We use holographic techniques to study meson quasiparticles moving through a thermal plasma in N=2 super-Yang-Mills theory, with gauge group SU(N_c) and coupled to N_f flavours of fundamental matter. This holographic approach reliably describes the system at large N_c, large 't Hooft coupling and N_f/N_c<<1. The meson states are destabilized by introducing a small quark density n_q. Spectral functions are used to examine the dispersion relations of these quasiparticles. In a low-momentum regime, the quasiparticles approach a limiting velocity which can be significantly less than the speed of light. In this regime, the widths of the quasiparticles also rise dramatically as their momentum approaches a critical value q_crit. While the spectral functions do not display isolated resonances for q>q_crit, the dispersion relations can be extended into this high-momentum regime by studying the dual quasinormal modes. A preliminary qualitative analysis of these modes suggests that the group velocity rises to the speed of light for q>>q_crit.
We have constructed a noncommutative deformation of the holographic QCD (Sakai-Sugimoto) model and evaluated the mass spectrum of low spin vector mesons at finite temperature. The masses of light vector- and pseudovector-meson in the noncommutative holographic QCD model reduces over the whole area in the intermediate-temperature regime compared to the commutative case. However, the space noncommutativity does not change the properties of temperature dependence for the mass spectrum of low spin mesons. The masses of meson also decrease with increasing temperature in noncommutative case.
We study fluctuations of a U(1) gauge field on the worldvolume of Nf probe D7-branes in the background of Nc black D3-branes with a finite baryon density. The choice of mode corresponds to vector mesons in the dual gauge theory whose mass and lifetime can be determined by a study of the quasinormal modes. The speed of propagation of these holographic mesons at large momenta is studied from the dispersion relations of the quasinormal modes of the system.
In this paper we study D-brane scalar fluctuations in global Pilch-Warner background geometry. We consider configurations of the probe branes compatible with the kappa symmetry preserving condition and the brane classical equations of motion. The corresponding meson spectra, obtained by the fluctuations along the transverse brane directions, admit equidistant structure for the higher modes, but some of them show additional shifts in their ground states.
We study two $1/N_c$ effects on the meson spectra by using the AdS/CFT correspondence where the $1/N_c$ corrections from the chiral condensate and the quark density are controlled by the gravitational backreaction of the massive scalar field and U(1) gauge field respectively. The dual geometries with zero and nonzero current quark masses are obtained numerically. We discuss meson spectra and binding energy of heavy quarkonium with the subleading corrections in the hard wall model.
We study holographically the zero and finite temperature behavior of the potential energy and holographic subregion complexity corresponding to a probe meson in a non-conformal model. We observe that in zero and low temperature non-conformality has a decreasing effect on the dimensionless meson potential energy. However, non-conformal corrections increase absolute value of the dimensionless holographic subregion complexity in both zero and finite temperature which means the non-conformal state needs less information to be specified. In other words, considering the effect of non-conformality, t…
We study the spectrum of scalar mesons in the holographic dual of walking technicolor, obtained by embedding D7 - anti-D7 probe branes in a certain type IIB background. The scalar mesons arise from fluctuations of the probe techniflavour branes and complement the (axial-)vector meson spectra that we investigated in earlier work. By explicitly finding the spectrum of scalar masses, we show that the nonsupersymmetric D7 - anti-D7 embedding is stable with respect to such fluctuations. Interestingly, it turns out that the mass splitting between the scalar and vector meson spectra is of subleading …
