Search

We present and discuss new determinations of metallicity, rotation, age, kinematics, and Galactic orbits for a complete, magnitude-limited, and kinematically unbiased sample of 16,682 nearby F and G dwarf stars. Our 63,000 new, accurate radial-velocity observations for nearly 13,500 stars allow identification of most of the binary stars in the sample and, together with published data complete the kinematic information for 14,139 stars. A major effort has been devoted to the determination of new isochrone ages for all stars for which this is possible. Particular attention has been given to a realistic treatment of statistical biases and error estimates, as standard techniques tend to underestimate these effects and introduce spurious features in the age distributions. We demonstrate, however, how strong observational and theoretical biases cause the distribution of the observed ages to be very different from that of the true age distribution of the sample. Our first results confirm the lack of metal-poor G dwarfs relative to closed-box model predictions (the ``G dwarf problem''), the existence of radial metallicity gradients in the disk, the small change in mean metallicity of the thin disk since its formation and the substantial scatter in metallicity at all ages, and the continuing kinematic heating of the thin disk with an efficiency consistent with that expected for a combination of spiral arms and giant molecular clouds. Distinct features in the distribution of the V component of the space motion are extended in age and metallicity, corresponding to the effects of stochastic spiral waves rather than classical moving groups, and may complicate the identification of thick-disk stars from kinematic criteria. (abridged), Comment: 33 pages, 32 figures

This report documents the results obtained by the Working Group on Quantum Chromodynamics and the Standard Model for the Workshop `Physics at TeV Colliders'', Les Houches, France, 26 May - 6 June 2003. After a Monte Guide description, the first contributions report on progress in describing multiple interactions, important for the LHC, and underlying events. An announcement of a Monte Carlo database, under construction, is then followed by a number of contributions improving parton shower descriptions. Subsequently, a large number of contributions address resummations in various forms, after which follow studies of QCD effects in pion pair, top quark pair and photon pair plus jet production. After a study of electroweak corrections to hadronic precision observables, the report ends by presenting recent progress in methods to compute finite order corrections at one-loop with many legs, and at two-loop., Comment: 119pp

We show that, provided one focuses on properly selected episodes, one can apply to the social sciences the same observational strategy that has proved successful in natural sciences such as astrophysics or geodynamics. For instance, in order to probe the cohesion of a policy, one can, in different countries, study the reactions to some huge and sudden exogenous shocks, which we call Dirac shocks. This approach naturally leads to the notion of structural (as opposed or complementary to temporal) forecast. Although structural predictions are by far the most common way to test theories in the natural sciences, they have been much less used in the social sciences. The Dirac shock approach opens the way to testing structural predictions in the social sciences. The examples reported here suggest that critical events are able to reveal pre-existing ``cracks'' because they probe the social cohesion which is an indicator and predictor of future evolution of the system, and in some cases foreshadows a bifurcation. We complement our empirical work with numerical simulations of the response function (``damage spreading'') to Dirac shocks in the Sznajd model of consensus build-up. We quantify the slow relaxation of the difference between perturbed and unperturbed systems, the conditions under which the consensus is modified by the shock and the large variability from one realization to another.

A second workshop on small x physics, within the Small x Collaboration, was held in Lund in June 2002 with the aim of over-viewing recent theoretical progress in this area and summarizing the experimental status. This paper is dedicated to the memory of Jan Kwiecinski, who died unexpectedly on August 29, 2003., Comment: 32 pages, 33 figures

The oxidation of the Pd(100) surface at oxygen pressures in the 10^-6 to 10^3 mbar range and temperatures up to 1000 K has been studied in-situ by surface x-ray diffraction (SXRD). The results provide direct structural information on the phases present in the surface region and on the kinetics of the oxide formation. Depending on the (T,p) environmental conditions we either observe a thin sqrt(5) x sqrt(5) R27 surface oxide or the growth of a rough, poorly ordered bulk oxide film of PdO predominantly with (001) orientation. By either comparison to the surface phase diagram from first-principles atomistic thermodynamics or by explicit time-resolved measurements we identify a strong kinetic hindrance to the bulk oxide formation even at temperatures as high as 675 K., Comment: 4 pages including 4 figures, Related publications can be found at http://www.fhi-berlin.mpg.de/th/paper.html

