Narrow Results

We perform the first study of baryons in holographic QCD with multi-D-brane system in type IIA superstring theory. The baryon is described as a chiral soliton solution in the four-dimensional meson effective action derived from holographic QCD. We also present a brief review of the holographic model from the viewpoints of recent hadron physics and QCD phenomenologies.

We study the thermodynamics of soft wall model in AdS/QCD framework. The low temperature phase of QCD is described by thermal AdS and high temperature phase by AdS black hole solution of five-dimensional gravity with negative cosmological constant. The chemical potential is introduced via the solution of U(1) vector field in the bulk. The difference of action densities in two phases is studied and the results are compared with hard wall model. The quark number susceptibility is also calculated in both models.

AdS/QCD is an extra-dimensional approach to modeling hadronic physics, motivated by the AdS/CFT correspondence in string theory. AdS/QCD models are often more accurate than would have been expected at energies below a few GeV. We address the question of why these models are so successful, and respond to some of the criticisms that have been waged against these models.

We discuss some recent results on a holographic description of QCD on the basis of a - brane configuration in type IIA superstring theory. A special attention is paid to studies of the baryon dynamics in that model. Using the fact that baryons in large N_c QCD should be regarded as a soliton, it is seen that this model reproduces the experimental data quite nicely.

The AdS/QCD models are known to be closely related to the QCD sum rules in the large-N_c (called also planar) limit. Rewriting the theory of infinite tower of free stable mesons expected in the large-N_c QCD as a five-dimensional theory, we scrutinize to what extend the bottom-up holographic models may be viewed as an alternative language expressing the phenomenology of planar QCD sum rules. It is found that many features of AdS/QCD models can be thereby obtained without invoking prescriptions from the original AdS/CFT correspondence. Under some assumptions, all possibilities leading to simple Regge trajectories are classified, and it is argued that the most phenomenologically consistent model is the one called "soft wall model" in the holographic approach, with a preference to the positive-sign dilaton background.

We study the Renormalization Group (RG) flow of AC conductivity in soft wall model of holographic QCD. We consider the charged black hole metric and the explicit form of AC conductivity is obtained at the cutoff surface. We plot the numerical solution of conductivity flow as a function of radial coordinate. The equation of gauge field is also considered and the numerical solution is obtained for AC conductivity as a function of frequency. The results for AC conductivity are also obtained for different values of chemical potential and Gauss–Bonnet couplings.

We present the calculations of isospin splitting mass of pions and nucleons in the Sakai–Sugimoto model of holographic QCD. We find that $m_{{\pi }^{\pm }}-m_{{\pi }^0}\simeq 1.8\mathrm{\text{MeV}}$ and the electromagnetic mass difference of nucleons, ${(M_p-M_n)}_{\mathrm{\text{QED}}}=0.48\mathrm{\text{MeV}}$, taking the Kaluza–Klein scale, $M_{\mathrm{\text{KK}}}=949\mathrm{\text{MeV}}$.

We calculate the $a_1$-meson-nucleon ($\mathrm{\Delta }$-baryon) coupling constant in the framework of soft-wall and hard-wall AdS/QCD models. Interaction Lagrangian in the bulk of AdS space was written for a minimal gauge coupling, a magnetic type coupling and a triple coupling of bulk fields. Applying AdS/CFT correspondence from the bulk interaction Lagrangian, we obtain holographic expressions for the $a_1$-axial-vector meson-nucleon ($\mathrm{\Delta }$-baryon) coupling constant in the boundary QCD theory. Numerical results for the $g_{a_{1}NN}$ coupling constant in the framework of both models are close to the known phenomenological estimates. The $g_{a_1\mathrm{\Delta }\mathrm{\Delta }}$-axial-vector meson-$\mathrm{\Delta }$-baryon coupling constant was considered in the framework of hard-wall model.

In this paper, we consider the soft-wall holographic model with the linear dilaton background. The model leads to a Hydrogen-like meson spectrum which can be interpreted as the static limit with very large quark masses when the Coulomb interaction dominates. The mass scale introduced by the linear dilaton is matched to the quark mass. The resulting model is analyzed for the scalar, vector and tensor cases. The electromagnetic coupling constants predicted by the model are decreasing with the radial number in contrast to the soft-wall model with quadratic dilaton where these couplings represent a universal constant. The given prediction is qualitatively consistent with the corresponding experimental data in vector quarkonia. The proposed model can thus be used as a constituent part of more elaborated holographic models for heavy quarkonia. A particular example of such a model is put forward.