In the context of gauge/gravity duals with flavor, we examine heavy-light mesons which involve a heavy and a light quark. For this purpose we embed two D7 brane probes at different positions into the gravity background. We establish the non-Abelian Dirac-Born-Infeld (DBI) action for these probes, in which the U(2) matrix describing the embedding is diagonal. The fluctuations of the brane probes correspond to the mesons. In particular, the off-diagonal elements of the U(2) fluctuation matrix correspond to the heavy-light mesons, while the diagonal elements correspond to the light-light and heav…
We discuss Regge trajectories of dynamical mesons in large-N_c QCD, using the supergravity background describing N_c D4-branes compactified on a thermal circle. The flavor degrees of freedom arise from the addition of N_f<<N_c D6 probe branes. Our work provides a string theoretical derivation, via the gauge/string correspondence, of a phenomenological model describing the meson as rotating point-like massive particles connected by a flux string. The massive endpoints induce nonlinearities for the Regge trajectory. For light quarks the Regge trajectories of mesons are essentially linear. For ma…
A holographic model for QCD is employed to investigate the effects of the gluon condensate on the spectrum and melting of scalar mesons. We find the evolution of the free energy density with the temperature, and the result shows that the temperature of the confinement/deconfinement transition is sensitive to the gluon-condensate parameter. The spectral functions (SPFs) are also obtained and show a series of peaks in the low-temperature regime, indicating the presence of quasiparticle states associated to the mesons, while the number of peaks decreases with the increment of the temperature, cha…
We study the energy dispersions of holographic light mesons and their decay constants on dense nuclear medium. As the spatial momenta of mesons along the boundary direction increase, both observables of the mesons not only increase but also split according to the isospin charges. The decay constant of the negative meson is more large than that of the positive meson of the same type due to the chemical potentials of the background nucleons.
Within a holographic framework, we consider vector mesons riding on a gravity-dilaton background. The latter one is determined directly from a Schrödinger equivalent potential which delivers a proper $ρ$ meson Regge trajectory. The mapping on the dilaton potential yields a thermodynamic phase structure with a first-order transition.
We revisit holographic mesons in the D4/D6 model to study holographic light vector mesons and the properties of heavy quarkonium in confining and deconfining phases. To treat the light mesons and heavy quarkonium on the same footing, we use the same compactification scale MKK in both systems. We observe that like scalar and pseudo-scalar mesons the vector meson mass is linearly proportional to the square root of the quark mass, when the quark mass is large. With a MKK fixed by light meson masses, we calculate the mass of heavy quarkonium in confining and deconfining phases. We also obtain the …
We study baryons in holographic QCD with $D4/D8/\bar{D8}$ multi $D$ brane system. In holographic QCD, the baryon appears as a topologically non-trivial chiral soliton in a four-dimensional effective theory of mesons, which is called `Brane-induced Skyrmion'. We derive and calculate the Euler-Lagrange equation for the hedgehog configuration with chiral profile $F(r)$ and $ρ$-meson profile $\tilde G(r)$, and obtain the soliton solution of the holographic QCD.
We study a new holographic gauge theory based on probe D4-branes in the background dual to D4-branes on a circle with antiperiodic boundary conditions for fermions. Field theory configurations with baryons correspond to smooth embeddings of the probe D4-branes with nontrivial winding around an S^4 in the geometry. As a consequence, physics of baryons and nuclei can be studied reliably in this model using the abelian Born-Infeld action. However, surprisingly, we find that the meson spectrum is not discrete. This is related to a curious result that the action governing small fluctuations of the …
A holographic model of probe vector mesons (quarkonia) is presented, where the dynamical gravity-dilaton background is adjusted to the thermodynamics of 2 +1 flavor QCD with physical quark masses. The vector meson action is modified to account for various quark masses. We focus on the $Φ$, $J/ψ$ and $Υ$ meson melting in agreement with hadron phenomenology in heavy-ion collisions at LHC, that is the formation of hadrons at the observed freeze-out temperature of 155 MeV.