Using a recently introduced rational expectation model of bubbles, based on the interplay between stochasticity and positive feedbacks of prices on returns and volatility, we develop a new methodology to test how this model classifies 9 time series that have been previously considered as bubbles ending in crashes. The model predicts the existence of two anomalous behaviors occurring simultaneously: (i) super-exponential price growth and (ii) volatility growth, that we refer to as the ``fearful singular bubble'' regime. Out of the 9 time series, we find that 5 pass our tests and can be characterized as ``fearful singular bubbles.'' The 4 other cases are the information technology Nasdaq bubble and three bubbles of the Hang Seng index ending in crashes in 1987, 1994 and 1997. According to our analysis, these four bubbles have developed with essentially no significant increase of their volatility. This paper thus proposes that speculative bubbles ending in crashes form two groups hitherto unrecognized, namely those accompanied by increasing volatility (reflecting increasing risk perception) and those without change of volatility (reflecting an absence of risk perception)., Comment: 12 pages + 9 figures + 9 tables

In the framework of an ESO Large Programme high quality spectra of 70 very metal-poor dwarfs and giants were obtained with the VLT-UVES combination. This paper reports the detailed analyses of the 35 giants of the sample. At the exception of a few template stars, all the targets are from the H&K Beers et al. survey. No less than 22 stars have [Fe/H] below -3.0. The imprint of yields of the first galactic or protogalactic supernovae is sampled in the photospheres of these stars. If [C/Fe], [Na/Fe] and [Al/Fe] show a spread significantly above the observational scatter, several abundance ratios present an amazing low scatter when plotted against [Fe/H], as [Cr/Fe] but also odd elements, as [K/Fe] or [Sc/Fe]. The abundance of oxygen has been derived from the [O I] line for 16 of these giants, in spite of the extreme weakness of the line. No significant slope with [Fe/H] is found. Similar plots have been made using Mg instead of Fe as reference element. With Mg, no clear trend with metallicity is obvious below [Mg/H]=-3., except perhaps for [Zn/Mg]. It is contemplated that the mild slope found in the very low scatter diagram [Cr/Fe] versus [Fe/H] might be spurious due for example to the LTE approximation plus use of 1-D models. This would relax the absence of scatter in the dilution of the SN ejectas within the ambient medium, as needed if [Fe/H] is a well defined function of [Cr/Fe]., Comment: 29 pages, 15 figures, 11 tables, LateX, aa.cls macros, accepted in A&A

We present an abundance analysis of the very metal-poor, carbon-enhanced star CS 29497-030. Our results indicate that this unusually hot turnoff star (Teff = 6650K, log g = 3.5) has a metallicity [Fe/H] = -2.8, and exhibits large overabundances of carbon ([C/Fe] = +2.38), nitrogen ([N/Fe]= +1.88), and oxygen ([O/Fe]= +1.67). This star also exhibits a large enhancement in its neutron-capture elements; the pattern follows that expected to arise from the s-process. In particular, the Pb abundance is found to be very high with respect to iron ([Pb/Fe]= +3.5), and also with respect to the second peak s-process elements (e.g., Ba, La, Ce, Nd), which fits into the newly introduced classification of lead (Pb) stars. The known spectroscopic binary status of this star, along with the observed s-process abundance pattern, suggest that it has accreted matter from a companion, which formerly was an Asymptotic Giant-Branch(AGB) star. In a preliminary analysis, we have also identified broad absorption lines of metallic species that suggest a large axial rotational velocity for this star, which may be the result of spin-up associated with the accretion of material from its previous AGB companion. In addition, this star is clearly depleted in the light element Li. When considered along with its rather high inferred temperature, these observations are consistent with the expected properties of a very low metallicity halo blue straggler., Comment: A&A accepted

In a previous work [Helmstetter, 2003], we have proposed a simple physical model to explain the accelerating displacements preceding some catastrophic landslides, based on a slider-block model with a state and velocity dependent friction law. This model predicts two regimes of sliding, stable and unstable leading to a critical finite-time singularity. This model was calibrated quantitatively to the displacement and velocity data preceding two landslides, Vaiont (Italian Alps) and La Clapi\`ere (French Alps), showing that the former (resp. later) landslide is in the unstable (resp. stable) sliding regime. Here, we test the predictive skills of the state-and-velocity-dependent model on these two landslides, using a variety of techniques. For the Vaiont landslide, our model provides good predictions of the critical time of failure up to 20 days before the collapse. Tests are also presented on the predictability of the time of the change of regime for la Clapi\`ere landslide., Comment: 30 pages with 12 eps figures

