7,291 research outputs found
Causal cascade in the stock market from the ``infrared'' to the ``ultraviolet''
Modelling accurately financial price variations is an essential step
underlying portfolio allocation optimization, derivative pricing and hedging,
fund management and trading. The observed complex price fluctuations guide and
constraint our theoretical understanding of agent interactions and of the
organization of the market. The gaussian paradigm of independent normally
distributed price increments has long been known to be incorrect with many
attempts to improve it. Econometric nonlinear autoregressive models with
conditional heteroskedasticity (ARCH) and their generalizations capture only
imperfectly the volatility correlations and the fat tails of the probability
distribution function (pdf) of price variations. Moreover, as far as changes in
time scales are concerned, the so-called ``aggregation'' properties of these
models are not easy to control. More recently, the leptokurticity of the full
pdf was described by a truncated ``additive'' L\'evy flight model (TLF).
Alternatively, Ghashghaie et al. proposed an analogy between price dynamics and
hydrodynamic turbulence. In this letter, we use wavelets to decompose the
volatility of intraday (S&P500) return data across scales. We show that when
investigating two-points correlation functions of the volatility logarithms
across different time scales, one reveals the existence of a causal information
cascade from large scales (i.e. small frequencies, hence to vocable
``infrared'') to fine scales (``ultraviolet''). We quantify and visualize the
information flux across scales. We provide a possible interpretation of our
findings in terms of market dynamics.Comment: 9 pages, 3 figure
A multifractal random walk
We introduce a class of multifractal processes, referred to as Multifractal
Random Walks (MRWs). To our knowledge, it is the first multifractal processes
with continuous dilation invariance properties and stationary increments. MRWs
are very attractive alternative processes to classical cascade-like
multifractal models since they do not involve any particular scale ratio. The
MRWs are indexed by few parameters that are shown to control in a very direct
way the multifractal spectrum and the correlation structure of the increments.
We briefly explain how, in the same way, one can build stationary multifractal
processes or positive random measures.Comment: 5 pages, 4 figures, uses RevTe
The impact of new neutrino DIS and Drell-Yan data on large-x parton distributions
New data sets have recently become available for neutrino and antineutrino
deep inelastic scattering on nuclear targets and for inclusive dimuon
production in pp pd interactions. These data sets are sensitive to different
combinations of parton distribution functions in the large-x region and,
therefore, provide different constraints when incorporated into global parton
distribution function fits. We compare and contrast the effects of these new
data on parton distribution fits, with special emphasis on the effects at large
x. The effects of the use of nuclear targets in the neutrino and antineutrino
data sets are also investigated.Comment: 24 pages, 13 figure
Polarized Parton Densities
In this talk we summarize main results of a recent determination of the
polarized deeply inelastic parton distributions to NLO from the world data. In
the analysis the LO and NLO parton densities and their statistical
errors were derived and parameterized. The strong coupling constant
is determined Comparisons of the
low moments of the parton densities with recent lattice results are given. A
detailed error-analysis of the gluon density is performed.Comment: 3 pages LATEX, 1 style file, 1 eps file, to appear in the Proceedings
of PANIC '02, Osaka, Ocrober 200
EPS09 - Nuclear PDFs and Their Uncertainties at NLO
In this talk, we present our recent next-to-leading order (NLO) nuclear
parton distribution functions (nPDFs), which we call EPS09. As an extension to
earlier NLO analyses, we supplement the deep inelastic scattering and Drell-Yan
dilepton data by inclusive midrapidity pion measurements from RHIC in order to
reduce the otherwize large freedom in the nuclear gluon densities. Our
Hessian-type error analysis leading to a collection of nPDF error sets, is the
first of its kind among the nPDF analyses.Comment: 4 pages, 4 figures - To appear in the conference proceedings for
Quark Matter 2009, March 30 - April 4, Knoxville, Tennesse
Nucleus polarizability contribution to the hydrogen-deuterium isotope shift
The correction to the hydrogen-deuterium isotope shift due to the proton and
deuteron polarizability is evaluated on the basis of modern experimental data
on the structure functions of inelastic lepton-nucleus scattering. The
numerical value of this contribution is equal 63\pm 12 Hz.Comment: 5 page
Relating high-energy lepton-hadron, proton-nucleus and nucleus-nucleus collisions through geometric scaling
A characteristic feature of small-x lepton-proton data from HERA is geometric
scaling -- the fact that over a wide range of x and Q^2 all data can be
described by a single variable , with all x-dependence
encoded in the so-called saturation momentum . Here, we observe
that the same scaling ansatz accounts for nuclear photoabsorption cross
sections and favors the nuclear dependence , . We then make the empirical finding
that the same A-dependence accounts for the centrality evolution of the
multiplicities measured in Au+Au collisions at RHIC. It also allows to
parametrize the high-p_t particle suppression in d+Au collisions at forward
rapidities. If these geometric scaling properties have a common dynamical
origin, then this A-dependence of should emerge as a consequence
of the underlying dynamical model.Comment: 4 pages, 3 postscript figure
Nuclear parton distributions at next to leading order
We perform a next to leading order QCD global analysis of nuclear deep
inelastic scattering and Drell-Yan data using the convolution approach to
parameterize nuclear parton densities. We find both a significant improvement
in the agreement with data compared to previous extractions, and substantial
differences in the scale dependence of nuclear effects compared to leading
order analyses.Comment: 9 pages, 10 figure
Resummed QCD Power Corrections to Nuclear Shadowing
We calculate and resum a perturbative expansion of nuclear enhanced power
corrections to the structure functions measured in deeply inelastic scattering
of leptons on a nuclear target. Our results for the Bjorken -, - and
-dependence of nuclear shadowing in and the nuclear
modifications to , obtained in terms of the QCD factorization
approach, are consistent with the existing data. We demonstrate that the
low- behavior of these data and the measured large longitudinal structure
function point to a critical role for the power corrections when compared to
other theoretical approaches.Comment: 4 pages, 3 figures, uses RevTeX 4. As published in Phys.Rev.Let
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