127 research outputs found
Dark Matter at the Center and in the Halo of the Galaxy
All presently known stellar-dynamical constraints on the size and mass of the
supermassive compact dark object at the Galactic center are consistent with a
ball of self-gravitating, nearly non-interacting, degenerate fermions with mass
between 76 and 491 keV, for degeneracy factor g=2. Sterile neutrinos of 76 keV
mass, which are mixed with at least one of the active neutrinos with a mixing
angele ~10^{-7}, are produced in about the right amount in the early Universe
by incoherent resonant and non-resonant scattering of active neutrinos having
asymmetry of ~0.01. The former process yields sterile neutrinos with a
quasi-degenerate spectrum while the latter leads to a thermal spectrum. As the
production mechanism of the sterile neutrino is consistent with the constraints
from large scale structure formation, core collapse supernovae, and diffuse
X-ray background, it could be the dark matter particle of the Universe.Comment: 6 pages, to appear in the Beyond 2003 conference proceeding
Sgr A^*: A supermassive black hole or a spatially extended object?
We report here on a calculation of possible orbits of the fast moving
infrared source S1 which has been recently observed by Eckart and Genzel (1997)
near the Galactic center. It is shown that tracking of the orbit of S1 or any
other fast moving star near Sgr A^* offers a possibility of distinguishing
between the supermassive black hole and extended object scenarios of Sgr A^*.
In our calculations we assumed that the extended object at the Galactic center
is a non-baryonic ball made of degenerate, self-gravitating heavy neutrino
matter, as it has been recently proposed by Tsiklauri & Viollier (1998a,b).Comment: AASTEX, 5 postscript figs., submitted to ApJ Let
Ethyl 3-ferrocenyl-1-(pyridin-2-ylmethyl)-1H-pyrazole-5-carboxylate
The title compound, [Fe(C5H5)(C17H16N3O2)], crystallizes with an essentially eclipsed conformation of the cyclopentadienyl (Cp) rings. The unsubstituted ring is disordered over two positions with the major component being present 90 (1)% of the time. The substituted Cp ring, the pyrazole ring and three atoms of the ethoxycarbonyl group form a conjugated π-system. These 13 atoms are coplanar within 0.09 Å
Lightest sterile neutrino abundance within the nuMSM
We determine the abundance of the lightest (dark matter) sterile neutrinos
created in the Early Universe due to active-sterile neutrino transitions from
the thermal plasma. Our starting point is the field-theoretic formula for the
sterile neutrino production rate, derived in our previous work [JHEP
06(2006)053], which allows to systematically incorporate all relevant effects,
and also to analyse various hadronic uncertainties. Our numerical results
differ moderately from previous computations in the literature, and lead to an
absolute upper bound on the mixing angles of the dark matter sterile neutrino.
Comparing this bound with existing astrophysical X-ray constraints, we find
that the Dodelson-Widrow scenario, which proposes sterile neutrinos generated
by active-sterile neutrino transitions to be the sole source of dark matter, is
only possible for sterile neutrino masses lighter than 3.5 keV (6 keV if all
hadronic uncertainties are pushed in one direction and the most stringent X-ray
bounds are relaxed by a factor of two). This upper bound may conflict with a
lower bound from structure formation, but a definitive conclusion necessitates
numerical simulations with the non-equilibrium momentum distribution function
that we derive. If other production mechanisms are also operative, no upper
bound on the sterile neutrino mass can be established.Comment: 34 pages. v2: clarifications and a reference added; published
version. v3: erratum appende
Sterile neutrino production via active-sterile oscillations: the quantum Zeno effect
We study several aspects of the kinetic approach to sterile neutrino
production via active-sterile mixing. We obtain the neutrino propagator in the
medium including self-energy corrections up to , from which
we extract the dispersion relations and damping rates of the propagating modes.
