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J. Wang

Publications and source records attributed to J. Wang.

466 records · Page 26Linked to original sources

Zeroes of the Jones polynomial

We study the distribution of zeroes of the Jones polynomial $V_K(t)$ for a knot $K$. We have computed numerically the roots of the Jones polynomial for all prime knots with $N\leq 10$ crossings, and found the zeroes scattered about the unit circle $|t|=1$ with the average distance to the circle approaching a nonzero value as $N$ increases. For torus knots of the type $(m,n)$ we show that all zeroes lie on the unit circle with a uniform density in the limit of either $m$ or $n\to \infty$, a fact confirmed by our numerical findings. We have also elucidated the relation connecting the Jones polynomial with the Potts model, and used this relation to derive the Jones polynomial for a repeating chain knot with $3n$ crossings for general $n$. It is found that zeroes of its Jones polynomial lie on three closed curves centered about the points $1, i$ and $-i$. In addition, there are two isolated zeroes located one each near the points $t_\pm = e^{\pm 2πi/3}$ at a distance of the order of $3^{-(n+2)/2}$. Closed-form expressions are deduced for the closed curves in the limit of $n\to \infty$.

cond-mat.stat-mech↗

Modeling two-state cooperativity in protein folding

A protein model with the pairwise interaction energies varying as local environment changes, i.e., including some kinds of collective effect between the contacts, is proposed. Lattice Monte Carlo simulations on the thermodynamical characteristics and free energy profile show a well-defined two-state behavior and cooperativity of folding for such a model. As a comparison, related simulations for the usual Gō model, where the interaction energies are independent of the local conformations, are also made. Our results indicate that the evolution of interactions during the folding process plays an important role in the two-state cooperativity in protein folding.

cond-mat.soft↗

Chandra Grating Spectroscopy of the Seyfert Galaxy Ton S180

This paper presents results from spectral observations of Ton S180 using Chandra and ASCA. The data confirm the presence of the soft excess but the Chandra LETG spectrum reveals it to be broad and smooth, rather than resolved into individual emission lines. This excess may represent either a primary or reprocessed continuum component or a blend of broad lines from an ionized accretion disk. The occurrence of a similar feature in five other NLSy1s leads us to conclude that this soft X-ray component may be a characteristic of sources accreting at a very high rate. The X-ray spectrum shows no evidence for absorption lines, indicating that if gas exists in the line-of-sight then it is in a very high ionization-state or has an extremely broad velocity distribution. The new ASCA data confirm that the narrow component of the Fe Kalpha line peaks close to a rest-energy of 7 keV, indicating the presence of a significant amount of highly-ionized material in the nuclear environs.

astro-ph↗

The Cleo III Ring Imaging Cherenkov Detector

The CLEO detector has been upgraded to include a state of the art particle identification system, based on the Ring Imaging Cherenkov Detector (RICH) technology, in order to take data at the upgraded CESR electron positron collider. The expected performance is reviewed, as well as the preliminary results from an engineering run during the first few months of operation of the CLEO III detector.

hep-ex↗

Blowing-Up the Four-Dimensional Z_3 Orientifold

We study the blowing-up of the four-dimensional Z_3 orientifold of Angelantonj, Bianchi, Pradisi, Sagnotti and Stanev (ABPSS) by giving nonzero vacuum expectation values (VEV's) to the twisted sector moduli blowing-up modes. The blowing-up procedure induces a Fayet-Iliopoulos (FI) term for the ``anomalous'' U(1), whose magnitude depends linearly on the VEV's of the blowing-up modes. To preserve the N=1 supersymmetry, non-Abelian matter fields are forced to acquire nonzero VEV's, thus breaking (some of) the non-Abelian gauge structure and decoupling some of the matter fields. We determine the form of the FI term, construct explicit examples of (non-Abelian) D and F flat directions, and determine the surviving gauge groups of the restabilized vacua. We also determine the mass spectra, for which the restabilization reduces the number of families.

