13,916 research outputs found
Neutrino masses and mixings in a Minimal S_3-invariant Extension of the Standard Model
The mass matrices of the charged leptons and neutrinos, that had been derived
in the framework of a Minimal S_3-invariant Extension of the Standard Model,
are here reparametrized in terms of their eigenvalues. The neutrino mixing
matrix, V_PMNS, is then computed and exact, explicit analytical expressions for
the neutrino mixing angles as functions of the masses of the neutrinos and
charged leptons are obtained. The reactor, theta_13, and the atmosferic,
theta_23, mixing angles are found to be functions only of the masses of the
charged leptons. The numerical values of theta_13{th} and theta_23{th} computed
from our theoretical expressions are found to be in excellent agreement with
the latest experimental determinations. The solar mixing angle, theta_12{th},
is found to be a function of both, the charged lepton and neutrino masses, as
well as of a Majorana phase phi_nu. A comparison of our theoretical expression
for the solar angle theta_12{th} with the latest experimental value
theta_12{exp} ~ 34 deg allowed us to fix the scale and origin of the neutrino
mass spectrum and obtain the mass values |m_nu1|=0.0507 eV, |m_nu2|=0.0499 eV
and |m_nu3|=0.0193 eV, in very good agreement with the observations of neutrino
oscillations, the bounds extracted from neutrinoless double beta decay and the
precision cosmological measurements of the CMB.Comment: To appear in the Proceedings of the XXIX Symposium on Nuclear
Physics, Cocoyoc, Mex., January 2006. Some typographical errors on formulae
correcte
Implications of the VHE Gamma-Ray Detection of the Quasar 3C279
The MAGIC collaboration recently reported the detection of the quasar 3C279
at > 100 GeV gamma-ray energies. Here we present simultaneous optical (BVRI)
and X-ray (RXTE PCA) data from the day of the VHE detection and discuss the
implications of the snap-shot spectral energy distribution for jet models of
blazars. A one-zone synchrotron-self-Compton origin of the entire SED,
including the VHE gamma-ray emission can be ruled out. The VHE emission could,
in principle, be interpreted as Compton upscattering of external radiation
(e.g., from the broad-line regions). However, such an interpretation would
require either an unusually low magnetic field of B ~ 0.03 G or an
unrealistically high Doppler factor of Gamma ~ 140. In addition, such a model
fails to reproduce the observed X-ray flux. This as well as the lack of
correlated variability in the optical with the VHE gamma-ray emission and the
substantial gamma-gamma opacity of the BLR radiation field to VHE gamma-rays
suggests a multi-zone model. In particular, an SSC model with an emission
region far outside the BLR reproduces the simultaneous X-ray -- VHE gamma-ray
spectrum of 3C279. Alternatively, a hadronic model is capable of reproducing
the observed SED of 3C279 reasonably well. However, the hadronic model requires
a rather extreme jet power of L_j ~ 10^{49} erg s^{-1}, compared to a
requirement of L_j ~ 2 X 10^{47} erg s^{-1} for a multi-zone leptonic model.Comment: Accepted for pulication. Several clarifications and additions to the
manuscript to match the accepted versio
Gamma rays from compact binary system
Some of the very high energy (VHE) gamma-ray sources detected with the modern
generation of Cherenkov telescopes have been identified with previously known
X-ray binary systems. These detections demonstrate the richness of non-thermal
phenomena in compact galactic objects containing relativistic outflows or winds
produced near black holes and neutron stars. Recently, the well-known
microquasar Cygnus X-3 seems to be associated with a gamma-ray source detected
with AGILE. Here I summarise the main observational results on gamma-ray
emission from X-ray binaries, as well as some of the proposed scenarios to
explain the production of VHE gamma-rays.Comment: 12 pages, 7 figures. Invited talk at the "Fourth Heidelberg
International Symposium on High Energy Gamma-Ray Astronomy 2008
Morphology and hardness ratio exploitation under limited statistics
Gamma-ray astronomy has produced for several years now sky maps for low
photon statistics, non-negligible background and comparatively poor angular
resolution. Quantifying the significance of spatial features remains difficult.
