25,861 research outputs found
An unified cosmological evolution driven by a mass dimension one fermionic field
An unified cosmological model for an Universe filled with a mass dimension
one (MDO) fermionic field plus the standard matter fields is considered. After
a primordial quantum fluctuation the field slowly rolls down to the bottom of a
symmetry breaking potential, driving the Universe to an inflationary regime
that increases the scale factor for about 71 e-folds. After the end of
inflation, the field starts to oscillate and can transfer its energy to the
standard model particles through a reheating mechanism. Such a process is
briefly discussed in terms of the admissible couplings of the MDO field with
the electromagnetic and Higgs fields. We show that even if the field loses all
its kinetic energy during reheating, it can evolve as dark matter due a
gravitational coupling (of spinorial origin) with baryonic matter. Since the
field acquires a constant value at the bottom of the potential, a non-null,
although tiny, mass term acts as a dark energy component nowadays. Therefore,
we conclude that MDO fermionic field is a good candidate to drive the whole
evolution of the Universe, in such a way that the inflationary field, dark
matter and dark energy are described by different manifestations of a single
field.Comment: 22 pages, 5 figure
Low frequency measurements of synchrotron absorbing HII regions and modeling of observed synchrotron emissivity
Cosmic rays (CRs) and magnetic fields are dynamically important components in
the Galaxy, and their energy densities are comparable to that of the turbulent
interstellar gas. The interaction of CRs and Galactic magnetic fields produces
synchrotron radiation clearly visible in the radio regime. Detailed
measurements of synchrotron radiation averaged over the line-of-sight (LOS),
so-called synchrotron emissivities, can be used as a tracer of the CR density
and Galactic magnetic field (GMF) strength. Our aim is to model the synchrotron
emissivity in the Milky Way using a 3 dimensional dataset instead of
LOS-integrated intensity maps on the sky. Using absorbed HII regions we can
measure the synchrotron emissivity over a part of the LOS through the Galaxy,
changing from a 2 dimensional to a 3 dimensional view. Performing these
measurements on a large scale is one of the new applications of the window
opened by current low frequency arrays. Using various simple axisymmetric
emissivity models and a number of GMF-based emissivity models we can simulate
the synchrotron emissivities and compare them to the observed values in the
catalog. We present a catalog of low-frequency absorption measurements of HII
regions, their distances and electron temperatures, compiled from literature.
These data show that the axisymmetric emissivity models are not complex enough,
but the GMF-based emissivity models deliver a reasonable fit. These models
suggest that the fit can be improved by either an enhanced synchrotron
emissivity in the outer reaches of the Milky Way, or an emissivity drop near
the Galactic center. State-of-the-art GMF models plus a constant CR density
model cannot explain low-frequency absorption measurements, but the fits
improved with slight (ad-hoc) adaptations. It is clear that more detailed
models are needed, but the current results are very promising.Comment: 14 pages, 9 figures, accepted for publication in A&
A low-mass stellar companion of the planet host star HD75289
We report on the detection of a new low-mass stellar companion of HD75289, a
G0V star that harbors one known radial-velocity planet (Udry et al. 2000).
Comparing an image of 2MASS with an image we obtained with SofI at the ESO
3.58m NTT three years later, we detected a co-moving companion located
21.465+-0.023arcsecs (621+-10AU at 29pc) east of HD75289. A second SofI image
taken 10 months later confirmed the common proper motion of HD75289B with its
host star. The infrared spectrum and colors of the companion are consistent
with an M2 to M5 main-sequence star at the distance of HD75289. No further
(sub)stellar companion down to H = 19mag could be detected. With the SofI
detection limit we can rule out additional stellar companions beyond 140AU and
substellar companions with masses m > 0.050Msun from 400AU up to 2000AU.Comment: accepted in A&
Structural and optical properties of Zn0.9 Mn0.1 O/ZnO core-shell nanowires designed by pulsed laser deposition
Partilhar documento na coleção da comunidade Laboratório Associado I3NCore-shell ZnO/ZnMnO nanowires on a-Al2O3 and GaN (buffer layer)/Si (111) substrates were fabricated by pulsed laser deposition using a Au catalyst. Two ZnO targets with a Mn content of 10% were sintered at 1150 and 550 °C in order to achieve the domination in them of paramagnetic MnO2 and ferromagnetic Mn2O3 phases, respectively. Cluster mechanism of laser ablation as a source of possible incorporation of secondary phases to the wire shell is discussed. Raman spectroscopy under excitation by an Ar+ laser revealed a broad peak related to the Mn-induced disorder and a redshift in the A1-LO phonon. Resonant Raman measurements revealed an increase in the multiphonon scattering caused by disorder in ZnO upon doping by Mn. Besides the UV emission, a vibronic green emission band assisted by a ∼ 71 meV LO phonon is also observed in the photoluminescence spectra. Core-shell structures with smooth shells show a high exciton to green band intensity ratio ( ∼ 10) even at room temperature.
© 2009 American Institute of PhysicsSANDiE Network of Excellence of the EUFCT-PTDC/FIS/72843/200
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