19,816 research outputs found
Neutral heavy lepton production at next high energy linear colliders
The discovery potential for detecting new heavy Majorana and Dirac neutrinos
at some recently proposed high energy colliders is discussed. These
new particles are suggested by grand unified theories and superstring-inspired
models. For these models the production of a single heavy neutrino is shown to
be more relevant than pair production when comparing cross sections and
neutrino mass ranges.
The process is calculated
including on-shell and off-shell heavy neutrino effects.
We present a detailed study of cross sections and distributions that shows a
clear separation between the signal and standard model contributions, even
after including hadronization effects.Comment: 4 pages including 15 figures, 1 table. RevTex. Accepted in Physical
Review
Cosmology in the Universe with distance dependent Lorentz-violating bakground
We consider a cosmological setup with the inflaton field in the presence of a
redshift dependent Lorentz-violating time-like background to address the
inflationary regime and other phases of the Universe. We also show that the
regime of dark energy at large distances (low redshifts) is essentially
dominated by the presence of the Lorentz-violating background.Comment: 8 pages, no figure, Latex, to appear in AHE
The Phoenix Deep Survey: spectroscopic catalog
The Phoenix Deep Survey is a multi-wavelength survey based on deep 1.4 GHz
radio imaging, reaching well into the sub-100 microJy level. One of the aims of
this survey is to characterize the sub-mJy radio population, exploring its
nature and evolution. In this paper we present the catalog and results of the
spectroscopic observations aimed at characterizing the optically ``bright''
(R<~ 21.5 mag) counterparts of faint radio sources. Out of 371 sources with
redshift determination, 21% have absorption lines only, 11% show AGN
signatures, 32% are star-forming galaxies, 34% show narrow emission lines that
do not allow detailed spectral classification (due to poor signal-to-noise
ratio and/or lack of diagnostic emission lines) and the remaining 2% are
identified with stars. For the star-forming galaxies with a Balmer decrement
measurement we find a median extinction of A(Ha)=1.9 mag, higher than that of
optically selected samples. This is a result of the radio selection, which is
not biased against dusty systems. Using the available spectroscopic
information, we estimate the radio luminosity function of star-forming galaxies
in two independent redshift bins at z~0.1 and 0.3 respectively. We find direct
evidence for strong luminosity evolution of these systems consistent with L(1.4
GHz) ~ (1+z)^(2.7).Comment: 39 pages, 12 figures. References added, and minor changes to reflect
published versio
Tetragonal tungsten bronze compounds: relaxor vs mixed ferroelectric - dipole glass behavior
We demonstrate that recent experimental data (E. Castel et al J.Phys. Cond.
Mat. {\bf 21} (2009), 452201) on tungsten bronze compound (TBC)
BaPrNdFeNbO can be well explained in our model
predicting a crossover from ferroelectric () to orientational (dipole)
glass (), rather then relaxor, behavior. We show, that since a "classical"
perovskite relaxor like Pb(Mn Nb)O is never a
ferroelectric, the presence of ferroelectric hysteresis loops in TBC shows that
this substance actually transits from ferroelectric to orientational glass
phase with growth. To describe the above crossover theoretically, we use
the simple replica-symmetric solution for disordered Ising model.Comment: 5 two-column pages, 4 figure
Detecção de vírus por RT-PCR, hibridização "DOT-BLOT" e DOT-ELISA em milho com mosaico comum.
O mosaico comum do milho e causado por um complexo viral constituido por quatro potyvirus distintos e pode reduzir significativamente a producao do milho (Zea mays). Frequentemente, a diagnose dessa virose e dificultada devido a recuperacao dos sintomas pelas plantas ou a ocorrencia de infeccoes simultaneas com outros virus e/ou com fitoplasmas e espiroplasmas. O objetivo deste trabalho foi desenvolver metodos eficazes para a deteccao do complexo viral utilizando-se RT-PCR com "primers" degenerados, hibridizacao "dot-blot" e dot-ELISA. O complexo viral foi multiplicado com plantas de milho por meio de inoculacao mecanica e posteriormente purificado. A preparacao purificada foi utilizada para a producao de antisoro policlonal e as IgGs purificadas foram utilizadas para a realizacao do teste dot-ELISA. A RT-PCR foi realizada a partir de RNA total extraido de folhas infetadas, utilizando-se "primers" universais para a deteccao de potyvirus. Os resultados apresentados indicam que as tres tecnicas podem ser utilizadas para a deteccao do complexo viral do mosaico comum do milho
Replica symmetry breaking in long-range glass models without quenched disorder
We discuss mean field theory of glasses without quenched disorder focusing on
the justification of the replica approach to thermodynamics. We emphasize the
assumptions implicit in this method and discuss how they can be verified. The
formalism is applied to the long range Ising model with orthogonal coupling
matrix. We find the one step replica-symmetry breaking solution and show that
it is stable in the intermediate temperature range that includes the glass
state but excludes very low temperatures. At very low temperatures this
solution becomes unstable and this approach fails.Comment: 6 pages, 2 figure
Identification of the critical temperature from non-equilibrium time-dependent quantities
We present a new procedure able to identify and measure the critical
temperature. This method is based on the divergence of the relaxation time
approaching the critical point in quenches from infinite temperature. We
introduce a dimensionless quantity that turns out to be time-independent at the
critical temperature. The procedure does not need equilibration and allows for
a relatively fast identification of the critical temperature. The method is
first tested in the ferromagnetic Ising model and then applied to the
one-dimensional Ising spin glass with power-law interactions. Here we always
find a finite critical temperature also in presence of a uniform external
field, in agreement with the mean-field picture for the low temperature phase
of spin glasses.Comment: 6 pages, 10 figure
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