July 1997 arXiv papers — page 4

A. R. Offer, J. Bland-Hawthorn

Ground-based observations at near-infrared wavelengths are severely affected by atmospheric OH bands. Many authors have recognized the potential gains in sensitivity from suppressing these features. Dispersive instruments show some promise but are both expensive and complicated to build. OH suppression filters using single or periodic notches have the advant

Dante R. Chialvo, Per Bak

A simple model of self-organised learning with no classical (Hebbian) reinforcement is presented. Synaptic connections involved in mistakes are depressed. The model operates at a highly adaptive, probably critical, state reached by extremal dynamics similar to that of recent evolution models. Thus, one might think of the mechanism as synaptic Darwinism.

J. Blümlein, A. Vogt

The impact of the resummed next-to-leading logarithmic small-$x$ contributions to the anomalous dimension $γ_{gg}$ is evaluated for the unpolarized parton densities and structure functions of the nucleon. These new terms diminish the gluon distribution and overcompensate the contribution caused by the resummed leading logarithmic small-$x$ anomalous dimensio

Dan Pirjol, Tung-Mow Yan

We derive consistency conditions which constrain the possible form of the strong couplings of the excited baryons to the pions. The consistency conditions follow from requiring the pion-excited baryon scattering amplitudes to satisfy the large-N_c Witten counting rules and are analogous to consistency conditions used by Dashen, Jenkins and Manohar and others

S. F. Edwards, D. V. Grinev

We propose a theory which describes the density relaxation of loosely packed, cohesionless granular material under mechanical tapping. Using the compactivity concept we develope a formalism of statistical mechanics which allows us to calculate the density of a powder as a function of time and compactivity. A simple fluctuation-dissipation relation which rela

Seong-Youl Choi, C. S. Kim, Youngjoon Kwon, Sam-Hyeon Lee

We study the potential impacts of a new type of particle collider -- an $eμ$ collider -- on the search for new physics beyond the Standard Model. As our first attempt for exploring its physics potential, we demonstrate that the the $eμ$ collision experiment can be highly efficient in searching for lepton-number-violating Flavor Changing Neutral Current pheno

Keshav Dasgupta, Dileep P. Jatkar, Sunil Mukhi

The interplay between gravitational couplings on branes and the occurrence of fractional flux in low dimensional orientifolds is examined. It is argued that gravitational couplings need to be assigned not only to D-branes but also to orientifold planes. The fractional charges of the orientifold $d$-planes can be understood in terms of flux quantization of th

Hong-Yi Zhou, Yu-Ping Kuang, Chong-Xing Yue, Hua Wang

We study pseudo-Goldstone boson corrections to top quark pair production rates in technicolor models with and without topcolor at the E=0.5 teV and 1.5 TeV photon colliders. We find that, for reasonable ranges of the parameters, the corrections are large enough to be observable, and the corrections in models with topcolor are considerably larger than those i

Ayako Yoshisato, Takahiko Matsubara, Masahiro Morikawa

Among various analytic approximations for the growth of density fluctuations in the expanding Universe, Zel'dovich approximation and its extensions in Lagrangian scheme are known to be accurate even in mildly non-linear regime. The aim of this paper is to investigate the reason why these Zel'dovich-type approximations work accurately beyond the linea

Edward A. Baltz, Nickolay Y. Gnedin, Joseph Silk

Emission lines in hydrogen can be used to measure the approximate redshift of the reionization of the universe. This is an important measurement given the lack of a convincing theoretical prediction of this epoch. There is a rapid change in absorption at the reionization event, which can leave sharp features in the spectrum of recombining hydrogen. These fea

Jiin-Chang Shaw, Ming-Hsien Tu

In this letter, we consider the second Hamiltonian structure of the constrained modified KP hierarchy. After mapping the Lax operator to a pure differential operator the second structure becomes the sum of the second and the third Gelfand-Dickey brackets defined by this differential operator. We simplify this Hamiltonian structure by factorizing the Lax oper

P. A. Yecko, S. P. Meacham

The structure of boundary currents formed from intermediately dense water introduced into a rotating, stably stratified, two-layer environment is investigated in a series of laboratory experiments, performed for Froude numbers ranging from 0.01 to 1. The thickness and streamwise velocity profiles in quasi-steady currents are measured using a pH activated tra

Li Guo

In this paper we establish the explicit exponential map for the Galois representation from a Hecke character at an ordinary prime. Such explicit maps are important in verifying the Bloch-Kato conjecture for Hecke characters.

