May 2003 arXiv papers — page 33

Ignacio Navarro

We consider compactifications of six dimensional gravity in four dimensional Minkowski or de Sitter space times a two dimensional sphere, S^2. As has been recently pointed out, it is possible to introduce 3-branes in these backgrounds with arbitrary tension without affecting the effective four dimensional cosmological constant, since its only effect is to in

Falk Bruckmann, Doerte Hansen

We consider the superposition of infinitely many instantons on a circle in R^4. The construction yields a self-dual solution of the Yang-Mills equations with action density concentrated on the ring. We show that this configuration is reducible in which case magnetic charge can be defined in a gauge invariant way. Indeed, we find a unit charge monopole (world

H. Hata, H. Kogetsu, S. Teraguchi

We study the gauge structure of vacuum string field theory expanded around the D-brane solution, namely, the gauge transformation and the transversality condition of the massless vector fluctuation mode. We find that the gauge transformation on massless vector field is induced as an anomaly; an infinity multiplied by an infinitesimal factor. The infinity com

D. G. C. McKeon

Antisymmetric tensor gauge fields phi_{ab}(eta) are formulated on the surface of a sphere S_4t(eta^2 = a^2) embedded in five dimensions. The free field model is equivalent to a scalar model on this sphere. Interactions with gauge fields are discussed. It is feasable to formulate models for interactions with U(1) gauge fields A_a(eta) that are akin to those o

T. Asakawa, S. Sugimoto, S. Terashima

We summarize how to describe D-branes in a matrix theory based on unstable D-instantons, which we call K-matrix theory, and explicity show that D-branes can be constructed as bound states of infinitly many unstable D-instantons. We examine the fluctuations around Dp-brane solutions in the matrix theory and show that they correctly reproduce fields on the Dp-

Dennis Silverman, W. K. Sze, Herng Yao

In the Left-Right Symmetric Model (LRSM), box diagrams involving the charged right-handed gauge boson W_R may affect B-Bbar mixing as well as CP asymmetries in neutral B decays. The smallness of the epsilon_K parameter in the neutral K-meson system places severe constraints on the right-handed quark mixing matrix V^R, and reduces the number of its effective

Rouzbeh Allahverdi, Chris Bird, Stefan Groot Nibbelink, Maxim Pospelov

The existing cosmological constraints on theories with large extra dimensions rely on the thermal production of the Kaluza-Klein modes of gravitons and radions in the early Universe. Successful inflation and reheating, as well as baryogenesis, typically requires the existence of a TeV-scale field in the bulk, most notably the inflaton. The non-thermal produc

A. C. Davis

In these lectures we review the constraints on particle physics models arising from cosmic defects. This includes constraints on theories where stable cosmic string loops, or vortons result. These can arise in supersymmetric theories. We discuss the possibility of embedded defects being stabilised by the surrounding plasma, and the constraints imposed on suc

E. Iltan, H. Sundu

We study τ\to μ\bar{ν_i} ν_i, i=e,μ,τdecay in the model III version of the two Higgs doublet model. We calculated the BR at the order of the magnitude of 10^{-6}-10^{-4} for the intermediate values of the Yukawa couplings. Furthermore, we predict the upper limit of the coupling for the τ-h^0 (A^0)-τtransition as \sim 0.3 in the case that the BR is \sim 10^{-

Francesco Sannino, Kimmo Tuominen

Recently the Bose-Einstein phenomenon has been proposed as possible physical mechanism underlying the spontaneous symmetry breaking in cold gauge theories. The mechanism is natural and we use it to drive the electroweak symmetry breaking. It can be implemented in different ways while here we present a simple model in which the Bose-Einstein sector is felt on

Simon Catterall, Sergey Karamov

We present results from a numerical simulation of the two-dimensional Euclidean Wess-Zumino model. In the continuum the theory possesses N=1 supersymmetry. The lattice model we employ was analyzed by Golterman and Petcher in \cite{susy} where a perturbative proof was given that the continuum supersymmetric Ward identities are recovered without finite tuning

M. W. Choptuik, E. W. Hirschmann, S. L. Liebling, F. Pretorius

We present results from a numerical study of critical gravitational collapse of axisymmetric distributions of massless scalar field energy. We find threshold behavior that can be described by the spherically symmetric critical solution with axisymmetric perturbations. However, we see indications of a growing, non-spherical mode about the spherically symmetri

G. F. Torres del Castillo, J. E. Rojas Marcial

The Helmholtz equation for symmetric, traceless, second-rank tensor fields in three-dimensional flat space is solved in spherical and cylindrical coordinates by separation of variables making use of the corresponding spin-weighted harmonics. It is shown that any symmetric, traceless, divergenceless second-rank tensor field that satisfies the Helmholtz equati

