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Shapes of relative emission sources can be accessed by expanding shapes of correlations at low relative velocities in pair center of mass in Cartesian harmonics. Coefficients of expansion for correlations are related to the respective coefficients of expansion for the sources through one dimensional integral transforms involving properties of pair relative wavefunctions. The methodology is illustrated with analyses of NA49 and PHENIX correlation data.
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arxiv:0707.0377
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Encapsulation layers are explored for passivating the surfaces of silicon to reduce optical absorption in the 1500-nm wavelength band. Surface-sensitive test structures consisting of microdisk resonators are fabricated for this purpose. Based on previous work in silicon photovoltaics, coatings of SiNx and SiO2 are applied under varying deposition and annealing conditions. A short dry thermal oxidation followed by a long high-temperature N2 anneal is found to be most effective at long-term encapsulation and reduction of interface absorption. Minimization of the optical loss is attributed to simultaneous reduction in sub-bandgap silicon surface states and hydrogen in the capping material.
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arxiv:0707.0415
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The construction of optimal template banks for matched-filtering searches is an example of the sphere covering problem. For parameter spaces with constant-coefficient metrics a (near-) optimal template bank is achieved by the A_n* lattice, which is the best lattice-covering in dimensions n <= 5, and is close to the best covering known for dimensions n <= 16. Generally this provides a substantially more efficient covering than the simpler hyper-cubic lattice. We present an algorithm for generating lattice template banks for constant-coefficient metrics and we illustrate its implementation by generating A_n* template banks in n=2,3,4 dimensions.
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arxiv:0707.0428
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Consider n non-intersecting particles on the real line (Dyson Brownian motions), all starting from the origin at time=0, and forced to return to x=0 at time=1. For large n, the average mean density of particles has its support, for each 0<t<1, within the interior of an ellipse. The Airy process is defined as the motion of these non-intersecting Brownian motions for large n, but viewed from an arbitrary point on the ellipse with an appropriate space-time rescaling. Assume now a finite number r of these particles are forced to a different target point. Does it affect the Brownian fluctuations along the ellipse for large n? In this paper, we show that no new process appears as long as one considers points on the ellipse, for which the t-coordinate is smaller than the t-coordinate of the point of tangency of the tangent to the curve passing through the target point. At this point of tangency the fluctuations obey a new statistics: the Airy process with r outliers (in short: {\bf r-Airy process}). The log of the transition probability of this new process is given by the Fredholm determinant of a new kernel (extending the Airy kernel) and it satisfies a non-linear PDE in x and the time.
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arxiv:0707.0442
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Complex networks display various types of percolation transitions. We show that the degree distribution and the degree-degree correlation alone are not sufficient to describe diverse percolation critical phenomena. This suggests that a genuine structural correlation is an essential ingredient in characterizing networks. As a signature of the correlation we investigate a scaling behavior in $M_N(h)$, the number of finite loops of size $h$, with respect to a network size $N$. We find that networks, whose degree distributions are not too broad, fall into two classes exhibiting $M_N(h)\sim ({constant})$ and $M_N(h) \sim (\ln N)^\psi$, respectively. This classification coincides with the one according to the percolation critical phenomena.
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arxiv:0707.0560
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We calculate, in the continuum limit of quenched lattice QCD, the matrix elements of the heavy-heavy vector current between heavy-light pseudoscalar meson states. We present the form factors for different values of the initial and final meson masses at finite momentum transfer. In particular, we calculate the non-perturbative correction to the differential decay rate of the process B --> D l nu including the case of a non-vanishing lepton mass.
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arxiv:0707.0587
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We provide a refined approach to the classical Magnus and Fer expansion, unveiling a new structure by using the language of dendriform and pre-Lie algebras. The recursive formula for the logarithm of the solutions of the equations X=1+ta<X and Y=1-tY> a in A[[t]] is provided, where (A,<,>) is a dendriform algebra. Then, we present the solutions to these equations as an infinite product expansion of exponentials. Both formulae involve the pre-Lie product naturally associated with the dendriform structure. Several applications are presented.
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arxiv:0707.0607
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The deformation at the core-mantle boundary produced by the 2004 Sumatra earthquake is investigated by means of a semi-analytic theoretical model of global coseismic and postseismic deformation, predicting a millimetric coseismic perturbation over a large portion of the core-mantle boundary. Spectral features of such deformations are analysed and discussed. The time-dependent postseismic evolution of the elliptical part of the gravity field (J2) is also computed for different asthenosphere viscosity models. Our results show that, for asthenospheric viscosities smaller than 10^18 Pa s, the postseismic J2 variation in the next years is expected to leave a detectable signal in geodetic observations.
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arxiv:0707.0638
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In this paper we describe how representation theory of groups can be used to shorten the derivation of two loop partition functions in string theory, giving an intrinsic description of modular forms appearing in the results of D'Hoker and Phong [1]. Our method has the advantage of using only algebraic properties of modular functions and it can be extended to any genus g.
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arxiv:0707.0646
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(Abridged) We present a study of the optical spectra of a sample of eight star-forming nuclear rings and the nuclei of their host galaxies. The spectra were obtained with the ISIS spectrograph on the William Herschel Telescope and cover a wide range in wavelength, enabling the measurement of several stellar absorption features and gas emission lines. We compared the strength of the absorption lines to a variety of population synthesis models for the star-formation history in the nuclear rings, including also the contribution of the older bulge and disc stellar components. We find that the stars in our sample of nuclear rings have most likely formed over a prolonged period of time characterised by episodic bursts of star-formation activity. Constant star formation is firmly ruled out by the data, whereas a one-off formation event is an unlikely explanation for a common galactic component such as nuclear rings. We have used emission-line measurements to constrain the physical conditions of the ionised gas within the rings. Emission in all nuclear rings originates from HII-regions with electron densities typical for these kinds of objects, and that the rings are characterised by values for the gas metallicity ranging from slightly below to just above solar. As 20% of nearby spiral galaxies hosts nuclear rings that are currently forming massive stars, our finding of an episodic star formation history in nuclear rings implies that a significant population remains to be identified of young nuclear rings that are not currently in a massive star formation phase.
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arxiv:0707.0651
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Cobalt nanowires with a diameter in the range between 50 to 100nm can be prepared as single-crystal wires with the easy axis (the c-axis) perpendicular to the wire axis. The competition between the crystal anisotropy and demagnetization energy frustrates the magnetization direction. A periodic modulation of the angle between M and the wire axis yields a lower energy.
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arxiv:0707.0663
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This paper presents a simple geometrical fact which could relate to the history of mathematics and astronomy. This fact shows a natural link between the circle and the multiples of 6 and it makes it possible to obtain a simple representation of the 12 months of the year, the 24 hours of the day, the 30 days (average number) of the month and the 360 days (approximate number) of the year, which brings us closer to the sexagesimal division of time. Moreover this representation reminds one of the movement of the planets around a centre. Using this fact one will be able also to find geometrically the principal divisor of number 60, to represent numbers in base 60 with a kind of abacus or calculation table and to make a division of the circle into 6 and 12 equal parts. Afterwards one will be able to obtain a division in 360 unequal parts but relatively close to one another, and the goal isn't precisely to obtain an optimal division of the circle in 360 equal parts but to prove that the idea to divide the circle in 360 equal parts can subsequently be suggested by these geometrical facts that have been showed. In this article the author will not answer the following questions: a) What is the origin of the sexagesimal system? b) By which way could one manage to adopt the sexagesimal system starting from the knowledge of the facts exposed in this article and starting from the knowledge of the astronomical data? These questions could be treated, using information of this article, by the readers or later on by the author.
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arxiv:0707.0676
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The \emph{canonical structures of the plane} are those that result, up to isomorphism, from the rings that have the form $\mathds{R}[x]/(ax^2+bx+c)$ with $a\neq 0$.That ring is isomorphic to $\mathds{R}[\theta]$, where $\theta$ is the equivalence class of x, which satisfies $\theta^2 = (-\dfrac{c}{a}) + \theta (-\dfrac{b}{a})$. On the other hand, it is known that, up to isomorphism, there are only three canonical structures: the corresponding to $\theta^2 = -1$ (the complex numbers), $\theta^2 = 1$ (the perplex or hyperbolic numbers) and $\theta^2 = 0$ (the parabolic numbers). This article copes with the algebraic structure of the rings of integers $\mathds{Z}[\theta]$ in the perplex and parabolic cases by \emph{analogy} to the complex cases: the ring of Gaussian integers. For those rings a \emph{division algorithm} is proved and it is obtained, as a consequence, the characterization of the prime and irreducible elements.
