March 1998 arXiv papers — page 7

X. Chatellier, D. Andelman

Insoluble surfactant monolayers at the air/water interface undergo a phase transition from a high-temperature homogeneous state to a low-temperature demixed state, where dilute and dense phases coexist. Alternatively, the transition from a dilute phase to a dense one may be induced by compressing the monolayer at constant temperature. We consider the case wh

R. R. Netz, D. Andelman, H. Orland

We investigate theoretically the behavior of proteins as well as other large macromolecules which are incorporated into amphiphilic monolayers at the air-water interface. We assume the monolayer to be in the coexistence region of the ``main'' transition, where domains of the liquid condensed phase coexist with the liquid expanded background. Using a

R. R. Netz, D. Andelman

We investigate theoretically the possibility of a wetting transition induced by geometric roughness of a solid substrate for the case where the flat substrate does not show a wetting layer. Our approach makes use of a novel closed-form expression which relates the interaction between two sinusoidally modulated interfaces to the interaction between two flat i

R. R. Netz, D. Andelman, M. Schick

Numerically minimizing a continuous free-energy functional which yields several modulated phases, we obtain the order-parameter profiles and interfacial free energies of symmetric and non-symmetric tilt boundaries within the lamellar phase, and of interfaces between coexisting lamellar, hexagonal, and disordered phases. Our findings agree well with chevron,

M. M. Kozlov, D. Lichtenberg, D. Andelman

We develop a theoretical model for the solubilization of phospholipid bilayers by micelle-forming surfactants. Cylindrical micelles, disc-like micelles and spherical micelles are considered as alternative resultant structures. The main question addressed is what kind of micelles can be expected under various thermodynamical conditions. Our analysis is based

I. Borukhov, D. Andelman, H. Orland

The adsorption of large ions from solution to a charged surface is investigated theoretically. A generalized Poisson--Boltzmann equation, which takes into account the finite size of the ions is presented. We obtain analytical expressions for the electrostatic potential and ion concentrations at the surface, leading to a modified Grahame equation. At high sur

Mahendra K. Verma, Gaurav Dar

The energy spectrum and the nolinear cascade rates of MHD turbulence is not clearly understood. We have addressed this problem using direct numerical simulation and analytical calculations. Our numerical simulations indicate that Kolmogorov-like phenomenology with $k^{-5/3}$ energy spectrum, rather than Kraichnan's $k^{-3/2}$, appears to be applicable in

G. A. Tammann

A linearity test shows H_0 to decrease by 7% out to 18000 km/s. The value at 10000 km/s is a good approximation to the mean value of Ho over very large scales. The construction of the extragalactic distance scale is discussed. Field galaxies, cluster distances relative to Virgo, and blue supernovae of type Ia yield Ho(cosmic) with increasing weight; they giv

M. S. Seigar, P. A. James

We have imaged a sample of 45 face-on spiral galaxies in the K-band, to determine the morphology of the old stellar population, which dominates the mass in the disk. The K-band images of the spiral galaxies have been used to calculate different characteristics of the underlying density perturbation such as arm strengths, profiles and cross-sections, and spir

M. S. Seigar, P. A. James

We present data for a sample of 45 spiral galaxies over a range of Hubble types, imaged in the near-IR J and K bands. Parameters are calculated describing the bulge, disk and bar K-band light distributions, and we look for correlations showing the interrelation between these components. We find that bulge profiles are not well-fitted by the classic de Vaucou

Michael J. Kurtz, Douglas J. Mink

RVSAO is a set of programs to obtain redshifts and radial velocities from digital spectra. RVSAO operates in the IRAF(Tody 1986, 1993) environment. The heart of the system is xcsao, which implements the cross-correlation method, and is a direct descendant of the system built by Tonry and Davis (1979). emsao uses intelligent heuristics to search for emission

Victor Pham, Michael W. Deem

We present computer simulations of anomalous diffusion, $< r^2(t) > \sim a t^{1-δ}$, in two dimensions. The Monte Carlo calculations are in excellent agreement with previous renormalization group calculations. Interestingly, use of a high quality pseudo-random number generator is necessary to observe the anomalous diffusion. A linear-feedback, shift-register