We show that holographic models of QCD predict the presence of a Chern-Simons coupling between vector and axial-vector mesons at finite baryon density. In the AdS/CFT dictionary, the coefficient of this coupling is proportional to the baryon number density, and is fixed uniquely in the five-dimensional holographic dual by anomalies in the flavor currents. For the lightest mesons, the coupling mixes transverse $ρ$ and $a_1$ polarization states. At sufficiently large baryon number densities, it produces an instability, which causes the $ρ$ and $a_1$ mesons to condense in a state breaking both ro…
We calculate the spectrum of fluctuations of a probe Dk-brane in the background of N Dp-branes, for k=p,p+2,p+4 and p< 5. The result corresponds to the mesonic spectrum of a (p+1)-dimensional super-Yang-Mills (SYM) theory coupled to `dynamical quarks', i.e., fields in the fundamental representation -- the latter are confined to a defect for k=p and p+2. We find a universal behaviour where the spectrum is discrete and the mesons are deeply bound. The mass gap and spectrum are set by the scale M ~ m_q/g_{eff}(m_q), where m_q is the mass of the fundamental fields and g_{eff}(m_q) is the effective…
We study the meson potential energy in a non-conformal model at both zero and finite temperature via gauge/gravity duality. This model consists of five-dimensional Einstein gravity coupled to a scalar field with a non-trivial potential. Interestingly, at both zero and finite temperature we find that the relative meson potential energy can be considered as a measure of non-conformality of the theory. At zero temperature we show that parameters of the Cornell potential, i.e. Coulomb strength parameter $κ$ and constant $C$ depends on the energy scale $Λ$ that breaks conformal symmetry and the dif…
We compute meson scattering amplitudes using the holographic duality between confining gauge theories and string theory, in order to consider holographic corrections to the Veneziano amplitude and associated higher-point functions. The generic nature of such computations is explained, thanks to the well-understood nature of confining string backgrounds, and two different examples of the calculation in given backgrounds are used to illustrate the details. The effect we discover, whilst only qualitative, is re-obtainable in many such examples, in four-point but also higher point amplitudes.
Based on the expectation that constituent quark model may capture right physics in the large N limit, we point out that orbital angular momentum of the quark-antiquark pair inside light mesons of low spins in the constituent quark model may provide a clue for the holographic dual string model of large N QCD. Our discussion, relying on a few suggestive assumptions, leads to a necessity of world-sheet fermions in the bulk of dual strings that can incorporate intrinsic spins of fundamental QCD degrees of freedom. We also comment on an interesting issue of the size of mesons in the context of holo…
We calculate elastic and non-elastic electromagnetic form factors for vector and axial-vector mesons in the holographic D4-D8 brane model. We obtain the mass spectrum and Regge trajectories for these particles. From the elastic form factors we extract the electric radius, the magnetic and quadrupole moments. Form factors for transverse and longitudinal polarizations are also obtained. We find superconvergence sum rules for the vector and axial-vector meson couplings that determine the asymptotic behavior of the form factors at large momentum transfer. Our results show good agreement with other…
Recent Holographic studies have shown that N=4 super Yang-Mills theory coupled to fundamental matter with finite chemical potential undergoes a first order phase transition. In this paper, we study Nf D6 probe branes with or without electric field on it in the black D4 brane background compactified on a circle with supersymmetry breaking boundary condition. At energy scales much lower than the compactification scale, the dual gauge theory is effectively four dimensional non-supersymmetric SU(Nc) Yang-Mills theory coupled to fundamental matter with or without baryon number charge. Within the su…
We present the results of a holographic model for heavy vector mesons inside a plasma at finite temperature and density. The spectral function shows a nice description of the dissociation of the mesons in the medium, corresponding to the decrease in the height of the peaks as the temperature and (or) the density increase. We consider the case of bottomonium states at finite temperature and also the case of charmonium dissociation at zero temperature but finite chemical potential.