Hernando Quevedo, Michael P. Ryan,

We consider three methods by which one can generate new cosmological models. Two of these are based on the Lorentzian structure of spacetime. In a Lorentzian manifold there can exist horizons that separate regions of spacetime that can be interpreted as cosmological models from others that have the character of ``black holes.'' A number of well known

Ambuj Mahanti, Supriyo Ghose, Samir K. Sadhukhan

Search in cyclic AND/OR graphs was traditionally known to be an unsolved problem. In the recent past several important studies have been reported in this domain. In this paper, we have taken a fresh look at the problem. First, a new and comprehensive theoretical framework for cyclic AND/OR graphs has been presented, which was found missing in the recent lite

Pascal Hitzler, Matthias Wendt

We relate two formerly independent areas: Formal concept analysis and logic of domains. We will establish a correspondene between contextual attribute logic on formal contexts resp. concept lattices and a clausal logic on coherent algebraic cpos. We show how to identify the notion of formal concept in the domain theoretic setting. In particular, we show that

C. A. Regal, C. Ticknor, J. L. Bohn, D. S. Jin

Since the realization of Bose-Einstein condensates (BEC) in atomic gases an experimental challenge has been the production of molecular gases in the quantum regime. A promising approach is to create the molecular gas directly from an ultracold atomic gas; for example, atoms in a BEC have been coupled to electronic ground-state molecules through photoassociat

A. Serquis, X. Z. Liao, L. Civale, Y. T. Zhu

Bulk MgB2 samples were prepared under different synthesis conditions and analyzed by scanning and transmission electron microscopy. The critical current densities were determined from the magnetization versus magnetic field curves of bulk and powder-dispersed-in-epoxy samples. Results show that through a slow cooling process, the oxygen dissolved in bulk MgB

B. Kozma, G. Korniss

We considered the Edwards-Wilkinson model on a small-world network. We studied the finite-size behavior of the surface width by performing exact numerical diagonalization for the underlying coupling matrix. We found that the spectrum exhibits a gap or a pseudo-gap, which is responsible for a finite width in the thermodynamic limit for an arbitrarily weak but

Marcus Mueller, Kurt Binder

We study the interplay between wetting and miscibility of a symmetric polymer mixture via MC simulations and SCF calculations. The film surfaces interact with the monomers via short ranged potentials and the wetting transition is of first order. If both surfaces in a film attract the same component, capillary condensation occurs and the critical point is clo

P. Vargas, D. Altbir, M. Knobel, D. Laroze

It is shown that there is bi-stability in a two dimensional system consisting of non interacting magnetic nanoparticles with equal uniaxial anisotropies. It is also shown that bi-stability still remains in three dimensions. The only consideration is that the applied magnetic field has to be perpendicular to the anisotropy axis.

A. V. Chubukov, D. L. Maslov

The issue of non-analytic corrections to the Fermi-liquid behavior is revisited. Previous studies have indicated that the corrections to the Fermi-liquid forms of the specific heat and the static spin susceptibility scale as $T^{D}$ and $T^{D-1}$, respectively (with extra logarithms for $D=1,3$). In addition, the non-uniform spin susceptibility is expected t

Severiano R. Curras, Gonzalo Ferro, M. Teresa Gonzalez, Manuel V. Ramallo

The in-plane resistivity has been measured in $La_{2-x}Sr_xCuO_4$ (LSxCO) superconducting thin films of underdoped ($x=0.10,0.12$), optimally-doped ($x=0.15$) and overdoped ($x=0.20,0.25$) compositions. These films were grown on (100)SrTiO$_3$ substrates, and have about 150 nm thickness. The in-plane conductivity induced by superconducting fluctuations above

M. T. Gonzalez, J. Vina, S. R. Curras, J. A. Veira

Current-voltage characteristics of top seeded melt-textured YBa2Cu3O7-d are presented. The samples were cut out of centimetric monoliths. Films characteristics were also measured on microbridges patterned on thin films grown by dc sputtering. For both types of samples, a quasi-discontinuity or quenching was observed for a current density J* several times the

S. D. Wang, Z. Z. Sun, N. Cue, X. R. Wang

Electron tunneling through a coupled quantum-dot dimer under a dc-bias is investigated. We find that a peak in the $I$-$V$ curve appears at low temperature when two discrete electronic states in the two quantum dots are aligned with each other -- resonance coupling. This leads to a negative differential resistance. The peak height and width depend on the dot

Lorenzo Sabatelli, Peter Richmond

We introduce a consensus model inspired by the Sznajd Model. The updating is synchronous and memory plays here a decisive role in making possible the reaching of total consensus. We study the phase transition between the state with no-consensus to the state with total consensus.