Gregory Mahlon, Stephen Parke

We apply a generalized spin-basis analysis to associated Higgs production and gauge boson pair production at LEP. This framework allows us to identify a choice of spin axes for the processes e+ e- --> ZH,ZZ which leads to strikingly different correlations among the decay products, even well above threshold. This spin basis optimizes the difference in the ang

Carlos Gonzalez-Buxton, Kevin Ingersent

Thermodynamic properties are presented for four magnetic impurity models describing delocalized fermions scattering from a localized orbital at an energy-dependent rate $Γ(ε)$ which vanishes precisely at the Fermi level, $ε= 0$. Specifically, it is assumed that for small $|ε|$, $Γ(ε)\propto|ε|^r$ with $r>0$. The cases $r=1$ and $r=2$ describe dilute magnetic

P. M. Hajac, T. Masuda

A symmetry extending the $T^2$-symmetry of the noncommutative torus $T^2_q$ is studied in the category of quantum groups. This extended symmetry is given by the quantum double-torus defined as a compact matrix quantum group consisting of the disjoint union of $T^2$ and $T^2_{q^2}$. The bicross-product structure of the polynomial Hopf algebra of the quantum d

C. Pepin, M. Lavagna

The dynamical spin susceptibility is studied in the magnetically-disordered phase of heavy-Fermion systems near the antiferromagnetic quantum phase transition. In the framework of the $S=1/2$ Kondo lattice model, we introduce a perturbative expansion treating the spin and Kondo-like degrees of freedom on an equal footing. The dynamical spin susceptibility di

A. Bialas, K. Zalewski

The influence of the HBT effect on the multiplicity distribution and charge ratios of independently produced pions is studied. It is shown that, for a wide class of models, there is a critical point, where the average number of pions becomes very large and the multiplicity distibution becomes very broad. In this regime unusual charge ratios (&#34;centauros&#

C. Abia, J. Isern, U. Lisenfeld

The observed Be and B relationships with metallicity clearly support the idea that both elements have a primary origin and that are produced by the same class of objects. Spallation by particles accelerated during gravitational events (SNII, SNIb/c) seems to be a likely origin. We show, in the context of a model of chemical evolution, that it is possible to

Oliver Haschke, Werner Ruehl

The Hamiltonian of the $N$-particle Calogero model can be expressed in terms of generators of a Lie algebra for a definite class of representations. Maintaining this Lie algebra, its representations, and the flatness of the Riemannian metric belonging to the second order differential operator, the set of all possible quadratic Lie algebra forms is investigat

Pedro T P Viana, Andrew R Liddle

The observed evolution of the galaxy cluster X-ray integral temperature distribution function between $z=0.05$ and $z=0.32$ is used in an attempt to constrain the value of the density parameter, $Ω_{0}$, for both open and spatially-flat universes. We estimate the overall uncertainty in the determination of both the observed and the predicted galaxy cluster X

C. A. Bertulani

A computer program is presented by which one may calculate the multiple electric dipole, electric quadrupole and magnetic dipole Coulomb excitation with relativistic heavy ions. The program applies to an arbitrary nucleus, specified by the spins and energies of the levels and by all E1, E2 and M1 matrix elements. Nuclear excitation is calculated optionally f

Tatsumi Aoyama, Yoshio Kikukawa

The vacuum overlap formalism is extended to describe the supersymmetric multiplet of a Weyl fermion, a complex scalar boson and an auxiliary field in the case without interaction, based on the fact that supersymmetry can be maintained upto quadratic terms by introducing bosonic species doublers. We also obtain a local action which describes the chiral multip

Tatiana A. Ivanova

Infinite-dimensional algebra of all infinitesimal transformations of solutions of the self-dual Yang-Mills equations is described. It contains as subalgebras the infinite-dimensional algebras of hidden symmetries related to gauge and conformal transformations.

Shiping Feng, Zhongbing Huang

The spin response in the copper oxide materials at finite temperatures in the underdoped and optimal doped regimes is studied within the framework of the fermion-spin theory. The integrated dynamical spin structure factor is almost temperature independent, the integrated susceptibility shows the particularly universal behavior as $I(ω, T) \propto arctan [ a_

G. Lazarides, Q. Shafi

The supersymmetric sector of minimal supersymmetric standard model (MSSM) possesses a U(1) R-symmetry which contains Z_2 matter parity. Non-zero neutrino masses, consistent with a &#39;redefined&#39; R-symmetry, are possible through the see-saw mechanism and/or a pair of superheavy (mass M) SU(2)_L triplets with vev of order M^2_W/M. If this R-symmetry is re