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arxiv:0707.0700
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We report on the appearance of magnetic stripes in MnAs/GaAs(100) epilayers at temperatures well below the ferromagnetic transition of the system. The study has been performed by ferromagnetic resonance experiments (FMR) on MnAs epilayers grown on (100) and (111) GaAs substrates. The FMR spectra of the MnAs/GaAs(100) samples at 180 K reveal the appearance of zones of different magnetic behavior with respect to the low-temperature homogeneous ferromagnetic phase. The angular and the temperature dependence of the spectra serve us to detect the inter-growth of the non-magnetic phase into the ferromagnetic phase at a very early stage of the process. The experimental data show that the new phase nucleates in a self-arranged array of stripes in MnAs/GaAs(100) thin films while it grows randomly in the same films grown on GaAs(111).
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arxiv:0707.0703
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We have studied the positive-parity states of $^{40}$Ca using antisymmetrized molecular dynamics (AMD) and the generator coordinate method (GCM). Imposing two different kinds of constraints on the variational calculation, we have found various kinds of $^{40}{\rm Ca}$ structures such as a deformed-shell structure, as well as $\alpha$-$^{36}$Ar and $^{12}$C-$^{28}$Si cluster structures. After the GCM calculation, we obtained a normal-deformed band and a superdeformed band together with their side bands associated with triaxial deformation. The calculated $B(E2)$ values agreed well with empirical data. It was also found that the normal-deformed and superdeformed bands have a non-negligible $\alpha$-$^{36}$Ar cluster component and $^{12}$C-$^{28}$Si cluster component, respectively. This leads to the presence of an $\alpha$-$^{36}$Ar higher-nodal band occurring above the normal-deformed band.
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arxiv:0707.0723
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The dynamics of an unbiased spin-boson model with Lorentzian spectral density is investigated theoretically in terms of the perturbation theory based on a unitary transformation. The non-equilibrium correlation function $P(t)$ and susceptibility $\chi^{\prime\prime}(\omega)$ are calculated for both the off-resonance case $\Delta\lesssim 0.5\Omega$ and the on-resonance case $\Delta\sim \Omega$. The approach is checked by the Shiba's relation and the sum rule. Besides, the coherent-incoherent transition point $\alpha_c$ can be determined, which has not been demonstrated for the structured bath by previous authors up to our knowledge.
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arxiv:0707.0725
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Quantum random walks are the quantum counterpart of classical random walks, and were recently studied in the context of quantum computation. A quantum random walker is subject to self interference, leading to a remarkably different behavior than that of classical random walks such as ballistic propagation or localization due to disorder. Physical implementations of quantum walks have only been made in very small scale systems severely limited by decoherence. Here we show that the propagation of photons in waveguide lattices, which have been studied extensively in recent years, are essentially an implementation of quantum walks. Since waveguide lattices are easily constructed at large scales and display negligible decoherence, they can serve as an ideal and versatile experimental playground for the study of quantum walks and quantum algorithms. We experimentally observe quantum walks in large systems (~100 sites) and confirm quantum walks effects which were studied theoretically, including ballistic propagation, disorder and boundary related effects.
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arxiv:0707.0741
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We prove the existence of primitive curves and positivity of intersections of $J$-complex curves for Lipschitz-continuous almost complex structures. These results are deduced from the Comparison Theorem for $J$-holomorphic maps in Lipschitz structures, previously known for $J$ of class $C^{1, Lip}$. We also give the optimal regularity of curves in Lipschitz structures. It occurs to be $C^{1,LnLip}$, i.e. the first derivatives of a $J$-complex curve for Lipschitz $J$ are Log-Lipschitz-continuous. A simple example that nothing better can be achieved is given. Further we prove the Genus Formula for $J$-complex curves and determine their principal Puisieux exponents (all this for Lipschitz-continuous $J$-s).
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arxiv:0707.0771
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In the paper, it is proved that any $C^{1}$-function on GL(n) which is locally $P$-invariant (here $P$ is the affine (sub)group of GL(n)) is locally $G$-invairant. There is also a statement for distributions (a very weak form of Baruch's results).
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arxiv:0707.0779
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We study the asymptotic properties of the number of open paths of length $n$ in an oriented $\rho$-percolation model. We show that this number is $e^{n\alpha(\rho)(1+o(1))}$ as $n \to \infty$. The exponent $\alpha$ is deterministic, it can be expressed in terms of the free energy of a polymer model, and it can be explicitely computed in some range of the parameters. Moreover, in a restricted range of the parameters, we even show that the number of such paths is $n^{-1/2} W e^{n\alpha(\rho)}(1+o(1))$ for some nondegenerate random variable $W$. We build on connections with the model of directed polymers in random environment, and we use techniques and results developed in this context.
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arxiv:0707.0818
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This paper addresses the issues of conservativeness and computational complexity of probabilistic robustness analysis. We solve both issues by defining a new sampling strategy and robustness measure. The new measure is shown to be much less conservative than the existing one. The new sampling strategy enables the definition of efficient hierarchical sample reuse algorithms that reduce significantly the computational complexity and make it independent of the dimension of the uncertainty space. Moreover, we show that there exists a one to one correspondence between the new and the existing robustness measures and provide a computationally simple algorithm to derive one from the other.
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arxiv:0707.0823
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We consider dense rapid shear flow of inelastically colliding hard disks. Navier-Stokes granular hydrodynamics is applied accounting for the recent finding \cite{Luding,Khain} that shear viscosity diverges at a lower density than the rest of constitutive relations. New interpolation formulas for constitutive relations between dilute and dense cases are proposed and justified in molecular dynamics (MD) simulations. A linear stability analysis of the uniform shear flow is performed and the full phase diagram is presented. It is shown that when the inelasticity of particle collision becomes large enough, the uniform sheared flow gives way to a two-phase flow, where a dense "solid-like" striped cluster is surrounded by two fluid layers. The results of the analysis are verified in event-driven MD simulations, and a good agreement is observed.
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arxiv:0707.0872
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This is the third in a series of papers dealing with the algebraic theory of infinite classical lattices. This paper presents a theory of single measurements on a lattice which we represent as comprising a finite subvolume--the system of measurement--immersed in an infinite surround or ``heat bath'' which determines the system's state. We consider the class of all stationary distributions on the set of microcanonical states of the infinite lattice. The theory addresses the question, ``For a lattice initially in state A, say, what is the probability that measurement of a certain quantity will take a value in (a,b)?'' Discussion includes description of the source of randomness in a measurement as well as characterization of the given states A.
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arxiv:0707.0882
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We consider a six-dimensional axisymmetric Einstein-Maxwell model of warped braneworlds. The bulk is bounded by two branes, one of which is a conical 3-brane and the other is a 4-brane wrapped around the axis of symmetry. The latter brane is assumed to be our universe. If the tension of the 3-brane is fine-tuned, it folds the internal two-dimensional space in a narrow cone, making sufficiently small the Kaluza-Klein circle of the 4-brane. An arbitrary energy-momentum tensor can be accommodated on this ring-like 4-brane. We study linear perturbations sourced by matter on the brane, and show that weak gravity is apparently described by a four-dimensional scalar-tensor theory. The extra scalar degree of freedom can be interpreted as the fluctuation of the internal space volume (or that of the circumference of the ring), the effect of which turns out to be suppressed at long distances. Consequently, four-dimensional Einstein gravity is reproduced on the brane. We point out that as in the Randall-Sundrum model, the brane bending mode is crucial for recovering the four-dimensional tensor structure in this setup.
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arxiv:0707.0894
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We express the d=4, N=2 black hole effective potential for cubic holomorphic F functions and generic dyonic charges in terms of d=5 real special geometry data. The 4d critical points are computed from the 5d ones, and their relation is elucidated. For symmetric spaces, we identify the BPS and non-BPS classes of attractors and the respective entropies. These are related by simple formulae, interpolating between four and five dimensions, depending on the volume modulus and on the 4d magnetic (or electric) charges, and holding true also for generic field configurations and for non-symmetric cubic geometries.
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arxiv:0707.0964
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We investigate the orbital selective Mott transition in two-band Hubbard models by means of the Gutzwiller variational theory. In particular, we study the influence of a finite local hybridisation between electrons in different orbitals on the metal-insulator transition.
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arxiv:0707.0965
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We show that an internal localization mobility edge can appear around the Fermi energy in graphene by introducing impurities in the split-band regimen, or by producing vacancies in the lattice. The edge appears at the center of the spectrum and not at the band edges, in contrast with the usual picture of localization. Such result is explained by showing that the bipartite nature of lattice allows to renormalize the Hamiltonian, and the internal edge appears because of frustration effects in the renormalized lattice. The size in energy of the spectral region with localized states is similar in value to that observed in narrow gap semiconductors.