Combining high-resolution core-level spectroscopy (HRCLS), scanning tunneling microscopy (STM) and density-functional theory (DFT) calculations we reanalyze the Pd(100)-(SQRT(5) x SQRT(5) R27^o)-O surface oxide phase. We find that the prevalent structural model, a rumpled PdO(001) film suggested by previous low energy electron diffraction (LEED) work (M. Saidy et al., Surf. Sci. 494, L799 (2001)), is incompatible with all three employed methods. Instead, we suggest the two-dimensional film to consist of a strained PdO(101) layer on top of Pd(100). LEED intensity calculations show that this model is compatible with the experimental data of Saidy et al., Comment: 8 pages including 5 figures, Related publications can be found at http://www.fhi-berlin.mpg.de/th/paper.html

We investigate the long-range phase coherence of homogeneous and trapped Bose gases as a function of the geometry of the trap, the temperature, and the mean-field interactions in the weakly interacting limit. We explicitly take into account the (quasi)condensate depletion due to quantum and thermal fluctuations, i.e., we include the effects of both phase and density fluctuations. In particular, we determine the phase diagram of the gas by calculating the off-diagonal one-particle density matrix and discuss the various crossovers that occur in this phase diagram and the feasibility of their experimental observation in trapped Bose gases., Comment: One figure added, typos corrected, refernces added

We present a measurement of the microlensing optical depth toward the Galactic bulge based on the analysis of 15 contiguous1 square degrees fields centered on (l=2.5 deg, b=-4.0 deg) and containing 1.42 million clump-giant stars (belonging to the extended clump area) monitored during almost three bulge seasons by EROS (Experience de Recherche d'Objets Sombres). We find a microlensing optical depth towards the bulge tau_bulge=0.94 +/- 0.29 10^-6 averaged over all fields, based on 16 microlensing events with clump giants as sources. This value is substantially below several other determinations by the MACHO and OGLE groups and is more in agreement with what is expected from axisymmetric and non-axisymmetric bulge models., Comment: 18 pages, 15 images, accepted for publication in A&A

We study the associated jet multiplicity arising from t-channel BFKL gluon evolution in forward dijet production at hadron colliders. Previous results have shown that the effect of conserving overall energy and momentum is to introduce a pdf suppression that completely compensates the predicted exponential BFKL rise with rapidity difference between the leading dijets. However, we show that there is still expected to be a significant amount of BFKL radiation, especially in the central region, and we give predictions for the multiplicity of the resulting mini-jets at the LHC.

We present here the abundance analysis of a metal poor carbon rich lead star, CS29497-030. High resolution and high signal to noise spectra were obtained using the UVES spectrograph on the 8.2m VLT-Kueyen telescope. The observations were made as a part of the Large Programme 165.N-0276, P.I. R. Cayrel. Abundance analysis was done using the latest version of the MARCS model atmospheres (Plez et. al. 1992) and the turbospectrum spectrum synthesis code. We have derived Teff = 6650K from the FeI lines. Visible and infrared broad band colours using the Alonso et al. (1996) calibration, gives similar temperatures. A log g value of 3.5 was obtained from the ionisation equilibrium of FeI and FeII, we remark that this gravity also satisfies the MgI/MgII, TiI/TiII and MnI/MnII equilibria, within errors. The abundance analysis indicates a metallicity, [Fe/H] = --2.7. A large overabundance of carbon ([C/Fe]=2.7) was found. We have also found large enhancement in the s-process elements and in particular lead shows an extremely high abundance of [Pb/Fe]=3.5, which makes this the star with the highest Pb/Fe ratio, up to date. The Pb/Ba ratio is found to be high ([Pb/Ba]=1.2) and the same s true for other second-peak s-process elements(e.g La, Ce, Nd). The star is a known spectroscopic binary with a period of 346 days (Preston & Sneden 2000). The abundance pattern suggests that CS 29497-30 has accreted matter from its companion, when it was in the AGB phase., Comment: Talk given at the meeting on "Early Galactic Chemical Evolution with UVES" held at ESO Garching on 29-30th November 2002 8 pages, 4 tables and 6 figures

