We propose a deep learning method to build an AdS/QCD model from the data of hadron spectra. A major problem of generic AdS/QCD models is that a large ambiguity is allowed for the bulk gravity metric with which QCD observables are holographically calculated. We adopt the experimentally measured spectra of $ρ$ and $a_2$ mesons as training data, and perform a supervised machine learning which determines concretely a bulk metric and a dilaton profile of an AdS/QCD model. Our deep learning (DL) architecture is based on the AdS/DL correspondence (arXiv:1802.08313) where the deep neural network is identified with the emergent bulk spacetime.
We calculate the expectation value of one circular Wilson loop and the correlator of two concentric circular Wilson loops in AdS/QCD using the modified AdS_5-metric given in Ref.[1]. The confinement properties of this metric in AdS/QCD are analyzed and compared with QCD and Nambu-Goto theory in four dimensions.
We use AdS/QCD to analyze the quark and gluon scalar and pseudo-scalar condensates around static color sources described by a circular Wilson loop. We also derive the static dipole-dipole interactions between rectangular Wilson loops in AdS/QCD and discuss their relevance for static string interactions in QCD at strong coupling.
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.
The most straightforward use of AdS/CFT correspondence gives versions of QCD where quarks are in adjoint representations. Using an asymmetric orbifold approach we obtain nonsupersymmetric QCD with four quark flavors in fundamental representations of color.
We study the helicity-independent generalized parton distributions of nucleons in the zero skewness case, based on a particular light-front quark model derived in a soft-wall AdS/QCD approach.
We use a matching procedure of sum rules relating the electromagnetic form factors to generalized parton distributions (GPDs) and AdS modes. In this way, in the framework of an AdS/QCD hard-wall model, the helicity-independent GPDs of quarks for the nucleon in the zero skewness case are calculated.
We consider chiral symmetry breaking AdS / QCD models with cubic and quartic potentials in the scalar sector and a z dependent mass for scalars in the bulk. In these models it is possible to get good mesonic spectra using current quark masses.
We derive the four-point vector correlators in QCD from AdS/QCD correspondence. It is shown that meson poles are correctly reproduced. The final expression also suggests a nonzero amplitude in the limit of zero virtuality of two longitudinal gluons. This fact does not mean that one can produce, absorb or scatter real longitudinal gluons.
We discuss an AdS / QCD model that consider anomalous dimensions. The effect of this kind of dimensions is considered as a mass term that depend on holographical coordenate for duals modes in bulk.
The nucleon helicity-independent generalized parton distributions (GPDs) of quarks are calculated in the zero skewness case, in the framework of the AdS/QCD model. The present approach is based on a matching procedure of sum rules relating the electromagnetic form factors to GPDs and AdS modes.
New developments in holographic QCD are described in this talk in the context of the correspondence between string states in AdS and light-front wavefunctions of hadronic states in physical space-time.
We reanalyze high energy QCD scattering regimes from scattering in cut-off AdS via gravity-gauge dualities (a la Polchinski-Strassler). We look at 't Hooft scattering, Regge behaviour and black hole creation in AdS. Black hole creation in the gravity dual is analyzed via gravitational shockwave collisions. We prove the saturation of the QCD Froissart unitarity bound, corresponding to the creation of black holes of AdS size, as suggested by Giddings.
We consider an extension to finite temperature in an AdS/ QCD model, which regards anomalous dimension contributions to get a bulk mass depending on beta function. We study the effect of beta function on mass as a function of temperature and melting temperature for scalar glueballs.
Pomeron resonances in AdS/QCD are here studied using the configurational entropy (CE). The concept of CE Regge trajectories, associating the CE of the pomeron resonances with both their spin $J^{PC}$ and to their mass spectra, is used to derive the mass spectra of higher $J^{PC}$ pomeron resonances. For it, the linear, the exponential modified and the anomalous quadratic dilatonic models, each one with linear and logarithmic anomalous corrections, are employed. Several methods are implemented, hybridizing AdS/QCD and established data of lattice QCD.
A modified version of the usual soft wall quadratic dilaton, a dilaton which catches the variation of the proton mass inside nucleons in the nuclear medium is used. With this dilaton, called nuclear dilaton, we have calculated the electromagnetic form factors and magnetic moments associated with the in-medium proton following the AdS/QCD prescription.
