23,187 research outputs found
Statistical Analysis of Spectral Line Candidates in Gamma-Ray Burst GRB870303
The Ginga data for the gamma-ray burst GRB870303 exhibit low-energy dips in
two temporally distinct spectra, denoted S1 and S2. S1, spanning 4 s, exhibits
a single line candidate at ~ 20 keV, while S2, spanning 9 s, exhibits
apparently harmonically spaced line candidates at ~ 20 and 40 keV. We evaluate
the statistical evidence for these lines, using phenomenological continuum and
line models which in their details are independent of the distance scale to
gamma-ray bursts. We employ the methodologies based on both frequentist and
Bayesian statistical inference that we develop in Freeman et al. (1999b). These
methodologies utilize the information present in the data to select the
simplest model that adequately describes the data from among a wide range of
continuum and continuum-plus-line(s) models. This ensures that the chosen model
does not include free parameters that the data deem unnecessary and that would
act to reduce the frequentist significance and Bayesian odds of the
continuum-plus-line(s) model. We calculate the significance of the
continuum-plus-line(s) models using the Chi-Square Maximum Likelihood Ratio
test. We describe a parametrization of the exponentiated Gaussian absorption
line shape that makes the probability surface in parameter space
better-behaved, allowing us to estimate analytically the Bayesian odds. The
significance of the continuum-plus-line models requested by the S1 and S2 data
are 3.6 x 10^-5 and 1.7 x 10^-4 respectively, with the odds favoring them being
114:1 and 7:1. We also apply our methodology to the combined (S1+S2) data. The
significance of the continuum-plus-lines model requested by the combined data
is 4.2 x 10^-8, with the odds favoring it being 40,300:1.Comment: LaTeX2e (aastex.cls included); 41 pages text, 10 figures (on 11
pages); accepted by ApJ (to be published 1 Nov 1999, v. 525
On the Formation Age of the First Planetary System
Recently, it has been observed the extreme metal-poor stars in the Galactic
halo, which must be formed just after Pop III objects. On the other hand, the
first gas clouds of mass are supposed to be formed at 10, 20, and 30 for the , and , where the
density perturbations are assumed of the standard CDM cosmology. If we
could apply this gaussian distribution to the extreme small probability, the
gas clouds would be formed at 40, 60, and 80 for the ,
, and . The first gas clouds within our galaxy must be formed
around . Even if the gas cloud is metal poor, there is a lot of
possibility to form the planets around such stars. The first planetary systems
could be formed within years after the Big Bang in the
universe. Even in our galaxies, it could be formed within
years. It is interesting to wait the observations of planets around metal-poor
stars. For the panspermia theory, the origin of life could be expected in such
systems.Comment: 5 pages,Proceedings IAU Symposium No. 249, 2007, Exoplanets:Y-S. Sun,
S. Ferraz-Mello and J.-L, Zhou, eds. (p325
Inhomogeneity in the Supernova Remnant Distribution as the Origin of the PAMELA Anomaly
Recent measurements of the positron/electron ratio in the cosmic ray (CR)
flux exhibits an apparent anomaly, whereby this ratio increases between 10 and
100 GeV. We show that inhomogeneity of CR sources on a scale of order a kpc,
can naturally explain this anomaly. If the nearest major CR source is about a
kpc away, then low energy electrons ( GeV) can easily reach us. At
higher energies ( GeV), the source electrons cool via synchrotron
and inverse-Compton before reaching Earth. Pairs formed in the local vicinity
through the proton/ISM interactions can reach Earth also at high energies, thus
increasing the positron/electron ratio. A natural origin of source
inhomogeneity is the strong concentration of supernovae in the galactic spiral
arms. Assuming supernova remnants (SNRs) as the sole primary source of CRs, and
taking into account their concentration near the galactic spiral arms, we
consistently recover the observed positron fraction between 1 and 100 GeV.
ATIC's electron excess at GeV is explained, in this picture, as the
contribution of a few known nearby SNRs. The apparent coincident similarity
between the cooling time of electrons at 10 GeV (where the positron/electron
ratio upturn), Myr, and the CRs protons cosmogenic age at the same
energy is predicted by this model
Reconciliation of CDM abundance and in a radiative seesaw model
We reexamine relic abundance of a singlet fermion as a CDM candidate, which
contributes to the neutrino mass generation through radiative seesaw mechanism.
We search solutions for Yukawa couplings and the mass spectrum of relevant
fields to explain neutrino oscillation data. For such solutions, we show that
an abundance of a lightest singlet fermion can be consistent with WMAP data
without conflicting with both bounds of and . This reconciliation does not need any modification of the original
radiative seesaw model other than by specifying flavor structure of Yukawa
couplings and taking account of coannihilation effects.Comment: 16 pages, 2 figures, accepted version for publication
V-V Bond-Length Fluctuations in Vox
We report a significantly stronger suppression of the phonon contribution to
the thermal conductivity in VOx than can be accounted for by disorder of the 16
% atomic vacancies present in VO. Since the transition from localized to
itinerant electronic behavior is first-order and has been shown to be
characterized by bond-length fluctuations in several transition-metal oxides
with the perovskite structure, we propose that cooperative V-V bond-length
fluctuations play a role in VO similar to the M-O bond-length fluctuations in
the perovskites. This model is able to account for the strong suppression of
the thermal conductivity, the existence of a pseudogap confirmed by
thermoelectric power, an anomalously large Debye-Waller factor, the temperature
dependence of the magnetic susceptibility, and the inability to order atomic
vacancies in VO.Comment: 5 pages, 5 figure
Cosmic Ray in the Northern Hemisphere: Results from the Telescope Array Experiment
The Telescope Array (TA) is the largest ultrahigh energy (UHE) cosmic ray
observatory in the northern hemisphere TA is a hybrid experiment with a unique
combination of fluorescence detectors and a stand-alone surface array of
scintillation counters. We will present the spectrum measured by the surface
array alone, along with those measured by the fluorescence detectors in
monocular, hybrid, and stereo mode. The composition results from stereo TA data
will be discussed. Our report will also include results from the search for
correlations between the pointing directions of cosmic rays, seen by the TA
surface array, with active galactic nuclei.Comment: 8 pages 11 figure, Proceedings of the APS Division of Particle and
Fields (DPF) Meeting, Aug 2011, Brown University, Providence, RI, US
Neutrino masses and terms in a supersymmetric extra U(1) model
We propose a supersymmetric extra U(1) model, which can generate small
neutrino masses and necessary terms, simultaneously. Fields including
quarks and leptons are embedded in three s of in a different
way among generations. The model has an extra U(1) gauge symmetry at TeV
regions, which has discriminating features from other models studied
previously. Since a neutrino mass matrix induced in the model has a constrained
texture with limited parameters, it can give a prediction. If we impose
neutrino oscillation data to fix those parameters, a value of
can be determined. We also discuss several phenomenological features which are
discriminated from the ones of the MSSM.Comment: 27 pages, 2 figures, final version for publicatio
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