884 research outputs found
The microlocal spectrum condition and Wick polynomials of free fields on curved spacetimes
Quantum fields propagating on a curved spacetime are investigated in terms of
microlocal analysis. We discuss a condition on the wave front set for the
corresponding n-point distributions, called ``microlocal spectrum condition''
(SC). On Minkowski space, this condition is satisfied as a consequence of
the usual spectrum condition. Based on Radzikowski's determination of the wave
front set of the two-point function of a free scalar field, satisfying the
Hadamard condition in the Kay and Wald sense, we construct in the second part
of this paper all Wick polynomials including the energy-momentum tensor for
this field as operator valued distributions on the manifold and prove that they
satisfy our microlocal spectrum condition.Comment: 21 pages, AMS-LaTeX, 2 figures appended as Postscript file
Running Spectral Index from Inflation with Modulations
We argue that a large negative running spectral index, if confirmed, might
suggest that there are abundant structures in the inflaton potential, which
result in a fairly large (both positive and negative) running of the spectral
index at all scales. It is shown that the center value of the running spectral
index suggested by the recent CMB data can be easily explained by an inflaton
potential with superimposed periodic oscillations. In contrast to cases with
constant running, the perturbation spectrum is enhanced at small scales, due to
the repeated modulations. We mention that such features at small scales may be
seen by 21 cm observations in the future.Comment: 7 pages, 6 figures, v2: published in JCA
Inflation with improved D3-brane potential and the fine tunings associated with the model
We investigate brane-antibrane inflation in a warped deformed conifold
background that includes contributions to the potential arising from imaginary
anti-self-dual (IASD) fluxes including the term with irrational scaling
dimension discovered recently. We find that the model can give rise to required
number of e-foldings; observational constraint on COBE normalization is easily
satisfied and low value of the tensor to scalar ratio of perturbations is
achieved. We observe that these corrections to the effective potential help in
relaxing the severe fine tunings associated with the earlier analysis.Comment: 8 pages, 4 figures; typos corrected, minor clarifications and new
refs added, to appear in epj
An isotopic effect in phi photoproduction at a few GeV
A distinct isotopic effect in phi photoproduction at 2-5 GeV region is
identified by examining the production amplitudes due to Pomeron-exchange and
meson-exchange mechanisms. This effect is mainly caused by the pi-eta
interference constrained by SU(3) symmetry and the isotopic structure of the
gamma NN coupling in the direct phi-radiation amplitude. It can be tested
experimentally by measuring differences in the polarization observables between
the gamma-p and gamma-n reactions.Comment: 11 pages, 6 figure
Electronic structure investigation of CeB6 by means of soft X-ray scattering
The electronic structure of the heavy fermion compound CeB6 is probed by
resonant inelastic soft X-ray scattering using photon energies across the Ce 3d
and 4d absorption edges. The hybridization between the localized 4f orbitals
and the delocalized valence-band states is studied by identifying the different
spectral contributions from inelastic Raman scattering and normal fluorescence.
Pronounced energy-loss structures are observed below the elastic peak at both
the 3d and 4d thresholds. The origin and character of the inelastic scattering
structures are discussed in terms of charge-transfer excitations in connection
to the dipole allowed transitions with 4f character. Calculations within the
single impurity Anderson model with full multiplet effects are found to yield
consistent spectral functions to the experimental data.Comment: 9 pages, 4 figures, 1 table,
http://link.aps.org/doi/10.1103/PhysRevB.63.07510
Evidence for Shape Co-existence at medium spin in 76Rb
Four previously known rotational bands in 76Rb have been extended to moderate
spins using the Gammasphere and Microball gamma ray and charged particle
detector arrays and the 40Ca(40Ca,3pn) reaction at a beam energy of 165 MeV.
The properties of two of the negative-parity bands can only readily be
interpreted in terms of the highly successful Cranked Nilsson-Strutinsky model
calculations if they have the same configuration in terms of the number of g9/2
particles, but they result from different nuclear shapes (one near-oblate and
the other near-prolate). These data appear to constitute a unique example of
shape co-existing structures at medium spins.Comment: Accepted for publication in Physics Letters
From GHz to mHz: A Multiwavelength Study of the Acoustically Active 14 August 2004 M7.4 Solar Flare
We carried out an electromagnetic acoustic analysis of the solar flare of 14
August 2004 in active region AR10656 from the radio to the hard X-ray spectrum.
