439 research outputs found
Power-law persistence and trends in the atmosphere: A detailed study of long temperature records
We use several variants of the detrended fluctuation analysis to study the
appearance of long-term persistence in temperature records, obtained at 95
stations all over the globe. Our results basically confirm earlier studies. We
find that the persistence, characterized by the correlation C(s) of temperature
variations separated by s days, decays for large s as a power law, C(s) ~
s^(-gamma). For continental stations, including stations along the coastlines,
we find that gamma is always close to 0.7. For stations on islands, we find
that gamma ranges between 0.3 and 0.7, with a maximum at gamma = 0.4. This is
consistent with earlier studies of the persistence in sea surface temperature
records where gamma is close to 0.4. In all cases, the exponent gamma does not
depend on the distance of the stations to the continental coastlines. By
varying the degree of detrending in the fluctuation analysis we obtain also
information about trends in the temperature records.Comment: 5 pages, 4 including eps figure
Clan Structure Analysis and Rapidity Gap Probability
Clan structure analysis in rapidity intervals is generalized from negative
binomial multiplicity distribution to the wide class of compound Poisson
distributions. The link of generalized clan structure analysis with correlation
functions is also established. These theoretical results are then applied to
minimum bias events and evidentiate new interesting features, which can be
inspiring and useful in order to discuss data on rapidity gap probability at
TEVATRON and HERA.Comment: (14 pages in Plain TeX plus 5 Postscript Figures, all compressed via
uufiles) DFTT 28/9
Multifractal stationary random measures and multifractal random walks with log-infinitely divisible scaling laws
We define a large class of continuous time multifractal random measures and
processes with arbitrary log-infinitely divisible exact or asymptotic scaling
law. These processes generalize within a unified framework both the recently
defined log-normal Multifractal Random Walk (MRW) [Bacry-Delour-Muzy] and the
log-Poisson "product of cynlindrical pulses" [Barral-Mandelbrot]. Our
construction is based on some ``continuous stochastic multiplication'' from
coarse to fine scales that can be seen as a continuous interpolation of
discrete multiplicative cascades. We prove the stochastic convergence of the
defined processes and study their main statistical properties. The question of
genericity (universality) of limit multifractal processes is addressed within
this new framework. We finally provide some methods for numerical simulations
and discuss some specific examples.Comment: 24 pages, 4 figure
Meson Cloud of the Nucleon in Polarized Semi-Inclusive Deep-Inelastic Scattering
We investigate the possibility of identifying an explicit pionic component of
the nucleon through measurements of polarized baryon fragments
produced in deep-inelastic leptoproduction off polarized protons, which may
help to identify the physical mechanism responsible for the breaking of the
Gottfried sum rule. The pion-exchange model predicts highly correlated
polarizations of the and target proton, in marked contrast with
the competing diquark fragmentation process. Measurement of asymmetries in
polarized production may also reveal the presence of a kaon cloud in
the nucleon.Comment: 23 pages REVTeX, 7 uuencoded figures, accepted for publication in
Zeit. Phys.
Nonperturbative \gamma^* p Interaction in the Diffractive Regime
One of the challenging aspects of electroproduction at high-energy is the
understanding of the transition from real photons to virtual photons in the
GeV^2 region. We study inclusive electroproduction on the proton at small x_B
using a nonperturbative dipole-proton cross section calculated from the gauge
invariant gluon field correlators as input. By quark-hadron duality, we
construct a photon light cone wave function which links the ``hadronic''
behavior at small Q^2 to the ``perturbative'' behavior at large Q^2. It
contains quark masses which implement the transition from constituent quarks at
low Q^2 to current quarks at high Q^2. Our calculation gives a good description
of the structure function at fixed energy for Q^2<=10 GeV^2. Indications for a
chiral transition may already have been seen in the photon-proton cross
section.Comment: 28 pages, LaTeX, eps
Subprocess Size in Hard Exclusive Scattering
The interaction region of hard exclusive hadron scattering can have a large
transverse size due to endpoint contributions, where one parton carries most of
the hadron momentum. The endpoint region is enhanced and can dominate in
processes involving multiple scattering and quark helicity flip. The endpoint
Fock states have perturbatively short lifetimes and scatter softly in the
target. We give plausible arguments that endpoint contributions can explain the
apparent absence of color transparency in fixed angle exclusive scattering and
the dimensional scaling of transverse rho photoproduction at high momentum
transfer, which requires quark helicity flip. We also present a quantitative
estimate of Sudakov effects.Comment: 16 pages, 4 figures, JHEP style; v2: quantitative estimate of Sudakov
effects and more detailed discussion of endpoint behaviour of meson
distribution amplitude added, few other clarifications, version to appear in
Phys. Rev.
Fermi-Dirac statistics plus liquid description of quark partons
A previous approach with Fermi-Dirac distributions for fermion partons is
here improved to comply with the expected low behaviour of structure
functions. We are so able to get a fair description of the unpolarized and
polarized structure functions of the nucleons as well as of neutrino data. We
cannot reach definite conclusions, but confirm our suspicion of a relationship
between the defects in Gottfried and spin sum rules.Comment: 15 pages, plain LaTex, 10 compressed tarred uuencoded figures in a
separate fil
Role of the Delta (1232) in DIS on polarized He and extraction of the neutron spin structure function
We consider the effect of the transitions and in deep inelastic scattering on polarized He on the extraction
of the neutron spin structure function . Making the natural
assumption that these transitions are the dominant non-nucleonic contributions
to the renormalization of the axial vector coupling constant in the A=3 system,
we find that the effect of increases by % in the range , where our considerations are applicable
and most of the data for exist.Comment: 23 pages, 6 figures, revte
SU(4) Chiral Quark Model with Configuration Mixing
Chiral quark model with configuration mixing and broken SU(3)\times U(1)
symmetry has been extended to include the contribution from c\bar c
fluctuations by considering broken SU(4) instead of SU(3). The implications of
such a model have been studied for quark flavor and spin distribution functions
corresponding to E866 and the NMC data. The predicted parameters regarding the
charm spin distribution functions, for example, \Delta c, \frac{\Delta
c}{{\Delta \Sigma}}, \frac{\Delta c}{c} as well as the charm quark distribution
functions, for example, \bar c, \frac{2\bar c}{(\bar u+\bar d)}, \frac{2 \bar
c}{(u+d)} and \frac{(c+ \bar c)}{\sum (q+\bar q)} are in agreement with other
similar calculations. Specifically, we find \Delta c=-0.009, \frac{\Delta
c}{{\Delta \Sigma}}=-0.02, \bar c=0.03 and \frac{(c+ \bar c)}{\sum (q+\bar
q)}=0.02 for the \chiQM parameters a=0.1, \alpha=0.4, \beta=0.7,
\zeta_{E866}=-1-2 \beta, \zeta_{NMC}=-2-2 \beta and \gamma=0.3, the latter
appears due to the extension of SU(3) to SU(4).Comment: 10 RevTeX pages. Accepted for publication in Phys. Rev.
The Effect of Shadowing on Initial Conditions, Transverse Energy and Hard Probes in Ultrarelativistic Heavy Ion Collisions
The effect of shadowing on the early state of ultrarelativistic heavy ion
collisions is investigated along with transverse energy and hard process
production, specifically Drell-Yan, , and production. We
choose several parton distributions and parameterizations of nuclear shadowing,
as well as the spatial dependence of shadowing, to study the influence of
shadowing on relevant observables. Results are presented for Au+Au collisions
at GeV and Pb+Pb collisions at TeV.Comment: Submitted to Phys. Rev.
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