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arxiv:0707.1013
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Recent computations of scattering amplitudes show that N=8 supergravity is surprisingly well behaved in the ultraviolet and may even be ultraviolet finite in perturbation theory. The novel cancellations necessary for ultraviolet finiteness first appear at one loop in the guise of the "no-triangle hypothesis". We study one-loop amplitudes in pure Einstein gravity and point out the existence of cancellations similar to those found previously in N=8 supergravity. These cancellations go beyond those found in the one-loop effective action. Using unitarity, this suggests that generic theories of quantum gravity based on the Einstein-Hilbert action may be better behaved in the ultraviolet at higher loops than suggested by naive power counting, though without additional (supersymmetric) cancellations they diverge. We comment on future studies that should be performed to support this proposal.
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arxiv:0707.1035
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We present a comparison between the rotation period distributions of solar-type single stars and primary stars in close binaries (0.1 AU ~< a ~< 5 AU) in the young (150 Myr) open cluster M35 (NGC 2168). We find that the primary stars in the close binaries rotate faster than the single stars, on average. The differences in the means and medians between the period distributions are statistically significant at the 99.9% level or higher. The faster rotation among the primary stars in close binaries is not due to tidal synchronization as tidally evolved stars are excluded from the comparison. We discuss this result in the context of different early-evolution accretion processes and star-disk interactions for single stars and stars in close binaries.
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arxiv:0707.1087
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This paper presents the basic ideas and properties of elliptic functions and elliptic integrals as an expository essay. It explores some of their numerous consequences and includes applications to some problems such as the simple pendulum, the Euler rigid body motion and some others integrable hamiltonian systems.
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arxiv:0707.1137
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In this paper, we investigate the structure of the multiplier module of a Hilbert module over a locally C*-algebra and the relationship between the set of all adjointable operators from a Hilbert A-module E to a Hilbert A-module F and the set of all adjointable operators from the multiplier module M(E)of E to the multiplier module M(F) of F.
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arxiv:0707.1139
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First Laszlo Szekely and more recently Saharon Shelah and Alexander Soifer have presented examples of infinite graphs whose chromatic numbers depend on the axioms chosen for set theory. The existence of such graphs may be relevant to the Chromatic Number of the Plane problem. In this paper we construct a new class of graphs with ambiguous chromatic number. They are unit distance graphs with vertex set R^n, and hence may be seen as further evidence that the chromatic number of the plane might depend on set theory.
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arxiv:0707.1177
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We study the quantization of abelian gauge theories of principal torus bundles over compact manifolds with and without boundary. It is shown that these gauge theories suffer from a Gribov ambiguity originating in the non-triviality of the bundle of connections whose geometrical structure will be analyzed in detail. Motivated by the stochastic quantization approach we propose a modified functional integral measure on the space of connections that takes the Gribov problem into account. This functional integral measure is used to calculate the partition function, the Greens functions and the field strength correlating functions in any dimension using the fact that the space of inequivalent connections itself admits the structure of a bundle over a finite dimensional torus. The Greens functions are shown to be affected by the non-trivial topology, giving rise to non-vanishing vacuum expectation values for the gauge fields.
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arxiv:0707.1186
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Fix an integer k, and let I(l), l=1,2,..., be a sequence of k-dimensional vectors of multiple Wiener-It\^o integrals with respect to a general Gaussian process. We establish necessary and sufficient conditions to have that, as l diverges, the law of I(l) is asymptotically close (for example, in the sense of Prokhorov's distance) to the law of a k-dimensional Gaussian vector having the same covariance matrix as I(l). The main feature of our results is that they require minimal assumptions (basically, boundedness of variances) on the asymptotic behaviour of the variances and covariances of the elements of I(l). In particular, we will not assume that the covariance matrix of I(l) is convergent. This generalizes the results proved in Nualart and Peccati (2005), Peccati and Tudor (2005) and Nualart and Ortiz-Latorre (2007). As shown in Marinucci and Peccati (2007b), the criteria established in this paper are crucial in the study of the high-frequency behaviour of stationary fields defined on homogeneous spaces.
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arxiv:0707.1220
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The success of an infectious disease to invade a population is strongly controlled by the population's specific connectivity structure. Here a network model is presented as an aid in understanding the role of social behavior and heterogeneous connectivity in determining the spatio-temporal patterns of disease dynamics. We explore the controversial origins of long-term recurrent oscillations believed to be characteristic to diseases that have a period of temporary immunity after infection. In particular, we focus on sexually transmitted diseases such as syphilis, where this controversy is currently under review. Although temporary immunity plays a key role, it is found that in realistic small-world networks, the social and sexual behavior of individuals also has great influence in generating long-term cycles. The model generates circular waves of infection with unusual spatial dynamics that depend on focal areas that act as pacemakers in the population. Eradication of the disease can be efficiently achieved by eliminating the pacemakers with a targeted vaccination scheme. A simple difference equation model is derived, that captures the infection dynamics of the network model and gives insights into their origins and their eradication through vaccination.
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arxiv:0707.1222
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We propose how to generate genuine multipartite entanglement of electron spin qubits in a chain of quantum dots using the naturally available single-qubit rotations and two-qubit Heisenberg exchange interaction in the system. We show that the minimum number of required operations to generate entangled states of the GHZ-, cluster and W-type scales linearly with the number of qubits and estimate the fidelities of the generated entangled cluster states. As the required single and two-qubit operations have recently been realized, our proposed scheme opens the way for experimental investigation of multipartite entanglement with electron spin qubits.
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arxiv:0707.1267
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We study the top intersection numbers of the boundary and Hodge class divisors on toroidal compactifications of the moduli space $A_g$ of principally polarized abelian varieties and compute those numbers that live away from the stratum which lies over the closure of $A_{g-3}$ in the Satake compactification.
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arxiv:0707.1274
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A (bounded) manifold of circular type is a complex manifold M of dimension n admitting a (bounded) exhaustive real function u, defined on M minus a point x_o, so that: a) it is a smooth solution on $M\setminus {x_o}$ to the Monge-Amp\`ere equation $(d d^c u)^n = 0$; b) x_o is a singular point for u of logarithmic type and e^u extends smoothly on the blow up of M at x_o; c) $d d^c (e^u) >0$ at any point of $M\setminus {x_o}$. This class of manifolds naturally includes all smoothly bounded, strictly linearly convex domains and all smoothly bounded, strongly pseudoconvex circular domains of $\bC^n$. The moduli spaces of bounded manifolds of circular type are studied. In particular, for each biholomorphic equivalence class of them it is proved the existence of an essentially unique manifold in normal form. It is also shown that the class of normalizing maps for an n-dimensional manifold M is a new holomorphic invariant with the following property: it is parameterized by the points of a finite dimensional real manifold of dimension n^2 when M is a (non-convex) circular domain while it is of dimension $n^2 + 2 n$ when M is a strictly convex domain. New characterizations of the circular domains and of the unit ball are also obtained.
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arxiv:0707.1287
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Statements analogous to the Hard Lefschetz Theorem (HLT) and the Hodge-Riemann bilinear relations (HRR) hold in a variety of contexts: they impose restrictions on the cohomology algebra of a smooth compact K\"ahler manifold or on the intersection cohomology of a projective toric variety; they restrict the local monodromy of a polarized variation of Hodge structure; they impose conditions on the possible $f$-vectors of convex polytopes. While the statements of these theorems depend on the choice of a K\"ahler class, or its analog, there is usually a cone of possible K\"ahler classes. It is then natural to ask whether the HLT and HRR remain true in a mixed context. In this note we present a unified approach to proving the mixed HLT and HRR, generalizing the previously known results, and proving it in new cases such as the intersection cohomology of non-rational polytopes.
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arxiv:0707.1352
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Beam asymmetry and differential cross section for the reaction gamma+p->eta+p were measured from production threshold to 1500 MeV photon laboratory energy. The two dominant neutral decay modes of the eta meson, eta->2g and eta->3pi0, were analyzed. The full set of measurements is in good agreement with previously published results. Our data were compared with three models. They all fit satisfactorily the results but their respective resonance contributions are quite different. The possible photoexcitation of a narrow state N(1670) was investigated and no evidence was found.