The flare was a GOES soft X-ray class M7.4 and produced a detectable sun quake,
confirming earlier inferences that relatively low-energy flares may be able to
generate sun quakes. We introduce the hypothesis that the seismicity of the
active region is closely related to the heights of coronal magnetic loops that
conduct high-energy particles from the flare. In the case of relatively short
magnetic loops, chromospheric evaporation populates the loop interior with
ionized gas relatively rapidly, expediting the scattering of remaining trapped
high-energy electrons into the magnetic loss cone and their rapid precipitation
into the chromosphere. This increases both the intensity and suddenness of the
chromospheric heating, satisfying the basic conditions for an acoustic emission
that penetrates into the solar interior.Comment: Accepted in Solar Physic
The design, construction and performance of the MICE scintillating fibre trackers
This is the Pre-print version of the Article. The official published version can be accessed from the link below - Copyright @ 2011 ElsevierCharged-particle tracking in the international Muon Ionisation Cooling Experiment (MICE) will be performed using two solenoidal spectrometers, each instrumented with a tracking detector based on diameter scintillating fibres. The design and construction of the trackers is described along with the quality-assurance procedures, photon-detection system, readout electronics, reconstruction and simulation software and the data-acquisition system. Finally, the performance of the MICE tracker, determined using cosmic rays, is presented.This work was supported by the Science and Technology Facilities Council under grant numbers PP/E003214/1, PP/E000479/1, PP/E000509/1, PP/E000444/1, and through SLAs with STFC-supported laboratories. This work was also supportedby the Fermi National Accelerator Laboratory, which is operated by the Fermi Research Alliance, under contract No. DE-AC02-76CH03000 with the U.S. Department of Energy, and by the U.S. National Science Foundation under grants PHY-0301737,PHY-0521313, PHY-0758173 and PHY-0630052. The authors also acknowledge the support of the World Premier International Research Center Initiative (WPI Initiative), MEXT, Japan
PSA based multi objective evolutionary algorithms
It has generally been acknowledged that both proximity to the Pareto front and a certain diversity along the front, should be targeted when using evolutionary multiobjective optimization. Recently, a new partitioning mechanism, the Part and Select Algorithm (PSA), has been introduced. It was shown that this partitioning allows for the selection of a well-diversified set out of an arbitrary given set, while maintaining low computational cost. When embedded into an evolutionary search (NSGA-II), the PSA has significantly enhanced the exploitation of diversity. In this paper, the ability of the PSA to enhance evolutionary multiobjective algorithms (EMOAs) is further investigated. Two research directions are explored here. The first one deals with the integration of the PSA within an EMOA with a novel strategy. Contrary to most EMOAs, that give a higher priority to proximity over diversity, this new strategy promotes the balance between the two. The suggested algorithm allows some dominated solutions to survive, if they contribute to diversity. It is shown that such an approach substantially reduces the risk of the algorithm to fail in finding the Pareto front. The second research direction explores the use of the PSA as an archiving selection mechanism, to improve the averaged Hausdorff distance obtained by existing EMOAs. It is shown that the integration of the PSA into NSGA-II-I and Δ p -EMOA as an archiving mechanism leads to algorithms that are superior to base EMOAS on problems with disconnected Pareto fronts. © 2014 Springer International Publishing Switzerland
MICE: the Muon Ionization Cooling Experiment. Step I: First Measurement of Emittance with Particle Physics Detectors
The Muon Ionization Cooling Experiment (MICE) is a strategic R&D project intended to demonstrate the only practical solution to providing high brilliance beams necessary for a neutrino factory or muon collider. MICE is under development at the Rutherford Appleton Laboratory (RAL) in the United Kingdom. It comprises a dedicated beamline to generate a range of input muon emittances and momenta, with time-of-flight and Cherenkov detectors to ensure a pure muon beam. The emittance of the incoming beam will be measured in the upstream magnetic spectrometer with a scintillating fiber tracker. A cooling cell will then follow, alternating energy loss in Liquid Hydrogen (LH2) absorbers to RF cavity acceleration. A second spectrometer, identical to the first, and a second muon identification system will measure the outgoing emittance. In the 2010 run at RAL the muon beamline and most detectors were fully commissioned and a first measurement of the emittance of the muon beam with particle physics (time-of-flight) detectors was performed. The analysis of these data was recently completed and is discussed in this paper. Future steps for MICE, where beam emittance and emittance reduction (cooling) are to be measured with greater accuracy, are also presented
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