Alexander Nabutovsky, Shmuel Weinberger

We will describe some results regarding the algorithmic nature of homeomorphism problems for manifolds; in particular, the following theorem. Theorem 1: Every PL or smooth simply connected manifold M^n of dimension n at least 5 can be recognized among simply connected manifolds. That is, there is an algorithm to decide whether or not another simply connected

M. A. Doncheski, R. W. Robinett

Collider searches for first-, second-, and third-generation scalar (S) or vector (V) leptoquarks (LQs) focus on the quark-lepton decay modes S,V -> q l. For SU(2)-doublet and -triplet leptoquarks with a sufficiently large splitting between the components, decays involving real W-boson emission (such as S_2^{(+5/3)} -> S_2^{(+2/3)} W^{+} and others) become po

Gregorio Bernardi

Recent deep inelastic results from the H1 collaboration are presented. The topics covered include inclusive diffractive physics, the determination of alpha_S using the event shapes, the study of the hadronic final state at low x with single particles and with jets, the structure function measurements in particular F_2 at low Q^2 and the high Q^2 physics both

Nakwoo Kim, Yoonbai Kim, Kyoungtae Kimm

We study global vortices coupled to (2+1) dimensional gravity with negative cosmological constant. We found nonsingular vortex solutions in $ϕ^4$-theory with a broken U(1) symmetry, of which the spacetimes do not involve physical curvature singularity. When the magnitude of negative cosmological constant is larger than a critical value at a given symmetry br

S. M. Cronenwett, S. R. Patel, C. M. Marcus, K. Campman

We report measurements of mesoscopic fluctuations of elastic cotunneling in Coulomb blockaded quantum dots. Unlike resonant tunneling on Coulomb peaks, cotunneling in the valleys is sensitive to charging effects. We observe a larger magnetic field scale for the cotunneling (valley) fluctuations compared to the peaks, as well as an absence of "weak locali

J. Robert Buchler, M. -J. Goupil, R. Piciullo

The Galactic Cepheid period histogram has a strong dip between 8 and 10 days that has defied an explanation based on evolutionary and linear pulsation studies. We show here that this deficiency is caused by the instability of the nonlinear fundamental pulsation cycle in this period range. The strong metallicity dependence of this instability is consistent wi

D. Kranich, T. Deckers, E. Lorenz, D. Petry

Since February 1997 the BL Lac object Mkn 501 is in a ``high state'' of gamma-ray emission. The HEGRA collaboration has studied Mkn 501 with their air Cherenkov telescopes on La Palma. Here we report on observations with the 5 m^2 telescope (threshold approx. 1.5 TeV) operated in a stand alone mode. We observed a rapidly varying flux between 0.5 to 6

Andrzej J. Buras, Axel Kwiatkowski, Nicolas Pott

We analyze the theoretical uncertainties in $Br(B\to X_sγ)$ due to the choice of the high energy matching scale $μ_W=\ord(\mw)$ and the scale $μ_t$ at which the running top quark mass is defined: $\mtb(μ_t)$. To this end we have repeated the calculation of the initial conditions confirming the final results of Adel and Yao and Greub and Hurth and generalizin

A. Pineda, J. Soto

We propose an effective field theory for heavy quark-antiquark bound states once the soft gluons have been integrated out. We also give new results for the matching between QCD (QED) and NRQCD (NRQED).

Edward R. Floyd

A generalized Hamilton-Jacobi representation describes microstates of the Schrödinger wave function for bound states. At the very points that boundary values are applied to the bound state Schrödinger wave function, the generalized Hamilton-Jacobi equation for quantum mechanics exhibits a nodal singularity. For initial value problems, the two representations

M. V. Medvedev, P. H. Diamond, V. I. Shevchenko, V. L. Galinsky

The nonlinear dynamics of collisionless Alfven trains, including resonant particle effects is studied using the kinetic nonlinear Schroedinger (KNLS) equation model. Numerical solutions of the KNLS reveal the dynamics of Alfven waves to be sensitive to the sense of polarization as well as the angle of propagation with respect to the ambient magnetic field. T