The dispersion relations are the usual ones in terms of the index of refraction
in the medium, and the damping rates are where
is the active neutrino scattering rate and
is the mixing angle in the medium. We provide a generalization of
the transition probability in the \emph{medium from expectation values in the
density matrix}: and
study the conditions for its quantum Zeno suppression directly in real time. We
find the general conditions for quantum Zeno suppression, which for sterile neutrinos with \emph{may
only be} fulfilled near an MSW resonance. We discuss the implications for
sterile neutrino production and argue that in the early Universe the wide
separation of relaxation scales far away from MSW resonances suggests the
breakdown of the current kinetic approach.Comment: version to appear in JHE
Examining the early distribution of the artemisinin-resistant Plasmodium falciparum kelch13 R561H mutation in areas of higher transmission in Rwanda
BACKGROUND: Artemisinin resistance mutations in Plasmodium falciparum kelch13 (Pfk13) have begun to emerge in Africa, with Pfk13-R561H being the first reported in Rwanda in 2014, but limited sampling left questions about its early distribution and origin. METHODS: We genotyped P. falciparum positive dried blood spot (DBS) samples from a nationally representative 2014-2015 Rwanda Demographic Health Surveys (DHS) HIV study. DBS were subsampled from DHS sampling clusters with >15% P. falciparum prevalence, as determined by rapid testing or microscopy done during the DHS study (n clusters = 67, n samples = 1873). RESULTS: We detected 476 parasitemias among 1873 residual blood spots from a 2014-2015 Rwanda Demographic Health Survey. We sequenced 351 samples: 341/351 were wild-type (97.03% weighted), and 4 samples (1.34% weighted) harbored R561H that were significantly spatially clustered. Other nonsynonymous mutations found were V555A (3), C532W (1), and G533A (1). CONCLUSIONS: Our study better defines the early distribution of R561H in Rwanda. Previous studies only observed the mutation in Masaka as of 2014, but our study indicates its presence in higher-transmission regions in the southeast of the country at that time
Astrophysical implications of gravitational microlensing of gravitational waves
Astrophysical implications of gravitational microlensing of gravitational
waves emitted by rotating neutron stars (NSs) are investigated. In particular,
attention is focused on the following situations: i) NSs in the galactic bulge
lensed by a central black hole of or by stars and
MACHOs distributed in the galactic bulge, disk and halo between Earth and the
sources; ii) NSs in globular clusters lensed by a central black hole of or by stars and MACHOs distributed throughout the Galaxy. The
detection of such kind of microlensing events will give a unique opportunity
for the unambiguous mapping of the central region of the Galaxy and of globular
clusters. In addition, the detection of such events will provide a new test of
the General Theory of Relativity. Gravitational microlensing will, moreover,
increase the challenge of detecting gravitational waves from NSs.Comment: 5 pages, laa.sty required. Accepted for pubblication on Astronomy and
Astrophysics on November, 7 200
The Pioneer anomaly in the context of the braneworld scenario
We examine the Pioneer anomaly - a reported anomalous acceleration affecting
the Pioneer 10/11, Galileo and Ulysses spacecrafts - in the context of a
braneworld scenario. We show that effects due to the radion field cannot
account for the anomaly, but that a scalar field with an appropriate potential
is able to explain the phenomena. Implications and features of our solution are
analyzed.Comment: Final version to appear at Classical & Quantum Gravity. Plainlatex 19
page
The motion of stars near the Galactic center: A comparison of the black hole and fermion ball scenarios
After a discussion of the properties of degenerate fermion balls, we analyze
the orbits of the stars S0-1 and S0-2, which have the smallest projected
distances to Sgr A*, in the supermassive black hole as well as in the fermion
ball scenarios of the Galactic center. It is shown that both scenarios are
consistent with the data, as measured during the last six years by Genzel et
al. and Ghez et al. The free parameters of the projected orbit of a star are
the unknown components of its velocity v_z and distance z to Sgr A* in 1995.4,
with the z-axis being in the line of sight. We show, in the case of S0-1 and
S0-2, that the z-v_z phase-space which fits the data, is much larger for the
fermion ball than for the black hole scenario. Future measurements of the
positions or radial velocities of S0-1 and S0-2 could reduce this allowed
phase-space and eventually rule out one of the currently acceptable scenarios.
This may shed some light into the nature of the supermassive compact dark
object, or dark matter in general at the center of our Galaxy.Comment: 30 pages, 12 figures, Latex, aasms4 styl
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