1,449 research outputs found
Statistical properties of the GALEX spectroscopic stellar sample
The GALEX General Data Release 4/5 includes 174 spectroscopic tiles, obtained
from slitless grism observations, for a total of more than 60,000 ultraviolet
spectra. We have determined statistical properties of the sample of GALEX
stars. We have defined a suitable system of spectroscopic indices, which
measure the main mid-UV features at the GALEX low spectral resolution and we
have employed it to determine the atmospheric parameters of of stars in the
range 4500<Teff<9000 K. Our preliminary results indicate that the sample is
formed by a majority of main sequence F- and G-type stars, with metallicity
[M/H]>-1 dex.Comment: 9 pages, 9 figures, accepted for publication in Astrophysics & Space
Science, UV universe special issu
Probing the Nature of the Weakest Intergalactic Magnetic Fields with the High Energy Emission of Gamma-Ray Bursts
We investigate the delayed, secondary GeV-TeV emission of gamma-ray bursts
and its potential to probe the nature of intergalactic magnetic fields.
Geometrical effects are properly taken into account for the time delay between
primary high energy photons and secondary inverse Compton photons from
electron-positron pairs, which are produced in - interactions
with background radiation fields and deflected by intervening magnetic fields.
The time-dependent spectra of the delayed emission are evaluated for a wide
range of magnetic field strengths and redshifts. The typical flux and delay
time of secondary photons from bursts at are respectively GeV cm s and s if the field strengths are
G, as might be the case in intergalactic void regions. We find
crucial differences between the cases of coherent and tangled magnetic fields,
as well as dependences on the field coherence length.Comment: 19 pages, 9 figures, formulation revised, accepted for publication in
Ap
Handling and Transport of Oversized Accelerator Components and Physics Detectors
For cost, planning and organisational reasons, it is often decided to install large pre-built accelerators components and physics detectors. As a result surface exceptional transports are required from the construction to the installation sites. Such heavy transports have been numerous during the LHC installation phase. This paper will describe the different types of transport techniques used to fit the particularities of accelerators and detectors components (weight, height, acceleration, planarity) as well as the measurement techniques for monitoring and the logistical aspects (organisation with the police, obstacles on the roads, etc). As far as oversized equipment is concerned, the lowering into the pit is challenging, as well as the transport in tunnel galleries in a very scare space and without handling means attached to the structure like overhead travelling cranes. From the PS accelerator to the LHC, handling systems have been developed at CERN to fit with these particular working conditions. This paper will expose the operating conditions of the main transport equipments used at CERN in PS, SPS and LHC tunnels
The WIMP Forest: Indirect Detection of a Chiral Square
The spectrum of photons arising from WIMP annihilation carries a detailed
imprint of the structure of the dark sector. In particular, loop-level
annihilations into a photon and another boson can in principle lead to a series
of lines (a WIMP forest) at energies up to the WIMP mass. A specific model
which illustrates this feature nicely is a theory of two universal extra
dimensions compactified on a chiral square. Aside from the continuum emission,
which is a generic prediction of most dark matter candidates, we find a
"forest" of prominent annihilation lines that, after convolution with the
angular resolution of current experiments, leads to a distinctive (2-bump plus
continuum) spectrum, which may be visible in the near future with the Fermi
Gamma-Ray Space Telescope (formerly known as GLAST).Comment: 11 pages, 4 figure
Systematic uncertainties in the determination of the local dark matter density
A precise determination of the local dark matter density and an accurate
control over the corresponding uncertainties are of paramount importance for
Dark Matter (DM) searches. Using very recent high-resolution numerical
simulations of a Milky Way like object, we study the systematic uncertainties
that affect the determination of the local dark matter density based on
dynamical measurements in the Galaxy. In particular, extracting from the
simulation with baryons the orientation of the Galactic stellar disk with
respect to the DM distribution, we study the DM density for an observer located
at 8 kpc from the Galactic center {\it on the stellar disk}, .
This quantity is found to be always larger than the average density in a
spherical shell of same radius , which is the quantity inferred
from dynamical measurements in the Galaxy, and to vary in the range
. This suggests that the actual dark matter
density in the solar neighbourhood is on average 21\% larger than the value
inferred from most dynamical measurements, and that the associated systematic
errors are larger than the statistical errors recently discussed in the
literature.Comment: 6 pages, 3 figures, matches published versio
The Abundance of New Kind of Dark Matter Structures
A new kind of dark matter structures, ultracompact minihalos (UCMHs) was
proposed recently. They would be formed during the radiation dominated epoch if
the large density perturbations are existent. Moreover, if the dark matter is
made up of weakly interacting massive particles, the UCMHs can have effect on
cosmological evolution because of the high density and dark matter annihilation
within them. In this paper, one new parameter is introduced to consider the
contributions of UCMHs due to the dark matter annihilation to the evolution of
cosmology, and we use the current and future CMB observations to obtain the
constraint on the new parameter and then the abundance of UCMHs. The final
results are applicable for a wider range of dark matter parametersComment: 4 pages, 1 tabl
The moment of truth for WIMP Dark Matter
We know that dark matter constitutes 85% of all the matter in the Universe,
but we do not know of what it is made. Amongst the many Dark Matter candidates
proposed, WIMPs (weakly interacting massive particles) occupy a special place,
as they arise naturally from well motivated extensions of the standard model of
particle physics. With the advent of the Large Hadron Collider at CERN, and a
new generation of astroparticle experiments, the moment of truth has come for
WIMPs: either we will discover them in the next five to ten years, or we will
witness the inevitable decline of WIMP paradigm.Comment: To appear in Nature (Nov 18, 2010
Kaon oscillations in the Standard Model and Beyond using Nf=2 dynamical quarks
We compute non-perturbatively the B-parameters of the complete basis of
four-fermion operators needed to study the Kaon oscillations in the SM and in
its supersymmetric extension. We perform numerical simulations with two
dynamical maximally twisted sea quarks at three values of the lattice spacing
on configurations generated by the ETMC. Unwanted operator mixings and O(a)
discretization effects are removed by discretizing the valence quarks with a
suitable Osterwalder-Seiler variant of the Twisted Mass action. Operators are
renormalized non-perturbatively in the RI/MOM scheme. Our preliminary result
for BK(RGI) is 0.73(3)(3).Comment: 7 pages, 3 figures, 1 table, proceedings of the XXVII Int'l Symposyum
on Lattice Field Theory (LAT2009), July 26-31 2009, Peking University,
Beijing (China
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