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arxiv:0707.1385
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Control of the living cell functions with remarkable reliability despite the stochastic nature of the underlying molecular networks -- a property presumably optimized by biological evolution. We here ask to what extent the property of a stochastic dynamical network to produce reliable dynamics is an evolvable trait. Using an evolutionary algorithm based on a deterministic selection criterion for the reliability of dynamical attractors, we evolve dynamical networks of noisy discrete threshold nodes. We find that, starting from any random network, reliability of the attractor landscape can often be achieved with only few small changes to the network structure. Further, the evolvability of networks towards reliable dynamics while retaining their function is investigated and a high success rate is found.
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arxiv:0707.1407
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Using unitarized Chiral Perturbation Theory methods, we perform a detailed analysis of the $\pi\pi$ scattering poles $f_0(600)$ and $\rho(770)$ behaviour when medium effects such as temperature or density drive the system towards Chiral Symmetry Restoration. In the analysis of real poles below threshold, we show that it is crucial to extend properly the unitarized amplitudes so that they match the perturbative Adler zeros. Our results do not show threshold enhancement effects at finite temperature in the $f_0(600)$ channel, which remains as a pole of broad nature. We also implement T=0 finite density effects related to chiral symmetry restoration, by varying the pole position with the pion decay constant. Although this approach takes into account only a limited class of contributions, we reproduce the expected finite density restoration behaviour, which drives the poles towards the real axis, producing threshold enhancement and $\pi\pi$ bound states. We compare our results with several model approaches and discuss the experimental consequences, both in Relativistic Heavy Ion Collisions and in $\pi\to \pi\pi$ and $\gamma\to \pi\pi$ reactions in nuclei.
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arxiv:0707.1424
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For AdS boundary conditions, we give a solution of the H3+ two point function involving degenerate field with SL(2)-label b^{-2}/2, which is defined on the full (u,z) unit square. It consists of two patches, one for z<u and one for u<z. Along the u=z "singularity", the solutions from both patches are shown to have finite limits and are merged continuously as suggested by the work of Hosomichi and Ribault. From this two point function, we can derive b^{-2}/2-shift equations for AdS_2 D-branes. We show that discrete as well as continuous AdS_2 branes are consistent with our novel shift equations without any new restrictions.
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arxiv:0707.1463
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It was argued in literature that traversable wormholes can exist with arbitrarily small violation of null energy conditions. We show that if the amount of exotic material near the wormhole throat tends to zero, either this leads to a horn instead of a wormhole or the throat approaches the horizon in such a way that infnitely large stresses develop on the throat.
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arxiv:0707.1487
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In this paper we uses an I.I. Hirschman-W. Beckner entropy argument to give an uncertainty inequality for the $q$-Bessel Fourier transform: $$ \mathcal{F}_{q,v}f(x)=c_{q,v}\int_{0}^{\infty}f(t)j_{v}(xt,q^{2})t^{2v +1}d_{q}t, $$ where $j_v(x,q)$ is the normalized Hahn-Exton $q$-Bessel function.
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arxiv:0707.1494
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STAR has measured a variety of strange particle species in p + p collisions at $\sqrt{s}$ = 200 GeV. These high statistics data are ideal for comparing to existing leading- and next-to-leading order perturbative QCD (pQCD) models. Next-to-leading (NLO) models have been successful in describing inclusive hadron production using parameterized fragmentation functions (FF) for quarks and gluons. However, in order to describe identied strange particle spectra at NLO, knowledge of flavor separated FF is essential. Such FF have recently been parameterized using data by the OPAL experiment and allow for the first time to perform NLO calculation for strange baryons. In fact, comparing the STAR Lambda data with these calculations allow to put a constraint on the gluon fragmentation function. We show that the Leading-order (LO) event generator PYTHIA has to be tuned significantly to reproduce the STAR identified strange particle data. In particular, it fails to describe the observed enhancement of baryon-to-meson ratio at intermediate pT (2-6 GeV/c). In heavy-ion (HI) collisions this observable has been extensively compared with models and shows a strong dependency on collision centrality or parton density. In the HI context the observed enhancement has been explained by recent approaches in terms of parton coalescense and recombination models.
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arxiv:0707.1508
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Fermilab operates the world's most intense antiproton source, now exclusively dedicated to serving the needs of the Tevatron Collider. The anticipated 2009 shutdown of the Tevatron presents the opportunity for a world-leading low- and medium-energy antiproton program. We summarize the status of the Fermilab antiproton facility and review physics topics for which a future experiment could make the world's best measurements.
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arxiv:0707.1543
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We study a class of flux compactifications that have all the moduli stabilised, a high (GUT) string scale and a low (TeV) gravitino mass that is generated dynamically. These non-geometric compactifications correspond to type II string theories on SU(3)xSU(3) structure orientifolds. The resulting superpotentials admit, excluding non-perturbative effects, supersymmetric Minkowski vacua with any number of moduli stabilised. We argue that non-perturbative effects are present and introduce terms in the superpotential that are exponentially suppressed by the same moduli that appear perturbatively. These deform the supersymmetric Minkowski vacua to supersymmetric AdS vacua with an exponentially small gravitino mass. The resulting vacua allow for low scale supersymmetry breaking which can be realised by a number of mechanisms.
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arxiv:0707.1595
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We first report a novel phenomenon that manifests itself in a colossal difference in soft x-ray reflectivity from ferromagnetic transition-metal films between the left- and right-handed circular polarization (LCP and RCP) modes at a resonance near normal Brewster's angle. Theoretical and numerical studies of sft x-ray resonant magnetic scattering using the circular-polarization-mode basis reveal that this effect arises from a totally destructive interference of photons scattered individually from chargem orbital, and spin degrees of freedom in magnetized thin films that selectively occurs only for one helicity of the opposite circular modes when the required criteria are fulfilled. Across the normal Brewster's angle. the polarization state of scattered soft x-ray is continuously variable from the RCP to the LCP mode (or vice versa) through the linear s polarization mode by changing the incidence angle of linear p-polarized x rays at the resonance.
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arxiv:0707.1627
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Analytic execution architectures have been proposed by the same authors as a means to conceptualize the cooperation between heterogeneous collectives of components such as programs, threads, states and services. Interface groups have been proposed as a means to formalize interface information concerning analytic execution architectures. These concepts are adapted to organization architectures with a focus on financial transfers. Interface groups (and monoids) now provide a technique to combine interface elements into interfaces with the flexibility to distinguish between directions of flow dependent on entity naming. The main principle exploiting interface groups is that when composing a closed system of a collection of interacting components, the sum of their interfaces must vanish in the interface group modulo reflection. This certainly matters for financial transfer interfaces. As an example of this, we specify an interface group and within it some specific interfaces concerning the financial transfer architecture for a part of our local academic organization. Financial transfer interface groups arise as a special case of more general service architecture interfaces.
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arxiv:0707.1639
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We present sensitive near-infrared spectroscopic observations for a sample of five z ~ 6 quasars. These are amongst the most distant, currently known quasars in the universe. The spectra have been obtained using ISAAC at the VLT and include the CIV, MgII and FeII lines. We measure the FeII/MgII line ratio, as an observational proxy for the Fe/alpha element ratio. We derive a ratio of 2.7+/-0.8 for our sample, which is similar to that found for lower redshift quasars, i.e., we provide additional evidence for the lack of evolution in the FeII/MgII line ratio of quasars up to the highest redshifts. This result demonstrates that the sample quasars must have undergone a major episode of iron enrichment in less than one Gyr and star formation must have commenced at z > 8. The linewidths of the MgII and CIV lines give two estimates for the black hole masses. A third estimate is given by assuming that the quasars emit at their Eddington luminosity. The derived masses using these three methods agree well, implying that the quasars are not likely to be strongly lensed. We derive central black hole masses of 0.3-5.2 10^9 solar masses. We use the difference between the redshift of MgII (a proxy for the systemic redshift of the quasar) and the onset of the Gunn Peterson trough to derive the extent of the ionized Stromgren spheres around our target quasars. The derived physical radii are about five Mpc. Using a simple ionization model, the emission of the central quasars would need of order 10^6-10^8 year to create these cavities in a surrounding intergalactic medium with a neutral fraction between 0.1 and 1.0. As the e-folding time scale for the central accreting black hole is on the order of a few times 10^7 year, it can grow by one e-folding or less within this time span.