Skyrmions are topological solitons that describe baryons within a nonlinear theory of pions. In holographic QCD, baryons correspond to topological solitons in a bulk theory with an extra spatial dimension. Thus, the three-dimensional Skyrmion lifts to a four-dimensional holographic Skyrmion in the bulk. We begin this review with a description of the simplest example of this correspondence, where the holographic Skyrmion is exactly the self-dual Yang–Mills instanton in flat space. This places an old result of Atiyah and Manton within a holographic framework and reveals that the associated Skyrme model extends the nonlinear pion theory to include an infinite tower of vector mesons, with specific couplings for a BPS theory. We then describe the more complicated curved space version that arises from the string theory construction of Sakai and Sugimoto. The basic concepts remain the same but the technical difficulty increases as the holographic Skyrmion is a curved space version of the Yang–Mills instanton, so self-duality and integrability are lost. Finally, we turn to a low-dimensional analog of holographic Skyrmions, where aspects such as multi-baryons and finite baryon density are amenable to both numerical computation and an approximate analytic treatment.

We study the chiral condensate in dense baryonic medium by the use of the generalized Sakai-Sugimoto model of holographic QCD. The chiral condensate is identified with the vacuum expectation value of the open Wilson line operator. We evaluate it by the minimal area of open string world-sheet whose boundary is the V-shape flavor D8-branes. As a result, we find that the chiral condensate decreases in low baryon density and increases in high density. This decreasing behavior is in agreement with the expectation from QCD.

We reconsider the realization of baryons in the Sakai-Sugimoto model. It has previously been shown that, at least with the standard approach to calculations of baryon properties in the theory, one does not reproduce some model-independent predictions for the behavior of baryon electromagnetic form factors connected with long-range pion physics. It is suspected that the pion contributions has been dropped because of the linearization approximations. We study the long-range properties of baryons without relying on the approximations. The baryon solution we obtain gives the correct result for the model-independent ratio of the form factors.

In this work we discuss how to construct the Regge trajectories for light mesons and baryons in the context of a bottom-up holographic model, consisting on a 5-dimensional AdS background, deformed with a quadratic function in the holographic coordinate. We fit the scalar meson f₀, vector meson ρ, baryons with spin 1/2⁺ and 3/2^* trajectories. These results are in fine agreement with those exposed in PDG. We also found in this model a universal Regge slope near to 1.1 GeV².

The interrelation between the deconfinement temperature of hadron medium and parameters of radial Regge trajectories within the bottom-up holographic models for QCD is scrutinized. We show that the lattice data on the deconfinement temperature can yield a powerful restriction on the spectrum of excited mesons and glueballs within the framework of holographic approach. The best phenomenological agreement and theoretical self-consistency are achieved if the scalar meson f₀(1500) is considered as the lightest glueball.

In this talk we discuss the holographic approximation to the calculation of mesonic decay constants in the context of the bottom-up AdS/QCD models such as the soft wall-like approaches. We show some of the technical difficulties and some possible solutions to them.

We present the calculations of isospin splitting mass of pions and nucleons in the Sakai- Sugimoto model of holographic QCD. We find that m_π± − m_π0 ≃ 1.8 MeV and the electromagnetic mass difference of nucleons, (M_p − M_n)_QED = 0.48 MeV, taking the Kaluza-Klein scale, M_KK = 949 MeV.

AdS/QCD is an extra-dimensional approach to modeling hadronic physics, motivated by the AdS/CFT correspondence in string theory. AdS/QCD models are often more accurate than would have been expected at energies below a few GeV. We address the question of why these models are so successful, and respond to some of the criticisms that have been waged against these models.

We discuss some recent results on a holographic description of QCD on the basis of a configuration in type IIA superstring theory. A special attention is paid to studies of the baryon dynamics in that model. Using the fact that baryons in large N_c QCD should be regarded as a soliton, it is seen that this model reproduces the experimental data quite nicely.

We compute nuclear forces at short distance, by applying gauge/gravity correspondence to large N_c QCD. This talk is based on work in collaboration with T. Sakai and S. Sugimoto.

We study the spectra of excited mesons with spins higher than one from gauge/string duality. We work with a model that is formulated on the basis of an intersecting D4/D8/-system. The meson spectra are computed by making a semi-classical quantization of an open string that ends on the flavor D8-brane.We compare the results with experiments and find a good agreement.