1,040 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
On the spectrum of the transfer operators of a one-parameter family with intermittency transition
We study the transfer operators for a family depending
on the parameter , which interpolates between the tent map and the
Farey map. In particular, considering the action of the transfer operator on a
suitable Hilbert space, we can define a family of infinite matrices associated
to the operators and study their spectrum by numerical methods.Comment: 6 pages, 3 figure
The correlation between soft and hard X-rays component in flares: from the Sun to the stars
In this work we study the correlation between the soft (1.6--12.4 keV, mostly
thermal) and the hard (20--40 and 60--80 keV, mostly non-thermal) X-ray
emission in solar flares up to the most energetic events, spanning about 4
orders of magnitude in peak flux, establishing a general scaling law and
extending it to the most intense stellar flaring events observed to date. We
used the data from the Reuven Ramaty High-Energy Solar Spectroscopic Imager
(RHESSI) spacecraft, a NASA Small Explorer launched in February 2002. RHESSI
has good spectral resolution (~1 keV in the X-ray range) and broad energy
coverage (3 keV--20 MeV), which makes it well suited to distinguish the thermal
from non-thermal emission in solar flares. Our study is based on the detailed
analysis of 45 flares ranging from the GOES C-class, to the strongest X-class
events, using the peak photon fluxes in the GOES 1.6--12.4 keV and in two bands
selected from RHESSI data, i.e.20--40 keV and 60--80 keV. We find a significant
correlation between the soft and hard peak X-ray fluxes spanning the complete
sample studied. The resulting scaling law has been extrapolated to the case of
the most intense stellar flares observed, comparing it with the stellar
observations. Our results show that an extrapolation of the scaling law derived
for solar flares to the most active stellar events is compatible with the
available observations of intense stellar flares in hard X-rays.Comment: 9 pages, 10 figures. To be published in Astronomy and Astrophysic
Statistics of energy levels and zero temperature dynamics for deterministic spin models with glassy behaviour
We consider the zero-temperature dynamics for the infinite-range, non
translation invariant one-dimensional spin model introduced by Marinari, Parisi
and Ritort to generate glassy behaviour out of a deterministic interaction. It
is shown that there can be a large number of metatastable (i.e., one-flip
stable) states with very small overlap with the ground state but very close in
energy to it, and that their total number increases exponentially with the size
of the system.Comment: 25 pages, 8 figure
Neutrino self-energy in a magnetized medium in arbitrary -gauge
We calculate the one-loop neutrino self-energy in a magnetized plasma to all
orders in the magnetic field. The calculation is done in a general gauge. We
obtain the dispersion relation and effective potential for neutrinos in a
CP-symmetric plasma under various conditions, and show that, while the
self-energy depends on the gauge parameter , the dispersion relation and
effective potential to leading order are independent of it.Comment: 13 pages, RevTeX, epsfig, axodra
On the leading eigenvalue of transfer operators of the Farey map with real temperature
We study the spectral properties of a family of generalized transfer
operators associated to the Farey map. We show that when acting on a suitable
space of holomorphic functions, the operators are self-adjoint and the positive
dominant eigenvalue can be approximated by means of the matrix expression of
the operators.Comment: 9 pages, 3 figure
Power Corrections in Charmless B Decays
In this paper, we focus on the role of power corrections in QCD
factorization(QCDF) method in charmless two-body nonleptonic meson decays.
We use the ratio of the branching fraction of to
that of , for which the theoretical uncertainties are
greatly reduced, to show clearly that the power corrections in charmless B
decays are probably large. With other similar ratios considered, for example,
for the decay, it is very likely that, among various
sources of power corrections, annihilation topology plays an indispensable role
at least for penguin dominated channels. We also consider some
selective ratios of direct CP asymmetries. Among these, we find that, if power
corrections other than the chirally enhanced power corrections and annihilation
topology were negligible, QCDF would predict the direct CP asymmetry of to be about 3 times larger than that of ,
with opposite sign. Experimentally any significant deviation from this
prediction would suggest either new physics or possibly the importance of
long-distance rescattering effects.Comment: references and note added, to appear in Phys. Rev.
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