J. P. Ma, B. H. J. McKellar, C. B. Paranavitane

We study $J/Ψ$ production at photon-photon colliders, which can be realised with Compton scaterring of laser photons at $e^+e^-$ colliders. We find that the production rate through the color-octet channel is comparable to that through the color-singlet channel. Experimentally the two mechanisms can be studied separately because the processes have different s

V. A. Ilyin, L. B. Okun, A. N. Rozanov

Conserved muonic number may turn out to be a conserved muonic charge, coupled to muonic photons, gamma_mu. Muons and muonic neutrinos would emit gamma_mu's, which might be discovered by analysing the data from the past and future high energy neutrino experiments (like CHARM II, CCFR, CHORUS, NOMAD, etc.). There are two sources of gamma_mu's in these

E. A. De Wolf, A. T. Doyle, N. Varelas, D. Zeppenfeld

Progress in the study of hadronic final states in deep inelastic scattering as well as $p\bar{p}$, photoproduction and $e^+e^-$ annihilation, as presented at the DIS97 workshop, is reviewed.

Vladimir S. Mashkevich

The conservative model of a black hole is advanced. The model incorporates conservation laws such as those of baryon and lepton numbers, which lifts the information loss paradox. A scenario of black hole evaporation is considered. Keywords: entropy, emission, radiation, universe, chemical potential

Anton Alekseev, Anton Malkin, Eckhard Meinrenken

We develop a theory of "quasi"-Hamiltonian G-spaces for which the moment map takes values in the group G itself rather than in the dual of the Lie algebra. The theory includes counterparts of Hamiltonian reductions, the Guillemin-Sternberg symplectic cross-section theorem and of convexity properties of the moment map. As an application we obtain modu

O. M. Auslaender, S. Fishman

The interest in the properties of quantum systems, whose classical dynamics are chaotic, derives from their abundance in nature. The spectrum of such systems can be related, in the semiclassical approximation (SCA), to the unstable classical periodic orbits, through Gutzwiller's trace formula. The class of systems studied in this work, tiling billiards o

Boudewijn F. Roukema, Bruce A. Peterson, Peter J. Quinn, Brigitte Rocca-Volmerange

A method of deriving and using merging history trees of dark matter galaxy haloes directly from pure gravity N-body simulations is presented. This combines the full non-linearity of N-body simulations with the flexibility of the semi-analytical approach. Merging history trees derived from power-law initial perturbation spectrum simulations (for indices $n=-2

Jaume Garriga, Alexander Vilenkin

If the effective cosmological constant is non-zero, our observable universe may enter a stage of exponential expansion. In such case, regions of it may tunnel back to the false vacuum of an inflaton scalar field, and inflation with a high expansion rate may resume in those regions. An ``ideal'' eternal observer would then witness an infinite successi

D. Petry, S. M. Bradbury, A. Konopelko, D. Kranich

The HEGRA 5 m^2 air Cherenkov telescope (CT1) was used to search for gamma-ray emission above 1.5 TeV from a series of low redshift AGN (Mkn 421, Mkn 501, MS 0116+319, PKS 2209+236, NGC 315 and W Comae). Here we present results from a total of 383 hours of ON-source observations at zenith angles up to 35$^\circ$ made between February 1996 and April 1997 show

Zygmunt Lalak, Steven Thomas

We derive the explicit form, and discuss some properties of the moduli dependent effective potential arising from M-theory compactified on $M_4 \times X\times S^1 / Z_2 $, when one of the boundaries supports a strongly interacting gauge sector and induces gaugino condensation. We discuss the relation between the explicit gaugino condensate and effective supe

Stephane Courteau, Hans-Walter Rix

We show that for luminous, non-barred, high-surface brightness (HSB) spirals the Tully-Fisher (TF) relation residuals can be used to estimate the relative mass contributions of the stellar disk and the dark halo at the peak of the disk rotation, near 2.2 exponential scale lengths (Rh). For "maximal disks", a large fraction (0.85 +/- 0.10) of the tota

G. F. Bertsch, K. Hencken, H. Esbensen

We study the eikonal model for the nuclear-induced breakup of Borromean nuclei, using Li11 and He6 as examples. The full eikonal model is difficult to realize because of six-dimensional integrals, but a number of simplifying approximations are found to be accurate. The integrated diffractive and one-nucleon stripping cross sections are rather insensitive to

M. E. J. Newman, Cristopher Moore

We introduce a simple two-dimensional spin model with short-range interactions which shows glassy behavior despite a Hamiltonian which is completely homogeneous and possesses no randomness. We solve exactly for both the static partition function of the model and the distribution of energy barriers, giving us the equilibration time-scales at low temperature.

