1,458 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
Theoretical Overview of the Pentaquark Baryons
A review is given of the theoretical ideas concerning the mysterious
pentaquark baryons proposed during the first year after its discovery. We focus
on the difficulties involved with the constituent quark models and the
discrepancy between the QCD predictions and most of the phenomenological
models.Comment: Review based on the talk given at the YITP Workshop on ``Multi-quark
Hadrons; Four, Five and More?'', held on Feb. 17-19, 2004. To be published in
Progress of Theoretical Physics as an invited pape
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
Continuum HFB calculations with finite range pairing interactions
A new method of calculating pairing correlations in coordinate space with
finite range interactions is presented. In the Hartree-Fock-Bogoliubov (HFB)
approach the mean field part is derived from a Skyrme-type force whereas the
pairing field is constructed with a Gogny force. An iterative scheme is used
for solving the integro-differential HFB equations via the introduction of a
local equivalent potential. The method is illustrated on the case of the
nucleus C. It is shown that the results are insensitive to the cut off
value in the quasiparticle spectrum if this value is above 100 MeV.Comment: 3 figures, in press, Phys. Lett.
Skyrme Strings
We construct nontopological string solutions with U(1) Noether charge in the
Skyrme model with a pion mass term, and examine their stability by taking
linear perturbations. The solution exhibits a critical angular velocity beyond
which the configuration energetically prefers to decay by emitting pions. This
critical point is observed as a cusp in the relation between energy and charge.
We find that the maximum length for the string to be stable is comparable to
the size of one skyrmion. Beyond the length, it is unstable to decay. This
instability raises the possiblity of dynamical realization of Skyrme strings
from monopole strings inside a domain wall.Comment: 7 pages, 3 figures, references adde
Normal Mode Spectrum of the Deuteron in the Skyrme Model
The normal mode spectrum of the deuteron in the Skyrme model is computed. We
find a bound doublet mode below the pion mass, which can be related to the
well-known scattering of two skyrmions. We also find a singlet
`breather' mode and another doublet above the pion mass. The qualitative
pattern of the spectrum is similar to that recently found for the B=4
multiskyrmion. The symmetries of all the vibrational modes are presented.Comment: LaTeX, 10 pages, 3 figure
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]
Effective Theory Approach to the Skyrme model and Application to Pentaquarks
The Skyrme model is reconsidered from an effective theory point of view. From
the most general chiral Lagrangian up to including terms of order ,
and (), new interactions, which have never
been considered before, appear upon collective coordinate quantization. We
obtain the parameter set best fitted to the observed low-lying baryon masses,
by performing the second order perturbative calculations with respect to
. We calculate the masses and the decay widths of the other members
of (mainly) anti-decuplet pentaquark states. The formula for the decay widths
is reconsidered and its baryon mass dependence is clarified.Comment: 65 pages, 1 figure. Revised version:the complete second order
perturbative calculations performed and two appendices adde
Towards the resolution of the e+e- --> Nbar N puzzle
We discuss the puzzling experimental results on baryon-antibaryon production
in e+e- annihilation close to the threshold, in particular the fact that
sigma(e+e- --> nbar n) is somewhat greater than sigma(e+e- --> pbar p). We
discuss an interpretation in terms of a two-step process, via an intermediate
coherent isovector state serving as an intermediary between e+e- and the
baryon-antibaryon system. We provide evidence that the isovector channel
dominates both e+e- --> pions and from Nbar N annihilation at rest, and show
that the observed ratio of sigma(e+e- --> nbar n)/sigma(e+e- --> pbar p) can be
understood quantitatively in this picture.Comment: Invited talk at the Int. Workshop "Light-cone Physics: Particles and
Strings", Trento, Sept. 3-11, 200
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