425 research outputs found
Phenomenology on the QCD dipole picture revisited
We perform an adjust to the most recent structure function data, considering
the QCD dipole picture applied to ep scattering. The structure function F2 at
small x and intermediate Q2 can be described by the model containing an
economical number of free-parameters, which encodes the hard Pomeron physics.
The longitudinal structure function and the gluon distribution are predicted
without further adjustments. The data description is effective, whereas a
resummed next-to-leading level analysis is deserved.Comment: 18 pages, 6 figures. Version to be published in Eur. Phys. J.
Time dependent neutrino billiards
Quantum dynamica of a massless Dirac particle in time-dependent 1D box and
circular billiard with time-dependent radius is studied. An exact analytical
wave functions and eigenvalues are obtained for the case of linear
time-dependence of the boundary position
The Schrodinger particle in an oscillating spherical cavity
We study a Schrodinger particle in an infinite spherical well with an
oscillating wall. Parametric resonances emerge when the oscillation frequency
is equal to the energy difference between two eigenstates of the static cavity.
Whereas an analytic calculation based on a two-level system approximation
reproduces the numerical results at low driving amplitudes, epsilon, we observe
a drastic change of behaviour when epsilon > 0.1, when new resonance states
appear bearing no apparent relation to the eigenstates of the static system.Comment: 9 pages, 6 figures, corrected typo
Prompt neutrino fluxes from atmospheric charm
We calculate the prompt neutrino flux from atmospheric charm production by
cosmic rays, using the dipole picture in a perturbative QCD framework, which
incorporates the parton saturation effects present at high energies. We compare
our results with the next-to-leading order perturbative QCD result and find
that saturation effects are large for neutrino energies above 10^6 GeV, leading
to a substantial suppression of the prompt neutrino flux. We comment on the
range of prompt neutrino fluxes due to theoretical uncertainties.Comment: 13 pages with 11 figures; expanded discussion, added references,
version to be published in Phys. Rev.
On the linearization of the generalized Ermakov systems
A linearization procedure is proposed for Ermakov systems with frequency
depending on dynamic variables. The procedure applies to a wide class of
generalized Ermakov systems which are linearizable in a manner similar to that
applicable to usual Ermakov systems. The Kepler--Ermakov systems belong into
this category but others, more generic, systems are also included
Geometric Scaling in Inclusive Charm Production
We show that the cross section for inclusive charm production exhibits
geometric scaling in a large range of photon virtualities. In the HERA
kinematic domain the saturation momentum stays below the hard
scale , implying charm production probing mostly the color
transparency regime and unitarization effects being almost negligible. We
derive our results considering two saturation models which are able to describe
the DESY ep collider HERA data for the proton structure function at small
values of the Bjorken variable . A striking feature is the scaling on
above saturation limit, corroborating recent
theoretical studies.Comment: 4 pages, 2 figures. Version to be published in Physical Review
Letter
Geometric Scaling in a Symmetric Saturation Model
We illustrate geometric scaling for the photon-proton cross section with a
very simple saturation model. We describe the proton structure function F2 at
small x in a wide kinematical range with an elementary functional form and a
small number of free parameters. We speculate that the symmetry between low and
high Q2 recently discovered in the data could be related to a well-known
symmetry of the two-gluon- exchange dipole-dipole cross section.Comment: 15 pages, 4 figure
Lie symmetries for two-dimensional charged particle motion
We find the Lie point symmetries for non-relativistic two-dimensional charged
particle motion. These symmetries comprise a quasi-invariance transformation, a
time-dependent rotation, a time-dependent spatial translation and a dilation.
The associated electromagnetic fields satisfy a system of first-order linear
partial differential equations. This system is solved exactly, yielding four
classes of electromagnetic fields compatible with Lie point symmetries
Quantum metastability in a class of moving potentials
In this paper we consider quantum metastability in a class of moving
potentials introduced by Berry and Klein. Potential in this class has its
height and width scaled in a specific way so that it can be transformed into a
stationary one. In deriving the non-decay probability of the system, we argue
that the appropriate technique to use is the less known method of scattering
states. This method is illustrated through two examples, namely, a moving
delta-potential and a moving barrier potential. For expanding potentials, one
finds that a small but finite non-decay probability persists at large times.
Generalization to scaling potentials of arbitrary shape is briefly indicated.Comment: 10 pages, 1 figure
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