16 research outputs found
Constraints on the Intergalactic Transport of Cosmic Rays
Motivated by recent experimental proposals to search for extragalactic cosmic
rays (including anti-matter from distant galaxies), we study particle
propagation through the intergalactic medium (IGM). We first use estimates of
the magnetic field strength between galaxies to constrain the mean free path
for diffusion of particles through the IGM. We then develop a simple analytic
model to describe the diffusion of cosmic rays. Given the current age of
galaxies, our results indicate that, in reasonable models, a completely
negligible number of particles can enter our Galaxy from distances greater than
Mpc for relatively low energies ( GeV/n). We also find
that particle destruction in galaxies along the diffusion path produces an
exponential suppression of the possible flux of extragalactic cosmic rays.
Finally, we use gamma ray constraints to argue that the distance to any
hypothetical domains of anti-matter must be roughly comparable to the horizon
scale.Comment: 24 pages, AAS LaTex, 1 figure, accepted to Ap
Measurement of the cosmic ray antiproton/proton flux ratio at TeV energies with the ARGO-YBJ detector
Cosmic ray antiprotons provide an important probe to study the cosmic ray
propagation in the interstellar space and to investigate the existence of dark
matter. Acting the Earth-Moon system as a magnetic spectrometer, paths of
primary antiprotons are deflected in the opposite sense with respect to those
of the protons in their way to the Earth. This effect allows, in principle, the
search for antiparticles in the direction opposite to the observed deficit of
cosmic rays due to the Moon (the so-called `Moon shadow').
The ARGO-YBJ experiment, located at the Yangbajing Cosmic Ray Laboratory
(Tibet, P.R. China, 4300 m a.s.l., 606 g/cm), is particularly effective in
measuring the cosmic ray antimatter content via the observation of the cosmic
rays shadowing effect due to: (1) good angular resolution, pointing accuracy
and long-term stability; (2) low energy threshold; (3) real sensitivity to the
geomagnetic field.
Based on all the data recorded during the period from July 2006 through
November 2009 and on a full Monte Carlo simulation, we searched for the
existence of the shadow cast by antiprotons in the TeV energy region. No
evidence of the existence of antiprotons is found in this energy region. Upper
limits to the flux ratio are set to 5 % at a median energy of 1.4
TeV and 6 % at 5 TeV with a confidence level of 90%. In the TeV energy range
these limits are the lowest available.Comment: Contact authors: G. Di Sciascio ([email protected]) and R.
Iuppa ([email protected]), INFN Sezione di Roma Tor Vergata, Roma, Ital
The Role of N-Acetyltransferase 2 Polymorphism in the Etiopathogenesis of Inflammatory Bowel Disease
A MATTER–ANTIMATTER UNIVERSE?
We ask whether the universe can be a patchwork consisting of distinct regions of matter and antimatter. We demonstrate that, after recombination, it is impossible to avoid annihilation near regional boundaries. We study the dynamics of this process to estimate two of its signatures: a contribution to the cosmic diffuse γ-ray background and a distortion of the cosmic microwave background. The former signal exceeds observational limits unless the matter domain we inhabit is virtually the entire visible universe. On general grounds, we conclude that a matter–antimatter symmetric universe is empirically excluded.
Rapid aneuploidy detection or karyotyping? Ethical reflection
No consensus exists whether women at increased risk for trisomy 21, 13, and 18 should be offered stand-alone rapid aneuploidy detection (RAD) or karyotyping. In this paper, the ethical implications of a fast, relatively cheap and targeted RAD are examined. The advantages of RAD seem less robust than its proponents suggest. Fast test results only give a short-term psychological benefit. The cost advantage of RAD is apparent, but must be weighed against consequences like missed abnormalities, which are evaluated differently by professionals and pregnant women. Since pre-test information about RAD will have to include telling women about karyotyping as a possible alternative, the advantage of RAD in terms of the quantity of information that needs to be given may also be smaller than suggested. We conclude that none of the supposed arguments in favour of RAD is decisive in itself. Whether the case for RAD may still be regarded as convincing when taking these arguments together seems to depend on one's implicit view of what prenatal screening is about. Are we basically dealing with a test for trisomy 21 and a few conditions more? Or are there good grounds for also testing for the wider range of abnormalities that karyotyping can detect? As professionals and pregnant women may have different views about this, we suggest that the best approach is to offer women a choice between RAD and karyotyping. This approach is most in line with the general aim of prenatal screening: providing opportunities for autonomous reproductive choic