We discuss some subtleties regarding the depletion of the condensate in homogeneous two and three-dimensional Bose at zero temperature. We find agreement with the results of Popov theory. Other results in the paper cond-mat/0202085 are not affected by this., Comment: An erratum for cond-mat/0202085

Accelerating displacements preceding some catastrophic landslides have been found empirically to follow a time-to-failure power law, corresponding to a finite-time singularity of the velocity $v \sim 1/(t_c-t)$ [{\it Voight}, 1988]. Here, we provide a physical basis for this phenomenological law based on a slider-block model using a state and velocity dependent friction law established in the laboratory and used to model earthquake friction. This physical model accounts for and generalizes Voight's observation: depending on the ratio $B/A$ of two parameters of the rate and state friction law and on the initial frictional state of the sliding surfaces characterized by a reduced parameter $x_i$, four possible regimes are found. Two regimes can account for an acceleration of the displacement. We use the slider-block friction model to analyze quantitatively the displacement and velocity data preceding two landslides, Vaiont and La Clapi\`ere. The Vaiont landslide was the catastrophic culmination of an accelerated slope velocity. La Clapi\`ere landslide was characterized by a peak of slope acceleration that followed decades of ongoing accelerating displacements, succeeded by a restabilizing phase. Our inversion of the slider-block model on these data sets shows good fits and suggest to classify the Vaiont (respectively La Clapi\`ere) landslide as belonging to the velocity weakening unstable (respectively strengthening stable) sliding regime., Comment: shortened by focusing of the frictional model, Latex document with AGU style file of 14 pages + 11 figures (1 jpeg photo of figure 6 given separately) + 1 table

We are conducting a 377-square-degree proper motion survey in the ~V and I bands in order to determine the cool white dwarf contribution to the Galactic dark matter. Using the 250 square degrees for which we possess three epochs, and applying selection criteria designed to isolate halo-type objects, we find no candidates in a 5500 pc^3 effective volume for old, fast M_V=17 white dwarfs. We check the detection efficiency by cross-matching our catalogue with Luyten's NLTT catalogue. The halo white dwarf contribution cannot exceed 5% (95% C.L.) for objects with M_V=17 and 1

CS 22949--037 is one of the most metal-poor giants known ([Fe/H]$ \approx-4.0$), and it exhibits large overabundances of carbon and nitrogen (Norris et al.). Using VLT-UVES spectra of unprecedented quality, regarding resolution and S/N ratio, covering a wide wavelength range (from $\lambda = 350$ to 900 nm), we have determined abundances for 21 elements in this star over a wide range of atomic mass. The major new discovery is an exceptionally large oxygen enhancement, [O/Fe] $= 1.97\pm0.1$, as measured from the [OI] line at 630.0 nm. We find an enhancement of [N/Fe] of $2.56\pm 0.2$, and a milder one of [C/Fe] $= 1.17\pm$0.1, similar to those already reported in the literature. This implies $Z_{\star}=0.01 Z_{\odot}$. We also find carbon isotopic ratios $^{12}$C/$^{13}$C$ =4\pm2.0$ and $^{13}$C/$^{14}$N$ =0.03 ^{+0.035}_{-0.015}$, close to the equilibrium value of the CN cycle. Lithium is not detected. Na is strongly enhanced ([Na/Fe] $= +2.1 \pm 0.2$), while S and K are not detected. The silicon-burning elements Cr and Mn are underabundant, while Co and Zn are overabundant ([Zn/Fe]$ = +0.7$). Zn is measured for the first time in such an extremely metal-poor star. The abundances of the neutron-capture elements Sr, Y, and Ba are strongly decreasing with the atomic number of the element: [Sr/Fe] $\approx +0.3$, [Y/Fe] $\approx -0.1$, and [Ba/Fe] $\approx -0.6$. Among possible progenitors of CS 22949--037, we discuss the pair-instability supernovae. Such very massive objects indeed produce large amounts of oxygen, and have been found to be possible sources of primary nitrogen. Other scenarios are also discussed. A 30-40$M_{\odot}$ supernova, with fallback, seems the most likely progenitor for CS 22949--037., Comment: 12 Pages, 10 figures, accepted for publication in Astronomy and Astrophysics

We briefly summarise the main results presented at the IPPP Workshop on Multiparticle Production in QCD Jets, held in Durham in December 2001.

