3,001 research outputs found
Ultimate parameters of the photon collider at the ILC
At linear colliders, the e+e- luminosity is limited by beam-collision
effects, which determine the required emittances of beams in damping rings
(DRs). While in gamma-gamma collisions at the photon collider, these effects
are absent, and so smaller emittances are desirable. In present damping rings
designs, nominal DR parameters correspond to those required for e+e-
collisions. In this note, I would like to stress once again that as soon as we
plan the photon-collider mode of ILC operation, the damping-ring emittances are
dictated by the photon-collider requirements--namely, they should be as small
as possible. This can be achieved by adding more wigglers to the DRs; the
incremental cost is easily justified by a considerable potential improvement of
the gamma-gamma luminosity. No expert analysis exists as of yet, but it seems
realistic to obtain a factor five increase of the gamma-gamma luminosity
compared to the ``nominal'' DR design.Comment: Talk at LCWS06, Bangalore, India, March 2006, to be published in
Indian Journal of Physics, 5 pp, Latex, 1 .eps figur
The Far-Infrared Properties of Spatially Resolved AKARI Observations
We present the spatially resolved observations of IRAS sources from the
Japanese infrared astronomy satellite AKARI All-Sky Survey during the
performance verification (PV) phase of the mission. We extracted reliable point
sources matched with IRAS point source catalogue. By comparing IRAS and AKARI
fluxes, we found that the flux measurements of some IRAS sources could have
been over or underestimated and affected by the local background rather than
the global background. We also found possible candidates for new AKARI sources
and confirmed that AKARI observations resolved IRAS sources into multiple
sources. All-Sky Survey observations are expected to verify the accuracies of
IRAS flux measurements and to find new extragalactic point sources.Comment: 11 pages, 7 figures, accepted publication in PASJ AKARI special issu
Convective Motion in a Vibrated Granular Layer
Experimental results are presented for a vertically shaken granular layer. In
the range of accelerations explored, the layer develops a convective motion in
the form of one or more rolls. The velocity of the grains near the wall has
been measured. It grows linearly with the acceleration, then the growing rate
slows down. A rescaling with the amplitude of the wall velocity and the height
of the granular layer makes all data collapse in a single curve. This can
provide insights on the mechanism driving the motion.Comment: 10 pages, 5 figures submitted to Phys. Rev. Let
Early GRB Optical and Infrared Afterglow Observations with the 2-m Robotic Liverpool Telescope
We present the first optical observations of a Gamma Ray Burst (GRB)
afterglow using the 2-m robotic Liverpool Telescope (LT), which is owned and
operated by Liverpool John Moores University and situated on La Palma. We
briefly discuss the capabilities of LT and its suitability for rapid follow-up
observations of early optical and infrared GRB light curves. In particular, the
combination of aperture, site, instrumentation and rapid response (robotic
over-ride mode aided by telescope's rapid slew and fully-opening enclosure)
makes the LT ideal for investigating the nature of short bursts, optically-dark
bursts, and GRB blast-wave physics in general. We briefly describe the LT's key
position in the RoboNet-1.0 network of robotic telescopes. We present the LT
observations of GRB041006 and use its gamma-ray properties to predict the time
of the break in optical light curve, a prediction consistent with the
observations.Comment: 4 pages, 1 figure, accepted for publication in Il nuovo cimento (4th
Workshop Gamma-Ray Bursts in the Afterglow Era, Rome, 18-22 October 2004
Towards Higgs boson production in gluon fusion to NNLO in the MSSM
We consider the Higgs boson production in the gluon-fusion channel to
next-to-next-to-leading order within the Minimal Supersymmetric Standard Model.
In particular, we present analytical results for the matching coefficient of
the effective theory and study its influence on the total production cross
section in the limit where the masses of all MSSM particles coincide. For
supersymmetric masses below 500 GeV it is possible to find parameters leading
to a significant enhancement of the Standard Model cross section, the
-factors, however, change only marginally.Comment: 20 pages; v2: modification of discussion of numerical effect, version
to appear in EPJC; v3: eq.(18) corrected, minor correction
Transitions in the Horizontal Transport of Vertically Vibrated Granular Layers
Motivated by recent advances in the investigation of fluctuation-driven
ratchets and flows in excited granular media, we have carried out experimental
and simulational studies to explore the horizontal transport of granular
particles in a vertically vibrated system whose base has a sawtooth-shaped
profile. The resulting material flow exhibits novel collective behavior, both
as a function of the number of layers of particles and the driving frequency;
in particular, under certain conditions, increasing the layer thickness leads
to a reversal of the current, while the onset of transport as a function of
frequency occurs gradually in a manner reminiscent of a phase transition. Our
experimental findings are interpreted here with the help of extensive, event
driven Molecular Dynamics simulations. In addition to reproducing the
experimental results, the simulations revealed that the current may be reversed
as a function of the driving frequency as well. We also give details about the
simulations so that similar numerical studies can be carried out in a more
straightforward manner in the future.Comment: 12 pages, 18 figure
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