We study the response of confining gauge theory to the external electric field by using holographic Yang-Mills theories in the large $N_c$ limit. Although the theories are in the confinement phase, we find a transition from the insulator to the conductor phase when the electric field exceeds its critical value. Then, the baryon number current is generated in the conductor phase. At the same time, in this phase, the meson melting is observed through the quasi-normal modes of meson spectrum. Possible ideas are given for the string state corresponding to the melted mesons, and they lead to the id…
We study meson decays using instanton methods in two string models. The first model is the old string model in flat space which combines strings and massive particles and the second is the holographic, Sakai-Sugimoto model. Using the the old string model, we reproduce the QCD formula for the probability of splitting of the QCD flux tube derived by Casher-Neuberger-Nussinov (CNN). In the holographic model we construct a string worldsheet instanton which interpolates between a single and double string configuration, which determines the decay from one to two dual mesonic particles. The resulting…
Top-down holographic QCD models often work in the "probe" (or "quenched") limit, which assumes that the number of colors is much greater than the number of flavors. Relaxing this limit is essential to a fuller understanding of holography and more accurate phenomenological predictions. In this work, we focus on a mixing of glueball and meson mass eigenstates that arises from the DBI action as a finite Nf/Nc effect. For concreteness, we work in the Witten-Sakai-Sugimoto model, and show that this mixing must be treated in conjunction with the backreaction of the flavor branes onto the background …
We study the fermionic sector of a probe D8-brane in the supergravity background made of D4-branes compactified on a circle with supersymmetry broken explicitly by the boundary conditions. At low energies the dual field theory is effectively four-dimensional and has proved surprisingly successful in recovering qualitative and quantitative properties of QCD. We investigate fluctuations of the fermionic fields on the probe D8-brane and interpret these as mesinos (fermionic superpartners of mesons). We demonstrate that the masses of these modes are comparable to meson masses and show that their i…
We study phenomenological aspects of the holographic model of chiral symmetry breaking recently introduced by Kuperstein and Sonnenschein (KS). As a first step, we calculate the spectrum of vector and axial-vector mesons in the KS model. We numerically compute various coupling constants of the mesons and pions. Our analysis indicates that vector meson dominance is realized in this model. The pion, vector meson and axial-vector meson form factors are obtained and studied in detail. We find good agreement with QCD results. In particular, the pion form factor closely matches available experimenta…
In the present letter we use holographic methods to show that a very intense magnetic field lowers the temperature at which the mesons melt and decreases the mass gap of the spectrum along with their masses. Consequently, there is a range of temperatures for which mesons can be melted by applying a magnetic field instead of increasing the temperature. We term this effect Magnetic Meson Melting (MMM), and we are able to observe it by constructing a configuration that makes it possible to apply gauge/gravity methods to study fundamental degrees of freedom in a quark-gluon plasma subject to a mag…
We study deep inelastic scattering for vector and axial vector mesons in the holographic D4-D8 brane model. We consider tree level contributions with one particle in the final hadronic state. We obtain the unpolarized structure functions F1 and F2 for the rho and a1 mesons for q2 < 80 GeV2 and 0.2 < x < 1. We find that the ratio F2/(2xF1) is approximately equal to one for some ranges of x and q2, satisfying the Callan-Gross relation.
We analyze the sector of dimension-three vector meson operators in the "hard wall" model of holographic QCD, including the vector and axial currents, dual to gauge fields in the bulk, and the tensor operator $\barψσ^{μν}ψ$, dual to a two-form field satisfying a complex self-duality condition. The model includes the effect of chiral symmetry breaking on vector mesons, that involves a coupling between the dual gauge field and the two-form field. We compute the leading logarithmic terms in the operator product expansion of two-point functions and the leading non-perturbative contribution to the t…
Using holographic subregion complexity, we study the confinement-deconfinement phase transition of quantum chromodynamics. In the model we consider here, we observe a connection between the potential energy of probe meson and the behavior of its complexity. Moreover, near the critical point, at which the phase transition takes place, our numerical calculations indicate that we need less information to specify a meson in the non-conformal vacuum than in the conformal one, despite the fact that the non-conformal vacuum has larger energy!
