5,554 research outputs found
Scalar perturbations and the possible self-destruction of the phantom menace
Some analysis of the supernovae type Ia observational data seems to indicate
that the Universe today is dominated by a phantom field, for which all energy
conditions are violated. Such phantom field may imply a singularity in a future
finite time, called big rip. Studying the evolution of scalar perturbations for
such a field, we show that if the pressure is negative enough, the Universe can
become highly inhomogeneous and this phantom menace may be avoided.Comment: Latex file, 5 page
Double vector meson production in interactions at hadronic colliders
In this paper we revisit the double vector meson production in interactions at heavy ion collisions and present, by the first time,
predictions for the and production in proton --
nucleus and proton -- proton collisions. In order to obtain realistic
predictions for rapidity distributions and total cross sections for the double
vector production in ultra peripheral hadronic collisions we take into account
of the description of cross section at low
energies as well as its behaviour at large energies, associated to the gluonic
interaction between the color dipoles. Our results demonstrate that the double
production is dominated by the low energy behaviour of the cross section. In contrast, for the double
production, the contribution associated to the description of the QCD dynamics
at high energies contributes significantly, mainly in collisions.
Predictions for the RHIC, LHC, FCC and CEPC - SPPC energies are shown.Comment: 9 pages, 5 figures, 2 tables. arXiv admin note: text overlap with
arXiv:1504.0441
Exclusive photoproduction in hadronic collisions at CERN LHC energies
The exclusive photoproduction in proton-proton and proton -
nucleus collisions at LHC energies is investigated using the color dipole
formalism and considering different models for the wave function and
forward dipole - target scattering amplitude. Our goal is to update the color
dipole predictions and estimate the theoretical uncertainty present in these
predictions. We present predictions for the kinematical ranges probed by the
ALICE, CMS and LHCb Collaborations.Comment: 8 pages, 5 figures and 3 tables. Version to be published in Physics
Letters
Double vector meson production in photon - hadron interactions at hadronic colliders
In this paper we analyse the double vector meson production in photon --
hadron () interactions at collisions and present
predictions for the , and production
considering the double scattering mechanism. We estimate the total cross
sections and rapidity distributions at LHC energies and compare our results
with the predictions for the double vector meson production in
interactions at hadronic colliders. We present predictions for the different
rapidity ranges probed by the ALICE, ATLAS, CMS and LHCb Collaborations. Our
results demonstrate that the and production in
collisions is dominated by the double scattering mechanism, while the
two - photon mechanism dominates in collisions. Moreover, our results
indicate that the analysis of the production at LHC can be useful
to constrain the double scattering mechanism.Comment: 9 pages, 5 figures, 2 tables. Revised and enlarged version to be
published in the European Physical Journal
Gravitational waves in the generalized Chaplygin gas model
The consequences of taking the generalized Chaplygin gas as the dark energy
constituent of the Universe on the gravitational waves are studied and the
spectrum obtained from this model, for the flat case, is analyzed. Besides its
importance for the study of the primordial Universe, the gravitational waves
represent an additional perspective (besides the CMB temperature and
polarization anisotropies) to evaluate the consistence of the different dark
energy models and establish better constraints to their parameters. The
analysis presented here takes this fact into consideration to open one more
perspective of verification of the generalized Chapligin gas model
applicability. Nine particular cases are compared: one where no dark energy is
present; two that simulate the -CDM model; two where the gas acts like
the traditional Chaplygin gas; and four where the dark energy is the
generalized Chaplygin gas. The different spectra permit to distinguish the
-CDM and the Chaplygin gas scenarios.Comment: Latex file, 9 pages, 11 figures eps forma
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