673 research outputs found
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
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
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
Making Nuclei Out Of The Skyrme Crystal
A new method for approximating Skyrme solutions is developed. It consists of
cutting sections out of the Skyrme crystal and smoothly interpolating between
the boundary and spatial infinity. Several field configurations are
constructed, and their energies calculated. The surface energy (per unit area)
of an infinite flat plane of the crystal is also calculated, and the result
used to derive a formula analogous to the semi-empirical mass formula of
nuclear physics. This formula can be used to give some idea of what the Skyrme
model predicts about volume and surface energies of the nucleus over a broad
range of baryon numbers.Comment: 20 pages, uuencoded ps file `crystal.uu'. The LaTeX version can be
obtained by emailing [email protected] or [email protected]
Pion-delta sigma-term
We use a configuration space chiral model in order to evaluate nucleon and
delta sigma-terms. Analytic expressions are consistent with chiral counting
rules and give rise to expected non-analytic terms in the chiral limit. We
obtain the results MeV and MeV, which are
very close to values extracted from experiment and produced by other groups.Comment: 18 pages, 4 figure
The nucleus as a fluid of skyrmions: Energy levels and nucleon properties in the medium
A model of a fluid of skyrmions coupled to a scalar and to the \o meson
mean fields is developed. The central and spin-orbit potentials of a skyrmion
generated by the fields predict correct energy levels in selected closed shell
nuclei. The effect of the meson fields on the properties of skyrmions in nuclei
is investigated.Comment: Latex format, 6 figures, Journal of Physics G, to be publishe
Chiral symmetry breaking and vacuum polarization in a bag
We study the effects of a finite quark mass in the hedgehog configuration in
the two phase chiral bag model. We discuss the chiral properties, such as the
fractional baryon number and the chiral Casimir energy, by using the Debye
expansion for the analytical calculation and the Strutinsky's smearing method
for the numerical computation. It is shown that the fractional baryon number
carried by massive quarks in the vacuum is canceled by that in the meson
sector. A finite term of the chiral Casimir energy is obtained with subtraction
of the logarithmic divergence term
Topological Objects in Two-component Bose-Einstein Condensates
We study the topological objects in two-component Bose-Einstein condensates.
We compare two competing theories of two-component Bose-Einstein condensate,
the popular Gross-Pitaevskii theory and the recently proposed gauge theory of
two-component Bose-Einstein condensate which has an induced vorticity
interaction. We show that two theories produce very similar topological
objects, in spite of the obvious differences in dynamics. Furthermore we show
that the gauge theory of two-component Bose-Einstein condensate, with the U(1)
gauge symmetry, is remarkably similar to the Skyrme theory. Just like the
Skyrme theory the theory admits the non-Abelian vortex, the helical vortex, and
the vorticity knot. We construct the lightest knot solution in two-component
Bose-Einstein condensate numerically, and discuss how the knot can be
constructed in the spin-1/2 condensate of atoms.Comment: 18 pages, 15 figures, Phys. Rev. A in pres
SO(3) Gauged Soliton of an O(4) Sigma Model on
Vector gauged sigma models on are presented. The
topological charge supplying the lower bound on the energy and rendering the
soliton stable coincides with the Baryon number of the Skyrmion. These solitons
have vanishing magnetic monopole flux. To exhibit the existence of such
solitons, the equations of motion of one of these models is integrated
numerically. The structure of the conserved Baryon current is briefly
discussed.Comment: 14 pages, latex, 3 figures available from the authors on reques
Collective Quantisation of a Gravitating Skyrmion
Collective quantisation of a B=1 gravitating skyrmion is described. The
rotational and isorotational modes are quantised in the same manner as the
skyrmion without gravity. It is shown in this paper how the static properties
of nucleons such as masses, charge densities, magnetic moments are modified by
the gravitational interaction.Comment: 10 pages, 9 figures, minor corrections, published versio
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