Joel R. Primack

This chapter aims to present an introduction to current research on the nature of the cosmological dark matter and the origin of galaxies and large scale structure within the standard theoretical framework: gravitational collapse of fluctuations as the origin of structure in the expanding universe. General relativistic cosmology is summarized, and the data o

I. Antoniadis, B. Pioline, T. R. Taylor

We identify and evaluate a class of physical amplitudes in four-dimensional N=4 superstring theory, which receive, in the weak coupling limit, contributions of order e^{-1/λ}, where λis the type II superstring coupling constant. They correspond to four-derivative \Ftilde_1 interaction terms involving the universal type II dilaton supermultiplet. The exact re

Jonathan L. Rosner

The least well-known octet baryon mass is $M_{Ξ^0} = 1314.9 \pm 0.6$ MeV. The prospect of an improved measurement of its mass by the KTeV experimental program at Fermilab, and opportunities for improvements in charged and excited hyperon and $Δ$ mass measurements, makes it timely to re-examine descriptions of isospin splittings in baryons containing light qu

C. G. Torre, M. Varadarajan

The canonical quantum theory of a free field using arbitrary foliations of a flat two-dimensional spacetime is investigated. It is shown that dynamical evolution along arbitrary spacelike foliations is unitarily implemented on the same Fock space as that associated with inertial foliations. It follows that the Schrodinger picture exists for arbitrary foliati

O. W. Greenberg

I show that the spin-statistics theorem has been confused with another theorem that I call the spin-locality theorem. I also argue that the spin-statistics theorem properly depends on the properties of asymptotic fields which are free fields. In addition, I discuss how ghosts evade both theorems, give the basis of the spin-statistics theorem for fields witho

Norma Mankoc Borstnik, Anamarija Borstnik

It is shown, by using Grassmann space to describe the internal degrees of freedom of fermions and bosons, that the Weyl like equation exists not only for massless fermions but also for massless gauge bosons. The corresponding states have well defined helicity and handedness. It is shown that spinors and gauge bosons of the same handedness only interact.

Konstantin G. Zloshchastiev

In present paper we construct the classical and minisuperspace quantum models of an extended charged particle. The modelling is based on the radiation fluid singular hypersurface filled with physical vacuum. We demonstrate that both at classical and quantum levels such a model can have equilibrium states at the radius equal to the classical radius of a charg

S. Matarrese, S. Mollerach, M. Bruni

We consider the evolution of relativistic perturbations in the Einstein-de Sitter cosmological model, including second-order effects. The perturbations are considered in two different settings: the widely used synchronous gauge and the Poisson (generalized longitudinal) one. Since, in general, perturbations are gauge dependent, we start by considering gauge

G. Bimonte, D. Iñiguez, A. Tarancón, C. L. Ullod

We carry a Monte Carlo study of the coupled two-scalar $λϕ^2_1 ϕ^2_2$ model in three dimensions. We find no trace of Inverse Symmetry Breaking in the region of negative $λ$'s for which the one-loop effective potential predicts this phenomenon. Moreover, for $λ$'s negative enough, but still in the stability region for the potential, one of the transit

S. Elitzur, A. Giveon, D. Kutasov, E. Rabinovici

We study the exceptional U duality group $E_d$ of M-theory compactified on a d-torus and its representations using Matrix theory. We exhibit the $E_d$ structure and show that p-branes wrapped or unwrapped around the longitudinal direction form representations of the U duality group together with other, more mysterious, states.

D. Ghilencea, M. Lanzagorta, G. G. Ross

We investigate the possibility that unification occurs at strong coupling. We show that, despite the fact the couplings pass through a strong coupling regime, accurate predictions for their low energy values are possible because the couplings of the theory flow to infrared fixed points. We determine the low-energy QCD coupling in a favoured class of strong c

Ulf-G. Meißner

I review recent progress made in the description of pion-nucleon scattering, the $σ$--term, the scalar form factor and the strangeness content of the nucleon in the framework of heavy baryon chiral perturbation theory. Other topics are single pion production by real and virtual photons as well as in proton-proton collisions.