hep-th↗

Physics Implications of a Perturbative Superstring Construction

We investigate the low energy physics implications of a prototype quasi-realistic superstring model with an anomalous U(1). First, we present the techniques utilized to compute the mass spectrum and superpotential couplings at the string scale, and demonstrate the results for the effective theory along a particular flat direction/"restabilized vacuum" of the model. We then analyze the gauge symmetry breaking patterns and renormalization group equations to determine the mass spectrum at the electroweak scale for a particular numerical example with a realistic Z-Z' hierarchy. Although the model considered is not fully realistic, the results demonstrate general features of quasi-realistic string models, such as extra matter (e.g. Z' gauge bosons and an extended Higgs sector) at the electroweak/TeV scale, and noncanonical couplings (such as R-parity violating terms).

hep-ph↗

Physics Implications of Flat Directions in Free Fermionic Superstring Models I: Mass Spectrum and Couplings

From the "top-down" approach we investigate physics implications of the class of D- and F- flat directions formed from non-Abelian singlets which are proven flat to all orders in the nonrenormalizable superpotential, for a prototype quasi-realistic free fermionic string model with the standard model gauge group and three families (CHL5). These flat directions have at least an additional U(1)' unbroken at the string scale. For each flat direction, the complete set of effective mass terms and effective trilinear superpotential terms in the observable sector are computed to all orders in the VEV's of the fields in the flat direction. The "string selection-rules" disallow a large number of couplings allowed by gauge invariance, resulting in a massless spectrum with a large number of exotics, in most cases excluded by experiment, thus signifying a generic flaw of these models. Nevertheless, the resulting trilinear couplings of the massless spectrum possess a number of interesting features which we analyse for two representative flat directions: for the fermion texture; baryon- and lepton-number violating couplings; R-parity breaking; non-canonical mu terms; and the possibility of electroweak and intermediate scale symmetry breaking scenarios for U(1)'. The gauge coupling predictions are obtained in the electroweak scale case. Fermion masses possess t-b and tau-mu universality, with the string scale Yukawa couplings g and $g/\sqrt{2}$, respectively. Fermion textures are present for certain flat directions, but only in the down-quark sector. Baryon- and lepton- number violating couplings can trigger proton-decay, $N-{\bar N}$ oscillations, leptoquark interactions and R-parity violation, leading to the absence of a stable LSP.

hep-ph↗

Physics Implications of Flat Directions in Free Fermionic Superstring Models II: Renormalization Group Analysis

We continue the investigation of the physics implications of a class of flat directions for a prototype quasi-realistic free fermionic string model (CHL5), building upon the results of the previous paper in which the complete mass spectrum and effective trilinear couplings of the observable sector were calculated to all orders in the superpotential. We introduce soft supersymmetry breaking mass parameters into the model, and investigate the gauge symmetry breaking patterns and the renormalization group analysis for two representative flat directions, which leave an additional $U(1)'$ as well as the SM gauge group unbroken at the string scale. We study symmetry breaking patterns that lead to a phenomenologically acceptable $Z-Z'$ hierarchy, $M_{Z^{'}} \sim {\cal O}(1~{\rm TeV})$ and $ 10^{12}~{\rm GeV}$ for electroweak and intermediate scale $U(1)^{'}$ symmetry breaking, respectively, and the associated mass spectra after electroweak symmetry breaking. The fermion mass spectrum exhibits unrealistic features, including massless exotic fermions, but has an interesting $d$-quark hierarchy and associated CKM matrix in one case. There are (some) non-canonical effective $μ$ terms, which lead to a non-minimal Higgs sector with more than two Higgs doublets involved in the symmetry breaking, and a rich structure of Higgs particles, charginos, and neutralinos, some of which, however, are massless or ultralight. In the electroweak scale cases the scale of supersymmetry breaking is set by the $Z^{'}$ mass, with the sparticle masses in the several TeV range.

hep-ph↗

An X-ray and Optical Investigation of the Starburst-driven Superwind in the Galaxy Merger Arp 299

We present a detailed investigation of the X-ray and optical properties of the starburst-merger system Arp299 (NGC 3690, Mrk 171), with an emphasis on its spectacular gaseous nebula. We analyse \rosat and \asca X-ray data and optical spectra and narrow-band images. We suggest that the on-going galaxy collision has tidally-redistributed the ISM of the merging galaxies. The optical emission-line nebula results as this gas is photoionized by radiation that escapes from the starburst, and is shock-heated, accelerated, and pressurized by a `superwind' driven by the collective effect of the starburst supernovae and stellar winds. The X-ray nebula in Arp 299 is is plausibly a mass-loaded flow of adiabatically-cooling gas that carries out a substantial fraction of the energy and metals injected by the starburst at close to the escape velocity from Arp 299. The mass outflow rate likely exceeds the star-formation rate in this system. We conclude that powerful starbursts are able to heat (and possibly eject) a significant fraction of the ISM in merging galaxies.