We study baryons as Skyrmions in holographic QCD with D4/D8/D8-bar multi-D brane system in type IIA superstring theory, and also in the non-linear sigma model with hidden local symmetry (HLS). Comparing these two models, we find that the extra-dimension and its nontrivial curvature can largely change the role of (axial) vector mesons for baryons in four-dimensional space-time. In the HLS approach, the rho-meson field as a massive Yang-Mills field has a singular configuration in Skyrmion, which gives a strong repulsion for the baryon as a stabilizer. When a_1 meson is added in this approach, th…
We study the baryon in holographic QCD with $D4/D8/\bar{D8}$ multi-$D$ brane system. In holographic QCD, the baryon appears as a topologically non-trivial chiral soliton in a four-dimensional effective theory of mesons. We call this topological soliton as Brane-induced Skyrmion. Some review of $D4/D8/\bar{D8}$ holographic QCD is presented from the viewpoints of recent hadron physics and phenomenologies. Four-dimensional effective theory with pions and $ρ$ mesons is uniquely derived from the non-abelian Dirac-Born-Infeld (DBI) action of $D8$ brane with $D4$ supergravity background, without smal…
In this paper we review some results on the generalization of the gauge/gravity duality to include fundamental matter by means of probe branes. We compute the meson spectrum of maximally supersymmetric gauge theories in several dimensions, both in the Coulomb and Higgs branch. We also study the addition of flavor and compute the meson spectrum for non-commutative theories. Additionally, we present a thorough search of supersymmetric embeddings of probe branes in the Klebanov-Witten model.
We study meson spectrum obtained from massive open string modes in a holographic dual of QCD constructed on the basis of a D4/D8-brane configuration in type IIA string theory. The spectrum includes mesons with spin higher than one. Taking into account the effect of curved background perturbatively, we obtain a mass formula for these mesons, which exhibits the linear Regge behavior at the leading order with subleading non-linear corrections. We argue that the string spectrum captures some features of the observed meson spectrum. For example, a_2(1320), b_1(1235), π(1300), a_0(1450), etc., are i…
We derive an explicit form of the dilaton potential in improved holographic QCD (IHQCD) from the experimental data of the $ρ$ meson spectrum. For this purpose we make use of the emergent bulk geometry obtained by deep learning from the hadronic data in arXiv:2005.02636. Requiring that the geometry is a solution of an IHQCD derives the corresponding dilaton potential backwards. This determines the bulk action in a data-driven way, which enables us at the same time to ensure that the deep learning proposal is a consistent gravity. Furthermore, we find that the resulting potential satisfies the r…
This thesis is dedicated to the holographic study of flavor dynamics. The technique employed is a D7-brane probing of various D3-brane backgrounds. The first topic covered studies the influence of an external magnetic field on a flavored large N Yang-Mills theory. The theory exhibits spontaneous chiral symmetry breaking. The meson spectrum exhibits Zeeman splitting and characteristic GMOR relation. The second topic examines thermal properties of the dual gauge theory. The third topic studies the phase structure of the finite temperature dual gauge theory in the presence of magnetic field. A ph…
The Shannon based conditional entropy that underlies five-dimensional Einstein-Hilbert gravity coupled to a dilaton field is investigated in the context of dynamical holographic AdS/QCD models. Considering the UV and IR dominance limits of such AdS/QCD models, the conditional entropy is shown to shed some light onto the meson classification schemes, which corroborate with the existence of light-flavour mesons of lower spins in Nature. Our analysis is supported by a correspondence between statistical mechanics and information entropy which establishes the physical grounds to the Shannon informa…
We review in this proceedings some recent results for vector meson form factors obtained using the holographic D4-D8 brane model. The D4-D8 brane model, proposed by Sakai and Sugimoto, is a holographic dual of a semi-realistic strongly coupled large N_c QCD since it breaks supersymmetry and incorporates chiral symmetry breaking. We analyze the vector meson wave functions and Regge trajectories as well.