Itzhak Bars, Cemsinan Deliduman

We construct superstring theories that obey the new supersymmetry algebra {Q_a , Q_b}=γ_{ab}^{mn} P_{1m} P_{2n}, in a Green-Schwarz formalism, with kappa supersymmetry also of the new type. The superstring is in a system with a superparticle so that their total momenta are $P_{2n},P_{1m}$ respectively. The system is covariant and critical in (10,2) dimension

D. Veberic, P. Prelovsek, I. Sega

The influence of the homogeneous magnetic field on a single mobile hole in a magnetic insulator, as represented by the two-dimensional t-J model, is investigated by considering the coupling of the field to the orbital current. The energy of the J=0 system is analysed via the high-temperature expansion and the small system diagonalization. The susceptibility

S. Balaska, J. Maeder, W. Ruehl

An algorithm for the isolation of any singularity of f-matrix models in the double scaling limit is presented. In particular it is proved by construction that only those universality classes exist that are known from 2-matrix models.

I. Heckenberger, K. Schmuedgen

For transcendental values of $q$ all bicovariant first order differential calculi on the coordinate Hopf algebras of the quantum groups $SL_q(n+1)$ and $Sp_q(2n)$ are classified. It is shown that the irreducible bicovariant first order calculi are determined by an irreducible corepresentation of the quantum group and a complex number $ζ$ such that $ζ^{n+1}=1

Yao-Zhong Zhang, Huan-Qiang Zhou

The quantum integrability is established for the one-dimensional supersymmetric $U$ model with boundary terms by means of the quantum inverse scattering method. The boundary supersymmetric $U$ chain is solved by using the coordinate space Bethe ansatz technique and Bethe ansatz equations are derived. This provides us with a basis for computing the finite siz

Juan Pablo Paz, Wojciech Hubert Zurek

We propose a new approach to study the evolution of a quantum state that is encoded in a system which is continuously subject to the operations required to implement a quantum error correcting code. In the limit of continuous error correction we introduce a Markovian master equation that includes the effects of: a) Hamiltonian evolution, b) errors caused by

Phillial Oh, Chaiho Rim

We present various oscillator representations of the q-deformed su(1,1) algebra such as the Holstein-Primakoff, the Dyson, the Fock-Bargmann, the anyonic, and the parabose oscillator representations and discuss their coherent states with the resolution of unity.

K. K. Gan

We present a procedure for calculating an upper limit on the number of signal events which incorporates the Poisson uncertainty in the background, estimated from control regions of one or two dimensions. For small number of signal events, the upper limit obtained is more stringent than that extracted without including the Poisson uncertainty. This trend cont

F. X. Magdaleno, J. Casademunt

We study the minimal class of exact solutions of the Saffman-Taylor problem with zero surface tension, which contains the physical fixed points of the regularized (non-zero surface tension) problem. New fixed points are found and the basin of attraction of the Saffman-Taylor finger is determined within that class. Specific features of the physics of finger c

Jan-e Alam, J. Cleymans, K. Redlich, H. Satz

We compare the predictions of different models for transverse momentum spectra in relativistic heavy ion collisions. Particular emphasis is given to hydrodynamic flow with different assumptions for the radial expansion, and to models based on a superposition of fireballs along the transverse direction (random walk). It is shown that present experimental data

A. Sh. Georgadze, H. V. Klapdor-Kleingrothaus, H. Päs, Yu. G. Zdesenko

The neutrino capture by $^{131}$Xe with a threshold at 352 keV as reaction to detect solar neutrinos is examined. The most important feature of this process is its high sensitivity to beryllium neutrinos, which contribute approximately 40% to the total capture rate (45 SNU) assuming the fluxes predicted by the Standard Solar Model.

V. Cirigliano, G. Paffuti

We construct the Euclidean Green functions for the soliton (magnetic monopole) field in the U(1)_4 Lattice Gauge Theory with Wilson action. We show that in the strong coupling regime there is monopole condensation while in the QED phase the physical Hilbert space splits into orthogonal soliton sectors labelled by integer magnetic charge.