D. D. Dixon, D. H. Hartmann, E. D. Kolaczyk, J. Samimi

We present quantitative statistical evidence for a $\gamma$-ray emission halo surrounding the Galaxy. Maps of the emission are derived. EGRET data were analyzed in a wavelet-based non-parametric hypothesis testing framework, using a model of expected diffuse (Galactic + isotropic) emission as a null hypothesis. The results show a statistically significant la

P. Berglund, E. G. Gimon

We study F-theory duals of six dimensional heterotic vacua in extreme regions of moduli space where the heterotic string is very strongly coupled. We demonstrate how to use orientifold limits of these F-theory duals to regain a perturbative string description. As an example, we reproduce the spectrum of a $T^4/\ZZ_{4}$ orientifold as an F-theory vacuum with

Yaron Oz, John Terning

We study the relation between the large Nc limit of four dimensional N=2,1,0 conformal field theories and supergravity on orbifolds of AdS_5xS^5. We analyze the Kaluza-Klein states of the supergravity theory and relate them to the spectrum of (chiral) primary operators of the (super) conformal field theories.

Adam Doliwa, Manuel Manas, Luis Martinez Alonso, Elena Medina

We show that the quantum field theoretical formulation of the $τ$-function theory has a geometrical interpretation within the classical transformation theory of conjugate nets. In particular, we prove that i) the partial charge transformations preserving the neutral sector are Laplace transformations, ii) the basic vertex operators are Levy and adjoint Levy

Lorenza Viola, Seth Lloyd

The dynamics of a decohering two-level system driven by a suitable control Hamiltonian is studied. The control procedure is implemented as a sequence of radiofrequency pulses that repetitively flip the state of the system, a technique that can be termed quantum &#34;bang-bang&#34; control after its classical analog. Decoherence introduced by the system&#39;s

H. -J. Briegel, W. Dür, J. I. Cirac, P. Zoller

In quantum communication via noisy channels, the error probability scales exponentially with the length of the channel. We present a scheme of a quantum repeater that overcomes this limitation. The central idea is to connect a string of (imperfect) entangled pairs of particles by using a novel nested purification protocol, thereby creating a single distant p

Trevor W. Marshal

The theory of parametric down conversion of the vacuum, based on a real zeropoint, or &#34;vacuum&#34; electromagnetic field, has been treated in earlier articles. The same theory predicts a hitherto unsuspected phenomenon - parametric up conversion of the vacuum. This article describes how the phenomenon may be demonstrated experimentally.

Carson C. Chow, John A. White, Jason Ritt, Nancy Kopell

We analyze the control of frequency for a synchronized inhibitory neuronal network. The analysis is done for a reduced membrane model with a biophysically-based synaptic influence. We argue that such a reduced model can quantitatively capture the frequency behavior of a larger class of neuronal models. We show that in different parameter regimes, the network

W. M. Kloet, Wen-Tai Chiang, Frank Tabakin

For the photoproduction of vector mesons, all single and double spin observables involving vector meson two-body decays are defined consistently in the $γN$ center of mass. These definitions yield a procedure for extracting physically meaningful single and double spin observables that are subject to known rules concerning their angle and energy evolution. As

S. B. Dubovichenko, A. V. Dzhazairov-Kakhramanov

Photodisintegration and radiative capture in the N2H, N3H, N3He, 2H2H, 2H3He, 2H4He, 3He3H, 4He3H, and 4He3He channels are studied on the basis of the corresponding two-cluster potential models. The astrophysical S factors at low energies are calculated. It is shown that various electromagnetic characteristics of light nuclei, including the Coulomb form fact

S. B. Dubovichenko, A. V. Dzhazairov-Kakhramanov

Photodisintegration and radiative capture in the N2H, N3H, N3He, 2H2H, 2H3He, 2H4He, 3He3H, 4He3H, and 4He3He channels are studied on the basis of the corresponding two-cluster potential models. The astrophysical S factors at low energies are calculated. It is shown that various electromagnetic characteristics of light nuclei, including the Coulomb form fact

