29,372 research outputs found
On timelike and spacelike hard exclusive reactions
We show to next-to-leading order accuracy in the strong coupling alpha_s how
the collinear factorization properties of QCD in the generalized Bjorken regime
relate exclusive amplitudes for spacelike and timelike hadronic processes. This
yields simple space--to--timelike relations linking the amplitudes for
electroproduction of a photon or meson to those for photo- or meso-production
of a lepton pair. These relations constitute a new test of the relevance of
leading twist analyzes of experimental data.Comment: v2: major text revision; results, references, and author added; v3:
matches the published version Phys. Rev. D86, rapid communication
High temperature expansion applied to fermions near Feshbach resonance
We show that, apart from a difference in scale, all of the surprising
recently observed properties of a degenerate Fermi gas near a Feshbach
resonance persist in the high temperature Boltzmann regime. In this regime, the
Feshbach resonance is unshifted. By sweeping across the resonance, a thermal
distribution of bound states (molecules) can be reversibly generated.
Throughout this process, the interaction energy is negative and continuous. We
also show that this behavior must persist at lower temperatures unless there is
a phase transition as the temperature is lowered. We rigorously demonstrate
universal behavior near the resonance.Comment: 4 pages, 4 figures (3 color, 1 BW), RevTeX4; ver4 -- updated
references, changed title -- version accepted for publication in Physical
Review Letter
Quenching of hadron spectra in media
We determine how the yield of large transverse momentum hadrons is modified
due to induced gluon radiation off a hard parton traversing a QCD medium. The
quenching factor is formally a collinear- and infrared-safe quantity and can be
treated perturbatively. In spite of that, in the region of practical
interest, its value turns out to be extremely sensitive to large distances and
can be used to unravel the properties of dense quark-gluon final states
produced in heavy ion collisions. We also find that the standard modelling of
quenching by shifting in the hard parton cross section by the mean
energy loss is inadequate.Comment: 20 pp, 5 eps figure
Explanation of 100-fold reduction of spectral shifts for hydrogen on helium films
We show that helium film-mediated hydrogen-hydrogen interactions account for
a two orders of magnitude discrepancy between previous theory and recent
experiments on cold collision shifts in spin-polarized hydrogen adsorbed on a
helium film. These attractive interactions also explain the anomalous
dependence of the cold collision frequency shifts on the He covering of the
film. Our findings suggest that the gas will become mechanically unstable
before reaching the Kosterlitz-Thouless transition unless the experiment is
performed in a drastically different regime, for example with a much different
helium film geometry.Comment: 4+ pages, 1 figure (3 subfigures), revtex
Space Storable Rocket Technology (SSRT) basic program
The Space Storable Rocket Technology Program (SSRT) was conducted to establish a technology for a new class of high performance and long life bipropellant engines using space storable propellants. The results are described. Task 1 evaluated several characteristics for a number of fuels to determine the best space storable fuel for use with LO2. The results indicated that LO2-N2H4 is the best propellant combination and provides the maximum mission/system capability maximum payload into GEO of satellites. Task 2 developed two models, performance and thermal. The performance model indicated the performance goal of specific impulse greater than or = 340 seconds (sigma = 204) could be achieved. The thermal model was developed and anchored to hot fire test data. Task 3 consisted of design, fabrication, and testing of a 200 lbf thrust test engine operating at a chamber pressure of 200 psia using LO2-N2H4. A total of 76 hot fire tests were conducted demonstrating performance greater than 340 (sigma = 204) which is a 25 second specific impulse improvement over the existing highest performance flight apogee type engines
Heat flow in the postquasistatic approximation
We apply the postquasistatic approximation to study the evolution of
spherically symmetric fluid distributions undergoing dissipation in the form of
radial heat flow. For a model which corresponds to an incompressible fluid
departing from the static equilibrium, it is not possible to go far from the
initial state after the emission of a small amount of energy. Initially
collapsing distributions of matter are not permitted. Emission of energy can be
considered as a mechanism to avoid the collapse. If the distribution collapses
initially and emits one hundredth of the initial mass only the outermost layers
evolve. For a model which corresponds to a highly compressed Fermi gas, only
the outermost shell can evolve with a shorter hydrodynamic time scale.Comment: 5 pages, 5 figure
Local versus global equilibration near the bosonic Mott-superfluid transition
We study the response of trapped two dimensional cold bosons to time
dependent lattices. We find that in lattice ramps from 11 (superfluid,
ms, ms) to 16 recoils (Mott,
ms, ms) the local number
fluctuations remains at their equilibrium values if ramps are slower than 3 ms.
Global transport, however, is much slower (1s), especially in the presence of
Mott shells. This separation of timescales has practical implications for cold
atom experiments and cooling protocols.Comment: 4 pages, 4 figs. 6 subfigure
Small optic suspensions for Advanced LIGO input optics and other precision optical experiments
We report on the design and performance of small optic suspensions developed
to suppress seismic motion of out-of-cavity optics in the Input Optics
subsystem of the Advanced LIGO interferometric gravitational wave detector.
These compact single stage suspensions provide isolation in all six degrees of
freedom of the optic, local sensing and actuation in three of them, and passive
damping for the other three
Generalized parton distributions and rapidity gap survival in exclusive diffractive pp scattering
We propose a new approach to the problem of rapidity gap survival (RGS) in
the production of high-mass systems (H = dijet, heavy quarkonium, Higgs boson)
in double-gap exclusive diffractive pp scattering, pp -> p + (gap) + H + (gap)
+ p. It is based on the idea that hard and soft interactions proceed over
widely different time- and distance scales and are thus approximately
independent. The high-mass system is produced in a hard scattering process with
exchange of two gluons between the protons. Its amplitude is calculable in
terms of the gluon generalized parton distributions (GPDs) in the protons,
which can be measured in J/psi production in exclusive ep scattering. The hard
scattering process is modified by soft spectator interactions, which we
calculate in a model-independent way in terms of the pp elastic scattering
amplitude. Contributions from inelastic intermediate states are suppressed. A
simple geometric picture of the interplay of hard and soft interactions in
diffraction is obtained. The onset of the black-disk limit in pp scattering at
TeV energies strongly suppresses diffraction at small impact parameters and is
the main factor in determining the RGS probability. Correlations between hard
and soft interactions (e.g. due to scattering from the long-range pion field of
the proton, or due to possible short-range transverse correlations between
partons) further decrease the RGS probability. We also investigate the
dependence of the diffractive cross section on the transverse momenta of the
final-state protons ("diffraction pattern"). By measuring this dependence one
can perform detailed tests of the interplay of hard and soft interactions, and
even extract information about the gluon GPD in the proton. Such studies appear
to be feasible with the planned forward detectors at the LHC.Comment: 26 pages, 17 figures, uses revtex
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