22,102 research outputs found
Generalised Fractional Evolution Equations of Caputo Type
This paper is devoted to the study of generalised time-fractional evolution
equations involving Caputo type derivatives. Using analytical methods and
probabilistic arguments we obtain well-posedness results and stochastic
representations for the solutions. These results encompass known linear and
non-linear equations from classical fractional partial differential equations
such as the time-space-fractional diffusion equation, as well as their far
reaching extensions. \\ Meaning is given to a probabilistic generalisation of
Mittag-Leffler functions.Comment: To be published in 'Chaos, Solitons & Fractals
Coherent pion production off nuclei at T2K and MiniBooNE energies revisited
As a result of a new improved fit to old bubble chamber data of the dominant
axial C_5^A nucleon-to-Delta form factor, and due to the relevance of this form
factor for neutrino induced coherent pion production, we re-evaluate our model
predictions in Phys. Rev. D79, 013002 (2009) for different observables of the
latter reaction. Central values for the total cross sections increase by 20% to
30%, while differential cross sections do not change their shape appreciably.
Furthermore, we also compute the uncertainties on total, differential and flux
averaged cross sections induced by the errors in the determination of C_5^A.
Our new results turn out to be compatible within about 1 sigma with the former
ones. Finally, we stress the existing tension between the recent experimental
determination of the sigma(CC coh \pi^+)/sigma(NC coh \pi^0) ratio by the
SciBooNE Collaboration and the theoretical predictions.Comment: 6 latex pages, 1 table, 2 figures. Shortened versio
Spatial clustering of interacting bugs: Levy flights versus Gaussian jumps
A biological competition model where the individuals of the same species
perform a two-dimensional Markovian continuous-time random walk and undergo
reproduction and death is studied. The competition is introduced through the
assumption that the reproduction rate depends on the crowding in the
neighborhood. The spatial dynamics corresponds either to normal diffusion
characterized by Gaussian jumps or to superdiffusion characterized by L\'evy
flights. It is observed that in both cases periodic patterns occur for
appropriate parameters of the model, indicating that the general macroscopic
collective behavior of the system is more strongly influenced by the
competition for the resources than by the type of spatial dynamics. However,
some differences arise that are discussed.Comment: This version incorporates in the text the correction published as an
Erratum in Europhysics Letters (EPL) 95, 69902 (2011) [doi:
10.1209/0295-5075/95/69902
Ultrahigh dielectric constant of thin films obtained by electrostatic force microscopy and artificial neural networks
Copyright 2012 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics.A detailed analysis of the electrostatic interaction between an electrostatic force microscope tip and a thin film is presented. By using artificial neural networks, an equivalent semiinfinite sample has been described as an excellent approximation to characterize the whole thin film sample. A useful analytical expression has been also developed. In the case of very small thin film thicknesses (around 1 nm), the electric response of the material differs even for very high dielectric constants. This effect can be very important for thin materials where the finite size effect can be described by an ultrahigh thin filmdielectric constant.This work was supported by TIN2010-196079. G.M.S. acknowledges support from the Spanish Ramón y Cajal Program
New determination of the - axial form factors from weak pion production and coherent pion production off nuclei at T2K and MiniBooNE energies revisited
We re-evaluate our model predictions in Phys. Rev. D 79, 013002 (2009) for
different observables in neutrino induced coherent pion production. This comes
as a result of the new improved fit to old bubble chamber data of the dominant
axial C_5^A nucleon-to-Delta form factor. We find an increase of 20%-30% in the
values for the total cross sections. Uncertainties induced by the errors in the
determination of C_5^A are computed. Our new results turn out to be compatible
within about with the former ones. We also stress the existing
tension between the recent experimental determination of the \sigma(CC coh
\pi^+)}/\sigma(NC coh \pi^0)} $ ratio by the SciBooNE Collaboration and the
theoretical predictions.Comment: 3 latex pages, 1 figure. Talk given at the NuFact10 Conferenc
Neutrino induced coherent pion production
We discuss different parameterizations of the axial
form factor, fitted to the old Argonne bubble chamber data for pion production
by neutrinos, and we use coherent pion production to test their low
behavior. We find moderate effects that will be difficult to observe with the
accuracy of present experiments. We also discuss the use of the Rein-Sehgal
model for low energy coherent pion production. By comparison to a microscopic
calculation, we show the weaknesses of some of the approximations in that model
that lead to very large cross sections as well as to the wrong shapes for
differential ones. Finally we show that models based on the partial
conservation of the axial current hypothesis are not fully reliable for
differential cross sections that depend on the angle formed by the pion and the
incident neutrino.Comment: Talk given at NUFACT09. 6 latex pages, 7 figures, 1 tabl
Masses and semileptonic decays of doubly heavy baryons in a nonrelativistic quark model
We evaluate masses and semileptonic decay widths for the ground state of
doubly heavy and baryons in the framework of a nonrelativistic
quark model. We solve the three-body problem by means of a variational ansatz
made possible by heavy-quark spin symmetry constraints. Our masses are
comparable to the ones obtained in relativistic calculations and we get one of
the best agreements with lattice data. Our simple wave functions are used to
evaluate semileptonic decays of doubly heavy and baryons. Our results for the decay widths are in reasonable
agreement with calculations done in a relativistic calculation in the
quark-diquark approximation. We also check that our wave functions comply with
what it is expected in the infinite heavy quark mass limit.Comment: 3 latex pages, two tables. To appear in the INPC07 proceeding
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