S. B. Dubovichenko, A. V. Dzhazairov-Kakhramanov

Photodisintegration and radiative capture in the N2H, N3H, N3He, 2H2H, 2H3He, 2H4He, 3He3H, 4He3H, and 4He3He channels are studied on the basis of the corresponding two-cluster potential models. The astrophysical S factors at low energies are calculated. It is shown that various electromagnetic characteristics of light nuclei, including the Coulomb form fact

Dimitrios I. Dais, Utz-Uwe Haus, Martin Henk

An immediate generalization of the classical McKay correspondence for Gorenstein quotient spaces $\Bbb{C}^{r}/G$ in dimensions $r\geq 4$ would primarily demand the existence of projective, crepant, full desingularizations. Since this is not always possible, it is natural to ask about special classes of such quotient spaces which would satisfy the above prope

V. K. Dobrev, A. Sudbery

We construct finite-dimensional irreducible representations of two quantum algebras related to the generalized Lie algebra $\ssll (2)_q$ introduced by Lyubashenko and the second named author. We consider separately the cases of $q$ generic and $q$ at roots of unity. Some of the representations have no classical analog even for generic $q$. Some of the repres

Dimitrios I. Dais, Martin Henk

In this paper we prove that the Gorenstein cyclic quotient singularities of type \frac 1l (1,..., 1,l-(r-1)) with $l\geq r\geq 2$, have a \textit{unique}torus-equivariant projective, crepant, partial resolution, which is ``full&#39;&#39; iff either $l\equiv 0$ mod $% (r-1) $ or $l\equiv 1$ mod $(r-1) $. As it turns out, if one of these two conditions is fulf

Manfred Lehn

We give an algorithmic description of the action of the Chern classes of tautological bundles on the cohomology of Hilbert schemes of points on surfaces within the framework of Nakajima&#39;s oscillator algebra. This leads to an identification of the cohomology ring of Hilbert schemes of the affine plane with a ring of differential operators on a Fock space.

Helga Baum

We prove that there exist global solutions of the twistor equation on the Fefferman spaces of strictly pseudoconvex spin manifolds of arbitrary dimension and we study their properties.

Helga Baum

We solve the twistor equation on all indecomposable Lorentzian symmetric spaces explicity.

T. Masson

In this letter we investigate some aspects of the noncommutative differential geometry based on derivations of the algebra of endomorphisms of an oriented complex hermitian vector bundle. We relate it, in a natural way, to the geometry of the underlying principal bundle and compute the cohomology of its complex of noncommutative differential forms.

Michael Strickland, Sen-Ben Liao

The finite-temperature renormalization group is formulated via the Wilson-Kadanoff blocking transformation. Momentum modes and the Matsubara frequencies are coupled by constraints from a smearing function which plays the role of an infrared cutoff regulator. Using the scalar lambda phi^4 theory as an example, we consider four general types of smearing functi

R. Amorim, J. Barcelos-Neto

We study the problem of axial and gauge anomalies in a reducible theory involving vector and tensor gauge fields coupled in a topological way. We consider that vector and axial fermionic currents couple with the tensor field in the same topological manner as the vector gauge one. This kind of coupling leads to an anomalous axial current, contrarily to the re

Laura Andrianopoli, Sergio Ferrara

We show that the K-K spectrum of IIB string on AdS_5 x S_5 is described by ``twisted chiral&#39;&#39; N=4 superfields, naturally described in ``harmonic superspace&#39;&#39;, obtained by taking suitable gauge singlets polynomials of the D3-brane boundary SU(n) superconformal field theory. To each p-order polynomial is associated a massive K-K short represent

F. Antonuccio, O. Lunin, S. Pinsky

We consider the dimensional reduction of N = 1 SYM_{2+1} to 1+1 dimensions, which has (1,1) supersymmetry. The gauge groups we consider are U(N) and SU(N), where N is a finite variable. We implement Discrete Light-Cone Quantization to determine non-perturbatively the bound states in this theory. A careful analysis of the spectrum is performed at various valu

S. A. Cherkis, A. Kapustin

We model A_k and D_k asymptotically locally flat gravitational instantons on the moduli spaces of solutions of U(2) Bogomolny equations with prescribed singularities. We study these moduli spaces using Ward correspondence and find their twistor description. This enables us to write down the Kähler potential for A_k and D_k gravitational instantons in a relat

A. V. Kisselev, V. A. Petrov

In the framework of the &#34;current scheme&#34; of $η- η&#39;$ mixing we calculate the amplitude of the decay $η&#39; \to π^+ π^- γ$ in the soft limit and compare our results with recently reported values of the phenomenological additive terms to the $ρ$--meson background.

