22,127 research outputs found
Relativistic deuteron structure function at large Q^2
The deuteron deep inelastic unpolarized structure function F_2^D is
calculated using the Wilson operator product expansion method. The long
distance behaviour, related to the deuteron bound state properties, is
evaluated using the Bethe-Salpeter equation with one particle on mass shell.
The calculation of the ratio F_2^D/F_2^N is compared with other convolution
models showing important deviations in the region of large x. The implications
in the evaluation of the neutron structure function from combined data on
deuterons and protons are discussed.Comment: 7 pages, 1 ps figure, RevTeX source, 1 tar.gz file. Submited to
Physical Letter
The impact of the air-fluorescence yield on the reconstructed shower parameters of ultra-high energy cosmic rays
An accurate knowledge of the fluorescence yield and its dependence on
atmospheric properties such as pressure, temperature or humidity is essential
to obtain a reliable measurement of the primary energy of cosmic rays in
experiments using the fluorescence technique. In this work, several sets of
fluorescence yield data (i.e. absolute value and quenching parameters) are
described and compared. A simple procedure to study the effect of the assumed
fluorescence yield on the reconstructed shower parameters (energy and shower
maximum depth) as a function of the primary features has been developed. As an
application, the effect of water vapor and temperature dependence of the
collisional cross section on the fluorescence yield and its impact on the
reconstruction of primary energy and shower maximum depth has been studied.Comment: Accepted in Astroparticle Physic
Measuring Baryon Acoustic Oscillations with Millions of Supernovae
Since type Ia Supernovae (SNe) explode in galaxies, they can, in principle,
be used as the same tracer of the large-scale structure as their hosts to
measure baryon acoustic oscillations (BAOs). To realize this, one must obtain a
dense integrated sampling of SNe over a large fraction of the sky, which may
only be achievable photometrically with future projects such as the Large
Synoptic Survey Telescope. The advantage of SN BAOs is that SNe have more
uniform luminosities and more accurate photometric redshifts than galaxies, but
the disadvantage is that they are transitory and hard to obtain in large number
at high redshift. We find that a half-sky photometric SN survey to redshift z =
0.8 is able to measure the baryon signature in the SN spatial power spectrum.
Although dark energy constraints from SN BAOs are weak, they can significantly
improve the results from SN luminosity distances of the same data, and the
combination of the two is no longer sensitive to cosmic microwave background
priors.Comment: 4 pages, 3 figures, ApJL accepte
Global extraction of the parton-to-pion fragmentation functions at NLO accuracy in QCD
In this review, we discuss the results on the parton-to-pion fragmentation
functions obtained in a combined NLO fit to data of single-inclusive hadron
production in electron-positron annihilation, proton-proton collisions, and
lepton-nucleon deep-inelastic scattering. A more complete discussion can be
found in Ref. [1].Comment: 6 pages, 1 figure. To be published in Journal of Physics Conference
Series (IOP). Joint Proceedings of the XV Mexican Workshop on Particles and
Fields & the XXX Annual Meeting of the Division of Particles and Fields of
the Mexican Physical Societ
Efeito de fertilizantes nitrogenados no comportamento de plantas de melão cultivadas em casa de vegetação.
Com o objetivo de avaliar o efeito de fontes de nitrogênio sobre a área foliar, a produção de matéria seca e o conteúdo de nitrogênio na parte aérea de plantas de melão (Cucumis melo L.) conduziu-se um ensaio em casa de vegetação, em Petrolina, PE, Brasil, com o híbrido Hy Mark
Schwinger's Method for the Massive Casimir Effect
We apply to the massive scalar field a method recently proposed by Schwinger
to calculate the Casimir effect. The method is applied with two different
regularization schemes: the Schwinger original one by means of Poisson formula
and another one by means of analytical continuation.Comment: plain TeX, 6 pages, DFTUZ-93-2
Self-Regulation of Star Formation in Low Metallicity Clouds
We investigate the process of self-regulated star formation via
photodissociation of hydrogen molecules in low metallicity clouds. We evaluate
the influence region's scale of a massive star in low metallicity gas clouds
whose temperatures are between 100 and 10000 Kelvin. A single O star can
photodissociate hydrogen molecules in the whole of the host cloud. If
metallicity is smaller than about 10^{-2.5} of the solar metallicity, the
depletion of coolant of the the host cloud is very serious so that the cloud
cannot cool in a free-fall time, and subsequent star formation is almost
quenched. On the contrary, if metallicity is larger than about 10^{-1.5} of the
solar metallicity, star formation regulation via photodissociation is not
efficient. The typical metallicity when this transition occurs is about 1/100
of the solar metallicity. This indicates that stars do not form efficiently
before the metallicity becomes larger than about 1/100 of the solar metallicity
and we considered that this value becomes the lower limit of the metallicity of
luminous objects such as galaxies.Comment: 14 pages, including 5 figures, To appear in ApJ, Vol. 53
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