6,453 research outputs found
Significant Gamma Lines from Inert Higgs Dark Matter
One way to unambiguously confirm the existence of particle dark matter and
determine its mass would be to detect its annihilation into monochromatic
gamma-rays in upcoming telescopes. One of the most minimal models for dark
matter is the inert doublet model, obtained by adding another Higgs doublet
with no direct coupling to fermions. For a mass between 40 and 80 GeV, the
lightest of the new inert Higgs particles can give the correct cosmic abundance
of cold dark matter in agreement with current observations. We show that for
this scalar dark matter candidate, the annihilation signal of monochromatic
\gamma\gamma and Z\gamma final states would be exceptionally strong. The energy
range and rates for these gamma-ray line signals make them ideal to search for
with the soon upcoming GLAST satellite.Comment: 4 pages, 3 figures; minor changes and text improvements; references
updated; published versio
Improving traffic sign recognition by active search
We describe an iterative active-learning algorithm to recognise rare traffic
signs. A standard ResNet is trained on a training set containing only a single
sample of the rare class. We demonstrate that by sorting the samples of a
large, unlabeled set by the estimated probability of belonging to the rare
class, we can efficiently identify samples from the rare class. This works
despite the fact that this estimated probability is usually quite low. A
reliable active-learning loop is obtained by labeling these candidate samples,
including them in the training set, and iterating the procedure. Further, we
show that we get similar results starting from a single synthetic sample. Our
results are important as they indicate a straightforward way of improving
traffic-sign recognition for automated driving systems. In addition, they show
that we can make use of the information hidden in low confidence outputs, which
is usually ignored.Comment: 6 pages, 7 Figure
Search for evidence of two photon contribution in elastic electron proton data
We reanalyze the most recent data on elastic electron proton scattering. We
look for a deviation from linearity of the Rosenbluth fit to the differential
cross section, which would be the signature of the presence of two photon
exchange. The two photon contribution is parametrized by a one parameter
formula, based on symmetry arguments. The present data do not show evidence for
such deviation.Comment: 15 pages 3 figures More details on the fitting procedure, more
explicit explanation
Mira's wind explored in scattering infrared CO lines
We have observed the intermediate regions of the circumstellar envelope of
Mira (o Ceti) in photospheric light scattered by three vibration-rotation
transitions of the fundamental band of CO, from low-excited rotational levels
of the ground vibrational state, at an angular distance of beta = 2"-7" away
from the star. The data were obtained with the Phoenix spectrometer mounted on
the 4 m Mayall telescope at Kitt Peak. The spatial resolution is approximately
0.5" and seeing limited. Our observations provide absolute fluxes, leading to
an independent new estimate of the mass-loss rate of approximately 3e-7
Msun/yr, as derived from a simple analytic wind model. We find that the
scattered intensity from the wind of Mira for 2" < beta < 7" decreases as
beta^-3, which suggests a time constant mass-loss rate, when averaged over 100
years, over the past 1200 years.Comment: accepted for publication in the Astrophysical Journa
New Abundances for Old Stars - Atomic Diffusion at Work in NGC 6397
A homogeneous spectroscopic analysis of unevolved and evolved stars in the
metal-poor globular cluster NGC 6397 with FLAMES-UVES reveals systematic trends
of stellar surface abundances that are likely caused by atomic diffusion. This
finding helps to understand, among other issues, why the lithium abundances of
old halo stars are significantly lower than the abundance found to be produced
shortly after the Big Bang.Comment: 8 pages, 7 colour figures, 1 table; can also be downloaded via
http://www.eso.org/messenger
Scaling Limits for Internal Aggregation Models with Multiple Sources
We study the scaling limits of three different aggregation models on Z^d:
internal DLA, in which particles perform random walks until reaching an
unoccupied site; the rotor-router model, in which particles perform
deterministic analogues of random walks; and the divisible sandpile, in which
each site distributes its excess mass equally among its neighbors. As the
lattice spacing tends to zero, all three models are found to have the same
scaling limit, which we describe as the solution to a certain PDE free boundary
problem in R^d. In particular, internal DLA has a deterministic scaling limit.
We find that the scaling limits are quadrature domains, which have arisen
independently in many fields such as potential theory and fluid dynamics. Our
results apply both to the case of multiple point sources and to the
Diaconis-Fulton smash sum of domains.Comment: 74 pages, 4 figures, to appear in J. d'Analyse Math. Main changes in
v2: added "least action principle" (Lemma 3.2); small corrections in section
4, and corrected the proof of Lemma 5.3 (Lemma 5.4 in the new version);
expanded section 6.
On the oxygen abundance of HE0107-5240
We have determined the oxygen abundance of HE0107-5240 from UV-OH lines
detected in VLT/UVES spectra. Using a plane-parallel LTE model atmosphere, we
derive [O/Fe] = +2.4, and a similar analysis of CD -38 245 yields [O/Fe] =
+1.0. We estimate systematic errors due to 3D effects to be in the order of 0.3
to 0.4 dex. That is, our derived O abundances are likely overestimates: effects
from thermal inhomogeneities due to convection may require that the abundances
should be reduced by 0.3-0.4 dex or even more. Radial velocity data for
HE0107-5240 based on high-resolution spectra show that over a time span of 373
days the radial velocity was constant at 44.5 km/s, with a 1 sigma scatter of
the measurements of 0.5 km/s. However, it can not yet be ruled out that
HE0107-5240 is a very long period and/or low amplitude binary. These results
provide new constraints on scenarios for the origin of the abundance pattern of
HE0107-5240. In particular, it seems unlikely that the large overabundances of
CNO have been produced in a medium-mass AGB star which later evolved to a white
dwarf. The oxygen abundance of HE0107-5240 is significantly smaller than the
prediction of Umeda & Nomoto (2003) from calculated yields of a ~25 solar mass
Population III star exploding as a supernova of low explosion energy (E_exp = 3
x 10^50 erg) with mixing and fallback. The scenario of Limongi et al. (2003),
involving two Population III supernovae, predicts an oxygen abundance of [O/Fe]
= +4.1 for HE0107-5240, in strong contradiction with the observed value. In
conclusion, none of the above mentioned scenarios, in their present
realizations, can satisfactorly explain the abundance pattern of HE0107-5240.Comment: Submitted to ApJ Letter
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