C. A de S. Pires, O. P. Ravinez

In the context of the standard model the quantization of the electric charge occurs only family by family. When we consider the three families together with massless neutrinos the electric charge is not quantized any more. Here we show that a chiral bilepton gauge model based on the gauge group SU(3)_C X SU(3)_L X U(1)_N explains the quantization of the elec

A. Ali, G. Hiller

We compute the leading order (in alpha_s) perturbative QCD and power (1/m_b^2) corrections to the hadronic invariant mass and hadron energy spectra in the decay B \to X_s \ell^+ \ell^- in standard model using the heavy quark expansion technique (HQET). Results for the first two hadronic moments < S_H^n> and <E_H^n>, n=1,2, are presented here working out thei

J. Dias de Deus, J. Seixas

We discuss the J/psi suppression in the framework of multiple collision models. From the analysis of the Pb-Pb NA50 data we conclude that the strength of the absorption has increased, but we find no clear evidence for the formation of the quark-gluon plasma.

I. Jack, D. R. T. Jones, A. Pickering

We present an exact formula for the $β$-function for the soft-breaking scalar mass in an N=1 supersymmetric gauge theory, in the form of an operator acting on the anomalous dimension. In particular we give the exact form for the correction due to the $ε$-scalar mass, and show that it has a particularly simple form in the renormalisation scheme corresponding

N. V. Krasnikov

We consider supersymmetric extension of standard electroweak model with Dirac neutrino masses. In such model for significant region of the parameters right-handed tau sneutrino is the lightest superparticle and right-handed charged tau slepton is the next to lightest superparticle. Due to the smallness of the neutrino masses the right-handed tau slepton is l

P. Zenczykowski

We study the question whether the pole-model VMD approach to weak radiative hyperon decays can be made consistent with Hara&#39;s theorem and still yield the pattern of asymmetries characteristic of the quark model. It is found that an essential ingredient which governs the pattern of asymmetries is the assumed off-shell behaviour of the parity-conserving 1/

S. A. Abel, W. N. Cottingham, I. B. Whittingham

Gluon mediated exclusive hadronic decays of b quarks are studied within the standard model (SM) and the constrained minimally supersymmetric standard model (MSSM). For all allowed regions of the MSSM parameter space (A, tan beta, m_0, m_{1/2}) the penguin magnetic dipole form factor F^R_2 is dominant over the electric dipole and can be larger than the magnet

M. Cacciari, M. Greco, P. Nason

We consider the transverse-momentum distribution of heavy flavours in hadronic collisions. We present a formalism in which large transverse-momentum logarithms are resummed at the next-to-leading level, and mass effects are included exactly up to order \alpha_strong^3, so as to retain predictivity at both small and large transverse momenta. As an example, we

K. Fialkowski, R. Wit, J. Wosiek

We present a method which incorporates the Bose-Einstein effect into Monte Carlo generators for multiple production by weighting the events. Various aspects of weight calculations are discussed in detail. We show that our method allows to describe reasonably well a sample of data and we outline the future tests and applications.

Thomas Mannel

In the infinite mass limit for a heavy quark its spin decouples from the QCD dynamics, which leads to the heavy-quark spin symmetry. After a short discussion of spin symmetry some applications are considered.

W. Slominski, J. Szwed

Advantages of introducing the electron structure function in electron induced processes are demonstrated. At present energies the same experiment gives more precise description of the electron than photon structure. The momentum scales entering the process are better controlled. At very high momenta probabilistic (partonic) interpretation can be preserved de

D. B. Leinweber, C. Parrinello, J. I. Skullerud, A. G. Williams

The gluon propagator is calculated in quenched QCD for two different lattice sizes (16^3x48 and 32^3x64) at beta=6.0. The volume dependence of the propagator in Landau gauge is studied. The smaller lattice is instrumental in revealing finite volume and anisotropic lattice artefacts. Methods for minimising these artefacts are developed and applied to the larg

T. Bergfeld

We have searched for two-body charmless decays of B mesons to purely hadronic exclusive final states including $ω$ or $ϕ$ mesons using data collected with the CLEO II detector. With this sample of $6.6 \times 10^6$ B mesons we observe a signal for the $ωK^+$ final state, and measure a branching fraction of B($B^+ \to ωK^+$) = 1.5 +0.7 -0.6 +-0.2 $\times 10^{