We present the results of a massive variability search based on a photometric survey of a six square degree region along the Galactic plane at ($l = 305^\circ$, $b = -0.8^\circ$) and ($l = 330^\circ$, $b = -2.5^\circ$). This survey was performed in the framework of the EROS II (Exp\'erience de Recherche d'Objets Sombres) microlensing program. The variable stars were found among 1,913,576 stars that were monitored between April and June 1998 in two passbands, with an average of 60 measurements. A new period-search technique is proposed which makes use of a statistical variable that characterizes the overall regularity of the flux versus phase diagram. This method is well suited when the photometric data are unevenly distributed in time, as is our case. 1,362 objects whose luminosity varies were selected. Among them we identified 9 Cepheids, 19 RR Lyrae, 34 Miras, 176 eclipsing binaries and 266 Semi-Regular stars. Most of them are newly identified objects. The cross-identification with known catalogues has been performed. The mean distance of the RR Lyrae is estimated to be $\sim 4.9 \pm 0.3$ kpc undergoing an average absorption of $\sim 3.4 \pm 0.2$ magnitudes. This distance is in good agreement with the one of disc stars which contribute to the microlensing source star population.Our catalogue and light curves are available electronically from the CDS, Strasbourg and from our Web site http://eros.in2p3.fr., Comment: 15 pages, 11 figures, accepted in A&A (april 2002)

We present a high-resolution spectroscopic analysis of the bright (V=11.7), extreme halo giant CS31082-001 ([Fe/H] = -2.9), obtained in an ESO-VLT Large Programme dedicated to very metal-poor stars. We find CS31082-001 to be extremely rich in r-process elements, comparable in this respect only to the similarly metal-poor, but carbon-enriched, giant CS22892-052. As a result of the extreme overabundance of the heaviest r-process elements, and negligible blending from CH and CN molecular lines, a reliable measurement is obtained of the U II line at 386 nm, for the first time in a halo star, along with numerous lines of Th II, as well as lines of 25 other r-process elements. Abundance estimates for a total of 43 elements are reported in CS31082-001, almost half of the entire periodic table. All elements with 56 \leq Z \leq 72 follow the Solar r-element pattern, reduced by about 1.25 dex ([r/Fe]=+1.7 dex, a factor 50). Pb, in contrast, seems to be below the shifted Solar r-process distribution, possibly indicating an error in the latter, while thorium is more enhanced than the lighter nuclides. Thus, while a universal production ratio for the r-process elements seems to hold in the interval 56 \leq Z \leq 72, it breaks down in the actinide region. When available, the U/Th is thus preferable to Th/Eu for radioactive dating: (i) because of its faster decay rate and smaller sensitivity to observational errors, and (ii) because the inital production ratio of the neighboring nuclides 238U and 232Th is more robustly predicted than the 151Eu/232Th ratio. Our current best estimate for the age of CS31082-001 is 14.0+/-2.4 Gyr., Comment: 20 pages, Latex, A&A style (aa.cls), Accepted for publication in A&A

We present an improved many-body T-matrix theory for partially Bose-Einstein condensed atomic gases by treating the phase fluctuations exactly. The resulting mean-field theory is valid in arbitrary dimensions and able to describe the low-temperature crossover between three, two and one-dimensional Bose gases. When applied to a degenerate two-dimensional atomic hydrogen gas, we obtain a reduction of the three-body recombination rate which compares favorably with experiment. Supplementing the mean-field theory with a renormalization-group approach to treat the critical fluctuations, we also incorporate into the theory the Kosterlitz-Thouless transition that occurs in a homogeneous Bose gas in two dimensions. In particular, we calculate the critical conditions for the Kosterlitz-Thouless phase transition as a function of the microscopic parameters of the theory. The proposed theory is further applied to a trapped one-dimensional Bose gas, where we find good agreement with exact numerical results obtained by solving a nonlinear Langevin field equation., Comment: 14 pages, 13 figures, revtex

We improve on the Popov theory for partially Bose-Einstein condensed atomic gases by treating the phase fluctuations exactly. As a result, the theory becomes valid in arbitrary dimensions and is able to describe the low-temperature crossover between three, two and one-dimensional Bose gases, which is currently being explored experimentally. We consider both homogeneous and trapped Bose gases., Comment: 4 pages. Title changed Major changes involve extension of theory to include trapped Bose gases. Deletion of reference to and comparison with hydrogen experiment. Due to these changes, second author added. Modified manuscript accepted for PRL

