1,143 research outputs found
Centaurus A as the Source of ultra-high energy cosmic rays?
We present numerical simulations for energy spectra and angular distributions
of nucleons above 10^{19} eV injected by the radio-galaxy Centaurus A at a
distance 3.4 Mpc and propagating in extra-galactic magnetic fields in the
sub-micro Gauss range. We show that field strengths B~0.3 micro Gauss, as
proposed by Farrar and Piran, cannot provide sufficient angular deflection to
explain the observational data. A magnetic field of intensity ~1 micro Gauss
could reproduce the observed large-scale isotropy and could marginally explain
the observed energy spectrum. However, it would not readily account for the
E=320 plusminus 93 EeV Fly's Eye event that was detected at an angle 136
degrees away from Cen-A. Such a strong magnetic field also saturates
observational upper limits from Faraday rotation observations and X-ray
bremsstrahlung emission from the ambient gas (assuming equipartition of
energy). This scenario may already be tested by improving magnetic field limits
with existing instruments. We also show that high energy cosmic ray experiments
now under construction will be able to detect the level of anisotropy predicted
by this scenario. We conclude that for magnetic fields B~0.1-0.5 micro Gauss,
considered as more reasonable for the local Supercluster environment, in all
likelihood at least a few sources within ~10 Mpc from the Earth should
contribute to the observed ultra high energy cosmic ray flux.Comment: 7 latex pages, 7 postscript figures included; for related numerical
simulations see also http://www.iap.fr/users/sigl/r2e.htm
Prolongation of Friction Dominated Evolution for Superconducting Cosmic Strings
This investigation is concerned with cosmological scenarios based on particle
physics theories that give rise to superconducting cosmic strings (whose
subsequent evolution may produce stable loop configurations known as vortons).
Cases in which electromagnetic coupling of the string current is absent or
unimportant have been dealt with in previous work. The purpose of the present
work is to provide quantitative estimates for cases in which electromagnetic
interaction with the surrounding plasma significantly affects the string
dynamics. In particular it will be shown that the current can become
sufficiently strong for the initial period of friction dominated string motion
to be substantially prolonged, which would entail a reinforcement of the short
length scale end of the spectrum of the string distribution, with potentially
observable cosmological implications if the friction dominated scenario lasts
until the time of plasma recombination.Comment: 10 pages Late
Gravitational wave background from neutron star phase transition for a new class of equation of state
We study the generation of a stochastic gravitational wave (GW) background
produced by a population of neutron stars (NSs) which go over a hadron-quark
phase transition in its inner shells. We obtain, for example, that the NS phase
transition, in cold dark matter scenarios, could generate a stochastic GW
background with a maximum amplitude of , in the
frequency band for stars forming at redshifts of up
to We study the possibility of detection of this isotropic GW
background by correlating signals of a pair of `advanced' LIGO observatories.Comment: 7 pages, 1 figur
Implications of a Possible Clustering of Highest Energy Cosmic Rays
Very recently, a possible clustering of a subset of observed ultrahigh energy
cosmic rays above about 40EeV (4x10^19eV) in pairs near the supergalactic plane
was reported. We show that a confirmation of this effect would provide
information on origin and nature of these events and, in case of charged
primaries, imply interesting constraints on the extragalactic magnetic field.
The observed time correlation would most likely rule out an association of
these events with cosmological gamma ray bursts. If no prominent astrophysical
source candidates such as powerful radiogalaxies can be found, the existence of
a mechanism involving new fundamental physics would be favored.Comment: 10 latex pages, 1 postscript figure, uses aaspp4.sty, submitted to
Astrophysical Journal Letter
Cosmological Magnetic Fields from Primordial Helical Seeds
Most early Universe scenarios predict negligible magnetic fields on
cosmological scales if they are unprocessed during subsequent expansion of the
Universe. We present a new numerical treatment of the evolution of primordial
fields and apply it to weakly helical seeds as they occur in certain early
Universe scenarios. We find that initial helicities not much larger than the
baryon to photon number can lead to fields of about 10^{-13} Gauss with
coherence scales slightly below a kilo-parsec today.Comment: 4 revtex pages, 2 postscript figures include
Ultra-High Energy Cosmic Ray Nuclei from Individual Magnetized Sources
We investigate the dependence of composition, spectrum and angular
distributions of ultra-high energy cosmic rays above 10^19 eV from individual
sources on their magnetization. We find that, especially for sources within a
few megaparsecs from the observer, observable spectra and composition are
severely modified if the source is surrounded by fields of ~ 10^-7 Gauss on
scales of a few megaparsecs. Low energy particles diffuse over larger distances
during their energy loss time. This leads to considerable hardening of the
spectrum up to the energy where the loss distance becomes comparable to the
source distance. Magnetized sources thus have very important consequences for
observations, even if cosmic rays arrive within a few degrees from the source
direction. At the same time, details in spectra and chemical composition may be
intrinsically unpredictable because they depend on the unknown magnetic field
structure. If primaries are predominantly nuclei of atomic mass A accelerated
up to a maximum energy E_max with spectra not much softer than E^-2, secondary
protons from photo-disintegration can produce a conspicuous peak in the
spectrum at energy ~ E_max/A. A related feature appears in the average mass
dependence on energy.Comment: 15 pages, 16 ps figures, published version with minor changes, see
http://stacks.iop.org/1475-7516/2004/i=08/a=01
The Role of Small to Moderate Volcanic Eruptions in the Early 19th Century Climate
Small-to-moderate volcanic eruptions can lead to significant surface cooling when they occur clustered, as observed in recent decades. In this study, based on new high-resolution ice-core data from Greenland, we produce a new volcanic forcing data set that includes several small-to-moderate eruptions not included in prior reconstructions and investigate their climate impacts of the early 19th century through ensemble simulations with the Max Planck Institute Earth System Model. We find that clustered small-to-moderate eruptions produce significant additional global surface cooling (âŒ0.07 K) during the period 1812â1820, superposing with the cooling by large eruptions in 1809 (unidentified location) and 1815 (Tambora). This additional cooling helps explain the reconstructed long-lasting cooling after the large eruptions, but simulated regional impacts cannot be confirmed with reconstructions due to a low signal-to-noise ratio. This study highlights the importance of small-to-moderate eruptions for climate simulations as their impacts can be comparable with that of solar irradiance changes
Do many-particle neutrino interactions cause a novel coherent effect?
We investigate whether coherent flavor conversion of neutrinos in a neutrino
background is substantially modified by many-body effects, with respect to the
conventional one-particle effective description. We study the evolution of a
system of interacting neutrino plane waves in a box. Using its equivalence to a
system of spins, we determine the character of its behavior completely
analytically. We find that, if the neutrinos are initially in flavor
eigenstates, no coherent flavor conversion is realized, in agreement with the
effective one-particle description. This result does not depend on the size of
the neutrino wavepackets and therefore has a general character. The validity of
the several important applications of the one-particle formalism is thus
confirmed.Comment: 25 pages, 1 figur
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