conversion of one half of neut

Steven Duplij

We consider a nonstandard odd reduction of supermatrices (as compared with the standard even one) which arises in connection with possible extension of manifold structure group reductions. The study was initiated by consideration of the generalized noninvertible superconformal-like transformations. The features of even- and odd-reduced supermatrices are inve

J. A. Eden, M. F. Gari

A parameter-free and relativistic extension of the RuhrPot meson-baryon model is used to define the dominant isoscalar meson-exchange currents. We compute pp-bremsstrahlung observables below the $π-$production threshold using a relativistic hadronic current density that includes impulse, wave function re-orthonormalization, meson-recoil, $\bar{\rm N}$N creat

Rainer Furhmann, Fernando Torres

We prove the following result which was conjectured by Stichtenoth and Xing: let $g$ be the genus of a projective, irreducible non-singular curve over the finite field $\Bbb F_{q^2}$ and whose number of $\Bbb F_{q^2}$-rational points attains the Hasse-Weil bound; then either $4g\le (q-1)^2$ or $2g=(q-1)q$.

Taejin Lee

We discuss the statistical mechanics of a two-dimensional gas of non-Abelian Chern-Simons particles which obey the non-Abelian braid statistics. The second virial coefficient is evaluated in the framework of the non-Abelian Chern-Simons quantum mechanics.

Martin Mueller, Joachim Niehren

We introduce constraints necessary for type checking a higher-order concurrent constraint language, and solve them with an incremental algorithm. Our constraint system extends rational unification by constraints x$\subseteq$ y saying that ``$x$ has at least the structure of $y$&#39;&#39;, modelled by a weak instance relation between trees. This notion of ins

Hong-Yi Zhou, Yu-Ping Kuang

We examine the detection of the intermediate-mass Higgs boson (IMH) at LHC through the associate production channel pp-->t+(anti-t)+H+X-->l+photon+ photon+X&#39;. It is shown that by applying kinematic cuts or b-tagging on the final state jets, the main backgrounds of W(-->l+nu)+photon+photon+(n-jet) can be reduced substantially without significant loss of s

Zdeněk Hradil, Robert Myška, Tomáš Opatrný, Jiří Bajer

The content of phase information of an arbitrary phase--sensitive measurement is evaluated using the maximum likelihood estimation. The phase distribution is characterized by the relative entropy--a nonlinear functional of input quantum state. As an explicit example the multiple measurement of quadrature operator is interpreted as quantum phase detection ach

J. A. Cizewski, R. Bijker

The ``identical&#39;&#39; bands in superdeformed mercury, thallium, and lead nuclei are interpreted as examples of orbital angular momentum rotors with the weak spin-orbit coupling of pseudo-$SU(3)$ symmetries and supersymmetries.

M. S. Baouendi, Xiaojun Huang, Linda Preiss Rothschild

We prove that if $M$ and $M&#39;$ are algebraic hypersurfaces in $ C^ N$, i.e. both defined by the vanishing of real polynomials, then any sufficiently smooth CR mapping with Jacobian not identically zero extends holomorphically provided the hypersurfaces are holomorphically nondegenerate . Conversely, we prove that holomorphic nondegeneracy is necessary for

U. Ellwanger, M. Hirsch, A. Weber

Wilson&#39;s exact renormalization group equations are derived and integrated for the relevant part of the pure Yang-Mills action. We discuss in detail how modified Slavnov-Taylor identities controle the breaking of BRST invariance in the presence of a finite infrared cutoff $k$ through relations among different parameters in the effective action. In particu

Robert W. Brown

Radiation symmetry is briefly reviewed, along with its historical, experimental, computational, and theoretical relevance. A sketch of the proof of a theorem for radiation zeros is used to highlight the connection between gauge-boson couplings and Poincare transformations. It is emphasized that while mostly bad things happen to good zeros, the weak-boson sel

Werner M. Seiler, Robin W. Tucker

We study the theory of systems with constraints from the point of view of the formal theory of partial differential equations. For finite-dimensional systems we show that the Dirac algorithm completes the equations of motion to an involutive system. We discuss the implications of this identification for field theories and argue that the involution analysis i

Martin Jörß

Starting from a chiral conformal Haag-Kastler net on 2 dimensional Minkowski space we construct associated charged pointlike localized fields which intertwine between arbitrary superselection sectors with finite statistics of the theory. This amounts to a proof of the Spin-Statistics theorem, the PCT theorem and the existence of operator product expansions.