In this talk we give a short review of forward jets and forward $W$-boson production at hadron colliders, in view of the extraction of footprints of BFKL physics. We argue that at Tevatron energies, dijet production at large rapidity intervals is still subasymptotic with respect to the BFKL regime, thus the cross section is strongly dependent on the various cuts applied in the experimental setup. In addition, the choice of equal transverse momentum cuts on the tagging jets makes the cross section dependent on large logarithms of non-BFKL origin, and thus may spoil the BFKL analysis. For vector boson production in association with two jets, we argue that the configurations that are kinematically favoured tend to have the vector boson forward in rapidity. Thus $W + 2$ jet production lends itself naturally to extensions to the high-energy limit., Comment: LaTeX, JHEP style, 10 pages, 3 figures. Based on a talk at EPS2001, Budapest, Hungary

We analyse W boson production at hadron colliders in association with one or two jets, both with the exact kinematics and in the high-energy limit. We argue that the configurations that are kinematically favoured tend to have the W boson forward in rapidity. Thus W boson production in association with jets lends itself naturally to extensions to the high-energy limit, which we examine both at leading order and by resumming higher-order corrections through the BFKL theory., Comment: 33 pages

The ages of the oldest stars in the Galaxy indicate when star formation began, and provide a minimum age for the Universe. Radioactive dating of meteoritic material and stars relies on comparing the present abundance ratios of radioactive and stable nuclear species to the theoretically predicted ratios of their production. The radioisotope $^{232}$Th (half-life 14 Gyr) has been used to date Galactic stars, but it decays by only a factor of two over the lifetime of the Universe. $^{238}$U (half-life 4.5 Gyr) is in principle a more precise age indicator, but even its strongest spectral line, from singly ionized uranium at a wavelength of 385.957 nm, has previously not been detected in stars. Here we report a measurement of this line in the very metal-poor star CS31082-001, a star which is strongly overabundant in its heavy elements. The derived uranium abundance, log(U/H) = -13.7+/-0.14+/-0.12 yields an age of 12.5+/-3 Gyr, though this is still model dependent. The observation of this cosmochronometer gives the most direct age determination of the Galaxy. Also, with improved theoretical and laboratory data, it will provide a highly precise lower limit to the age of the Universe., Comment: 3 pages, 1 figure, 1 table, published in Nature

Keeping a basic tenet of economic theory, rational expectations, we model the nonlinear positive feedback between agents in the stock market as an interplay between nonlinearity and multiplicative noise. The derived hyperbolic stochastic finite-time singularity formula transforms a Gaussian white noise into a rich time series possessing all the stylized facts of empirical prices, as well as accelerated speculative bubbles preceding crashes. We use the formula to invert the two years of price history prior to the recent crash on the Nasdaq (april 2000) and prior to the crash in the Hong Kong market associated with the Asian crisis in early 1994. These complex price dynamics are captured using only one exponent controlling the explosion, the variance and mean of the underlying random walk. This offers a new and powerful detection tool of speculative bubbles and herding behavior., Comment: Latex document of 24 pages including 5 eps figures

We critically examine the definition of dijet cross sections at large rapidity intervals in hadron-hadron collisions, taking proper account of the various cuts applied in a realistic experimental setup. We argue that the dependence of the cross section on the precise definition of the parton momentum fractions and the presence of an upper bound on the momentum transfer cannot be neglected, and we provide the relevant modifications to the analytical formulae by Mueller and Navelet. We also point out that the choice of equal transverse momentum cuts on the tagging jets can spoil the possibility of a clean extraction of signals of BFKL physics.

We develop theoretical formulas for the prediction of the rupture of systems which are known to exhibit a critical behavior, based solely on the knowledge of the early time evolution of an observable, such as the acoustic emission rate as a function of time or of stress. From the parameterization of such early time evolution in terms of a low-order polynomial, we use the functional renormalization approach introduced by Yukalov and Gluzman to transform this polynomial into a function which is asymptotically a power law. The value of the critical time tc,conditioned on the assumption that tc exists, is thus determined from the knowledge of the coefficients of the polynomials. We test with success this prediction scheme with respect to the order of the polynomials and as a function of noise., Comment: Latex 14 pages + 7 eps figures, submitted to the special issue of Computational Seismology dedicated to the 80-anniversary of Prof. Vladimir I. Keilis-Borok