astro-ph↗

Neutrino Anti-neutrino Transitions

We consider transitions between neutrinos and anti-neutrinos in laboratory experiments in five scenarios, including both helicity flipping and preserving cases.

hep-ph↗

Structure Function Subgroup Summary

We summarize the studies and discussions of the Structure Function subgroup of the QCD working group of the Snowmass 1996 Workshop: New Directions for High Energy Physics.

hep-ph↗

Current conservation in two-dimensional AC-transport

The electric current conservation in a two-dimensional quantum wire under a time dependent field is investigated. Such a conservation is obtained as the global density of states contribution to the emittance is balanced by the contribution due to the internal charge response inside the sample. However when the global partial density of states is approximately calculated using scattering matrix only, correction terms are needed to obtain precise current conservation. We have derived these corrections analytically using a specific two-dimensional system. We found that when the incident energy $E$ is near the first subband, our result reduces to the one-dimensional result. As $E$ approaches to the $n$-th subband with $n>1$, the correction term diverges. This explains the systematic deviation to precise current conservation observed in a previous numerical calculation.

cond-mat↗

Transitions and Probes in Turbulent Helium

Previous analysis of a Paris turbulence experiment \cite{zoc94,tab95} shows a transition at the Taylor Reynolds number $\rel \approx 700$. Here correlation function data is analyzed which gives further evidence for this transition. It is seen in both the power spectrum and in structure function measurements. Two possible explanations may be offered for this observed transition: that it is intrinsic to the turbulence flow in this closed box experiment or that it is an effect of a change in the flow around the anemometer. We particularly examine a pair of ``probe effects''. The first is a thermal boundary layer which does exist about the probe and does limit the probe response, particularly at high frequencies. Arguments based on simulations of the response and upon observations of dissipation suggests that this effect is only crucial beyond $\rel\approx 2000$. The second effect is produced by vortex shedding behind the probe. This has been seen to produce a large modification in some of the power spectra for large $\rel$. It might also complicate the interpretation of the experimental results. However, there seems to be a remaining range of data for $\rel < 1300$ uncomplicated by these effects, and which are thus suggestive of an intrinsic transition.

chao-dyn↗

The Quantum Hall Effect and Inter-edge State Tunneling Within a Barrier

We have introduced a controllable nano-scale incursion into a potential barrier imposed across a two-dimensional electron gas, and report on the phenomena that we observe as the incursion develops. In the quantum Hall regime, the conductance of this system displays quantized plateaus, broad minima and oscillations. We explain these features and their evolution with electrostatic potential geometry and magnetic field as a progression of current patterns formed by tunneling between edge and localized states within the barrier.

cond-mat↗

Finite size effects in metallic superlattice systems

Clean metallic superlattice systems composed of alternating layers of superconducting and normal materials are considered, particularly aspects of the proximity effect as it affects the critical temperature. A simple model is used to address the question of when a finite--sized system theoretically approximates well a true infinite superlattice. The methods used in the analysis afford some tests of the approximation used that the pair amplitude of the Cooper pairs is constant over a superconducting region. We also use these methods to construct a model of a single superconducting layer which intends to incorporate a more realistic form of the pair amplitude than a simple constant.

cond-mat↗

Universal Conductivity in the Two dimensional Boson Hubbard Model

We use Quantum Monte Carlo to evaluate the conductivity $σ$ of the 2--dimensional disordered boson Hubbard model at the superfluid-bose glass phase boundary. At the critical point for particle density $ρ=0.5$, we find $σ_{c}=(0.45 \pm 0.07) σ_{Q}$, where $σ_{Q}= e_{*}^{2} / h$ from a finite size scaling analysis of the superfluid density. We obtain $σ_{c}=(0.47 \pm 0.08) σ_{Q}$ from a direct calculation of the current--current correlation function. Simulations at the critical points for other particle densities, $ρ=0.75$ and $1.0$, give similar values for $σ$. We discuss possible origins of the difference in this value from that recently obtained by other numerical approaches.

cond-mat↗