2,568 research outputs found
Insertion device for pressure testing
Test device which introduces either pressure or vacuum into a test pipe or tube, is insertable into the tested item where it secures itself into position and requires no external support. The unit has an operating range from zero to 25,000 psig and to any vacuum level that available equipment can reach
Constraints on WIMP Dark Matter from the High Energy PAMELA data
A new calculation of the ratio in cosmic rays is compared to the
recent PAMELA data. The good match up to 100 GeV allows to set constraints on
exotic contributions from thermal WIMP dark matter candidates. We derive
stringent limits on possible enhancements of the WIMP \pbar flux: a =100 GeV (1 TeV) signal cannot be increased by more than a factor 6 (40)
without overrunning PAMELA data. Annihilation through the channel is
also inspected and cross-checked with data. This scenario is
strongly disfavored as it fails to simultaneously reproduce positron and
antiproton measurements.Comment: 5 pages, 5 figures, the bibliography has been updated, minor
modifications have been made in the tex
Galactic positrons and electrons from astrophysical sources and dark matter
A very interesting puzzle about the origin of electron and positron cosmic
rays is deduced from the latests experimental results. We model the propagation
of such cosmic rays in terms of a successfully tested two--zone propagation
model. Several theoretical uncertainties -- like ones related to propagation --
are considered to study different types of electron and positron sources: dark
matter annihilation, secondary production, and supernova remnants.Comment: 3 pages, 1 figure. Proceedings for conference "Topics in
Astroparticle and Underground Physics" (TAUP2009). Rome, July 1-5, 200
Galactic secondary positron flux at the Earth
Secondary positrons are produced by spallation of cosmic rays within the
interstellar gas. Measurements have been typically expressed in terms of the
positron fraction, which exhibits an increase above 10 GeV. Many scenarios have
been proposed to explain this feature, among them some additional primary
positrons originating from dark matter annihilation in the Galaxy. The PAMELA
satellite has provided high quality data that has enabled high accuracy
statistical analyses to be made, showing that the increase in the positron
fraction extends up to about 100 GeV. It is therefore of paramount importance
to constrain theoretically the expected secondary positron flux to interpret
the observations in an accurate way. We find the secondary positron flux to be
reproduced well by the available observations, and to have theoretical
uncertainties that we quantify to be as large as about one order of magnitude.
We also discuss the positron fraction issue and find that our predictions may
be consistent with the data taken before PAMELA. For PAMELA data, we find that
an excess is probably present after considering uncertainties in the positron
flux, although its amplitude depends strongly on the assumptions made in
relation to the electron flux. By fitting the current electron data, we show
that when considering a soft electron spectrum, the amplitude of the excess
might be far lower than usually claimed. We provide fresh insights that may
help to explain the positron data with or without new physical model
ingredients. PAMELA observations and the forthcoming AMS-02 mission will allow
stronger constraints to be aplaced on the cosmic--ray transport parameters, and
are likely to reduce drastically the theoretical uncertainties.Comment: 15 pages, 12 figures. The recent PAMELA data on the positron fraction
(arXiv:0810.4995) have been included and the ensuing discussion has been
extended. Accepted version in A&
Estimates on Green functions of second order differential operators with singular coefficients
We investigate the Green functions G(x,x^{\prime}) of some second order
differential operators on R^{d+1} with singular coefficients depending only on
one coordinate x_{0}. We express the Green functions by means of the Brownian
motion. Applying probabilistic methods we prove that when x=(0,{\bf x}) and
x^{\prime}=(0,{\bf x}^{\prime}) (here x_{0}=0) lie on the singular hyperplanes
then G(0,{\bf x};0,{\bf x}^{\prime}) is more regular than the Green function of
operators with regular coefficients.Comment: 16 page
Infinite barbarians
This paper discusses an infinite regress that looms behind a certain kind of historical explanation. The movement of one barbarian group is often explained by the movement of others, but those movements in turn call for an explanation. While their explanation can again be the movement of yet another group of barbarians, if this sort of explanation does not stop somewhere we are left with an infinite regress of barbarians. While that regress would be vicious, it cannot be accommodated by several general views about what viciousness in infinite regresses amounts to. This example is additional evidence that we should prefer a pluralist approach to infinite regresses
TeV cosmic-ray proton and helium spectra in the myriad model
Recent measurements of cosmic ray proton and helium spectra show a hardening
above a few hundreds of GeV. This excess is hard to understand in the framework
of the conventional models of Galactic cosmic ray production and propagation.