We report new measurements of turbulent mixing of temperature fluctuations in a low temperature helium gas experiment, spanning a range of microscale Reynolds number, $R_{\lambda}$, from 100 to 650. The exponents $\xi_{n}$ of the temperature structure functions $<|\theta(x+r)-\theta(x)|^n > \sim r^{\xi_{n}}$ are shown to saturate to $\xi_{\infty} \simeq 1.45 \pm 0.1$ for the highest orders, $n \sim 10$. This saturation is a signature of statistics dominated by front-like structures, the cliffs. Statistics of the cliff characteristics are performed, particularly their width are shown to scale as the Kolmogorov length scale., Comment: 4 pages, with 4 figures

We present the EROS nearby supernova ($z \sim 0.02 - 0.2$) search and the analysis of the first year of data (1997). A total of 80 square degrees were surveyed. Eight supernov{\ae} were detected, four of which were spectroscopically identified as type Ia supernov{\ae}. The search efficiency was determined with a Monte-Carlo simulation taking into account the efficiencies for both supernova detection and host galaxy identification. Assuming that for a given galaxy the supernova rate is proportional to the galactic luminosity, we compute a type Ia supernova explosion rate of: ${\cal R} = 0.44 {}_{-0.21}^{+0.35} {}_{-0.07}^{+0.13} h^2: / 10^{10} \lbsun / 100 {\rm yrs}$ at an average redshift of $\sim 0.1$ where the errors are respectively statistical and systematic (type misidentification included)., Comment: 8 pages, 6 figures, accepted in A&A

Launch of the Far Ultraviolet Spectroscopic Explorer (FUSE) has been followed by an extensive period of calibration and characterization as part of the preparation for normal satellite operations. Major tasks carried out during this period include initial coalignment, focusing and characterization of the four instrument channels, and a preliminary measurement of the resolution and throughput performance of the instrument. We describe the results from this test program, and present preliminary estimates of the on-orbit performance of the FUSE satellite based on a combination of this data and prelaunch laboratory measurements., Comment: 8 pages, including 3 figures. This paper will appear in the FUSE special issue of ApJ Letters

We present a simple and general result that the sign of the variations or increments of uncorrelated times series are predictable with a remarkably high success probability of 75% for symmetric sign distributions. The origin of this paradoxical result is explained in details. We also present some tests on synthetic, financial and global temperature time series., Comment: 8 pages, 3 figures

Starting from the characterization of the past time evolution of market prices in terms of two fundamental indicators, price velocity and price acceleration, we construct a general classification of the possible patterns characterizing the deviation or defects from the random walk market state and its time-translational invariant properties. The classification relies on two dimensionless parameters, the Froude number characterizing the relative strength of the acceleration with respect to the velocity and the time horizon forecast dimensionalized to the training period. Trend-following and contrarian patterns are found to coexist and depend on the dimensionless time horizon. The classification is based on the symmetry requirements of invariance with respect to change of price units and of functional scale-invariance in the space of scenarii. This ``renormalized scenario'' approach is fundamentally probabilistic in nature and exemplifies the view that multiple competing scenarii have to be taken into account for the same past history. Empirical tests are performed on on about nine to thirty years of daily returns of twelve data sets comprising some major indices (Dow Jones, SP500, Nasdaq, DAX, FTSE, Nikkei), some major bonds (JGB, TYX) and some major currencies against the US dollar (GBP, CHF, DEM, JPY). Our ``renormalized scenario'' exhibits statistically significant predictive power in essentially all market phases. In constrast, a trend following strategy and trend + acceleration following strategy perform well only on different and specific market phases. The value of the ``renormalized scenario'' approach lies in the fact that it always finds the best of the two, based on a calculation of the stability of their predicted market trajectories., Comment: Latex, 27 pages

Based on a faithful representation of the heavy tail multivariate distribution of asset returns introduced previously (Sornette et al., 1998, 1999) that we extend to the case of asymmetric return distributions, we generalize the return-risk efficient frontier concept to incorporate the dimensions of large risks embedded in the tail of the asset distributions. We demonstrate that it is often possible to increase the portfolio return while decreasing the large risks as quantified by the fourth and higher order cumulants. Exact theoretical formulas are validated by empirical tests., Comment: 10 pages, 5 figures

