Real time thermal propagtors for massive gauge bosons

We derive Feynman rules for gauge theories exhibiting spontaneous symmetry breaking using the real-time formalism of finite temperature field theory. We also derive the thermal propagators where only the physical degrees of freedom are given thermal boundary conditions. We analyse the abelian Higgs model and find that these new propagators simplify the calculation of the thermal contribution to the self energy.Comment: 7 pages, late

How do binary clusters form?

Approximately 10 per cent of star clusters are found in pairs, known as binary clusters. We propose a mechanism for binary cluster formation; we use N-body simulations to show that velocity substructure in a single (even fairly smooth) region can cause binary clusters to form. This process is highly stochastic and it is not obvious from a region's initial conditions whether a binary will form and, if it does, which stars will end up in which cluster. We find the probability that a region will divide is mainly determined by its virial ratio, and a virial ratio above 'equilibrium' is generally necessary for binary formation. We also find that the mass ratio of the two clusters is strongly influenced by the initial degree of spatial substructure in the region

Finite Temperature Effective Potential for the Abelian Higgs Model to the Order e4,λ2e^4,\lambda^2

A complete calculation of the finite temperature effective potential for the abelian Higgs model to the order $e^4,\lambda^2$ is presented and the result is expressed in terms of physical parameters defined at zero temperature. The absence of a linear term is verified explicitly to the given order and proven to survive to all orders. The first order phase transition has weakened in comparison with lower order calculation, which shows up in a considerable decrease of the surface tension. The only difference from the original version is the splitting of some overlong lines causing problems with certain mailers.Comment: 13 pages LaTex ( figures not included , hardcopy available on request : [email protected] or t00heb@dhhdesy3 ) , DESY 93-08

Linking and causality in globally hyperbolic spacetimes

The linking number $lk$ is defined if link components are zero homologous. Our affine linking invariant $alk$ generalizes $lk$ to the case of linked submanifolds with arbitrary homology classes. We apply $alk$ to the study of causality in Lorentz manifolds. Let $M^m$ be a spacelike Cauchy surface in a globally hyperbolic spacetime $(X^{m+1}, g)$. The spherical cotangent bundle $ST^*M$ is identified with the space $N$ of all null geodesics in $(X,g).$ Hence the set of null geodesics passing through a point $x\in X$ gives an embedded $(m-1)$-sphere $S_x$ in $N=ST^*M$ called the sky of $x.$ Low observed that if the link $(S_x, S_y)$ is nontrivial, then $x,y\in X$ are causally related. This motivated the problem (communicated by Penrose) on the Arnold's 1998 problem list to apply link theory to the study of causality. The spheres $S_x$ are isotopic to fibers of $(ST^*M)^{2m-1}\to M^m.$ They are nonzero homologous and $lk(S_x,S_y)$ is undefined when $M$ is closed, while $alk(S_x, S_y)$ is well defined. Moreover, $alk(S_x, S_y)\in Z$ if $M$ is not an odd-dimensional rational homology sphere. We give a formula for the increment of \alk under passages through Arnold dangerous tangencies. If $(X,g)$ is such that $alk$ takes values in $\Z$ and $g$ is conformal to $g'$ having all the timelike sectional curvatures nonnegative, then $x, y\in X$ are causally related if and only if $alk(S_x,S_y)\neq 0$. We show that $x,y$ in nonrefocussing $(X, g)$ are causally unrelated iff $(S_x, S_y)$ can be deformed to a pair of $S^{m-1}$-fibers of $ST^*M\to M$ by an isotopy through skies. Low showed that if (\ss, g) is refocussing, then $M$ is compact. We show that the universal cover of $M$ is also compact.Comment: We added: Theorem 11.5 saying that a Cauchy surface in a refocussing space time has finite pi_1; changed Theorem 7.5 to be in terms of conformal classes of Lorentz metrics and did a few more changes. 45 pages, 3 figures. A part of the paper (several results of sections 4,5,6,9,10) is an extension and development of our work math.GT/0207219 in the context of Lorentzian geometry. The results of sections 7,8,11,12 and Appendix B are ne

Harvesting graphics power for MD simulations

We discuss an implementation of molecular dynamics (MD) simulations on a graphic processing unit (GPU) in the NVIDIA CUDA language. We tested our code on a modern GPU, the NVIDIA GeForce 8800 GTX. Results for two MD algorithms suitable for short-ranged and long-ranged interactions, and a congruential shift random number generator are presented. The performance of the GPU's is compared to their main processor counterpart. We achieve speedups of up to 80, 40 and 150 fold, respectively. With newest generation of GPU's one can run standard MD simulations at 10^7 flops/$.Comment: 12 pages, 5 figures. Submitted to Mol. Si

