887 research outputs found
Review of the Safety of LHC Collisions
The safety of collisions at the Large Hadron Collider (LHC) was studied in
2003 by the LHC Safety Study Group, who concluded that they presented no
danger. Here we review their 2003 analysis in light of additional experimental
results and theoretical understanding, which enable us to confirm, update and
extend the conclusions of the LHC Safety Study Group. The LHC reproduces in the
laboratory, under controlled conditions, collisions at centre-of-mass energies
less than those reached in the atmosphere by some of the cosmic rays that have
been bombarding the Earth for billions of years. We recall the rates for the
collisions of cosmic rays with the Earth, Sun, neutron stars, white dwarfs and
other astronomical bodies at energies higher than the LHC. The stability of
astronomical bodies indicates that such collisions cannot be dangerous.
Specifically, we study the possible production at the LHC of hypothetical
objects such as vacuum bubbles, magnetic monopoles, microscopic black holes and
strangelets, and find no associated risks. Any microscopic black holes produced
at the LHC are expected to decay by Hawking radiation before they reach the
detector walls. If some microscopic black holes were stable, those produced by
cosmic rays would be stopped inside the Earth or other astronomical bodies. The
stability of astronomical bodies constrains strongly the possible rate of
accretion by any such microscopic black holes, so that they present no
conceivable danger. In the case of strangelets, the good agreement of
measurements of particle production at RHIC with simple thermodynamic models
constrains severely the production of strangelets in heavy-ion collisions at
the LHC, which also present no danger.Comment: This revised version incorporates the "Addendum on strangelets" as
Appendix, and updates the bibliograph
Evolution of the Order Parameter after Bubble Collisions
If a first-order phase transition is terminated by collisions of new-phase
bubbles, there will exist a period of nonequilibrium between the time bubbles
collide and the time thermal equilibrium is established. We study the behavior
of the order parameter during this phase. We find that large nonthermal
fluctuations at this stage tend to restore symmetry, i.e., the order parameter
is smaller than its eventual thermal equilibrium value. We comment on possible
consequences for electroweak baryogenesis.Comment: 11 page LaTeX file with two figures, fig1.ps and fig2.p
Constrained Simulations of the Magnetic Field in the Local Universe and the Propagation of UHECRs
We use simulations of LSS formation to study the build-up of magnetic fields
(MFs) in the ICM. Our basic assumption is that cosmological MFs grow in a MHD
amplification process driven by structure formation out of a seed MF present at
high z. Our LCDM initial conditions for the density fluctuations have been
statistically constrained by the observed galaxies, based on the IRAS 1.2-Jy
all-sky redshift survey. As a result, prominent galaxy clusters in our
simulation coincide closely with their real counterparts. We find excellent
agreement between RMs of our simulated clusters and observational data. The
improved resolution compared to previous work also allows us to study the MF in
large-scale filaments, sheets and voids. By tracing the propagation of UHE
protons in the simulated MF we construct full-sky maps of expected deflection
angles of protons with arrival energies E=1e20eV and 4e19eV, respectively.
Strong deflections are only produced if UHE protons cross clusters, however
covering only a small area on the sky. Multiple crossings of sheets and
filaments over larger distances may give rise to noticeable deflections,
depending on the model adopted for the magnetic seed field. Based on our
results we argue that over a large fraction of the sky the deflections are
likely to remain smaller than the present experimental angular sensitivity.
Therefore, we conclude that forthcoming air shower experiments should be able
to locate sources of UHE protons and shed more light on the nature of
cosmological MFs.Comment: 3revised version, JCAP, accepte
Comment on "Correlation of the Highest-Energy Cosmic Rays with Nearby Extragalactic Objects"
We argue that the data published by the Pierre Auger Collaboration
(arXiv:0711.2256) disfavor at 99% confidence level their hypothesis that most
of the highest-energy cosmic rays are protons from nearby astrophysical
sources, either Active Galactic Nuclei or other objects with a similar spatial
distribution.Comment: 1000 words, 2 figures, scicite.st
BL Lacertae are probable sources of the observed ultra-high energy cosmic rays
We calculate angular correlation function between ultra-high energy cosmic
rays (UHECR) observed by Yakutsk and AGASA experiments, and most powerful BL
Lacertae objects. We find significant correlations which correspond to the
probability of statistical fluctuation less than , including penatly
for selecting the subset of brightest BL Lacs. We conclude that some of BL Lacs
are sources of the observed UHECR and present a list of most probable
candidates.Comment: Replaced with the version accepted for publication in JETP Let
Gamma photons from parametric resonance in neutron stars
Shock waves in cold nuclear matter, e.g. those induced by a collision of two
neutron stars, can generate a large number of gamma photons via parametric
resonance. We study the resonant production of gamma rays inside a shocked
neutron star and discuss the possible astrophysical consequences of this
phenomenon.Comment: 5 pages, ReVTeX, 5 figures inserted with epsf; replaced with a final
version (minor changes
Patterns from preheating
The formation of regular patterns is a well-known phenomenon in condensed
matter physics. Systems that exhibit pattern formation are typically driven and
dissipative with pattern formation occurring in the weakly non-linear regime
and sometimes even in more strongly non-linear regions of parameter space. In
the early universe, parametric resonance can drive explosive particle
production called preheating. The fields that are populated then decay quantum
mechanically if their particles are unstable. Thus, during preheating, a
driven-dissipative system exists. In this paper, we show that a self-coupled
inflaton oscillating in its potential at the end of inflation can exhibit
pattern formation.Comment: 4 pages, RevTex, 6 figure
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