G. Pradisi, A. Sagnotti, Ya. S. Stanev

We extend the construction of open descendants to the $SU(2)$ WZW models with non-diagonal left-right pairing, namely $E_7$ and the $D_{odd}$ series in the $ADE$ classification of Cappelli, Itzykson and Zuber. The structure of the resulting models is determined to a large extent by the ``crosscap constraint&#39;&#39;, while their Chan-Paton charge sectors ma

Takahiro Kubota, Hiroyuki Takashino

The idea of the effective topological theory for high-energy scattering proposed by H. and E. Verlinde is applied to the $(2+1)$ dimensional gravity with Einstein action plus Chern-Simons terms. The calculational steps in the topological description are compared with the eikonal approximation. It is shown that the Lagrangian of the effective topological theo

Jerome P. Gauntlett

The spectrum of $H$-monopoles of the heterotic string compactified on a six torus and its relationship to the $S$-duality conjecture is briefly reviewed. It is based on work done in collaboration with J. Harvey and is a contribution to the proceedings of Strings &#39;95, USC, March 1995.

Gerald B. Cleaver

Report in extended abstract form. Based on talk given at Strings &#39;95, Los Angeles, CA. This is a summary of the findings initially presented in hep-th/9505080. Results of a step (the complete classification of free fermionic solutions to $N=1$ spacetime) in the search for stringy three-generation SO(10) SUSY-GUTs are reviewed.

Pierre Sikivie

An imaginary character named TSP finds himself in a playroom whose floor is tilted to one side. However, the pooltable in the playroom is horizontal. TSP wonders how this can be. In doing so, he embarks upon an intellectual journey which parallels that which has been travelled during the past two decades by physicists interested in the Strong $CP$ Problem an

Juha T. Peltoniemi

The sterile neutrino solutions to different irregular results and observations in neutrino physics are studied. It is pointed out that introducing sterile neutrinos helps to solve simultaneously the observed anomalies. It is argued that sterile neutrinos can solve the conflict between dark matter neutrinos, LSND result and supernova nucleosynthesis. Other su

C. L. Schat, C. Gobbi, N. N. Scoccola

The radiative decays of hyperons are studied in the framework of the bound state soliton model. Detailed predictions for the total decay widths and the E2/M1 ratios corresponding to decuplet--to--octet electromagnetic transitions are presented in relation to future planned experiments at CEBAF and Fermilab. The results are compared to those obtained in quark

M. GOURDIN, Y. Y. KEUM, X. Y. PHAM

We propose a phenomenological three component model describing the decay amplitude of the process $D_{s}^{+} \ra 3π$. The first component is a constant background, the second one is a Breit-Wigner amplitude associated to a quasi two-body $f_{0}(980) π^{+}$ state and the third one another Breit-Wigner amplitude corresponding to a possible quasi two-body $ρ(77

G. Kramer, H. Spiesberger

We have calculated the leading and next-to-leading logarithm coefficients of $O(α_s^2)$ $e^+e^-$ annihilation jet cross sections, thrust distribution and energy-energy correlation in the two-jet limit when the jet resolution and the event shape variables vanish. We have compared our results with expectations based on leading logarithm approximations used to

S. A. Gurvitz

We analyze the proton and deuteron structure functions at large $x$ using a recently introduced scaling variable $\bar x$. This variable includes power corrections to $x$-scaling, and thus allows us to reach the Bjorken limit at moderate $Q^2$. Using available data we extract the ratio $F_2^n(x)/F_2^p(x)$ for $x\leq 0.85$. Contrary to earlier expectations th

M. Bastero--Gil, J. Perez--Mercader

In this paper we study the influence of the threshold effects due to massive degrees of freedom in the evolution with scale of gauge coupling constants. We first describe in detail the (standard) mass dependent renormalization prescription we use. This guides us to introduce and work with effective couplings, which are finite, process independent, and includ

E. Roulet

We compute the one-loop effects on the neutrino propagation through matter induced by virtual supersymmetric particles. We show that, in the minimal version of the supersymmetric standard model, a non-degeneracy between sleptons of the second and third generations can have sizeable effects on the $ν_μ$--$ν_τ$ oscillations in matter. In particular, we discuss

R. N. Faustov, V. O. Galkin, A. Yu. Mishurov

Using quasipotential approach, we have studied exclusive semileptonic decays of heavy mesons with the account of relativistic effects. Due to more complete relativistic description of the $s$ quark more precise expressions for semileptonic form factors are obtained. Various differential distributions in exclusive semileptonic decays of heavy mesons are calcu