Paolo De Los Rios, Yi-Cheng Zhang

We study the Directed Polymer model subject to a particular form of disorder, $η(x,t)=η_X(x) η_T(t)$, recently proposed in biological applications. We find that two new universality classes arise, depending on the the lattice geometry. Using an intermediate model linking the two different orientations continuously, we find that there is a phase transition se

Stefano Zapperi, Pierre Cizeau, Gianfranco Durin, H. Eugene Stanley

We study the dynamics of a ferromagnetic domain wall driven by an external magnetic field through a disordered medium. The avalanche-like motion of the domain walls between pinned configurations produces a noise known as the Barkhausen effect. We discuss experimental results on soft ferromagnetic materials, with reference to the domain structure and the samp

Boris Neubert, Michel Pleimling, Rolf Siems

A Double Ising Spin model for uniaxially structurally modulated materials exhibits as a special feature phase transitions between phases with equal wave numbers but different pseudo spin configurations. The character of these `internal&#39; transitions is investigated in mean field approximation, with the mean field transfer matrix method, and in Monte Carlo

Daniel C. Hong, Su Yue

We investigate both numerically and analytically the convective instability of granular materials by two dimensional traffic equations. In the absence of vibrations the traffic equations assume two distinctive classes of fixed bed solutions with either a spatially uniform or nonuniform density profile. The former one exists only when the function V(ρ) that m

S. Siegert, R. Friedrich, J. Peinke

This paper deals with the analysis of stochastic systems which can be described by a Langevin equation. By the method presented in this paper drift and diffusion terms of the corresponding Fokker-Planck equation can be extracted from the noisy data sets, and deterministic laws and fluctuating forces of the dynamics can be identified. The method is validated

R. Oppermann, B. Rosenow

We present details of the phase diagrams of fermionic systems with random and frustrated interactions, emphasizing the important role of the chemical potential. The insulating fermionic Ising spin glass model is shown to reveal different entangled magnetic instabilities and phase transitions. We review tricritical phenomena related to the strong corresponden

M. Rovere, M. A. Ricci, D. Vellati, F. Bruni

A molecular dynamics simulation of water confined in a silica pore is performed in order to compare it with recent experimental results on water confined in porous Vycor glass at room temperature. A cylindrical pore of 40 A is created inside a vitreous SiO2 cell, obtained by computer simulation. The resulting cavity offers to water a rough hydrophilic surfac

Simon Villain-Guillot, David Andelman

We study interfacial behavior of a lamellar (stripe) phase coexisting with a disordered phase. Systematic analytical expansions are obtained for the interfacial profile in the vicinity of a tricritical point. They are characterized by a wide interfacial region involving a large number of lamellae. Our analytical results apply to systems with one dimensional

Saugata Bhattacharyya, J. K. Bhattacharjee

The scaling function for the critical specific heat is obtained exactly for temperatures above the bulk transition temperature by working in the spherical limit. Generalization of the function to arbitrary $α$ (the specific heat exponent), gives an excellent account of the experimental data of Mehta and Gasparini near the superfluid transition.

Saugata Bhattacharyya, J. K. Bhattacharjee

The suppression of order parameter fluctuations at the boundaries causes the ultrasonic attenuation near the superfluid transition to be lowered below the bulk value. We calculate explicitly the first deviation from the bulk value for temperatures above the lambda point. This deviation is significantly larger than for static quantities like the thermodynamic

A. D. Mirlin, R. Pnini, B. Shapiro

We study the intensity distribution function, P(I), for monochromatic waves propagating in quasi one-dimensional disordered medium, assuming that a point source and a point detector are embedded in the bulk of the medium. We find deviations from the Rayleigh statistics at moderately large I and a logarithmically-normal asymptotic behavior of P(I). When the r

B. Jancovici, G. Tellez

We study the equilibrium statistical mechanics of classical two-dimensional Coulomb systems living on a pseudosphere (an infinite surface of constant negative curvature). The Coulomb potential created by one point charge exists and goes to zero at infinity. The pressure can be expanded as a series in integer powers of the density (the virial expansion). The

