1,356 research outputs found
Independence of hyperlogarithms over function fields via algebraic combinatorics
We obtain a necessary and sufficient condition for the linear independence of
solutions of differential equations for hyperlogarithms. The key fact is that
the multiplier (i.e. the factor in the differential equation ) has
only singularities of first order (Fuchsian-type equations) and this implies
that they freely span a space which contains no primitive. We give direct
applications where we extend the property of linear independence to the largest
known ring of coefficients
A multipurpose Hopf deformation of the Algebra of Feynman-like Diagrams
We construct a three parameter deformation of the Hopf algebra
. This new algebra is a true Hopf deformation which reduces to
on one hand and to on the other, relating
to other Hopf algebras of interest in contemporary physics.
Further, its product law reproduces that of the algebra of polyzeta functions.Comment: 5 page
A Three Parameter Hopf Deformation of the Algebra of Feynman-like Diagrams
We construct a three-parameter deformation of the Hopf algebra \LDIAG. This
is the algebra that appears in an expansion in terms of Feynman-like diagrams
of the {\em product formula} in a simplified version of Quantum Field Theory.
This new algebra is a true Hopf deformation which reduces to \LDIAG for some
parameter values and to the algebra of Matrix Quasi-Symmetric Functions
(\MQS) for others, and thus relates \LDIAG to other Hopf algebras of
contemporary physics. Moreover, there is an onto linear mapping preserving
products from our algebra to the algebra of Euler-Zagier sums
Sausu - Malonas - Tolai ou les leçons d'une transmigration réussie : étude agro-économique de 3 Centres de Transmigration dans la Province de Sulawesi Tengah
Cette étude concerne 3 centres de transmigration situés à Sulawesi Centre : Sausu,Malonas,Tolai.L'essentiel des données de base a été obtenu auprès des transmigrants.Un échantillon de 160 familles de colons a été suivi par enquête en quatre passages répétés espacés de 2 mois et observation sur le terrain.En Indonésie,les transferts de population commencés sous l'administration coloniale hollandaise avaient pour objectifs de réduire les déséquilibres démographiques entre les différentes iles.En 1980,la densité de population était de 690 habitants au km2 à Java et de 18 km2 à Sulawesi Centre.Dans la première partie de cette étude,les auteurs analysent l'origine,les motivations des transmigrants,ce qui fait l'originalité des 3 Centres qui jouissent d'un environnement favorable du point de vue de la pluviométrie,du relief,de la fertilité du sol.Pour chacun des centres,il est signalé les surfaces cultivées,les cultures adoptées (riz,soja) et les revenus dont bénéficient les transmigrants grace aux activités agricoles et non agricoles.Dans la dernière partie,les auteurs analysent les causes de certains échecs et des succès de l'opération en signalant le nombre trés important des transmigrants spontanés dans cette région et présentent des recommandations pour l'avenir
Small x Behavior of Parton Distributions from the Observed Froissart Energy Dependence of the Deep Inelastic Scattering Cross Section
We fit the reduced cross section for deep-inelastic electron scattering data
to a three parameter ln^2 s fit, A + beta ln^2 (s/s_0), where s= [Q^2/x] (1-x)
+ m^2, and Q^2 is the virtuality of the exchanged photon. Over a wide range in
Q^2 (0.11 < Q^2 < 1200 GeV^2) all of the fits satisfy the logarithmic energy
dependence of the Froissart bound. We can use these results to extrapolate to
very large energies and hence to very small values of Bjorken x -- well beyond
the range accessible experimentally. As Q^2 --> infinity, the structure
function F_2^p(x, Q^2) exhibits Bjorken scaling, within experimental errors. We
obtain new constraints on the behavior of quark and antiquark distribution
functions at small x.Comment: 10 pages, 2 figure
Analytic Expression for the Joint x and Q^2 Dependences of the Structure Functions of Deep Inelastic Scattering
We obtain a good analytic fit to the joint Bjorken-x and Q^2 dependences of
ZEUS data on the deep inelastic structure function F_2(x, Q^2). At fixed
virtuality Q^2, as we showed previously, our expression is an expansion in
powers of log (1/x) that satisfies the Froissart bound. Here we show that for
each x, the Q^2 dependence of the data is well described by an expansion in
powers of log Q^2. The resulting analytic expression allows us to predict the
logarithmic derivatives {({\partial}^n F_2^p/{{(\partial\ln Q^2}})^n)}_x for n
= 1,2 and to compare the results successfully with other data. We extrapolate
the proton structure function F_2^p(x,Q^2) to the very large Q^2 and the very
small x regions that are inaccessible to present day experiments and contrast
our expectations with those of conventional global fits of parton distribution
functions.Comment: 4 pages, 3 figures, a few changes in the text. Version to be
published in Physical Review Letter
Ultra-high energy neutrino scattering
Estimates are made of the ultra-high energy neutrino cross sections based on
an extrapolation to very small Bjorken x of the logarithmic Froissart
dependence in x shown previously to provide an excellent fit to the measured
proton structure function F_2^p(x,Q^2) over a broad range of the virtuality
Q^2. Expressions are obtained for both the neutral current and the charged
current cross sections. Comparison with an extrapolation based on perturbative
QCD shows good agreement for energies where both fit data, but our rates are as
much as a factor of 10 smaller for neutrino energies above 10^9 GeV, with
important implications for experiments searching for extra-galactic neutrinos.Comment: 4 pages, 1 figure, 1 table; Title, abstract and text changed,
conclusions unchanged. Version accepted for publication in Physical Review
Population Inversion in Monolayer and Bilayer Graphene
The recent demonstration of saturable absorption and negative optical
conductivity in the Terahertz range in graphene has opened up new opportunities
for optoelectronic applications based on this and other low dimensional
materials. Recently, population inversion across the Dirac point has been
observed directly by time- and angle-resolved photoemission spectroscopy
(tr-ARPES), revealing a relaxation time of only ~ 130 femtoseconds. This
severely limits the applicability of single layer graphene to, for example,
Terahertz light amplification. Here we use tr-ARPES to demonstrate long-lived
population inversion in bilayer graphene. The effect is attributed to the small
band gap found in this compound. We propose a microscopic model for these
observations and speculate that an enhancement of both the pump photon energy
and the pump fluence may further increase this lifetime.Comment: 18 pages, 6 figure
Light Gluino Constituents of Hadrons and a Global Analysis of Hadron Scattering Data
Light strongly interacting supersymmetric particles may be treated as
partonic constituents of nucleons in high energy scattering processes. We
construct parton distribution functions for protons in which a light gluino is
included along with standard model quark, antiquark, and gluon constituents. A
global analysis is performed of a large set of data from deep-inelastic lepton
scattering, massive lepton pair and vector boson production, and hadron jet
production at large values of transverse momentum. Constraints are obtained on
the allowed range of gluino mass as a function of the value of the strong
coupling strength alpha_s(M_Z) determined at the scale of the Z boson mass. We
find that gluino masses as small as 10 GeV are admissible provided that
alpha_s(M_Z) \ge 0.12. Current hadron scattering data are insensitive to the
presence of gluinos heavier than ~ 100 - 150 GeV.Comment: 31 pages, 12 figures, RevTe
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