Besides, spectrum extraction requires regions with large statistics while maps
in energy bands allow only qualitative interpretation. The two main competing
mechanisms in the VHE domain are the Inverse-Compton emission from accelerated
electrons radiating through synchrotron in the X-ray domain and the
interactions between accelerated hadrons and the surrounding medium, leading to
the production and subsequent decay of Pi0 mesons. The spectrum of the VHE
emission from leptons is predicted to steepen with increasing distance from the
acceleration zone, owing to synchrotron losses (i.e. cooled population). It
would remain approximately constant for hadrons. Ideally, spectro-imaging
analysis would have the same spatial scale in the TeV and X-ray domains, to
distinguish the local emission mechanisms. More realistically, we investigate
here the possibility of improving upon the currently published HESS results by
using more sophisticated tools.Comment: 4 pages, 6 figures, Proceeding for a poster at the GAMMA08 Heidelberg
Symposiu
Use of a liquid-crystal, heater-element composite for quantitative, high-resolution heat transfer coefficients on a turbine airfoil, including turbulence and surface roughness effects
Local heat transfer coefficients were measured along the midchord of a three-times-size turbine vane airfoil in a static cascade operated at roon temperature over a range of Reynolds numbers. The test surface consisted of a composite of commercially available materials: a Mylar sheet with a layer of cholestric liquid crystals, which change color with temperature, and a heater made of a polyester sheet coated with vapor-deposited gold, which produces uniform heat flux. After the initial selection and calibration of the composite sheet, accurate, quantitative, and continuous heat transfer coefficients were mapped over the airfoil surface. Tests were conducted at two free-stream turbulence intensities: 0.6 percent, which is typical of wind tunnels; and 10 percent, which is typical of real engine conditions. In addition to a smooth airfoil, the effects of local leading-edge sand roughness were also examined for a value greater than the critical roughness. The local heat transfer coefficients are presented for both free-stream turbulence intensities for inlet Reynolds numbers from 1.20 to 5.55 x 10 to the 5th power. Comparisons are also made with analytical values of heat transfer coefficients obtained from the STAN5 boundary layer code
Time Averaged VHE Spectrum of Mrk 421 in 2005
The blazar Mrk421 was observed independently, but contemporaneously, in 2005
at TeV energies by MAGIC, the Whipple 10m telescope, and by a single VERITAS
telescope during the construction phase of operations. A comparison of the time
averaged spectra, in what was a relatively quiescent state, demonstrates the
level of agreement between instruments. In addition, the increased sensitivity
of the new generation instruments, and ever decreasing energy thresholds,
questions how best to compare new observational data with archival results.Comment: Submitted to Proceedings of "4th Heidelberg International Symposium
on High Energy Gamma-Ray Astronomy 2008
A strict lower-limit EBL: Applications on gamma-ray absorption
A strict lower limit flux for the extragalactic background light from
ultraviolet to the far-infrared photon energies is presented. The spectral
energy distribution is derived using an established EBL model based on galaxy
formation. The model parameters are chosen to fit the lower limit data from
number count observations in particular recent results by the SPITZER infrared
space telescope. A lower limit EBL model is needed to calculate guaranteed
absorption due to pair production in extragalactic gamma-ray sources as in TeV
blazars.Comment: Comments: 4 pages, 2 figures, submitted to proceedings of "4th
Heidelberg International Symposium on High Energy Gamma-Ray Astronomy 2008
VERITAS Observations of Extragalactic Non-Blazars
During the 2007/2008 season, VERITAS was used for observations at E>200 GeV
of several extragalactic non-blazar objects such as galaxy clusters, starburst
and interacting galaxies, dwarf galaxies, and nearby galaxies. In these
proceedings, we present preliminary results from our observations of dwarf
galaxies and M87. Results from observation of other non-blazar sources are
presented in separate papers in the proceedings.Comment: Submitted to Proceedings of "4th Heidelberg International Symposium
on High Energy Gamma-Ray Astronomy 2008
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