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arxiv:0707.1662
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We obtain from the quark-gluon dynamics, the Gell'Mann-Ne'eman eightfold way baryons in an imaginary-time functional integral formulation of 3+1 lattice QCD in the strong coupling regime (small hopping parameter $\kappa>0$). The model has ${\rm SU}(3)_c$ gauge and global ${\rm SU}(3)_f$ flavor symmetries. In the subspace of the physical Hilbert space of vectors with an odd number of quarks, the baryons are associated with isolated dispersion curves in the energy-momentum spectrum. The spin 1/2 octet and spin 3/2 decuplet baryons have asymptotic mass $-3\ln\kappa$ and for each baryon there is an antibaryon with identical spectral properties. All the masses have the form $M=-3\ln\kappa-3\kappa^3/4+\kappa^6 r(\kappa)$, with $r(\kappa)$ real analytic. For each member of the octet $r(\kappa)$ is the same; for each member of the decuplet, $r(0)$ is the same. So, there is no mass splitting within the octet, and within the decuplet up to and including ${\cal O}(\kappa^6)$. However, there is an octet-decuplet mass difference of $3\kappa^6/4+{\cal O}(\kappa^7)$. The baryon and antibaryon spectrum is the only one up to near the meson-baryon threshold of nearly $-5\ln\kappa$. A decoupling of hyperplane method is used to naturally unveil the form of the baryon composite fields (no a priori guesswork), to show the existence of particles and their multiplicities using a spectral representation for the two-baryon correlation. We also obtain the (anti-)baryon dispersion curves which admit the representation $w(\kappa,\vec p)= -3\ln\kappa -3\kappa^3/4+\kappa^3\sum_{j=1,2,3} (1-\cos ^j)/4+r(\kappa,\vec p)$, where $r(\kappa,\vec p)$ is of ${\cal O}(\kappa^6)$.
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arxiv:0707.1677
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Macroscopic mechanical objects and electromagnetic degrees of freedom couple to each other via radiation pressure. Optomechanical systems with sufficiently strong coupling are predicted to exhibit quantum effects and are a topic of considerable interest. Devices reaching this regime would offer new types of control of the quantum state of both light and matter and would provide a new arena in which to explore the boundary between quantum and classical physics. Experiments to date have achieved sufficient optomechanical coupling to laser-cool mechanical devices but have not yet reached the quantum regime. The outstanding technical challenge in this field is integrating sensitive micromechanical elements (which must be small, light, and flexible) into high finesse cavities (which are typically much more rigid and massive) without compromising the mechanical or optical properties of either. A second, and more fundamental, challenge is to read out the mechanical element's quantum state: displacement measurements (no matter how sensitive) cannot determine the energy eigenstate of an oscillator, and measurements which couple to quantities other than displacement have been difficult to realize. Here we present a novel optomechanical system which seems to resolve both these challenges. We demonstrate a cavity which is detuned by the motion of a thin dielectric membrane placed between two macroscopic, rigid, high-finesse mirrors. This approach segregates optical and mechanical functionality to physically distinct structures and avoids compromising either. It also allows for direct measurement of the square of the membrane's displacement, and thus in principle the membrane's energy eigenstate. We estimate it should be practical to use this scheme to observe quantum jumps of a mechanical system.
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arxiv:0707.1724
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We discuss the ratio of the angular diameter distances from the source to the lens, $D_{ds}$, and to the observer at present, $D_{s}$, for various dark energy models. It is well known that the difference of $D_s$s between the models is apparent and this quantity is used for the analysis of Type Ia supernovae. However we investigate the difference between the ratio of the angular diameter distances for a cosmological constant, $(D_{ds}/D_{s})^{\Lambda}$ and that for other dark energy models, $(D_{ds}/D_{s})^{\rm{other}}$ in this paper. It has been known that there is lens model degeneracy in using strong gravitational lensing. Thus, we investigate the model independent observable quantity, Einstein radius ($\theta_E$), which is proportional to both $D_{ds}/D_s$ and velocity dispersion squared, $\sigma_v^2$. $D_{ds}/D_s$ values depend on the parameters of each dark energy model individually. However, $(D_{ds}/D_s)^{\Lambda} - (D_{ds}/D_{s})^{\rm{other}}$ for the various dark energy models, is well within the error of $\sigma_v$ for most of the parameter spaces of the dark energy models. Thus, a single strong gravitational lensing by use of the Einstein radius may not be a proper method to investigate the property of dark energy. However, better understanding to the mass profile of clusters in the future or other methods related to arc statistics rather than the distances may be used for constraints on dark energy.
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arxiv:0707.1730
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Two versions of a fast, purely reflective Paul-Baker type telescope are discussed, each with an 8.4-m aperture, 3 deg diameter flat field and f/1.25 focal ratio. The first version is based on a common, even asphere type of surface with zero conic constant. The primary and tertiary mirrors are 6th order aspheres, while the secondary mirror is an 8th order asphere (referred to here for brevity, as the 6/8/6 configuration). The D_80 diameter of a star image varies from 0''.18 on the optical axis up to 0''.27 at the edge of the field (9.3-13.5 mcm). The second version of the telescope is based on a polysag surface type which uses a polynomial expansion in the sag z, r^2 = 2R_0z - (1+b)z^2 + a_3 z^3 + a_4 z^4 + ... + a_N z^N, instead of the common form of an aspheric surface. This approach results in somewhat better images, with D_80 ranging from 0''.16 to 0''.23, using a lower-order 3/4/3 combination of powers for the mirror surfaces. An additional example with 3.5-m aperture, 3.5 deg diameter flat field, and f/1.25 focal ratio featuring near-diffraction-limited image quality is also presented.
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arxiv:0707.1731
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We present a technique for reconstructing a semi-infinite Jacobi operator in the limit circle case from the spectra of two different self-adjoint extensions. Moreover, we give necessary and sufficient conditions for two real sequences to be the spectra of two different self-adjoint extensions of a Jacobi operator in the limit circle case.
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arxiv:0707.1732
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The one-dimensional Ginzburg-Landau (GL) Equation is considered. We use the recently developed extended F-expansion method to obtain spiral wave solution of one-dimensional GL Equation.
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arxiv:0707.1736
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Bipolaron formation in a two-dimensional lattice with harmonic confinement, representing a simplified model for a quantum dot, is investigated by means of quantum Monte Carlo simulations. This method treats all interactions exactly and takes into account quantum lattice fluctuations. Calculations of the bipolaron binding energy reveal that confinement opposes bipolaron formation for weak electron-phonon coupling, but abets a bound state at intermediate to strong coupling. Tuning the system from weak to strong confinement gives rise to a small reduction of the minimum Frohlich coupling parameter for the existence of a bound state.
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arxiv:0707.1770
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In this paper we consider supercritical nonlinear Schr\"odinger equations in an analytic Riemannian manifold $(M^d,g)$, where the metric $g$ is analytic. Using an analytic WKB method, we are able to construct an Ansatz for the semiclassical equation for times independent of the small parameter. These approximate solutions will help to show two different types of instabilities. The first is in the energy space, and the second is an immediate loss of regularity in higher Sobolev norms.
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arxiv:0707.1785
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We prove the existence of a positive radial solution for the H\'enon equation with arbitrary growth. The solution is found by means of a shooting method and turns out to be an increasing function of the radial variable. Some numerical experiments suggest the existence of many positive oscillating solutions.
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arxiv:0707.1790
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The conductivity of graphene samples with various levels of disorder is investigated for a set of specimens with mobility in the range of $1-20\times10^3$ cm$^2$/V sec. Comparing the experimental data with the theoretical transport calculations based on charged impurity scattering, we estimate that the impurity concentration in the samples varies from $2-15\times 10^{11}$ cm$^{-2}$. In the low carrier density limit, the conductivity exhibits values in the range of $2-12e^2/h$, which can be related to the residual density induced by the inhomogeneous charge distribution in the samples. The shape of the conductivity curves indicates that high mobility samples contain some short range disorder whereas low mobility samples are dominated by long range scatterers.
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arxiv:0707.1807
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The low-temperature (up to about 100K) collisional (de)excitation cross sections are computed using the full coupled-channel (CC) quantum dynamics for both Li$_2$ and Li$_2^+$ molecular targets in collision with $^4$He. The interaction forces are obtained from fairly accurate {\it ab initio} calculations and the corresponding pseudo-rates are also computed. The results show surprising similarities between sizes of inelastic flux distributions within final states in both systems and the findings are connected with the structural change in the molecular rotor features when the neutral species is replaced by its ionic counterpart.
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arxiv:0707.1832
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We present a review of the field of formaldehyde (H2CO) 6cm masers in the Galaxy. Previous to our ongoing work, H2CO 6cm masers had been detected in the Galaxy only toward three regions: NGC7538 IRS1, Sgr B2, and G29.96-0.02. Current efforts by our group using the Very Large Array, Arecibo, and the Green Bank Telescope have resulted in the detection of four new H2CO 6cm maser regions. We discuss the characteristics of the known H2CO masers and the association of H2CO 6cm masers with very young regions of massive star formation. We also review the current ideas on the pumping mechanism for H2CO 6cm masers.