Katsumi Hagita, Hiroshi Takano

Self-diffusion of a polymer chain in a melt is studied by Monte Carlo simulations of the bond fluctuation model, where only the excluded volume interaction is taken into account. Polymer chains, each of which consists of $N$ segments, are located on an $L \times L \times L$ simple cubic lattice under periodic boundary conditions, where each segment occupies

Susanne Moelbert, Paolo De Los Rios

Hydration of hydrophobic solutes in water is the cause of different phenomena, including the hydrophobic heat-capacity anomaly, which are not yet fully understood. Because of its topicality, there has recently been growing interest in the mechanism of hydrophobic aggregation, and in the physics on which it is based. In this study we use a simple yet powerful

Valentin O. Turin, Alexander N. Korotkov

We have analyzed the response and noise-limited sensitivity of the radio-frequency single-electron transistor (RF-SET), extending the previously developed theory to the case of arbitrary large quality factor Q of the RF-SET tank circuit. It is shown that while the RF-SET response reaches the maximum at Q roughly corresponding to the impedance matching condit

Gang Xiong, Shi-Dong Wang, Qian Niu, Yupeng Wang

The effect of inter-Landau-band mixing on electron localization in an integer quantum Hall system is studied. We find that mixing of localized states with {\it opposite chirality} tends to delocalize the states. This delocalization effect survives the quantum treatment. Extended states form bands because of this mixing, as we show through a numerical calcula

Luciano da F. Costa, Giancarlo Mutinari, David Schubert

This work describes a novel image analysis approach to characterize the uniformity of objects in agglomerates by using the propagation of normal wavefronts. The problem of width uniformity is discussed and its importance for the characterization of composite structures normally found in physics and biology highlighted. The methodology involves identifying ea

Yu. V. Pershin

We study a system in which electrons in a two-dimensional electron gas are confined by a nonhomogeneous nuclear spin polarization. The system consists of a heterostructure that has non-zero nuclei spins. We show that in this system electrons can be confined into a dot region through a local nuclear spin polarization. The nuclear-spin-polarization-induced qua

U. Leonhardt, P. Ohberg

A vortex in a Bose-Einstein condensate generates the optical analog of the Aharonov-Bohm effect when illuminated with slow light. In contrast to the original Aharonov-Bohm effect the vortex will exchange forces with the light that lead to a measurable motion of the vortex.

Jonathan J. Fortney, William B. Hubbard

We present the first models of Jupiter and Saturn to couple their evolution to both a radiative-atmosphere grid and to high-pressure phase diagrams of hydrogen with helium and other admixtures. We find that prior calculated phase diagrams in which Saturn's interior reaches a region of predicted helium immiscibility do not allow enough energy release to p

Y. Ohyama, Y. Taniguchi, K. S. Kawabata, Y. Shioya

We present deep optical spectroscopy of an extended Ly$α$ emission-line blob located in an over-dense region at redshift $z \approx 3.1$; `blob 1' of Steidel et al. (2000). The origin of such Ly$α$ blobs has been debated for some time; two of the most plausible models are (1) that it comes from a dust-enshrouded, extreme starburst galaxy with a large-sca

Weidong Li, Alexei V. Filippenko, Ryan Chornock, Saurabh Jha

We present the technical details of the gamma-ray burst (GRB) alert system of the Katzman Automatic Imaging Telescope (KAIT) at Lick Observatory, and the successful observations of the GRB 020813 optical afterglow with this system. KAIT responds to GRB alerts robotically, interrupts its pre-arranged program, and takes a sequence of images for each GRB alert.

Scott T. Miller, Sylvain Veilleux

The extraplanar diffuse ionized gas (eDIG) in 17 nearby, edge-on disk galaxies is studied using deep Taurus Tunable Filter Halpha and [N II] lambda 6583 images and conventional interference filter Halpha + [N II] lambda 6548, 6583 images which reach flux levels generally below about 1 x 10^{-17} erg s^{-1} cm^{-2} arcsec^{-2}. [N II] lambda 6583/Halpha excit

Pisin Chen

There have been proposals that primordial black hole remnants (BHRs) are the dark matter, but the idea is somewhat vague. Recently we argued that the generalized uncertainty principle (GUP) may prevent black holes from evaporating completely, in a similar way that the standard uncertainty principle prevents the hydrogen atom from collapsing. We further noted

Henry A. Kobulnicky, Christopher N. A. Willmer, Benjamin J. Weiner, David C. Koo

Using spectroscopic data from the Deep Extragalactic Evolutionary Probe (DEEP) Groth Strip survey (DGSS), we analyze the gas-phase oxygen abundances for 56 emission-line field galaxies in the redshift range 0.26<z<0.82. Oxygen abundances relative to hydrogen range between 8.4<12+log(O/H)<9.0 with typical uncertainties of 0.17 dex. The 56 DGSS galaxies collec

