8,830 research outputs found
Exact description of D-branes in K-matrix theory
We summarize how to describe D-branes in a matrix theory based on unstable
D-instantons, which we call K-matrix theory, and explicity show that D-branes
can be constructed as bound states of infinitly many unstable D-instantons. We
examine the fluctuations around Dp-brane solutions in the matrix theory and
show that they correctly reproduce fields on the Dp-brane world-volume.
Plugging them into the action of the matrix theory, we precisely obtain the
Dp-brane action as the effective action of the fluctuations.Comment: 19 pages, Talk given by S.S. at the 17th Nishinomiya-Yukawa Memorial
Symposium, Nishinomiya, November, 200
More on a holographic dual of QCD
We investigate the interactions among the pion, vector mesons and external
gauge fields in the holographic dual of massless QCD proposed in a previous
paper, hep-th/0412141, on the basis of probe D8-branes embedded in a D4-brane
background in type IIA string theory. We obtain the coupling constants by
performing both analytic and numerical calculations, and compare them with
experimental data. It is found that the vector meson dominance in the pion form
factor as well as in the Wess-Zumino-Witten term holds in an intriguing manner.
We also study the \omega to \pi\gamma and \omega to 3\pi decay amplitudes. It
is shown that the interactions relevant to these decay amplitudes have the same
structure as that proposed by Fujiwara et al. Various relations among the
masses and the coupling constants of an infinite tower of mesons are derived.
These relations play crucial roles in the analysis. We find that most of the
results are consistent with experiments.Comment: Latex2e, 40 pages, 6 figures, v2: references added, typos corrected,
v3: PTP-style, typos corrected, v4: minor correction
Gauge covariant formulation of Wigner representation through deformational quantization --Application to Keldysh formalism with electromagnetic field--
We developed a gauge-covariant formulation of the non-equilibrium Green
function method for the dynamical and/or non-uniform electromagnetic field by
means of the deformational quantization method. Such a formulation is realized
by replacing the Moyal product in the so-called Wigner space by the star
product, and facilitates the order-by-order calculation of a gauge-invariant
observable in terms of the electromagnetic field. An application of this
formalism to the linear response theory is discussed
Low energy hadron physics in holographic QCD
We present a holographic dual of four-dimensional, large N_c QCD with
massless flavors. This model is constructed by placing N_f probe D8-branes into
a D4 background, where supersymmetry is completely broken. The chiral symmetry
breaking in QCD is manifested as a smooth interpolation of D8 - anti-D8 pairs
in the supergravity background. The meson spectrum is examined by analyzing a
five-dimensional Yang-Mills theory that originates from the non-Abelian DBI
action of the probe D8-brane. It is found that our model yields massless pions,
which are identified with Nambu-Goldstone bosons associated with the chiral
symmetry breaking. We obtain the low-energy effective action of the pion field
and show that it contains the usual kinetic term of the chiral Lagrangian and
the Skyrme term. A brane configuration that defines a dynamical baryon is
identified with the Skyrmion. We also derive the effective action including the
lightest vector meson. Our model is closely related to that in the hidden local
symmetry approach, and we obtain a
Kawarabayashi-Suzuki-Riazuddin-Fayyazuddin-type relation among the couplings.
Furthermore, we investigate the Chern-Simons term on the probe brane and show
that it leads to the Wess-Zumino-Witten term. The mass of the \eta' meson is
also considered, and we formulate a simple derivation of the \eta' mass term
satisfying the Witten-Veneziano formula from supergravity.Comment: 46 pages, 1 figure, minor corrections, version to appear in Prog.
Theor. Phys, v4: typos corrected, v5: The normalization of the 5d Yang-Mills
action given in Eq. (5.1) is corrected. Some of the expressions in section 5
are modified accordingly, but all the conclusions remain unchange
Orientifolds, RR Torsion, and K-theory
We analyze the role of RR fluxes in orientifold backgrounds from the point of
view of K-theory, and demonstrate some physical implications of describing
these fluxes in K-theory rather than cohomology. In particular, we show that
certain fractional shifts in RR charge quantization due to discrete RR fluxes
are naturally explained in K-theory. We also show that some orientifold
backgrounds, which are considered distinct in the cohomology classification,
become equivalent in the K-theory description, while others become unphysical.Comment: 30 pages, 5 figures; typos corrected and references adde
Relativistic mean field theory for deformed nuclei with pairing correlations
We develop a relativistic mean field (RMF) description of deformed nuclei
with the pairing correlations in the BCS approximation. The treatment of the
pairing correlations for nuclei with the Fermi surface being close to the
threshold of unbound states needs a special attention. To this end, we take the
delta function interaction for the pairing interaction with the hope to pick up
those states with the wave function being concentrated in the nuclear region
and perform the standard BCS approximation for the single particle states
generated by the RMF theory with deformation. We apply the RMF + BCS method to
the Zr isotopes and obtain a good description of the binding energies and the
nuclear radii of nuclei from the proton drip line to the neutron drip line.Comment: the version to be published in Progress of Theoretical Physic
Baryons from instantons in holographic QCD
We consider aspects of dynamical baryons in a holographic dual of QCD that is
proposed on the basis of a D4/D8-brane configuration. We construct a soliton
solution carrying a unit baryon number and show that it is given by an
instanton solution of four-dimensional Yang-Mills theory with fixed size. The
Chern-Simons term on the flavor D8-branes plays a crucial role of protecting
the instanton from collapsing to zero size. By quantizing the collective
coordinates of the soliton, we work out the baryon spectra. Negative-parity
baryons as well as baryons with higher spins and isospins can be obtained in a
simple manner.Comment: 25 pages, v2: references added, minor changes, v3: PTP-style, minor
correction
Studies on organic semiconductors. 15: Effects of the substituents on the photoconductivities of substituted anthracenes
The photocurrents of the substituted anthracenes, 1,5-diacetylanthracene (2), 1-acetylanthracene (3), 9-acetylanthracene (4), 1,5-dichloroanthracene (5), 1,5-diethylanthracene (6), 1,5-dimethoxyanthracene (7), 9-cyanoanthracene (8), and anthracene (1) were measured by using their surface type cells in nitrogen. The compounds of (1), (5), (6), (7), and (8) showed the photocurrent spectra which corresponded to the absorption spectra of their evaporated films. In the cases of (2) and (3), however, the anomalous photocurrent appeared in the threshold region of their absorption spectra. The appearance of the anomalous photocurrent was characteristic of anthracenes having the acetyl group at 1- and/or 5-position. The magnitude of the photocurrents of the 1,5-disubstituted anthracenes was similar to that of (1). The photocurrents of the monosubstituted anthracenes were smaller than that of (1). Among the monosubstituted anthracenes, the compound (4) showed no photocurrent under the same conditions. Contrary to the results obtained in the cases of phenazines, the photoconductivities of the anthracene derivatives became better in air
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