We propose here to explain this anomaly by the presence of local sources
(myriad model). Cosmic ray propagation is described as a diffusion process
taking place inside a two-zone magnetic halo. We calculate the proton and
helium fluxes at the Earth between 50 GeV and 100 TeV. Improving over a similar
analysis, we consistently derive these fluxes by taking into account both local
and remote sources for which a unique injection rate is assumed. We find cosmic
ray propagation parameters compatible with B/C measurements and for which the
proton and helium spectra remarkably agree with the PAMELA and CREAM
measurements over four decades in energy.Comment: 5 pages, 3 figure
Implication of the PAMELA antiproton data for dark matter indirect detection at LHC
Since the PAMELA results on the "anomalously" high positron fraction and the
lack of antiproton excess in our Galaxy, there has been a tremendous number of
studies advocating new types of dark matter, with larger couplings to electrons
than to quarks.
This raises the question of the production of dark matter particles (and
heavy associated coloured states) at LHC. Here, we explore a very simple
benchmark dark matter model and show that, in spite of the agreement between
the PAMELA antiproton measurements and the expected astrophysical secondary
background, there is room for large couplings of a WIMP candidate to heavy
quarks. Contrary to what could have been naively anticipated, the PAMELA pbar/p
measurements do not challenge dark matter model building, as far as the quark
sector is concerned. A quarkophillic species is therefore not forbidden.Owing
to these large couplings, one would expect that a new production channel opens
up at the LHC, through quark--quark and quark--gluon interactions. Alas, when
the PDF of the quark is taken into account, prospects for a copious production
fade away.Comment: 7 pages, 2 figures, captions of some figures modified, main
conclusion unchange
Improved sensitivity of H.E.S.S.-II through the fifth telescope focus system
The Imaging Atmospheric Cherenkov Telescope (IACT) works by imaging the very
short flash of Cherenkov radiation generated by the cascade of relativistic
charged particles produced when a TeV gamma ray strikes the atmosphere. This
energetic air shower is initiated at an altitude of 10-30 km depending on the
energy and the arrival direction of the primary gamma ray. Whether the best
image of the shower is obtained by focusing the telescope at infinity and
measuring the Cherenkov photon angles or focusing on the central region of the
shower is a not obvious question. This is particularly true for large size IACT
for which the depth of the field is much smaller. We address this issue in
particular with the fifth telescope (CT5) of the High Energy Stereoscopic
System (H.E.S.S.); a 28 m dish large size telescope recently entered in
operation and sensitive to an energy threshold of tens of GeVs. CT5 is equipped
with a focus system, its working principle and the expected effect of focusing
depth on the telescope sensitivity at low energies (50-200 GeV) is discussed.Comment: In Proceedings of the 33rd International Cosmic Ray Conference
(ICRC2013), Rio de Janeiro (Brazil
Dark Matter detection via lepton cosmic rays
Recent observations of lepton cosmic rays, coming from the PAMELA and FERMI
experiments, have pushed our understanding of the interstellar medium and
cosmic rays sources to unprecedented levels. The imprint of dark matter on
lepton cosmic rays is the most exciting explanation of both PAMELA's positron
excess and FERMI's total flux of electrons. Alternatively, supernovae are
astrophysical objects with the same potential to explain these observations. In
this work, we present an updated study of the astrophysical sources of lepton
cosmic rays and the possible trace of a dark matter signal on the positron
excess and total flux of electrons.Comment: 6 pages and 3 figures. Proceedings for PASCOS 2010, Valencia, Spai
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