We perform a two-loop calculation in light-front phi^4 theory to determine the effective mass renormalization of the light-front Hamiltonian. The renormalization scheme adopted here is manifestly boost invariant, and yields results that are in perfect agreement with the explicitly covariant Feynman diagram approach., Comment: 7 pages, 1 Figure. Revised Introduction and references added

This paper offers a precise analytical characterization of the distribution of returns for a portfolio constituted of assets whose returns are described by an arbitrary joint multivariate distribution. In this goal, we introduce a non-linear transformation that maps the returns onto gaussian variables whose covariance matrix provides a new measure of dependence between the non-normal returns, generalizing the covariance matrix into a non-linear fractional covariance matrix. This nonlinear covariance matrix is chiseled to the specific fat tail structure of the underlying marginal distributions, thus ensuring stability and good-conditionning. The portfolio distribution is obtained as the solution of a mapping to a so-called phi-q field theory in particle physics, of which we offer an extensive treatment using Feynman diagrammatic techniques and large deviation theory, that we illustrate in details for multivariate Weibull distributions. The main result of our theory is that minimizing the portfolio variance (i.e. the relatively ``small'' risks) may often increase the large risks, as measured by higher normalized cumulants. Extensive empirical tests are presented on the foreign exchange market that validate satisfactorily the theory. For ``fat tail'' distributions, we show that an adequete prediction of the risks of a portfolio relies much more on the correct description of the tail structure rather than on their correlations., Comment: Latex, 76 pages

We introduce a faithful representation of the heavy tail multivariate distribution of asset returns, as parsimonous as the Gaussian framework. Using calculation techniques of functional integration and Feynman diagrams borrowed from particle physics, we characterize precisely, through its cumulants of high order, the distribution of wealth variations of a portfolio composed of an arbitrary mixture of assets. The portfolio which minimizes the variance, i.e. the relatively small risks, often increases larger risks as measured by higher normalized cumulants and by the Value-at-risk., Comment: 13 pages, 6 figures

We argue that the existence of abrupt failure in the democratic fiber bundle model is more general than concluded by da Silveira in his comment (cond-mat/9709327). We refute his claim that the nature of the rupture process in the DFBM depends on the ``disorder distribution only via its large failure strength behavior''., Comment: 1 page in revtex, reply to the comment to our letter J.V. Andersen, D. Sornette and K.-T. Leung, Phys. Rev. Lett. 78, 2140 (1997)

Chapter one is devoted to a study of fermions and bosons in two spatial dimensions in external electromagnetic fields. The effectve action is calculated by integrating out the matter fields. In chapter two, I investigate the resummation program of Braaten and Pisarski. I calculate the screening mass squared and the free energy in Yukwava theory to two and three-loop order, respectively, in resummed perturbation theory. The main part of the present work is on effective field theories at finite temperature. I discuss the concepts of dimensional reduction, modern renormalization theory, and renormalizable field theories (``fundamental theories'') versus non-renormalizable theories (``effective theories''). Two methods for constructing effective three dimensional field theories are discussed. The first is based on the effective potential, and is applied to field theory with $N$ charged U(N) symmetric scalar coupled to an Abelian gauge field. The second method is an effective field theory approach based on diagrammatical methods, recently developed by Braaten and Nieto. I apply the methods to various problems in spinor and scalar QED., Comment: PH. D. thesis June 1997, 132 pages, LATEX, 60 figures appear in text

Massless scalar electrodynamics is studied at high temperature and zero chemical potential. I derive the free energy to order $\lambda^2$, $\lambda e^2$ and $e^4$ by effective field theory methods. The first step consists of the construction of an effective three-dimensional field theory that is valid on distance scales $R\gg 1/T$ and whose parameters can be written as power series in $\lambda$ and $e^2$. These coupling constants encode the contribution to physical quantities from the scale $T$. The second step is the use of the effective Lagrangian and perturbative calculations yield the contributions to the free energy from the scale $eT\sim\sqrt{\lambda}T$., Comment: 23 pages, LATEX, 6 figures

We study massless $g^2\Phi^4$-theory at high temperature and with zero chemical potential. Using modern effective field theory methods,% recently developed by Braaten and Nieto, we derive the screening mass squared to order $g^5$. It is demonstrated that the result is renormalization group invariant to this order in the coupling constant. Renormalization group methods are used to sum up leading logarithms of $g$., Comment: 14 pages, LATEX, 5 figures. Replaces incorrect version sent august 7