P. Kuusk, J. Ord

A possible model for quantum kinematics of a test particle in a curved space-time is proposed. Every reasonable neighbourhood V_e of a curved space-time can be equipped with a nonassociative binary operation called the geodesic multiplication of space-time points. In the case of the Minkowski space-time, left and right translations of the geodesic multiplica

Michael R. Douglas, Brian R. Greene

We calculate the metric on the D-brane vacuum moduli space for backgrounds of the form C^3/Gamma for cyclic groups Gamma. In the simplest procedure --- starting with a flat ``seed'' metric on the covering space --- we find that the resulting D-brane metric is not Ricci-flat. We argue that this is likely to be true of the true 0-brane metric at weak s

A. Piccione, G. Ridolfi

We present a computation of nucleon mass corrections to nucleon structure functions for polarized deep-inelastic scattering. We perform a fit to existing data including mass corrections at first order in $m^2/Q^2$ and we study the effect of these corrections on physically interesting quantities. We conclude that mass corrections are generally small, and comp

R. J. Oakes, K. Whisnant, J. M. Yang, B. -L. Young

We investigate the ability of single top quark production via qq'-> squark->tb and q \bar q'->slepton->t\bar b at the LHC and Tevatron to probe the strength of R-parity violating couplings in the minimal supersymmetric model. We found that given the existing bounds on R-parity violating couplings, single top quark production may be greatly enhanced o

K. J. Abraham, K. Whisnant, B. -L. Young

We investigate the potential of a high-energy $γγ$ collider to detect an anomalous $\bar t q γ$ coupling from observation of the reaction $γγ\to t\bar q$, $\bar t q$, where $q=c$ or $u$. We find that with $b$-tagging and suitable kinematic cuts this process should be observable if the anomalous coupling $κ/Λ$ is no less than about 0.05/TeV, where $Λ$ is the

J. A. Casas

The presence of scalar fields with color and electric charge in supersymmetric theories makes feasible the existence of dangerous charge and color breaking (CCB) minima and unbounded from below directions (UFB) in the effective potential, which would make the standard vacuum unstable. The avoidance of these occurrences imposes severe constraints on the super

German Rodrigo, Antonio Pich, Arcadi Santamaria

Using the recent four-loop calculations of the QCD beta-function and the three-loop matching coefficients we study the induced error in $α_s(m_Z)$ obtained from $α_s(m_tau)$ due to the evolution procedure. We show that, when consistent matching and running is used at this order, these errors are pushed below 0.0005 in $α_s(m_Z)$.

V. Gogohia, Gy. Kluge, M. Prisznyák

The nonperturbative vacuum structure which emerges from the zero modes enhancement (ZME) model of the true QCD vacuum, appears to be well suited to describe quark confinement, dynamical chiral symmetry breaking (DCSB), current-effective (dynamical)-constituent, as well as constituent-valence quark transformations, the Okubo-Zweig-Iizuka (OZI) rule, dimension

D. J. Summers

We motivate the study of ``Minijets'' (that is jets soft with respect to the hard scattering, but hard with respect to Λ_QCD) as a means to study the underlying QCD colour flow in events. We discuss, with the aid of a simplistic model, currently available events in which minijets are observed, that is the events have high multiplicity, as a means of

J. -M. Virey

In a first step, we explore the discovery and analysis potentials of the HERA collider, with and without polarized beams, in the search for electron-quark compositeness in the neutral current channel. Then we study the parity violating effects, for jet production in polarized $pp$ collisions at RHIC, which could be due to the presence of quark subconstituent

E. W. N. Glover, D. J. Summers

We compute the W transverse momentum distribution at large transverse momentum at fixed next-to-leading order (i.e. O(alpha_s^2) and find good agreement with the preliminary measurements reported by D0. We find that the W transverse momentum distribution is typically significantly larger than the exclusive one-jet rate for a given value of p_T^W or E_T^jet,

Ya. I. Azimov, R. M. Ryndin

Particle motion in the fields of Aharonov-Bohm and Aharonov-Casher is considered in framework of the classical theory to reveal conditions admitting duality of the two configurations. Important role of orientation of the magnetic dipole moment is demonstrated. Duality becomes totally destroyed by addition of electric dipole and/or higher multipole moments. C

Glennys R. Farrar

Not yet. ALEPH's recent exclusion limit employs an aggressive determination of theoretical uncertainties using a simplified application of the Bayesian method. The validity of their analysis can be evaluated by its further implications, such as contradicting the existence a b quark and requiring relations between hadronic event-shape observables which ar