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arxiv:0707.1841
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We present observations and analysis of the first reported superoutburst of the dwarf nova SDSSp J082409.73+493124.4 during February/March 2007. From a maximum observed magnitude of 15.4C it declined at 0.09 mag/d for 7 days, flattened out around magnitude 16 for a further 5 days and then returned rapidly to quiescence at magnitude 19.4. The flattening of the light curve late in the outburst was not associated with a re-growth of superhumps. For the first 5 days we observed common superhumps with period 0.06954(5) d, thus confirming its classification as a UGSU-type dwarf nova. This was followed by a phase transition to late superhumps with period 0.06921(6) d. We found a small but persistent signal at 0.0687(6) d which we interpret as the orbital period.
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arxiv:0707.1865
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We present analysis of Chandra and XMM-Newton observations of three early-type galaxies, NGC 57, NGC 7796 and IC 1531. All three are found in very low density environments, and appear to have no neighbours of comparable size. NGC 57 has a halo of kT~0.9 keV, solar metallicity gas, while NGC 7796 and IC 1531 both have ~0.55 keV, 0.5-0.6 Zsol haloes. IC 1531 has a relatively compact halo, and we consider it likely that gas has been removed from the system by the effects of AGN heating. For NGC 57 and NGC 7796 we estimate mass, entropy and cooling time profiles and find that NGC 57 has a fairly massive dark halo with a mass-to-light ratio of 44.7 (4.0,-8.5) Msol/Lsol (1 sigma uncertainties) at 4.75 Re. This is very similar to the mass-to-light ratio found for NGC 4555 and confirms that isolated ellipticals can possess sizable dark matter haloes. We find a significantly lower mass-to-light ratio for NGC 7796, 10.6 (+2.5,-2.3) Msol/Lsol at 5 Re, and discuss the possibility that NGC 7796 hosts a galactic wind, causing us to underestimate its mass.
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arxiv:0707.1879
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Ages, metallicities, space velocities, and Galactic orbits of stars in the Solar neighbourhood are fundamental observational constraints on models of galactic disk evolution. We aim to consolidate the calibrations of uvby photometry into Te, [Fe/H], distance, and age for F and G stars and rediscuss the results of the Geneva-Copenhagen Survey (Nordstrom et al. 2004; GCS) in terms of the evolution of the disk. We substantially improve the Te and [Fe/H] calibrations for early F stars, where spectroscopic temperatures have large systematic errors. Our recomputed ages are in excellent agreement with the independent determinations by Takeda et al. (2007), indicating that isochrone ages can now be reliably determined. The revised G-dwarf metallicity distribution remains incompatible with closed-box models, and the age-metallicity relation for the thin disk remains almost flat, with large and real scatter at all ages (sigma intrinsic = 0.20 dex). Dynamical heating of the thin disk continues throughout its life; specific in-plane dynamical effects dominate the evolution of the U and V velocities, while the W velocities remain random at all ages. When assigning thick and thin-disk membership for stars from kinematic criteria, parameters for the oldest stars should be used to characterise the thin disk.
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arxiv:0707.1891
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Although both systems analyzed are described through two theories apparently different (quantum mechanics and game theory) it is shown that both are analogous and thus exactly equivalents. The quantum analogue of the replicator dynamics is the von Neumann equation. Quantum mechanics could be used to explain more correctly biological and economical processes. It could even encloses theories like games and evolutionary dynamics. We can take some concepts and definitions from quantum mechanics and physics for the best understanding of the behavior of economics and biology. Also, we could maybe understand nature like a game in where its players compete for a common welfare and the equilibrium of the system that they are members. All the members of our system will play a game in which its maximum payoff is the equilibrium of the system. They act as a whole besides individuals like they obey a rule in where they prefer to work for the welfare of the collective besides the individual welfare. A system where its members are in Nash Equilibrium (or ESS) is exactly equivalent to a system in a maximum entropy state. A system is stable only if it maximizes the welfare of the collective above the welfare of the individual. If it is maximized the welfare of the individual above the welfare of the collective the system gets unstable an eventually collapses. The results of this work shows that the "globalization" process has a behavior exactly equivalent to a system that is tending to a maximum entropy state and predicts the apparition of big common markets and strong common currencies that will find its "equilibrium" by decreasing its number until they get a state characterized by only one common currency and only one common market around the world.
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arxiv:0707.1897
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The gradual fall of the shear viscosity below 2.8K, observed in a liquid helium 4 flowing through a capillary, is examined. The disappearance of the shear viscosity in a capillary flow is a manifestation of superfluidity in dissipative phenomena, the onset mechanism of which is a subtle problem compared to that of superfluidity in non-dissipative phenomena. Applying the linear-response theory to the reciprocal of the shear viscosity coefficient, we relate these two types of superfluidity using the Kramers-Kronig relation. We obtain a formula describing the influence of Bose statistics on the kinematic shear viscosity in terms of the susceptibility. Compared to an ordinary liquid, a liquid helium 4 above the lambda point has a 1/1000 times smaller shear viscosity coefficient. Hence, although in the normal phase, it is already an anomalous liquid under the strong influence of Bose statistics. The coherent many-body wave function grows to an intermediate size between a macroscopic and a microscopic one, not as a thermal fluctuation but as a thermal equilibrium state. Beginning with bosons without the condensate, we make a perturbation calculation of its susceptibility with respect to the repulsive interaction. We examine how, with decreasing temperature, the growth of the coherent wave function gradually suppresses the shear viscosity, and finally leads to a frictionless flow at the lambda-point.
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arxiv:0707.1931
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We carry out numerical investigations of the perturbations in Nflation models where the mass spectrum is generated by random matrix theory. The tensor-to-scalar ratio and non-gaussianity are already known to take the single-field values, and so the density perturbation spectral index is the main parameter of interest. We study several types of random field initial conditions, and compute the spectral index as a function of mass spectrum parameters. Comparison with microwave anisotropy data from the Wilkinson Microwave Anisotropy Probe shows that the model is currently viable in the majority of its parameter space.
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arxiv:0707.1982
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Two nights of phase-resolved medium resolution VLT spectroscopy of the extra-galactic low mass X-ray binary LMC X-2 have revealed a 0.32+/-0.02 day spectroscopic period in the radial velocity curve of the HeII lambda4686 emission line that we interpret as the orbital period. However, similar to previous findings, this radial velocity curve shows a longer term variation that is most likely due to the presence of a precessing accretion disk in LMC X-2. This is strengthened by HeII lambda4686 Doppler maps that show a bright spot that is moving from night to night. Furthermore, we detect narrow emission lines in the Bowen region of LMC X-2,with a velocity of K_em=351+/-28 km/s, that we tentatively interpret as coming from the irradiated side of the donor star. Since K_em must be smaller than K_2, this leads to the first upper-limit on the mass function of LMC X-2 of f(M_1)>=0.86Msun (95% confidence), and the first constraints on its system parameters.
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arxiv:0707.2018
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We show that one can cool a micro-mechanical oscillator to its quantum ground state using radiation pressure in an appropriately detuned cavity (self-cooling). From a simple theory based on Heisenberg-Langevin equations we find that optimal self-cooling occurs in the good cavity regime, when the cavity bandwidth is smaller than the mechanical frequency, but still larger than the effective mechanical damping. In this case the intracavity field and the vibrational mechanical mode coherently exchange their fluctuations. We also present dynamical calculations which show how to access the mirror final temperature from the fluctuations of the field reflected by the cavity.
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arxiv:0707.2038
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The DGLAP improved color dipole approach provides a good description of data for inclusive direct photon spectra at the energies of RHIC and Tevatron. Within the same framework we predict the transverse momentum distribution of direct photons at the CERN LHC energies.
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arxiv:0707.2040
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We analyze the deviations of the mixing induced CP asymmetry in B-->phi Ks from sin(2beta), as well as the deviations of the asymmetries in Bs-->K*K*, Bs-->phi K* and Bs-->phi phi from sin(2beta_s), that arise in SM due to penguin pollution. We use a theoretical input which is short-distance dominated in QCD-factorization and thus free of IR-divergencies. We also provide alternative ways to extract angles of the unitarity triangle from penguin-mediated decays, and give predictions for Bs-->K*K* observables.
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arxiv:0707.2046
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Successful modern generalized gradient approximations (GGA) are biased toward atomic energies. Restoration of the first-principles gradient expansion for the exchange energy over a wide range of density gradients eliminates this bias. We introduce PBEsol, a revised Perdew-Burke-Ernzerhof GGA that improves equilibrium properties for many densely-packed solids and their surfaces.
