14,701 research outputs found
Fit to the Bjorken, Ellis-Jaffe and Gross-Llewellyn-Smith sum rules in a renormalon based approach
We study the large order behaviour in perturbation theory of the Bjorken,
Ellis-Jaffe and Gross-Llewellyn-Smith sum rules. In particular, we consider
their first infrared renormalons, for which we obtain their analytic structure
with logarithmic accuracy and also an approximate determination of their
normalization constant. Estimates of higher order terms of the perturbative
series are given. The Renormalon subtracted scheme is worked out for these
observables and compared with experimental data. Overall, good agreement with
experiment is found. This allows us to obtain {\hat a}_0 and some higher-twist
non-perturbative constants from experiment: {\hat a}_0=0.141\pm 0.089;
f_{3,RS}(1 GeV)=-0.124^{+0.137}_{-0.142} GeV^2.Comment: 23 pages, 18 figures, one reference added, journal versio
Stability and decay of Bloch oscillations in presence of time-dependent nonlinearity
We consider Bloch oscillations of Bose-Einstein condensates in presence of a
time-modulated s-wave scattering length. Generically, interaction leads to
dephasing and decay of the wave packet. Based on a cyclic-time argument, we
find---additionally to the linear Bloch oscillation and a rigid soliton
solution---an infinite family of modulations that lead to a periodic time
evolution of the wave packet. In order to quantitatively describe the dynamics
of Bloch oscillations in presence of time-modulated interactions, we employ two
complementary methods: collective-coordinates and the linear stability analysis
of an extended wave packet. We provide instructive examples and address the
question of robustness against external perturbations.Comment: 15 pages, 8 figures. Slightly amended final versio
Exact Random Walk Distributions using Noncommutative Geometry
Using the results obtained by the non commutative geometry techniques applied
to the Harper equation, we derive the areas distribution of random walks of
length on a two-dimensional square lattice for large , taking into
account finite size contributions.Comment: Latex, 3 pages, 1 figure, to be published in J. Phys. A : Math. Ge
Increasing returns to scale and international diffusion of technology: an empirical study for Brazil (1976-2000)
This article aims at exploring the empirical evidence regarding the effects of increasing returns to scale and international technological diffusion on the Brazilian manufacturing industry. Our departure point is a Kaldorian-type theoretical model that provides not only the positive effects of scale but also of diffusion on industrial performance. We use Vector Auto Regressive (VAR) for testing the model. VAR will estimate the coefficients related to industrial output, labor productivity, exports and the technological gap between the United States and Brazil. This technique also provides simulations for the short-term and long-term trajectories under exogenous shocks. The observations are on a three-month period basis and the sampling period runs from the second half of 1976 to the second half of 2000. The conclusion highlights both evidences of increasing returns on the Brazilian industry that faces, however, some structural constraints. Besides, the model also reveals Brazil's difficulties to catch uptechnological gap; increasing returns to scale; economic growth; Brazil
Ion condensation on charged patterned surfaces
We study ion condensation onto a patterned surface of alternating charges.
The competition between self-energy and ion-surface interactions leads to the
formation of ionic crystalline structures at low temperatures. We consider
different arrangements of underlying ionic crystals, including single ion
adsorption, as well as the formation of dipoles at the interface between
charged domains. Molecular dynamic simulation illustrates existence of single
and mixed phases. Our results contribute to understanding pattern recognition,
and molecular separation and synthesis near patterned surfaces.Comment: 3 figure
Supersymmetric Radiative Flavour
We examine possibilities for the radiative generation of the Yukawa couplings
and flavour structure in supersymmetric models in the supersymmetric phase. Not
withstanding the non-renormalisation of the Wilsonian superpotential, this can
occur through the 2-loop vertex renormalisation of the physical 1PI couplings.
We describe this effect and construct models in which this occurs. For models
attempting to reproduce the full flavour structure of the Standard Model, we
analyse the tension between such models and constraints from low-energy flavour
observables. We note that the tension is weakest for the case of generating
Dirac neutrino masses.Comment: 25 pages, 9 figure
Geometric properties of extremal domains for the -Laplacian operator
In this paper, we explore the geometric properties of unbounded extremal
domains for the -Laplacian operator in both Euclidean and hyperbolic spaces.
Assuming that the nonlinearity grows at least as the nonlinearity of the
eigenvalue problem, we prove that these domains exhibit remarkable geometric
properties and cannot be arbitrarily wide. In two dimensions, we prove that
such domains with connected complements must necessarily be balls. In the
hyperbolic space, we highlight the constraints on extremal domains and the
geometry of their asymptotic boundaries
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