17,564 research outputs found
c=1 String as a Topological Model
The discrete states in the string are shown to be the physical states
of a certain topological sigma model. We define a set of new fields directly
from variables, in terms of which the BRST charge and energy-momentum
tensor are rewritten as those of the topological sigma model. Remarkably,
ground ring generator turns out to be a coordinate of the sigma model. All
of the discrete states realize a graded ring which contains ground ring as a
subset.Comment: 23 pages + 3 figures in PostScript, LaTeX, UT-Komaba/93-7.
Description of the physical spectrum in terms of topological model is
improved. Some references and new figures added. (figures are available upon
request.
photoproduction off the deuteron and low-energy -nucleon interaction
We study photoproduction off the deuteron () at a
special kinematics: GeV of the photon beam energy and of the scattering angle of the proton. This kinematics is ideal to
extract the low-energy -nucleon scattering parameters such as (scattering length) and (effective range) because the
-nucleon elastic scattering is significantly enhanced. We show that if a
ratio , the cross section divided by the cross section convoluted with the proton momentum distribution in
the deuteron, is measured with 5% error, () can be determined at the precision of 0.1 fm
(0.5 fm), significantly narrowing down the currently estimated range
of the parameters. The measurement is ongoing at the Research Center for
Electron Photon Science (ELPH), Tohoku University.Comment: 4 pages, 5 figures, Contribution to the Proceedings for 8th
International Conference on Quarks and Nuclear Physics (QNP2018), November
13-17, 2018, Tsukuba, Japa
Evidence for Narrow S=+1 Baryon Resonance in Photo-production from Neutron
The gamma n -> K+ K- n reaction on 12C has been studied by measuring both K+
and K- at forward angles. A sharp baryon resonance peak was observed at 1.54 +-
0.01 GeV with a width smaller than 25 MeV and a Gaussian significance of 4.6
sigma. The strangeness quantum number (S) of the baryon resonance is +1. It can
be interpreted as a molecular meson-baryon resonance or alternatively as an
exotic 5-quark state (uudd{s_bar}) that decays into a K+ and a neutron. The
resonance is consistent with the lowest member of an anti-decuplet of baryons
predicted by the chiral soliton model.Comment: 12 pages, 3 encapsulated postscript figure
Visibility and aerosol measurement by diode-laser random-modulation CW lidar
Examples of diode laser (DL) random-modulation continuous wave (RM-CW) lidar measurements are reported. The ability of the measurement of the visibility, vertical aerosol profile, and the cloud ceiling height is demonstrated. Although the data shown here were all measured at night time, the daytime measurement is, of course, possible. For that purpose, accurate control of the laser frequency to the center frequency of a narrow band filter is required. Now a new system with a frequency control is under construction
Anisotropy, disorder, and superconductivity in CeCu2Si2 under high pressure
Resistivity measurements were carried out up to 8 GPa on single crystal and
polycrystalline samples of CeCu2Si2 from differing sources in the homogeneity
range. The anisotropic response to current direction and small uniaxial
stresses was explored, taking advantage of the quasi-hydrostatic environment of
the Bridgman anvil cell. It was found that both the superconducting transition
temperature Tc and the normal state properties are very sensitive to uniaxial
stress, which leads to a shift of the valence instability pressure Pv and a
small but significant change in Tc for different orientations with respect to
the tetragonal c-axis. Coexistence of superconductivity and residual
resistivity close to the Ioffe-Regel limit around 5 GPa provides a compelling
argument for the existence of a valence-fluctuation mediated pairing
interaction at high pressure in CeCu2Si2.Comment: 12 pages, 7 figure
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