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arxiv:0707.2088
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Single photons detected by the DELPHI experiment at LEP2 in the years 1997-2000 are used to investigate the existence of a single extra dimension in a modifed ADD scenario with slightly warped large extra dimensions. The data collected at centre-of-mass energies between 180 and 209 GeV for an integrated luminosity of ~650 pb^-1 agree with the predictions of the Standard Model and allow a limit to be set on graviton emission in one large extra dimension. The limit obtained on the fundamental mass scale MD is 1.69 TeV at 95% CL, with an expected limit of 1.71 TeV.
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arxiv:0707.2102
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We study nonlinear response of a spin $S>1/2$ with easy-axis anisotropy. The response displays sharp dips or peaks when the modulation frequency is adiabatically swept through multiphoton resonance. The effect is a consequence of a special symmetry of the spin dynamics in a magnetic field for the anisotropy energy $\propto S_z^2$. The occurrence of the dips or peaks is determined by the spin state. Their shape strongly depends on the modulation amplitude. Higher-order anisotropy breaks the symmetry, leading to sharp steps in the response as function of frequency. The results bear on the dynamics of molecular magnets in a static magnetic field.
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arxiv:0707.2107
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In this paper we show that we can use a modified version of the h-p spectral element method proposed in \cite{duttora1,duttom,duttora2,tomarth} to solve elliptic problems with general boundary conditions to exponential accuracy on polygonal domains using nonconforming spectral element functions. A geometrical mesh is used in a neighbourhood of the corners. With this mesh we seek a solution which minimizes the sum of a weighted squared norm of the residuals in the partial differential equation and the squared norm of the residuals in the boundary conditions in fractional Sobolev spaces and enforce continuity by adding a term which measures the jump in the function and its derivatives at inter-element boundaries, in fractional Sobolev norms, to the functional being minimized. In the neighbourhood of the corners, modified polar coordinates are used and a global coordinate system elsewhere. A stability estimate is derived for the functional which is minimized based on the regularity estimate in \cite{babguo1}. We examine how to parallelize the method and show that the set of common boundary values consists of the values of the function at the corners of the polygonal domain. The method is faster than that proposed in \cite{duttora1,duttom,tomarth} and the h-p finite element method and stronger error estimates are obtained.
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arxiv:0707.2135
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Let $R$ be a local ring and let ($x_1\biss x_r$) be part of a system of parameters of a finitely generated $R$-module $M,$ where $r < \dim_R M$. We will show that if ($y_1\biss y_r$) is part of a reducing system of parameters of $M$ with $(y_1\biss y_r)M=(x_1\biss x_r)M$ then $(x_1\biss x_r)$ is already reducing. Moreover, there is such a part of a reducing system of parameters of $M$ iff for all primes $P\in \supp M \cap V_R(x_1\biss x_r)$ with $\dim_R R/P = \dim_R M -r$ the localization $M_P$ of $M$ at $P$ is an $r$-dimensional \cm\ module over $R_P$. Furthermore, we will show that $M$ is a \cm module iff $y_d$ is a non zero divisor on $M/(y_1\biss y_{d-1})M$, where $(y_1\biss y_d)$ is a reducing system of parameters of $M$ ($d := \dim_R M$).
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arxiv:0707.2136
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The effective evolution of an inhomogeneous universe model in any theory of gravitation may be described in terms of spatially averaged variables. In Einstein's theory, restricting attention to scalar variables, this evolution can be modeled by solutions of a set of Friedmann equations for an effective volume scale factor, with matter and backreaction source terms. The latter can be represented by an effective scalar field (`morphon field') modeling Dark Energy. The present work provides an overview over the Dark Energy debate in connection with the impact of inhomogeneities, and formulates strategies for a comprehensive quantitative evaluation of backreaction effects both in theoretical and observational cosmology. We recall the basic steps of a description of backreaction effects in relativistic cosmology that lead to refurnishing the standard cosmological equations, but also lay down a number of challenges and unresolved issues in connection with their observational interpretation. The present status of this subject is intermediate: we have a good qualitative understanding of backreaction effects pointing to a global instability of the standard model of cosmology; exact solutions and perturbative results modeling this instability lie in the right sector to explain Dark Energy from inhomogeneities. It is fair to say that, even if backreaction effects turn out to be less important than anticipated by some researchers, the concordance high-precision cosmology, the architecture of current N-body simulations, as well as standard perturbative approaches may all fall short in correctly describing the Late Universe.
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arxiv:0707.2153
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We construct many new cyclic (v;r,s;lambda) difference families with v less than or equal 50. In particular we construct the difference families with parameters (45;18,10;9), (45;22,22;21), (47;21,12;12), (47;19,15;12), (47;22,14;14), (48;20,10;10), (48;24,4;12), (50;25,20;20) for which the existence question was an open problem. The (45;22,22;21) difference family gives a BIBD with parameters v=45, b=90, r=44, k=22 and lambda=21, and the one with parameters (50;25,20;20) gives a pair of binary sequences of length 50 with zero periodic autocorrelation function (the periodic analog of a Golay pair). We also construct nine new D-optimal designs. A normal form for cyclic difference families is proposed and used effectively in compiling the list of known and new difference families.
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arxiv:0707.2173
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We prove that for a large class of vorticity functions the crest of a corresponding travelling water wave is necessarily a point of maximal horizontal velocity. We also show that for waves with nonpositive vorticity the pressure in the flow is everywhere larger than the atmospheric pressure. A related a priori estimate for waves with nonnegative vorticity is also given.
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arxiv:0707.2221
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A spherical wrist of the serial type with n revolute (R) joints is said to be isotropic if it can attain a posture whereby the singular values of its Jacobian matrix are all equal to sqrt(n/3). What isotropy brings about is robustness to manufacturing, assembly, and measurement errors, thereby guaranteeing a maximum orientation accuracy. In this paper we investigate the existence of redundant isotropic architectures, which should add to the dexterity of the wrist under design by virtue of its extra degree of freedom. The problem formulation, for, leads to a system of eight quadratic equations with eight unknowns. The Bezout number of this system is thus 2^8=256, its BKK bound being 192. However, the actual number of solutions is shown to be 32. We list all solutions of the foregoing algebraic problem. All these solutions are real, but distinct solutions do not necessarily lead to distinct manipulators. Upon discarding those algebraic solutions that yield no new wrists, we end up with exactly eight distinct architectures, the eight corresponding manipulators being displayed at their isotropic postures.
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arxiv:0707.2229
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Talk based on work entitled ``Yukawa textures, new physics and nondecoupling,'' done in collaboration with G. C. Branco and J. I. Silva-Marcos, arXiv:hep-ph/0612252, to appear in Phys. Rev. D. In this work we pointed out that New Physics can play an important r\^ ole in rescuing some of the Yukawa texture zero ans\" atze which would otherwise be eliminated by the recent, more precise measurements of $V_{CKM}$. We have shown that the presence of an isosinglet vector-like quark which mixes with standard quarks, can render viable a particularly interesting four texture zero Yukawa ansatz. The crucial point is the nondecoupling of the effects of the isosinglet quark, even for arbitrary large values of its mass.
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arxiv:0707.2233
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Previously derived expressions for the characteristic function of work performed on a quantum system by a classical external force are generalized to arbitrary initial states of the considered system and to Hamiltonians with degenerate spectra. In the particular case of microcanonical initial states explicit expressions for the characteristic function and the corresponding probability density of work are formulated. Their classical limit as well as their relations to the respective canonical expressions are discussed. A fluctuation theorem is derived that expresses the ratio of probabilities of work for a process and its time reversal to the ratio of densities of states of the microcanonical equilibrium systems with corresponding initial and final Hamiltonians.From this Crooks-type fluctuation theorem a relation between entropies of different systems can be derived which does not involve the time reversed process. This entropy-from-work theorem provides an experimentally accessible way to measure entropies.
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arxiv:0707.2307
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I emphasize in this contribution how prompt photons can be used to probe nuclear parton densities as well as medium-modified fragmentation functions in heavy ion collisions. Various predictions in p-A and A-A collisions at LHC energies are given.
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arxiv:0707.2320
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In this note we define Chern-Simons classes of a superconnection $D+L$ on a complex supervector bundle $E$ such that $D$ is flat and preserves the grading, and $L$ is an odd endomorphism of $E$ on a supermanifold. As an application we obtain a definition of Chern-Simons classes of a (not necessarily flat) morphism between flat vector bundles on a smooth manifold. We extend Reznikov's theorem on triviality of these classes when the manifold is a compact K\"ahler manifold or a smooth complex quasi--projective variety, in degrees > 1.