Leo Blitz, David N. Spergel, Peter J. Teuben, Dap Hartmann

We suggest that the high--velocity clouds (HVCs) are large clouds, with typical diameters of 25 kpc and containing 5e7 solar masses of neutral gas and 3e8 solar masses of dark matter, falling onto the Local Group; altogether the HVCs contain 10$^{11}$ solar masses of neutral gas. Our reexamination of the Local-Group hypothesis for the HVCs connects their pro

Renyue Cen

This study shows one important effect of preexistent cosmic microwave background temperature fluctuations on the determination of the Hubble constant through Sunyaev-Zel&#39;dovich effect of clusters of galaxies, especially when coupled with the gravitational lensing effect by the same clusters. The effect results in a broad distribution of the apparent Hubb

Eric Woods, Abraham Loeb

We predict the rate at which Gamma-Ray Burst (GRB) afterglows should be detected in supernova searches as a function of limiting flux. Although GRB afterglows are rarer than supernovae, they are detectable at greater distances because of their higher intrinsic luminosity. Assuming that GRBs trace the cosmic star formation history and that every GRB gives ris

Fabrizio Fiore, Ari Laor, Martin Elvis, Fabrizio Nicastro

We have studied the variability of 6 low redshift, radio quiet `PG&#39; quasars on three timescales (days, weeks, and months) using the ROSAT HRI. The quasars were chosen to lie at the two extreme ends of the ROSAT PSPC spectral index distribution and hence of the H$β$ FWHM distribution. The observation strategy has been carefully designed to provide even sa

M. J. Harris, B. J. Teegarden, T. L. Cline, N. Gehrels

We have obtained spectra of the Galactic center at energies 400-600 keV from high-resolution data acquired by the TGRS Ge spectrometer on board the WIND mission during 1995-1997. The data were obtained using an on-board occulter, and are relatively free from systematics and backgrounds. Analysis of the spectra reveals a well-resolved electron-positron annihi

T. Theuns, A. Leonard, G. Efstathiou

The low-redshift evolution of the intergalactic medium is investigated using hydrodynamic cosmological simulations. The assumed cosmological model is a critical density cold dark matter universe. The imposed uniform background of ionizing radiation has the amplitude, shape and redshift evolution as computed from the observed quasar luminosity function by Haa

W. Lane, A. Smette, F. Briggs, S. Rao

We report the discovery of two low redshift HI 21cm absorbers, one at z = 0.2212 towards the z_{em} = 0.630 quasar OI 363 (B0738+313), and the other at z = 0.3127 towards PKS B1127-145 (z_{em} = 1.187). Both were found during a survey of MgII selected systems at redshifts 0.2 < z < 1 using the new UHF-high system at the Westerbork Synthesis Radio Telescope (

Jean-Marie Hameury, Kristen Menou, Guillaume Dubus, Jean-Pierre Lasota

We have developed 1D time-dependent numerical models of accretion discs, using an adaptive grid technique and an implicit numerical scheme, in which the disc size is allowed to vary with time. The code fully resolves the cooling and heating fronts propagating in the disc. We show that models in which the radius of the outer edge of the disc is fixed produce

Karl Mannheim

The active galaxy Markarian 501 was discovered with air-Cerenkov telescopes at photon energies of 10 tera-electron volts. Such high energies may indicate that the gamma rays from Markarian 501 are due to the acceleration of protons rather than electrons. Furthermore, the observed absence of gamma ray attenuation due to electron-positron pair production in co

Ramon Khanna

The generation of magnetic fields by a battery, operating in an ion-electron plasma around a Kerr black hole, is studied in the 3+1 split of the Kerr metric. It is found that the gravitomagnetic contributions to the electron partial pressure are able to drive currents. The strength of the equilibrium magnetic field should be higher than for the classical Bie

L. Homer, P. A. Charles, D. O&#39;Donoghue

We report the discovery of a 2.1hr optical modulation in the transient source GS1826-24, based on two independent high time-resolution photometric observing runs. There is additional irregular variability on shorter timescales. The source also exhibited an optical burst during each observation, with peak fluxes consistent with those of the three X-ray bursts

Philip R. Maloney, Mitchell C. Begelman, Michael A. Nowak

Recent work by Pringle and by Maloney, Begelman & Pringle has shown that geometrically thin, optically thick, accretion disks are unstable to warping driven by radiation torque from the central source. In this paper we generalize the study of radiation-driven warping to include general power-law surface density distributions, $Σ\propto R^{-δ}$. We consider t

