46,426 research outputs found
Majorana neutrino oscillations in vacuum
In the context of a type I seesaw scenario which leads to get light
left-handed and heavy right-handed Majorana neutrinos, we obtain expressions
for the transition probability densities between two flavor neutrinos in the
cases of left-handed and right-handed neutrinos. We obtain these expressions in
the context of an approach developed in the canonical formalism of Quantum
Field Theory for neutrinos which are considered as superpositions of
mass-eigenstate plane waves with specific momenta. The expressions obtained for
the left-handed neutrino case after the ultra-relativistic limit is taking lead
to the standard probability densities which describe light neutrino
oscillations. For the right-handed neutrino case, the expressions describing
heavy neutrino oscillations in the non-relativistic limit are different respect
to the ones of the standard neutrino oscillations. However, the right-handed
neutrino oscillations are phenomenologically restricted as is shown when the
propagation of heavy neutrinos is considered as superpositions of
mass-eigenstate wave packets.Comment: 25 pages, abstract changed, two sections added, some references adde
Preparation to the CMB PLANCK data analysis, estimation of the contamination due to the galactic polarized emissions
This work is point of the preparation to the analysis of the PLANCK satellite
data. The PLANCK satellite is an ESA mission which has been launched the 14th
of may 2009 and is dedicaced to the measurement of the Cosmic Microwave
Background (CMB) in temperature and polarization. The presence of diffuse
Galactic polarized emissions disturb the measurement of the CMB anisotropies,
in particular in polarization. Therefore a precise knowledge of these emissions
is needed to obtain the level of accuracy required for PLANCK. In this context,
we have developed and implemented a coherent 3D model of the two mains
polarized Galactic emissions : synchrotron and thermal dust. We have compared
these models to preexisting data: the 23 GHz band of the WMAP data, the 353 GHz
Archeops data and the 408 MHz all-sky continuum survey. We extrapolate these
models to the frequencies where the CMB dominates and we are able to estimate
the contribution of polarized foreground emissions to the polarized CMB
emission measured with PLANCK.Comment: Proceeding of the International Workshop on Cosmic Structure and
Evolution - Cosmology2009, September 23-25, 2009 Bielefeld, German
Cylindrical radiator analysis with interior insulated
Size and weight evaluation of insulated cylindrical radiators used in SNAP-8 heat rejection syste
Anisotropic thermal emission from magnetized neutron stars
The thermal emission from isolated neutron stars is not well understood. The
X-ray spectrum is very close to a blackbody but there is a systematic optical
excess flux with respect to the extrapolation to low energy of the best
blackbody fit. This fact, in combination with the observed pulsations in the
X-ray flux, can be explained by anisotropies in the surface temperature
distribution.We study the thermal emission from neutron stars with strong
magnetic fields in order to explain the origin of the anisotropy. We find
(numerically) stationary solutions in axial symmetry of the heat
transportequations in the neutron star crust and the condensed envelope. The
anisotropy in the conductivity tensor is included consistently. The presence of
magnetic fields of the expected strength leads to anisotropy in the surface
temperature. Models with toroidal components similar to or larger than the
poloidal field reproduce qualitatively the observed spectral properties and
variability of isolated neutron stars. Our models also predict spectral
features at energies between 0.2 and 0.6 keV.Comment: 18 pages, 19 figures, version accepted for publication in A&
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