1,689 research outputs found
Geophysical constraint on a relic background of the dilatons
According to a scenario in string cosmology, a relic background of light
dilatons can be a significant component of the dark matter in the Universe. A
new approach of searching for such a dilatonic background by observing Earth's
surface gravity was proposed in my previous work. In this paper, the concept of
the geophysical search is briefly reviewed, and the geophysical constraint on
the dilaton background is presented as a function of the strength of the
dilaton coupling, . For simplicity, I focus on massless dilatons and
assume a simple Earth model. With the current upper limit on , we obtain
the upper limit on the dimensionless energy density of the massless background,
, which is about one-order of
magnitude more stringent than the one from astrophysical observations, at the
frequency of 7 10 Hz. If the magnitude of is
experimentally found to be smaller than the current upper limit by one order of
magnitude, the geophysical upper limit on becomes less
stringent and comparable to the one obtained from the astrophysical
observations.Comment: 6 pages, Proceedings for the 8th Edoardo Amaldi Conference on
Gravitational Waves, 21-26 June, 2009, Columbia University, New York, US
Heat conduction of single-walled carbon nanotube isotope-superlattice structures: A molecular dynamics study
Heat conduction of single-walled carbon nanotubes (SWNTs)
isotope-superlattice is investigated by means of classical molecular dynamics
simulations. Superlattice structures were formed by alternately connecting
SWNTs with different masses. On varying the superlattice period, the critical
value with minimum effective thermal conductivity was identified, where
dominant physics switches from zone-folding effect to thermal boundary
resistance of lattice interface. The crossover mechanism is explained with the
energy density spectra where zone-folding effects can be clearly observed. The
results suggest that the critical superlattice period thickness depends on the
mean free path distribution of diffusive-ballistic phonons. The reduction of
the thermal conductivity with superlattice structures beats that of the
one-dimensional alloy structure, though the minimum thermal conductivity is
still slightly higher than the value obtained by two-dimensional random mixing
of isotopes.Comment: 7 Pages, 5 figures, accepted to Phys. Rev.
Negative Parity Baryons in the QCD Sum Rule
Masses and couplings of the negative parity excited baryons are studied in
the QCD sum rule. Separation of the negative-parity spectrum is proposed and is
applied to the flavor octet and singlet baryons. We find that the quark
condensate is responsible for the mass splitting of the ground and the
negative-parity excited states. This is expected from the chiral symmetry and
supports the idea that the negative-parity baryon forms a parity doublet with
the ground state. The meson-baryon coupling constants are also computed for the
excited states in the QCD sum rule. It is found that the \pi NN^* coupling
vanishes in the chiral limit.Comment: 13pp, LaTeX, 1 EPS figure, uses epsf.sty, Talk given by M.O. at
CEBAF/INT workshop "N* physics", Seattle, September (1996), to appear in the
proceeding
Hall effect of spin-chirality origin in a triangular-lattice helimagnet Fe1.3Sb
We report on a topological Hall effect possibly induced by scalar spin
chirality in a quasi-two- dimensional helimagnet FeSb. In the
low-temperature region where the spins on interstitial- Fe (concentration
) intervening the spin-ordered triangular planes tend to
freeze, a non-trivial component of Hall resistivity with opposite sign of the
conventional anomalous Hall term is observed under magnetic field applied
perpendicular to the triangular-lattice plane. The observed unconventional Hall
effect is ascribed to the scalar spin chirality arising from the heptamer
spin-clusters around the interstitial-Fe sites, which can be induced by the
spin modulation by the Dzyaloshinsky-Moriya interaction
Hyperon-nucleon coupling from QCD sum rules
The NKY coupling constant for and is evaluated in a
QCD sum rule calculation. We discuss and extend the result of a previous
analysis in the structure and compare it with the result
obtained with the use of the structure. We find a
huge violation of the SU(3) symmetry in the
structure.Comment: 4 pages, 2 figures, espcrc2.sty included. Talk presented at QCD99,
Montpellier, France (to appear in Nucl.Phys.B Proc.Suppl.
Development of a low-mass and high-efficiency charged particle detector
We developed a low-mass and high-efficiency charged particle detector for an
experimental study of the rare decay . The
detector is important to suppress the background with charged particles to the
level below the signal branching ratio predicted by the Standard Model
(O(10)). The detector consists of two layers of 3-mm-thick plastic
scintillators with wavelength shifting fibers embedded and Multi Pixel Photon
Counters for readout. We manufactured the counter and evaluated the performance
such as light yield, timing resolution, and efficiency. With this design, we
achieved the inefficiency per layer against penetrating charged particles to be
less than , which satisfies the requirement of the KOTO
experiment determined from simulation studies.Comment: 20 pages, 18 figure
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