19,597 research outputs found
Chaos and dynamical trends in barred galaxies: bridging the gap between N-body simulations and time-dependent analytical models
Self-consistent N-body simulations are efficient tools to study galactic
dynamics. However, using them to study individual trajectories (or ensembles)
in detail can be challenging. Such orbital studies are important to shed light
on global phase space properties, which are the underlying cause of observed
structures. The potentials needed to describe self-consistent models are
time-dependent. Here, we aim to investigate dynamical properties
(regular/chaotic motion) of a non-autonomous galactic system, whose
time-dependent potential adequately mimics certain realistic trends arising
from N-body barred galaxy simulations. We construct a fully time-dependent
analytical potential, modeling the gravitational potentials of disc, bar and
dark matter halo, whose time-dependent parameters are derived from a
simulation. We study the dynamical stability of its reduced time-independent
2-degrees of freedom model, charting the different islands of stability
associated with certain orbital morphologies and detecting the chaotic and
regular regions. In the full 3-degrees of freedom time-dependent case, we show
representative trajectories experiencing typical dynamical behaviours, i.e.,
interplay between regular and chaotic motion for different epochs. Finally, we
study its underlying global dynamical transitions, estimating fractions of
(un)stable motion of an ensemble of initial conditions taken from the
simulation. For such an ensemble, the fraction of regular motion increases with
time.Comment: 17 pages, 11 figures (revised version, accepted for publication in
Mon. Not. R. Astron. Soc.
Single and Central Diffractive Higgs Production at the LHC
The single and central diffractive production of the Standard Model Higgs
boson is computed using the diffractive factorization formalism, taking into
account a parametrization for the Pomeron structure function provided by the H1
Collaboration. We compute the cross sections at NLO accuracy for the gluon
fusion process, since it is the leading mechanism for the Higgs boson
production. The gap survival probability is also introduced to include the
rescattering corrections due to spectator particles present in the interaction.
The diffractive ratios are predicted for proton-proton collisions at the LHC,
since the beam luminosity is favorable to the Higgs boson detection. These
results provide updated estimations for the fraction of single and central
diffractive events in the LHC kinematical regime.Comment: To appear in the proceedings of Diffraction 2010: International
Workshop on Diffraction in High Energy Physics, Otranto, Italy, 10-15 Sep
201
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.
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
- …