Odd-spin glueballs in the dynamical AdS/QCD model are scrutinized, in the paradigm of the configurational entropy (CE). Configurational-entropic Regge trajectories, that relate the CE underlying odd-spin glueballs to their mass spectra and spin, are then engendered. They predict the mass spectra of odd-spin glueballs, besides pointing towards the configurational stability of odd-spin glueball resonances. The exponential modified dilaton with logarithmic anomalous dimensions comprises the most suitable choice to derive the mass spectra of odd-spin glueballs, compatible to lattice QCD. It is the…
The AdS/CFT correspondence is a powerful tool to study the properties of conformal QCD at strong coupling in terms of a higher dimensional dual gravity theory. The power-law falloff of scattering amplitudes in the non-perturbative regime and calculable hadron spectra follow from holographic models dual to QCD with conformal behavior at short distances and confinement at large distances. String modes and fluctuations about the AdS background are identified with QCD degrees of freedom and orbital excitations at the AdS boundary limit. A description of form factors in space and time-like regions …
Heavy multi-quark potential in the SU(N) color group using hard-wall AdS/QCD at both zero and finite temperature is studied. A Cornell-like potential is obtained for baryons and other exotic configurations and compared with those in the quenched lattice calculation in N=3 case. At the end we also discuss possible improvements in the UV region of potential.
We put forward a new bottom-up AdS/QCD holographic model bearing a distinct treatment of the pion fields. We argue that a standard approach to the pion description is neither transparent nor totally satisfactory. In the paper we provide a new one based on a broadened realization of some holographic principles. The reasoning and the effect of these modifications are explained in detail. The resulting model has a different set of parameters than the standard AdS/QCD case. We use them to calculate an extensive list of QCD quantities and find a rather good agreement with the experimental data.
We give an example of modeling phenomenological heavy-quark potentials in a five-dimensional framework nowadays known as AdS/QCD. In particular we emphasize the absence of infrared renormalons.
The mass spectra of isovector $Υ$, $ψ$, $ϕ$, and $ω$ meson resonances are investigated, in the AdS/QCD and information entropy setups. The differential configurational entropy is employed to obtain the mass spectra of radial $S$-wave resonances, with higher excitation levels, in each one of these meson families, whose respective first undisclosed states are discussed and matched up to candidates in the Particle Data Group.
The axial-vector form factor of the nucleons is considered in the framework of hard-wall model of holographic QCD. A new interaction term between the bulk gauge and matter fields was included into the interaction Lagrangian. We obtain the axial-vector form factor of nucleons in the boundary QCD from the bulk action using AdS/CFT correspondence. The momentum square dependence of the axial-vector form factor is analysed numerically.
Starting from the Hamiltonian equation of motion in QCD we find a single variable light-front equation for QCD which determines the eigenspectrum and the light-front wavefunctions of hadrons for general spin and orbital angular momentum. This light-front wave equation is equivalent to the equations of motion which describe the propagation of spin-$J$ modes on anti-de Sitter (AdS) space.
We perform a study of the doubly virtual Compton scattering off a spinless target gamma* P -> gamma* P' within the Anti-de Sitter(AdS)/QCD formalism. We find that the general structure allowed by the Lorentz invariance and gauge invariance of the Compton amplitude is not easily reproduced with the standard recipes of the AdS/QCD correspondence. In the soft-photon regime, where the semi-classical approximation is supposed to apply best, we show that the measurements of the electric and magnetic polarizabilities of a target like the charged pion in real Compton scattering, can already serve as s…
We construct a new, simple phenomenological model along the lines of AdS/QCD. The essential new ingredient is the brane-antibrane effective action including the open string tachyon proposed by Sen. Chiral symmetry breaking happens because of tachyon dynamics. We fit a large number of low-spin meson masses at the 10%-15% level. The only free parameters involved in the fits correspond to the overall QCD-scale and the quark masses. Several aspects of previous models are qualitatively improved.