A. Capella, A. Kaidalov, C. Merino, D. Pertermann

Gribov theory is applied to investigate the shadowing effects in the structure functions of nuclei. In this approach these effects are related to the process of diffractive dissociation of a virtual photon. A model for this diffractive process, which describes well the HERA data, is used to calculate the shadowing in nuclear structure functions. A reasonable

G. Kerley, G. Shaw

The strikingly different high energy behaviours of real photoabsorption cross-sections with Q^2 = 0 and the low x proton structure function at large Q^2 are studied from a laboratory frame viewpoint, in which the x and Q^2 dependence reflects the space-time structure of the interaction. This is done using a simple model which incorporates hadron dominance, b

L. E. Gordon

The cross section for photoproduction of an isolated prompt photon in association with a jet is studied in Next-to-Leading Order. The kinematics are those appropriate for the DESY $ep$ collider HERA. The effects on the cross section of various experimental cuts including isolation cuts on the photon is examined. Comparisons with the ZEUS preliminary data usi

N. N. Nikolaev, B. G. Zakharov, V. R. Zoller

We calculate the Regge trajectories of the subleading BFKL singularities and eigenfunctions for the running BFKL pomeron in the color dipole representation. We obtain a viable BFKL-Regge expansion of the proton structure function $F_{2p}(x,Q^2)$ in terms of several rightmost BFKL singularities. We find large subleading contributions to $F_{2p}(x,Q^2)$ in the

Vladimir Burdyuzha

With cooling of the cosmological plasma during phase transitions in the early Universe vacuum condensates of quantum fields were produced with negative energy density. Probably these condensates have compensated the initial vacuum energy. The present vacuum is the vacuum condensate of the last relativistic phase transition ($T_{cr}\sim 100$ MeV) (its informa

Fredrick I. Olness, Randall J. Scalise

In a consistently formulated pQCD framework incorporating non-zero mass heavy quark partons, there is still the freedom to define parton distributions obeying either mass-independent or mass-dependent evolution equations, contrary to statements made in a recent paper by MRRS. With properly matched hard cross-sections, different choices merely correspond to d

P. Bialas, Z. Burda

We extend the analysis of the Backgammon model to an ensemble with a fixed number of balls and a fluctuating number of boxes. In this ensemble the model exhibits a first order phase transition analogous to the one in higher dimensional simplicial gravity. The transition relies on a kinematic condensation and reflects a crisis of the integration measure which

Valerie A. Noyes

Recent results on the searches for new physics in ep collisions at HERA using the ZEUS and H1 detectors are presented. No evidence for excited fermions or supersymmetric particles within the context of the Minimal Supersymmetric Standard Model nor R-parity violation has been found using an integrated luminosity of up to 20 inv pb. New limits have therefore b

T. Kloesch, T. Strobl

Following Finkelstein and Misner, kinks are non-trivial field configurations of a field theory, and different kink-numbers correspond to different disconnected components of the space of allowed field configurations for a given topology of the base manifold. In a theory of gravity, non-vanishing kink-numbers are associated to a twisted causal structure. In t

V. Khatsymovsky

The renormalised vacuum expectation values of massless fermion (conventionally call it neutrino) stress-energy tensor are calculated in the static spherically-symmetrical wormhole topology. Consider the case when the derivatives of metric tensor over radial distance are sufficiently small (in the scale of radius) to justify studying a few first orders of qua

L. Andersson, R. Howard

The comparison theory for the Riccati equation satisfied by the shape operator of parallel hypersurfaces is generalized to semi-Riemannian manifolds of arbitrary index, using one-sided bounds on the Riemann tensor which in the Riemannian case correspond to one-sided bounds on the sectional curvatures. Starting from 2-dimensional rigidity results and using an

David A Huse, Lee-Fen Ko

We approximate a 2D Ising spin glass by tiling an infinite square lattice with large identical unit cells. The interactions within the unit cell are random. Each such sample shows one or more critical points. We examine the scaling of the critical temperatures with unit cell size. Due to chaos, the correlations between unit cells can change sign with changin

S. Ispolatov, P. L. Krapivsky

We study statistical properties of a one dimensional infinite system of coalescing particles. Each particle moves with constant velocity $\pm v$ towards its closest neighbor and merges with it upon collision. We propose a mean-field theory that confirms a $t^{-1}$ concentration decay obtained in simulations and provides qualitative description for the densit