Singularity, complexity, and quasi--integrability of rational mappings

We investigate global properties of the mappings entering the description of symmetries of integrable spin and vertex models, by exploiting their nature of birational transformations of projective spaces. We give an algorithmic analysis of the structure of invariants of such mappings. We discuss some characteristic conditions for their (quasi)--integrability, and in particular its links with their singularities (in the 2--plane). Finally, we describe some of their properties {\it qua\/} dynamical systems, making contact with Arnol'd's notion of complexity, and exemplify remarkable behaviours.Comment: Latex file. 17 pages. To appear in CM

Hubungan antara aktiviti enzim klon Eucalyptus dan kerentanan terhadap serangan penyengat puru, Leptocybe invasa, di selatan China

The activity levels of five defensive enzymes, namely, peroxidase (POD), polyphenol oxidase (PPO), superoxide dismutase (SOD), phenylalanine ammonia-lyase (PAL) and catalase (CAT) were assessed in shoots of four commercial Eucalyptus clones (DH201-2, DH32-29, U6, GL9) at ages of 13, 29 and 38 months. Levels were also assessed in healthy and damaged shoots of clone DH201-2 at 15 months, shortly after it was severely attacked by the shoot gall wasp Leptocybe invasa. Foliar levels of these five enzymes did not show any significant increase with age. The level of CAT was found to be significantly higher at ages 29 and 38 months in clone GL9, a clone relatively resistant to L. invasa, than in the three other clones. Clone DH201-2, which was relatively susceptible to L. invasa, had non-significantly lower CAT levels than the rest of the clones at all three ages examined. The levels of the other four enzymes showed no obvious differences between clones and overall activity levels of the five enzymes did not show any clear association with the qualitative ranking susceptibility of the clones to L. invasa. In 15-month-old DH201-2 trees, marked increases in the levels of CAT, SOD and PPO were observed in shoots attacked by L. invasa compared with shoots from healthy trees of the same age, while levels of PAL and POD decreased compared with those in shoots from healthy trees.Aras aktiviti lima enzim pertahanan iaitu peroksidase (POD), polifenol oksidase (PPO), superoksida dismutase (SOD), fenilalanin ammonia-liase (PAL) and katalase (CAT) dinilai dalam pucuk empat klon Eucalyptus komersial (DH201-2, DH32-29, U6, GL9) yang berusia 13 bulan, 29 bulan dan 38 bulan. Aras enzim turut dinilai dalam pucuk yang sihat serta yang rosak bagi klon DH201-2 yang berusia 15 bulan tidak lama selepas ia diserang penyengat puru, Leptocybe invasa. Aras kelima-lima enzim daun tidak menunjukkan peningkatan signifikan dengan usia. Aras CAT lebih tinggi pada klon GL9 yang berusia 29 and 38 bulan. Klon GL9 secara relatifnya lebih rintang terhadap L. invasa berbanding ketiga-tiga klon yang lain. Klon DH201-2 yang agak rentan terhadap L. invasa mempunyai kandungan CAT yang lebih rendah berbanding klon lain yang dikaji. Aras enzim empat lagi enzim tidak menunjukkan perbezaan ketara antara klon. Secara keseluruhannya, aras aktiviti kelima-lima enzim tidak menunjukkan sebarang hubungan yang jelas antara tahap kerentanan kualitatif klon terhadap L. invasa. Pokok DH201-2 yang berusia 15 bulan menunjukkan peningkatan ketara dalam aras CAT, SOD dan PPO bagi pucuk yang diserang L. invasa berbanding pucuk pokok sihat yang sama usianya. Aras PAL and POD pula menurun berbanding pucuk pokok sihat.This study was initiated through a bilateral agreement between South Africa and China, and funded through project 2008B050100014.http://www.frim.gov.my/am201

Cantor Spectrum for Schr\"odinger Operators with Potentials arising from Generalized Skew-shifts

We consider continuous $SL(2,\mathbb{R})$-cocycles over a strictly ergodic homeomorphism which fibers over an almost periodic dynamical system (generalized skew-shifts). We prove that any cocycle which is not uniformly hyperbolic can be approximated by one which is conjugate to an $SO(2,\mathbb{R})$-cocycle. Using this, we show that if a cocycle's homotopy class does not display a certain obstruction to uniform hyperbolicity, then it can be $C^0$-perturbed to become uniformly hyperbolic. For cocycles arising from Schr\"odinger operators, the obstruction vanishes and we conclude that uniform hyperbolicity is dense, which implies that for a generic continuous potential, the spectrum of the corresponding Schr\"odinger operator is a Cantor set.Comment: Final version. To appear in Duke Mathematical Journa

Aspen: A microsimulation model of the economy

This report presents, Aspen. Sandia National Laboratories is developing this new agent-based microeconomic simulation model of the U.S. economy. The model is notable because it allows a large number of individual economic agents to be modeled at a high level of detail and with a great degree of freedom. Some features of Aspen are (a) a sophisticated message-passing system that allows individual pairs of agents to communicate, (b) the use of genetic algorithms to simulate the learning of certain agents, and (c) a detailed financial sector that includes a banking system and a bond market. Results from runs of the model are also presented