61,295 research outputs found

### Exploring Vacuum Structure around Identity-Based Solutions

We explore the vacuum structure in bosonic open string field theory expanded
around an identity-based solution parameterized by $a(>=-1/2)$. Analyzing the
expanded theory using level truncation approximation up to level 20, we find
that the theory has the tachyon vacuum solution for $a>-1/2$. We also find
that, at $a=-1/2$, there exists an unstable vacuum solution in the expanded
theory and the solution is expected to be the perturbative open string vacuum.
These results reasonably support the expectation that the identity-based
solution is a trivial pure gauge configuration for $a>-1/2$, but it can be
regarded as the tachyon vacuum solution at $a=-1/2$.Comment: 12 pages, 5 figures; new numerical data up to level (20,60) included;
Contribution to the proceedings of "Second International Conference on String
Field Theory and Related Aspects" (Steklov Mathematical Institute, Moscow,
Russia, April 12-19, 2009

### Room Temperature Reversible Spin Hall Effect

Reversible spin Hall effect comprising the "direct" and "inverse" spin Hall
effects was successfully detected at room temperature. This experimental
demonstration proves the fundamental relations called Onsager reciprocal
relations between spin and charge currents. A platinum wire with a strong
spin-orbit interaction is used not only as a spin current absorber but also as
a spin current source in the present lateral structure specially designed for
clear detection of both charge and spin accumulations via the spin-orbit
interaction. The obtained spin Hall conductivity is much larger than the
reported value of Aluminum wire because of the larger spin-orbit interaction.Comment: 12 pages, 4 figure

### Nuclear force in Lattice QCD

We perform the quenched lattice QCD analysis on the nuclear force
(baryon-baryon interactions). We employ $20^3\times 24$ lattice at $\beta=5.7$
($a\simeq 0.19$ fm) with the standard gauge action and the Wilson quark action
with the hopping parameters $\kappa=0.1600, 0.1625, 0.1650$, and generate about
200 gauge configurations. We measure the temporal correlators of the two-baryon
system which consists of heavy-light-light quarks. We extract the inter-baryon
force as a function of the relative distance $r$. We also evaluate the
contribution to the nuclear force from each ``Feynman diagram'' such as the
quark-exchange diagram individually, and single out the roles of Pauli-blocking
effects or quark exchanges in the inter-baryon interactions.Comment: Presented at Particles and Nuclei International Conference (PANIC05),
Santa Fe, NM, Oct. 24-28, 2005; 3 pages, 2figure

### Lattice QCD Study of the Pentaquark Baryons

We study the spin $\frac12$ hadronic state in quenched lattice QCD to search
for a possible $S=+1$ pentaquark resonance. Simulations are carried out on
$8^3\times 24$, $10^3\times 24$, $12^3\times 24$ and $16^3\times 24$ lattices
at $\beta$=5.7 at the quenched level with the standard plaquette gauge action
and Wilson quark action. We adopt two independent operators with I=0 and
$J^P=\frac12$ to construct a $2\times 2$ correlation matrix. After the
diagonalization of the correlation matrix, we successfully obtain the energies
of the ground-state and the 1st excited-state in this channel. The volume
dependence of the energies suggests the existence of a possible resonance state
slightly above the NK threshold in I=0 and $J^P=\frac12^-$ channel.Comment: Talk given at the International Workshop on PENTAQUARK04, SPring-8,
Japan, 20-23 July 2004; 7 pages, 3 figure

### Low-lying Dirac eigenmodes and monopoles in 3+1D compact QED

We study the properties of low-lying Dirac modes in quenched compact QED at
$\beta =1.01$, employing $12^3\times N_t$ ($N_t =4,6,8,10,12$) lattices and the
overlap formalism for the fermion action. We pay attention to the spatial
distributions of low-lying Dirac modes below and above the ``phase transition
temperature'' $T_c$. Near-zero modes are found to have universal
anti-correlations with monopole currents, and are found to lose their temporal
structures above $T_c$ exhibiting stronger spatial localization properties. We
also study the nearest-neighbor level spacing distribution of Dirac eigenvalues
and find a Wigner-Poisson transition.Comment: 10 pages, 10 figures, 1 tabl

### Takahashi Integral Equation and High-Temperature Expansion of the Heisenberg Chain

Recently a new integral equation describing the thermodynamics of the 1D
Heisenberg model was discovered by Takahashi. Using the integral equation we
have succeeded in obtaining the high temperature expansion of the specific heat
and the magnetic susceptibility up to O((J/T)^{100}). This is much higher than
those obtained so far by the standard methods such as the linked-cluster
algorithm. Our results will be useful to examine various approximation methods
to extrapolate the high temperature expansion to the low temperature region.Comment: 5 pages, 4 figures, 2 table

### Bound States of (Anti-)Scalar-Quarks in SU(3)_c Lattice QCD

Light scalar-quarks \phi (colored scalar particles or idealized diquarks) and
their color-singlet hadronic states are studied with quenched SU(3)_c lattice
QCD in terms of mass generation. We investigate ``scalar-quark mesons''
\phi^\dagger \phi and ``scalar-quark baryons'' \phi\phi\phi as the bound states
of scalar-quarks \phi. We also investigate the bound states of scalar-quarks
\phi and quarks \psi, i.e., \phi^\dagger \psi, \psi\psi\phi and \phi\phi\psi,
which we name ``chimera hadrons''. All the new-type hadrons including \phi are
found to have a large mass due to large quantum corrections by gluons, even for
zero bare scalar-quark mass m_\phi=0 at a^{-1}\sim 1{\rm GeV}. We conjecture
that all colored particles generally acquire a large effective mass due to
dressed gluon effects.Comment: Talk given at The 17th International Spin Physics Symposium
(SPIN2006), Kyoto, Japan, 2-7 Oct 200

### Axial Charges of Octet Baryons in Two-flavor Lattice QCD

We evaluate the strangeness-conserving $N N$, $\Sigma\Sigma$, $\Xi\Xi$,
$\Lambda\Sigma$ and the strangeness-changing $\Lambda N$, $\Sigma N$,
$\Lambda\Xi$, $\Sigma\Xi$ axial charges in lattice QCD with two flavors of
dynamical quarks and extend our previous work on
pseudoscalar-meson-octet-baryon coupling constants so as to include
$\pi\Xi\Xi$, $K\Lambda\Xi$ and $K\Sigma\Xi$ coupling constants. We find that
the axial charges have rather weak quark-mass dependence and the breaking in
SU(3)-flavor symmetry is small at each quark-mass point we consider.Comment: 6 pages, 6 figures. Added discussions and a figure; version to appear
in Physics Letters

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