A. L. Barra, D. Gatteschi, R. Sessoli

EPR spectra have been recorded in very high field, up to 25T, and at high frequency, up to 525 GHz, on a polycristalline sample of Mn12ac (see paper for detailed formula), the first example of molecular cluster behaving like a nanomagnet. The simulation of the spectra has provided an accurate determination of the parameters of the spin hamiltonian (see paper

A. R. de Lima, T. J. P. Penna, P. M. C. de Oliveira

In this work we present some results from computer simulations of dynamical aspects of drop formation in a leaky faucet. Our results, which agree very well with the experiments, suggest that only a few elements, at the microscopic level, would be necessary to describe the most important features of the system. We were able to set all parameters of the model

Claudio Castellano, Federico Corberi

We study analytically a continuum model for phase-separation in binary polymer blends based on the Flory-Huggins-De Gennes free energy, by means of the self-consistent large-$n$ limit approach. The model is solved for values of the parameters corresponding to the weak and strong segregation limits. For deep quenches we identify a complex structure of interme

Joachim Altmann, Wolfram Brenig, Arno P. Kampf

We have investigated the evolution of the electronic properties of the t-t'-U Hubbard model with hole doping and temperature. Due to the shape of the Fermi surface, scattering from short wavelength spin fluctuations leads to strongly anisotropic quasi-particle scattering rates at low temperatures near half-filling. As a consequence, significant variation

Adolfo Avella, Ferdinando Mancini, Dario Villani

Magnetic properties of the two-dimensional t-t'-U model are investigated by studying the static spin magnetic susceptibility as a function of momentum for various temperatures. The calculations are performed by means of the Composite Operator Method in the static approximation. By increasing the value of the t' parameter the magnetic scattering in th

J. Röhler

In the pressure range 5-12 GPa the fractional valence of cerium is independent of pressure because of the coexistence of two or more structural phases. The observation of a single crystallographic structure in this pressure range arises from a non-equilibrium situation induced by the initial conditions of the high pressure experiment.

Y. Ohta, M. Yamaguchi, R. Eder

An exact-diagonalization technique on finite-size clusters is used to study the ground state and excitation spectra of the two-dimensional effective fermion model, a fictious model of hole quasiparticles derived from numerical studies of the two-dimensional t-J model at low doping. We show that there is actually a reasonable range of parameter values where t

Jo Calder

The increasing availability of corpora annotated for linguistic structure prompts the question: if we have the same texts, annotated for phrase structure under two different schemes, to what extent do the annotations agree on structuring within the text? We suggest the term tree alignment to indicate the situation where two markup schemes choose to bracket o

Francis Halzen

We update the science prospects for the recently completed AMANDA South Pole neutrino detector. With an effective telescope area of order 10^4 m^2 and a threshold of ~50 GeV, it represents the first instrument of a new generation of high energy neutrino detectors, envisaged over 25 years ago. We describe the instrument and its performance, and map its expans

Charles G. Hoopes, Rene A. M. Walterbos

We compare Far-UV, H-alpha, and optical broadband images of the nearby spiral galaxy M33, to investigate the massive stars associated with the diffuse ionized gas. The H-alpha/FUV ratio is higher in HII regions than in the DIG, possibly indicating that an older population ionizes the DIG. The broad-band colors support this conclusion. The HII region populati

Rene A. M. Walterbos

The Warm Ionized Medium (WIM), also referred to as Diffuse Ionized Gas, contains most of the mass of interstellar medium in ionized form, contributing as much as 30% of the total atomic gas mass in the solar neighborhood. The advent of CCDs has enabled unprecedented study of this medium in external galaxies, probing a variety of environments. In particular,

Pedro G. Ferreira, Michael Joyce

A scalar field with an exponential potential has the particular property that it is attracted into a solution in which its energy scales as the dominant component (radiation or matter) of the Universe, contributing a fixed fraction of the total energy density. We study the growth of perturbations in a CDM dominated $Ω=1$ universe with this extra field, with

S. Heinz, M. C. Begelman

We propose that the intensity changes and spectral evolution along the M87 jet can be explained by adiabatic changes to the particle momentum distribution function and the magnetic field. This is supported by the lack of any significant variation in the radio-to-optical spectral index along the jet and the moderate changes in radio brightness. Assuming a sim