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 $\sigma_N=46$ MeV and $\sigma_{\Delta}=32$ 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 $^{87}{\rm Rb}$ atoms.Comment: 18 pages, 15 figures, Phys. Rev. A in pres

SO(3) Gauged Soliton of an O(4) Sigma Model on R3R_3

Vector $SO(3)$ gauged $O(4)$ sigma models on $\R_3$ 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