Anton Kapustin, Zoltan Ligeti

The moments of the photon spectrum in the inclusive $B\to X_s\,γ$ decay can be calculated to order $α_s$ accuracy at present, without knowing the $α_s$ corrections to the effective Hamiltonian. We discuss the standard model predictions, and how the moments of the photon spectrum are related to certain matrix elements of the heavy quark effective theory. The

Robert D. Mawhinney

We discuss a class of saddle-point configurations in SU(2) lattice gauge theory in three Euclidean dimensions. These configurations are smooth on the scale of the lattice and have an action density exhibiting localized peaks, as has been seen in cooled and extremized Monte Carlo generated lattices. Large Wilson loops centered on the action peaks show a unit

G. Au

One of the greatest challenges facing theoretical physics lies in reconciling Einstein&#39;s classical theory of gravity - general relativity - with quantum field theory. Although both theories have been experimentally supported in their respective regimes, they seem mutually incompatible. This article summarises the current status of the superstring approac

C. Laurie, S. C. Power

The C*-envelope of the limit algebra (or limit space) of a contractive regular system of digraph algebras (or digraph spaces) is shown to be an approximately finite C*-algebra and the direct system for the C*-envelope is determined explicitly.

B. Kleine, G. S. Uhrig, E. Müller-Hartmann

Using a self-consistent mean-field theory for the $S=1/2$ Heisenberg antiferromagnet Krüger and Schuck recently derived an analytic expression for the dispersion. It is exact in one dimension ($d=1$) and agrees well with numerical results in $d=2$. With an expansion in powers of the inverse coordination number $1/Z$ ($Z=2d$) we investigate if this expression

K. Moulopoulos, S. Roche

An exact method that analytically provides transfer matrices in finite networks of quasicrystalline approximants of any dimensionality is discussed. We use these matrices in two ways: a) to exactly determine the band structure of an infinite approximant network in analytical form; b) to determine, also analytically, the quantum resistance of a finite strip o

Y. Morita, Y. Hatsugai, M. Kohmoto

We present a family of exactly solvable models at arbitrary filling in any dimensions which exhibit novel superconductivity with interband pairing. By the use of the hidden $SU(2)$ algebra the Hamiltonians were diagonalized explicitly. The zero-temperature phase diagrams and the thermodynamic properties are discussed. Several new properties are revealed whic

L. Y. Gorelik, M. Jonson, R. I. Shekhter

We show that electron transport in a ballistic microchannel supporting both propagating and reflected modes can be completely blocked by applying a microwave electromagnetic field. The effect is due to resonant reflection caused by multiple coherent electron-photon scattering involving at least two spatially localized scattering centers in the channel. With

Klaus Doll, Michael Dolg, Peter Fulde, Hermann Stoll

High-level quantum-chemical calculations, using the coupled-cluster approach and extended one-particle basis sets, have been performed for (Mg2+)n (O2-)m clusters embedded in a Madelung potential. The results of these calculations are used for setting up an incremental expansion for the correlation energy of bulk MgO. This way, 96% of the experimental cohesi

Matts Sporre

Statistical mechanics is used to study unrealizable generalization in two large feed-forward neural networks with binary weights and output, a perceptron and a tree committee machine. The student is trained by a teacher being larger, i.e. having more units than the student. It is shown that this is the same as using training data corrupted by Gaussian noise.

Michael Hammond

In this paper I argue that Optimality Theory provides for an explanatory model of syllabic parsing in English and French. The argument is based on psycholinguistic facts that have been mysterious up to now. This argument is further buttressed by the computational implementation developed here. This model is important for several reasons. First, it provides a

H. P. Fang

The universal bifurcation property of the Hénon map in parameter space is studied with symbolic dynamics. The universal-$L$ region is defined to characterize the bifurcation universality. It is found that the universal-$L$ region for relative small $L$ is not restricted to very small $b$ values. These results show that it is also a universal phenomenon that

K. Griest, C. Alcock, R. A. Allsman, T. S. Axelrod

Results are presented from the MACHO collaboration gravitational microlensing search. The experiment and the nearly 50 microlensing events that have been detected are described. Limits on the baryonic content of the halo are given, as are estimates of the Macho contribution to the dark halo. Optical depths toward the bulge, and several unusual events such as