Maki Suginohara, Tatsushi Suginohara, David N. Spergel

By redshift of 10, star formation in the first objects should have produced considerable amounts of Carbon, Nitrogen and Oxygen. The submillimeter lines of C, N and O redshift into the millimeter and centimeter bands (0.5 mm -- 1.2 cm), where they may be detectable. High spectral resolution observations could potentially detect inhomogeneities in C, N and O

Pei-Ming Ho

Following the recent work of Connes, Douglas and Schwarz, we study the M(atrix) model compactified on a torus with a background of the three-form field. This model is given by a super Yang-Mills theory on a quantum torus. To consider twisted gauge field configurations, we construct twisted U(n) bundles on the quantum torus as a deformation of its classical c

Arjun Berera, Marcelo Gleiser, Rudnei O. Ramos

We study under which conditions an overdamped regime can be attained in the dynamic evolution of a quantum field configuration. Using a real-time formulation of finite temperature field theory, we compute the effective evolution equation of a scalar field configuration, quadratically interacting with a given set of other scalar fields. We then show that, in

D. Bazeia, R. Jackiw

We consider a description of membranes by (2,1)-dimensional field theory, or alternatively a description of irrotational, isentropic fluid motion by a field theory in any dimension. We show that these Galileo-invariant systems, as well as others related to them, admit a peculiar diffeomorphism symmetry, where the transformation rule for coordinates involves

I. Ferreras, S. Charlot, J. Silk

We present an unbiased method for evaluating the ranges of ages and metallicities which are allowed by the photometric properties of the stellar populations that dominate the light of early-type galaxies in clusters. The method is based on the analysis of morphologically-classified early-type galaxies in 17 clusters at redshifts 0.3<z<0.9 and in the nearby C

G. W. Gibbons, G. Papadopoulos

We investigate the solutions of Nambu-Goto-type actions associated with calibrations. We determine the supersymmetry preserved by these solutions using the contact set of the calibration and examine their bulk interpretation as intersecting branes. We show that the supersymmetry preserved by such solutions is closely related to the spinor singlets of the sub

Michal Brhlik, G. L. Kane

The parameters of the supersymmetry Lagrangian are the place where experiment and theory will meet. We show that measuring them is harder than has been thought, particularly because of large unavoidable dependences on phases. Measurements are only guaranteed if a lepton collider with a polarized beam and sufficient energy to produce the relevant sparticles i

Norman K. Glendenning, Juergen Schaffner-Bielich

We study the influence of a possible H dibaryon condensate on the equation of state and the overall properties of neutron stars whose population otherwise contains nucleons and hyperons. In particular, we are interested in the question of whether neutron stars and their masses can be used to say anything about the existence and properties of the H dibaryon.

R. Abbaspur, H. Arfaei

A `reduced&#39; action formulation for a general class of the supergravity solutions, corresponding to the `marginally&#39; bound `distributed&#39; systems of various types of branes at arbitrary angles, is developed. It turns out that all the information regarding the classical features of such solutions is encoded in a first order Lagrangian (the `reduced&

Neil Turok, S. W. Hawking

Fundamental theories of quantum gravity such as supergravity include a four form field strength which contributes to the cosmological constant. The inclusion of such a field into our theory of open inflation (hep-th/9802030) allows an anthropic solution to the cosmological constant problem in which the cosmological constant gives a small but non-negligible c

Riccardo Guida, Jean Zinn-Justin

Recently the series for two RG functions (corresponding to the anomalous dimensions of the fields phi and phi^2) of the 3D phi^4 field theory have been extended to next order (seven loops) by Murray and Nickel. We examine here the influence of these additional terms on the estimates of critical exponents of the N-vector model, using some new ideas in the con

Elcio Abdalla, M. Reza Rahimi Tabar

We consider a gas of Newtonian self-gravitating particles in two-dimensional space, finding a phase transition, with a high temperature homogeneous phase and a low temperature clumped one. We argue that the system is described in terms of a gas with fractal behaviour.

Massimo Blasone, Peter A. Henning, Giuseppe Vitiello

We present the exact formula for neutrino oscillations. By resorting to recent results of Quantum Field Theory of fermion mixing, we work out the Green&#39;s function formalism for mixed neutrinos. The usual quantum mechanical Pontecorvo formula is recovered in the relativistic limit.