39,124 research outputs found
Universal Features of the Time Evolution of Evanescent Modes in a Left-Handed Perfect Lens
The time evolution of evanescent modes in Pendry's perfect lens proposal for
ideally lossless and homogeneous, left-handed materials is analyzed. We show
that time development of sub-wavelength resolution exhibits universal features,
independent of model details. This is due to the unavoidable near-degeneracy of
surface electromagnetic modes in the deep sub-wavelength region. By means of a
mechanical analog, it is shown that an intrinsic time scale (missed in
stationary studies) has to be associated with any desired lateral resolution. A
time-dependent cut-off length emerges, removing the problem of divergences
claimed to invalidate Pendry's proposal.Comment: 4 pages, 3 figures, title slightly changed, reference added, minor
correction
Exclusive photoproduction of quarkonium in proton-nucleus collisions at energies available at the CERN Large Hadron Collider
In this work we investigate the coherent photoproduction of psi(1S), psi(2S)
and Upsilon (1S) states in the proton-nucleus collisions in the LHC energies.
Predictions for the rapidity distributions are presented using the color dipole
formalism and including saturation effects that are expected to be relevant at
high energies. Calculations are done at the energy 5.02 TeV and also for the
next LHC run at 8.8 TeV in proton-lead mode. Discussion is performed on the
main theoretical uncertainties associated to the calculations.Comment: 05 pages, 5 figures. Version to be published in Phys. Rev.
Light vector meson photoproduction in hadron-hadron and nucleus-nucleus collisions at the energies available at the CERN Large Hadron Collider
In this work we analyse the theoretical uncertainties on the predictions for
the photoproduction of light vector mesons in coherent pp, pA and AA collisions
at the LHC energies using the color dipole approach. In particular, we present
our predictions for the rapidity distribution for rh0 and phi photoproduction
and perform an analysis on the uncertainties associated to the choice of vector
meson wavefunctionand the phenomenological models for the dipole cross section.
Comparison is done with the recent ALICE analysis on coherent production of rho
at 2.76 TeV in PbPb collisions.Comment: 07 pages, 6 figures. Version to be published in Phys. Rev.
Diffractive dissociation in proton-nucleus collisions at collider energies
The cross section for the nuclear diffractive dissociation in proton-lead
collisions at the LHC is estimated. Based on the current theoretical
uncertainties for the single (target) diffactive cross section in hadron-hadron
reactions one obtains sigma_SD(5.02 TeV) = 19.67 \pm 5.41 mb and sigma_SD(8.8
TeV) = 18.76 \pm 5.77 mb, respectively. The invariant mass M_X for the reaction
pPb -> pX is also analyzed. Discussion is performed on the main theoretical
uncertainties associated to the calculations.Comment: 04 pages, 2 figures. Final version to be published in European
Physical Journal A - "Hadrons and Nuclei
ARES v2 - new features and improved performance
Aims: We present a new upgraded version of ARES. The new version includes a
series of interesting new features such as automatic radial velocity
correction, a fully automatic continuum determination, and an estimation of the
errors for the equivalent widths. Methods: The automatic correction of the
radial velocity is achieved with a simple cross-correlation function, and the
automatic continuum determination, as well as the estimation of the errors,
relies on a new approach to evaluating the spectral noise at the continuum
level. Results: ARES v2 is totally compatible with its predecessor. We show
that the fully automatic continuum determination is consistent with the
previous methods applied for this task. It also presents a significant
improvement on its performance thanks to the implementation of a parallel
computation using the OpenMP library.Comment: 4 pages, 2 Figures; accepted in A&A; ARES Webpage:
www.astro.up.pt/~sousasag/are
Quantum Levy flights and multifractality of dipolar excitations in a random system
We consider dipolar excitations propagating via dipole-induced exchange among
immobile molecules randomly spaced in a lattice. The character of the
propagation is determined by long-range hops (Levy flights). We analyze the
eigen-energy spectra and the multifractal structure of the wavefunctions. In 1D
and 2D all states are localized, although in 2D the localization length can be
extremely large leading to an effective localization-delocalization crossover
in realistic systems. In 3D all eigenstates are extended but not always
ergodic, and we identify the energy intervals of ergodic and non-ergodic
states. The reduction of the lattice filling induces an ergodic to non-ergodic
transition, and the excitations are mostly non-ergodic at low filling.Comment: 5 pages, 6 figure
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