Steen Hannestad, Jes Madsen

A calculation of neutrino decoupling in the early Universe, including full Fermi-Dirac statistics and electron mass dependence in the weak reaction rates, is presented. We find that after decoupling, the electron neutrinos contribute 0.83\% more to the relativistic energy density than in the standard scenario, where neutrinos are assumed not to share the hea

P. E. J. Nulsen, A. C. Fabian

The present structure of galaxies is governed by the radiative dissipation of the gravitational and supernova energy injected during formation. A crucial aspect of this process is whether the gas cools as fast as it falls into the gravitational potential well. If it does then rapid normal star formation is assumed to ensue. If not, and the gas can still cool

Drury L O&#39;C, Völk H J, Berezhko E G

Studies of energetic particle acceleration at collisionless shocks by the diffusive shock acceleration process indicate that completely smooth cosmic ray dominated shock structures are possible. The existence of these is discussed and conditions for their existence derived. It is shown that such solutions cannot dominate the evolution of supernova remnants i

A. D. Dolgov, S. Pastor, J. W. F. Valle

We consider the scenario of large scale structure formation with tau neutrino with mass in the MeV range and lifetime of order of years which decays into a massive majoron with KeV mass. The latter are the present-day cold dark matter particles. In contrast to the usual collisionless dark matter, the majorons have a relatively strong self-interaction and the

J. B. Hutchings

Images are discussed of six QSOs at z=2.3, one QSO-like IRAS source at z=2.3, and one QSO at z=1.1, taken with resolution 0.6 to 0.9 arcsec. Five of the QSOs are radio-quiet. All QSOs except one are just resolved, while the IRAS source has definite structure. In some cases, part of the QSO fuzz appears to be a close companion rather than a concentric host ga

R. V. Gurjar, Shulim Kaliman, N. Mohan Kumar, Masayoshi Miyanishi

This report records a large number of open problems in Affine Algebraic Geometry that were proposed by participants in a Conference on Open Algebraic Varieties at the Centre de Recherches en Mathematiques in Montreal at December 1994.

Mikhail Zaidenberg

By an exotic algebraic structure on the affine space ${\bf C}^n$ we mean a smooth affine algebraic variety which is diffeomorphic to ${\bf R}^{2n}$ but not isomorphic to ${\bf C}^n$. This is a survey of the recent developement on the subject, which emphasizes its analytic aspects and points out some open problems.

Erik Verlinde

We show that the partition function of free Maxwell theory on a generic Euclidean four-manifold transforms in a non-trivial way under electric-magnetic duality. The classical part of the partition sum can be mapped onto the genus-one partition function of a 2d toroidal model, without the oscillator contributions. This map relates electric-magnetic duality to

H. Waelbroeck, F. Zertuche

We propose a theory of chaos for discrete systems, based on their representation in a space of ``binary histories'', $ {\cal B^{\infty}} $. We show that $ {\cal B^{\infty}} $ is a metrizable Cantor set which embeds the attractor $\Lambda$, itself also a Cantor set.

J. A. Gomez Tejedor, E. Oset

A model for the gamma p ----> pion+ pion- p reaction developed earlier is extended to account for all isospin channels. The model includes N, Delta(1232), N^*(1440) and N^*(1520) as intermediate baryonic states and the rho-meson as an intermediate two pion resonance. Although many terms contribute to the cross section, some channels exhibit particular sensit

M. Crisafulli, V. Gimenez, G. Martinelli, C. T. Sachrajda

We present the first lattice calculation of the B-meson binding energy $\labar$ and of the kinetic energy $-λ_1/2 m_Q$ of the heavy-quark inside the pseudoscalar B-meson. This calculation has required the non-perturbative subtraction of the power divergences present in matrix elements of the Lagrangian operator $\bar h D_4 h$ and of the kinetic energy operat

C. Porciani, F. Ferrini, F. Lucchin, S. Matarrese

We analyse the effect of two relevant physical constraints on the mass multiplicity function of dark matter halos in a Press--Schechter type algorithm. Considering the random--walk of linear Gaussian density fluctuations as a function of the smoothing scale, we simultaneously i) account for mass semi--positivity and ii) avoid the cloud--in--cloud problem. It

V. Castellani, M. Romaniello

We investigate the final fate of metal deficient (MD) H burning Red Giants under various assumptions about the amount of mass loss. Adopting a metallicity Z= 10^(-8), we follow the evolution of 0.8 Mo models from the Main Sequence phase till the onset of the He flash or the final cooling as a He White Dwarf, according to the amount of mass loss. We show that