19,395 research outputs found
Invisible Quarkonium Decays as a Sensitive Probe of Dark Matter
We examine in a model-independent manner the measurements that can be
performed at B-factories with sensitivity to dark matter. If a singlet scalar,
pseudo-scalar, or vector is present and mediates the Standard Model - dark
matter interaction, it can mediate invisible decays of quarkonium states such
as the , , and . Such scenarios have arisen in the
context of supersymmetry, extended Higgs sectors, solutions the supersymmetric
problem, and extra U(1) gauge groups from grand unified theories and
string theory. Existing B-factories running at the can produce
lower resonances by emitting an Initial State Radiation (ISR)
photon. Using a combination of ISR and radiative decays, the initial state of
an invisibly decaying quarkonium resonance can be tagged, giving sensitivity to
the spin and CP-nature of the particle that mediates standard model-dark matter
interactions. These measurements can discover or place strong constraints on
dark matter scenarios where the dark matter is approximately lighter than the
-quark. For the decay chains
(n=2,3) we analyze the dominant backgrounds and determine that with collected at the , the B-factories can limit
BR(\Upsilon(1S) \to invisible) \lsim 0.1%.Comment: 20 pages, 1 figure, accepted for publication in PR
Continuum and Spectral Line Radiation from a Random Clumpy Medium
We present a formalism for continuum and line emission from random clumpy
media together with its application to problems of current interest, including
CO spectral lines from ensembles of clouds and radio emission from HII regions,
supernovae and star-forming regions. For line emission we find that the effects
of clump opacity on observed line ratios can be indistinguishable from
variations of intrinsic line strengths, adding to the difficulties in
determining abundances from line observations. Our formalism is applicable to
arbitrary distributions of cloud properties, provided the cloud volume filling
factor is small; numerical simulations show it to hold up to filling factors of
about 10%. We show that irrespective of the complexity of the cloud ensemble,
the radiative effect of clumpiness can be parametrized at each frequency by a
single multiplicative correction to the overall optical depth; this multiplier
is derived from appropriate averaging over individual cloud properties. Our
main finding is that cloud shapes have only a negligible effect on radiation
propagation in clumpy media; the results of calculations employing point-like
clouds are practically indistinguishable from those for finite-size clouds with
arbitrary geometrical shapes.Comment: ApJ, to be publishe
Precovery of near-Earth asteroids by a citizen-science project of the Spanish Virtual Observatory
This article describes a citizen-science project conducted by the Spanish
Virtual Observatory (SVO) to improve the orbits of near-Earth asteroids (NEAs)
using data from astronomical archives. The list of NEAs maintained at the Minor
Planet Center (MPC) is checked daily to identify new objects or changes in the
orbital parameters of already catalogued objects. Using NEODyS we compute the
position and magnitude of these objects at the observing epochs of the 938 046
images comprising the Eigth Data Release of the Sloan Digitised Sky Survey
(SDSS). If the object lies within the image boundaries and the magnitude is
brighter than the limiting magnitude, then the associated image is visually
inspected by the project's collaborators (the citizens) to confirm or discard
the presence of the NEA. If confirmed, accurate coordinates and, sometimes,
magnitudes are submitted to the MPC. Using this methodology, 3,226 registered
users have made during the first fifteen months of the project more than
167,000 measurements which have improved the orbital elements of 551 NEAs (6%
of the total number of this type of asteroids). Even more remarkable is the
fact that these results have been obtained at zero cost to telescope time as
NEAs were serendipitously observed while the survey was being carried out. This
demonstrates the enormous scientific potential hidden in astronomical archives.
The great reception of the project as well as the results obtained makes it a
valuable and reliable tool for improving the orbital parameters of near-Earth
asteroids.Comment: 9 pages, 5 figures. Accepted in Astron. Nach
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