Chip Kobulnicky, Andrew Phillips

We develop a prescription for estimating the interstellar medium oxygen abundances of distant star-forming galaxies using the ratio EWR_{23} formed from the equivalent widths of the [O II] 3727, [O III] 4959,5007 and Hbeta nebular emission lines. This EWR_{23} approach essentially identical to the widely-used R_{23} method of Pagel et. al (1979). Using data

John C. Hodge, Michael W. Castelaz

The rotation velocity asymmetry v observed in spiral galaxy HI rotation curves linearly correlates with the effective potential force from the 10 closest neighboring galaxies normalized for the test particle mass and the gravitational constant. The magnitude of the potential force from a close galaxy is proportional to the luminosity of the close galaxy and

Artyom Yurov

There exists a variety of exact solutions of the scalar field Einstein equations, allowing for ``phantom regions&#39;&#39; with the negative kinetic field term. These regions can be cut out, their boundaries being sewn together in such a way that neither the scale factor (along with its first two derivatives) nor density or pressure will experience a jump. S

P. Richter, K. R. Sembach, J. C. Howk

We investigate interstellar absorption from molecular hydrogen (H_2) and metals in an intermediate-velocity cloud (IVC) in the direction of the LMC star Sk -68 80 (HD 36521), based on data from the Far Ultraviolet Spectroscopic Explorer (FUSE) satellite. H_2 absorption from the Lyman- and Werner bands is detected in 30 lines at radial velocities v=+50 km/s i

C. Motch, V. E. Zavlin, F. Haberl

ESO 4m class telescope and VLT deep imaging of the isolated neutron star RX J0720.4-3125 reveals a proper motion of mu = 97 +/-12 mas/yr and a blue U-B color index. We show that a neutron star atmosphere model modified to account for a limited amount of hydrogen on the star&#39;s surface can well represent both the optical and X-ray data without invoking any

Chris B. Brook, Daisuke Kawata, Brad K. Gibson

Observational evidence has suggested the possibility of a Galactic halo which is dominated by white dwarfs (WDs). While debate continues concerning the interpretation of this evidence, it is clear that an initial mass function (IMF) biased heavily toward WD precursors (1 < m/Msol < 8), at least in the early Universe, would be necessary in generating such a h

M. Vivekanand

Deshpande and Rankin (DR1999, DR2001) claim that the frequency of the very narrow feature, in the spectrum of radio flux variations of PSR B0943+10, is an alias of its actual value. They also claim to have detected an amplitude modulation on the above phase modulation. This paper argues that both these claims are unjustified.

M. Vivekanand

Deshpande and Rankin (DR1999, DR2001) claim that the frequency of the very narrow feature, in the spectrum of radio flux variations of PSR B0943+10, is an alias of its actual value. For this, they need to interpret the narrow feature as a very stable pattern of drifting sub pulses on the polar cap of this pulsar, within the framework of the Ruderman and Suth

A. I. Karakas, J. C. Lattanzio

We investigate the production of aluminium and the heavy magnesium isotopes in asymptotic giant branch models. We evolve models with a wide range in initial mass (between 1 and 6Msun), and composition (Z=0.02, 0.008, 0.004). We evolve the models from the pre-main sequence, through all intermediate stages including the core helium flash, to near the end of th

Emma Ryan-Weber, Rachel Webster, Lister Staveley-Smith

We have measured the column density distribution function, f(N), at z=0 using 21-cm HI emission from galaxies selected from a blind HI survey. f(N) is found to be smaller and flatter at z=0 than indicated by high-redshift measurements of Damped Lyman-alpha (DLA) systems, consistent with the predictions of hierarchical galaxy formation. The derived DLA number

S. W. Campbell

We present preliminary results of stellar structure and nucleosynthesis calculations for some early stars. The study (still in progress) seeks to explore the expected chemical signatures of second generation low- and intermediate-mass stars that may have formed out of a combination of Big Bang and Pop III (Z=0) supernovae material. Although the study is inco

John L. Tonry, Brian P. Schmidt, Brian Barris, Pablo Candia

The High-z Supernova Search Team has discovered and observed 8 new supernovae in the redshift interval z=0.3-1.2. These independent observations, confirm the result of Riess et al. (1998a) and Perlmutter et al. (1999) that supernova luminosity distances imply an accelerating universe. More importantly, they extend the redshift range of consistently observed

Dragan Huterer, Tanmay Vachaspati

Motivated by the recent claim for gravitational lensing by a cosmic string, we reinvestigate the probability of finding such an event with upcoming wide-field surveys. If an observed lensing event is suspected to be due to a string, observations of the vicinity of the event in a circle of diameter L centered on the observed lens should reveal several additio

Amri Wandel

Massive black holes detected in the centers of many nearby galaxies are linearly correlated with the luminosity of the host bulge, the black hole mass being about 0.1% of the bulge mass. An even stronger relation exists between the BH mass (Mbh) and the stellar velocity dispersion in the host bulge. We show that massive BHs of AGNs (measured by reverberation