In this review article we present the calculation of the splitting rate in flat space of a macroscopic fundamental string either intersecting at a generic angle a Dp-brane or lying on it. The result is then applied, in the context of the string/gauge theory correspondence, to the study of exclusive decay rates of large spin mesons into mesons. As examples, we discuss the cases of N=4 SYM with a small number of flavors, and of QCD-like theories in the quenched approximation. In the latter context, explicit analytic formulas are given for decay rates of mesons formed either by heavy quarks or by…
We study baryons of arbitrary isospin in a stringy holographic QCD model. In this D4-D8 holographic setting, the flavor symmetry is promoted to a gauge symmetry in the bulk, and produces, as KK modes of the gauge field, pions and spin one mesons of low energy QCD. Baryons of arbitrary isospins are represented as instanton solitons with isospin and spin quantum numbers locked, in a manner similar to the Skyrmion model. The soliton picture leads to a natural effective field theory of arbitrary baryons interacting with mesons. Couplings of baryons to axial mesons, including pions, are dominated i…
We study probe flavor branes supersymmetrically embedded in the Klebanov-Strassler background. The embedding is controlled by a single complex parameter mu related to the quark mass. We study the spectrum of the vector mesons as a function of mu and compare it with the experimental data. Assuming that the rho(2150) meson is a 3S mode we find a remarkable agreement with the masses of the lightest excited rho-mesons. Also, for a certain range of parameters our model exhibits an unusual behavior. The mesons built of the lighter quarks become more heavy than the ones built of the heavier quarks. W…
We construct the D4/D8 brane configuration in the Witten-Sakai-Sugimoto model by introducing a pair of heavy flavour brane with a heavy-light open string. The multiplets created by the heavy-light string acquire mass due to the finite separation of the heavy and light flavour branes thus they could be identified as the heavy-light meson fields in this model. On the other hand the glueball field is identified as the gravitational fluctuations carried by the close string in the bulk, so this model is able to describe the interaction of glueball and heavy-light meson through the open-close string…
Two-point current correlation functions of the large $N$ limit of supersymmetric and non-supersymmetric Yang-Mills theories at strong coupling are investigated in terms of their string theory dual models with quenched flavors. We consider non-Abelian global symmetry currents, which allow one to investigate vector mesons with $N_f > 1$. From the correlation functions we construct the deep inelastic scattering hadronic tensor of spin-one mesons, obtaining the corresponding eight structure functions for polarized vector mesons. We obtain several relations among the structure functions. Relations …
We propose a general method for finding a string-like meson spectrum which is based on a certain condition for the breaking of closed gluon string. A model is constructed that successfully realizes the proposed method. The model is based on the holographic Soft Wall model for QCD and the use of the Wilson confinement criterion. We applied our approach to the vector and scalar cases and obtained numerical predictions for the intercepts of corresponding Regge like radial meson spectra. A good agreement is obtained both with the existing experimental data and with some other known phenomenologica…
We consider the photo-excitation of charm and bottom pentaquarks with the holographic assignments $[\frac 12\frac 12^-]_{S=0,1}$ and $[\frac 12\frac 32^-]_{S=1}$, in the photo-production of heavy vector mesons such as charmonia and bottomonia near threshold. We use a Witten diagram to combine the s-channel photo-excitation of holographic pentaquarks with a massive t-channel graviton or tensor glueball exchange, to extract the scattering amplitude for heavy meson photo-production in the threshold region. The pentaquark signal is too weak to be detected at current electron facilities.
We study the Regge trajectories of holographic mesons and baryons by considering rotating strings and D5 brane, which is introduced as the baryon vertex. Our model is based on the type IIB superstring theory with the background of asymptotic $AdS_5\times S^5$. This background is dual to a confining supersymmetric Yang-Mills theory (SYM) with gauge condensate, $<F^2>$, which determines the tension of the linear potential between the quark and anti-quark. Then the slope of the meson trajectory ($α'_{M}$) is given by this condensate as $α'_{M}=1/\sqrt{π<F^2>}$ at large spin $J$. This relation is …
We study the holographic light meson spectra and their mass splitting in the nuclear medium. In order to describe the nuclear matter, we take into account the thermal charged AdS geometry with two flavor charges, which can be reinterpreted as the number densities of proton and neutron after some field redefinitions. We show that the meson mass splitting occurs when there exists the density difference between proton and neutron. Depending on the flavor charge, the mass of the positively (negatively) charged meson increases (decreases) as the density difference increases, whereas the neutral mes…