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arxiv:0707.2321
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We show that Selberg's eigenvalue conjecture concerning small eigenvalues of the automorphic Laplacian for congruence groups is equivalent to a conjecture about the non-existence of residual eigenvalues for a perturbed system. We prove this using a combination of methods from asymptotic perturbation theory and number theory.
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arxiv:0707.2332
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We propose several new schedules for Strassen-Winograd's matrix multiplication algorithm, they reduce the extra memory allocation requirements by three different means: by introducing a few pre-additions, by overwriting the input matrices, or by using a first recursive level of classical multiplication. In particular, we show two fully in-place schedules: one having the same number of operations, if the input matrices can be overwritten; the other one, slightly increasing the constant of the leading term of the complexity, if the input matrices are read-only. Many of these schedules have been found by an implementation of an exhaustive search algorithm based on a pebble game.
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arxiv:0707.2347
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We have searched for exclusive 2-photon production in proton-antiproton collisions at sqrt{s} = 1.96 TeV, using 532/pb of integrated luminosity taken by the Run II Collider Detector at Fermilab. The event signature requires two electromagnetic showers, each with transverse energy E_T > 5 GeV and pseudorapidity |eta|<1.0, with no other particles detected in the event. Three candidate events are observed. We discuss the consistency of the three events with gamma-gamma, pi0-pi0, or eta-eta production. The probability that other processes fluctuate to 3 events or more is 1.7x10^-4. An upper limit on the cross section of p+pbar --> p+gamma-gamma+pbar is set at 410 fb with 95% confidence level.
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arxiv:0707.2374
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Current steps in the current-voltage characteristics of wide superconducting Sn films exposed to a microwave irradiation were observed in the resistive state with phase slip lines. The behaviour of the magnitude of the steps on the applied irradiation power was found to be similar to that for the current steps in narrow superconducting channels with phase slip centers and, to some extent, for the Shapiro steps in Josephson junctions. This provides evidence for the Josephson properties of the phase slip lines in wide superconducting films and supports the assumption about similarity between the processes of phase slip in wide and narrow films.
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arxiv:0707.2381
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For the toric variety X associated to the Bruhat poset of Schubert varieties in a minuscule G/P, we describe the singular locus in terms of the faces of the associated polyhedral cone. We further show that the singular locus is pure of codimension 3 in X.
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arxiv:0707.2392
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Using the relativistic electrodynamics of continuous media formalism and main relativistic quantum field theory principles the covariant Lagrangian of electromagnetic field interaction with polarizable 1/2-spin particles have been obtained. This Lagrangian let us to determine canonical and metric energy-momentum tensors as well as low-energy Compton scattering amplitude. The application of this Lagrangian for the calculation of the radiative correction to the imaginary part of double virtual Compton scattering is demonstrated.
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arxiv:0707.2395
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We introduce a method based on the loudest event statistic to calculate an upper limit or interval on the astrophysical rate of binary coalescence. The calculation depends upon the sensitivity and noise background of the detectors, and a model for the astrophysical distribution of coalescing binaries. There are significant uncertainties in the calculation of the rate due to both astrophysical and instrumental uncertainties as well as errors introduced by using the post--Newtonian waveform to approximate the full signal. We catalog these uncertainties in detail and describe a method for marginalizing over them. Throughout, we provide an example based on the initial LIGO detectors.
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arxiv:0707.2410
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We construct a sequence of functions that uniformly converge (on compact sets) to the price of Asian option, which is written on a stock whose dynamics follows a jump diffusion, exponentially fast. Each of the element in this sequence solves a parabolic partial differen- tial equation (not an integro-differential equation). As a result we obtain a fast numerical approximation scheme whose accuracy versus speed characteristics can be controlled. We analyze the performance of our numerical algorithm on several examples.
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arxiv:0707.2432
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A combined experimental and numerical study of the boundary layer in a 4:1 aspect-ratio Rayleigh-B\'{e}nard cell over a four-decade range of Rayleigh numbers has been undertaken aimed at gaining a better insight into the character of the boundary layers. The experiments involved the simultaneous Laser Doppler Anemometry (LDA) measurements of fluid velocity at two locations, i.e. in the boundary layer and far away from it in the bulk, for Rayleigh numbers varying between $1.6 \times 10^7$ and $2.4 \times 10^9$. In parallel, direct numerical simulations (DNS) have been performed for the same configuration for Rayleigh numbers between $7.0 \times 10^4$ and $7.7 \times 10^7$. The temperature and velocity probability density functions and the power spectra of the horizontal velocity fluctuations measured in the boundary layer and in the bulk flow are found to be practically identical. Except for the smallest Rayleigh numbers, the spectra in the boundary layer and in the bulk central region are continuous and have a wide range of active scales. This indicates that both the bulk and the boundary layers are turbulent in the $\textrm{Ra}$ number range considered. However, molecular effects can still be observed and the boundary layer does not behave like a classical shear-driven turbulent boundary layer.
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arxiv:0707.2485
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We study the triple differential distribution of B-> Xu l nu, consistently including all perturbative and non-perturbative effects through O(alphas^2 beta_0) and O(1/mb^3). The Fermi motion is parameterized in terms of a single light-cone function for each structure function and for any value of q^2, accounting for all subleading effects. We discuss the problems and uncertainties related to the high-q^2 tail and to Weak Annihilation effects. We work in the kinetic scheme, a framework characterized by a Wilsonian treatment with a hard cutoff mu ~ 1GeV. Our method is illustrated with the extraction of |V_ub| from some of the latest experimental data, providing a detailed estimate of the theoretical uncertainty.
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arxiv:0707.2493
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In double quantum dots, the exchange interaction between two electron spins renormalizes the excitation energy of pair-flips in the nuclear spin bath, which in turn modifies the non-Markovian bath dynamics. As the energy renormalization varies with the Overhauser field mismatch between the quantum dots, the electron singlet-triplet decoherence resulting from the bath dynamics depends on sampling of nuclear spin states from an ensemble, leading to the transition from exponential decoherence in single-sample dynamics to power-law decay under ensemble averaging. In contrast, the decoherence of a single electron spin in one dot is essentially the same for different choices of the nuclear spin configuration.
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arxiv:0707.2529
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In this paper we will introduce a certain type of morphisms of log schemes (in the sense of Fontaine, Illusie, and Kato) and investigate their moduli. Then by applying this we define a notion of toric algebraic stacks over arbitrary schemes, which may be regarded as torus embeddings within the framework of algebraic stacks, and study some basic properties. Furthermore, we study the stack-theoretic analogue of toroidal embeddings.
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arxiv:0707.2568
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The most general covariant gauge fixing Lagrangian is considered for a spin-two gauge theory in the context of the Faddeev-Popov procedure. In general, five parameters characterize this gauge fixing. Certain limiting values for these parameters give rise to a spin-two propagator that is either traceless or transverse, but for no values of these parameters is this propagator simultaneously traceless and transverse. Having a traceless-transverse (TT) propagator ensures that only the physical degrees of freedom associated with the tensor field propagate, and hence it is analogous to the Landau gauge in electrodynamics. To obtain such a traceless-transverse propagator, a gauge fixing Lagrangian which is not quadratic must be employed; this sort of gauge fixing Lagrangian is not encountered in the usual Faddeev-Popov procedure. It is shown that when this non-quadratic gauge fixing Lagrangian is used, two Fermionic and one Bosonic ghost arise. As a simple application we discuss the energy-momentum tensor of the gravitational field at finite temperature.
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arxiv:0707.2590
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The spontaneous excitation of a two-level atom held static outside a four dimensional Schwarzschild black hole and in interaction with a massless scalar field in the Boulware, Unruh and Hartle-Hawking vacuum is investigated and the contributions of the vacuum fluctuations and radiation reaction to the rate of change of the mean atomic energy are calculated separately. We find that for the Boulware vacuum, the spontaneous excitation does not occur and the ground state atoms are stable, while the spontaneous emission rate for excited atoms in the Boulware vacuum, which is well-behaved at the event horizon, is not the same as that in the usual Minkowski vacuum. However, both for the Unruh vacuum and the Hartle-Hawking vacuum, our results show that the atom would spontaneously excite, as if there were an outgoing thermal flux of radiation or as if it were in a thermal bath of radiation at a proper temperature which reduces to the Hawking temperature in the spatial asymptotic region, depending on whether the scalar field is in the Unruh or Hartle-Hawking vacuum.
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arxiv:0707.2613
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