We revisit the $U(1)_A$ anomaly in the holographic model of low-energy QCD by Witten, Sakai, and Sugimoto, presenting a new and direct derivation of the Witten-Veneziano mechanism for generating the mass of the $η'$ through an anomalous mixing of the Ramond-Ramond $C_1$ field with the singlet component of the pseudoscalar mesons. The latter turns out to have a kinetic mixing with the normalizable modes of the $C_1$ field representing pseudoscalar glueballs, yielding additional vertices for their production and their decay that dominate over those of the unmixed case considered previously in th…
We consider the effect of the R^4 term in type IIA string theory on the supergravity background dual to N_c D4 branes compactified on a circle with supersymmetry breaking boundary conditions. We study the dynamics of D8 branes in this perturbed geometry in the probe approximation. This leads to an analysis of higher derivative corrections in holographic QCD beyond the supergravity approximation. We make a rough estimate of the corrections to the masses of some of the lightest (axial) vector mesons. The corrections are suppressed by a factor of (g_{YM}^2 N_c)^{-3} compared to their supergravity…
We extend the two-flavor hard-wall holographic model of Erlich, Katz, Son and Stephanov [Phys.\ Rev.\ Lett.\ {\bf 95}, 261602 (2005)] to four flavors to incorporate strange and charm quarks. The model incorporates chiral and flavor symmetry breaking and provides a reasonable description of masses and weak decay constants of a variety of scalar, pseudoscalar, vector and axial-vector strange and charmed mesons. In particular, we examine flavor symmetry breaking in the strong couplings of the $ρ$ meson to the charmed $D$ and $D^{*}$ mesons. We also compute electromagnetic form factors of the $π$,…
The plasma phase at high temperatures of a strongly coupled gauge theory can be holographically modelled by an AdS black hole. Matter in the fundamental representation and in the quenched approximation is introduced through embedding D7-branes in the AdS-Schwarzschild background. Low spin mesons correspond to the fluctuations of the D7-brane world volume. As is well known by now, there are two different kinds of embeddings, either reaching down to the black hole horizon or staying outside of it. In the latter case the fluctuations of the D7-brane world volume represent stable low spin mesons. …
We inspect the mass spectrum of heavy-light mesons in deformed N=2 super Yang-Mills theory using the AdS/CFT correspondence. We demonstrate how some of the degeneracies of the supersymmetric meson spectrum can be removed upon breaking the supersymmetry, thus leading to the emergence of hyperfine structure. The explicit SUSY breaking scenarios we consider involve on one hand tilting one of the two fundamental D7 branes inside the internal R^6 space, and on the other hand applying an external magnetic field on the (untilted) branes. The latter scenario leads to the well-known Zeeman effect, whic…
Wave functions and form factors of vector mesons are investigated in the holographic dual model of QCD with a smooth oscillator-like wall. We introduce wave functions conjugate to solutions of the 5D equation of motion and develop a formalism based on these wave functions, which are very similar to those of a quantum-mechanical oscillator. For the lowest bound state (rho-meson), we show that, in this model, the basic elastic form factor exhibits the perfect vector meson dominance, i.e., it is given by the rho-pole contribution alone. The electric radius of the rho-meson is calculated, <r^2_rho…
We develop a method for integrating out the heavy Kaluza-Klein modes of scalar type as well as those of vector and axial-vector types, in a class of hard-wall bottom-up approaches of holographic QCD models, including the Dirac-Born-Infeld and Chern-Simons parts. By keeping only the lowest-lying vector mesons, we first obtain an effective chiral Lagrangian of the vector mesons based on the hidden local symmetry, and all the low-energy constants in the HLS Lagrangian are expressed in terms of holographic integrals and, consequently, are fully determined by the holographic geometry and a few cons…
We analyse mesons at finite temperature in a chiral, confining string dual. The temperature dependence of low-spin as well as high-spin meson masses is shown to exhibit a pattern familiar from the lattice. Furthermore, we find the dissociation temperature of mesons as a function of their spin, showing that at a fixed quark mass, mesons with larger spins dissociate at lower temperatures. The Goldstone bosons associated with chiral symmetry breaking are shown to disappear above the chiral symmetry restoration temperature. Finally, we show that holographic consideration imply that large-spin meso…