We study the doubly virtual Compton scattering off a spinless target $γ^*P\toγ^*P'$ within the Anti-de Sitter(AdS)/QCD formalism. We find that the general structure allowed by the Lorentz invariance and gauge invariance of the Compton amplitude is not easily reproduced with the standard recipes of the AdS/QCD correspondence. In the soft-photon regime, where the semi-classical approximation is supposed to apply best, we show that the measurements of the electric and magnetic polarizabilities of a target like the charged pion in real Compton scattering, can already serve as stringent tests.
We calculate the $a_1$ meson-nucleon coupling constant in the framework of soft-wall and hard-wall AdS/QCD models. In the bulk of AdS space were written bulk interaction Lagrangians for a minimal gauge coupling, a magnetic gauge coupling and a triple coupling. To use AdS/CFT correspondence and these bulk interaction Lagrangians we calculate the $a_1$ axial-vector meson-nucleon coupling constant in the boundary of AdS space within both models. We observe that the numerical values for the $g_{a_1 NN}$ coupling constant in the framework of both models are more close to the experimental value than…
In the framework of the soft-wall model of AdS/QCD we calculated the $ρ$ meson nucleon coupling constant. Bulk-to boundary propagators for the free vector and spinor fields are presented, whose boundary values correspond to $ρ$ meson and to the nucleon respectively. The interaction Lagrangian between these fields is written in the bulk of AdS space and includes magnetic type interactions as well. Using the AdS/CFT correspondence from the bulk interaction action we derived the $g_{ρNN}$ coupling constant in the boundary QCD. We found that the soft-wall model result for the $g_{ρNN}$ constant is…
The Kaluza-Klein tower of higher spin-$S$ tensor meson resonances is here scrutinized in the AdS/QCD hard wall model, encompassing the already established resonances $ρ(770)$, $f_2(1270)$, $ω_3(1670)$, $f_4(2050)$, $ρ_5(2350)$, $f_6(2510)$ in PDG. A hybrid model employs both information theory and AdS/QCD, where configurational-entropic Regge trajectories, relating the configurational entropy of the tensor mesons family to their $S$ spin, and also to their experimental mass spectra, are derived and analyzed. Therefore, the mass spectra of higher spin-$S$ tensor meson resonances is obtained and…
We study the low-energy theorems of QCD from the point of view of the dual AdS/QCD models and demonstrate that these models are compatible with the theorems in the chiral limit, i.e. the arising expressions have the same analytical behavior at the pole when the quark mass tends to zero. Low-energy theorems are formulated in terms of the spectral density of the Dirac operator. In order to calculate the spectral density in the dual holographic models we express it in terms of a partition function of a QCD-like theory.
We study the temperature dependence of the $a_1$ meson-nucleon coupling constant in the framework of the soft-wall AdS/QCD model with thermal dilaton field. Profile functions for the axial-vector and fermion fields in the AdS-Schwarzschild metric are presented. It is constructed an interaction Lagrangian for the fermion-axial-vector-thermal dilaton fields system in the bulk of space-time. From this Lagrangian integral representation for the $g_{a_1NN}$ coupling constant is derived. The temperature dependence of this coupling constant is numerically analyzed.
In the bottom-up approach to AdS/QCD based on a five-dimensional gravity dilaton action the exponential of the dilaton field is usually identified as the strong or 't Hooft coupling. There is currently no model known which fits the measurements of the running coupling and lattice results for pressure at the same time. With a one parametric toy model we demonstrate the effect of fitting the pressure on the coupling and vice versa.
We derive the scaling dimension of antisymmetric tensor operators in the boundary theory of the AdS/CFT correspondence using a functional integral representation of the boundary-to-boundary propagators of their dual fields in the bulk. We then apply this technique to AdS/QCD in which the bulk metric is warped, resulting in non-constant scaling dimensions. In particular, we compute the two-point correlation function of gluon field strength operators, for which it is prerequisite to know the ow of the anomalous scaling dimension under rescaling. The results are in very good agreement with quench…
In this note, two important transport observables in the RHIC experiment, relaxation time constant and jet quenching parameter, are calculated from an AdS/QCD model. A quark moving in the viscous medium such as the Quark-Gluon-Plasma is modelled by an open string whose end point travels on the boundary of a deformed AdS_5 black hole. The correction introduced via the deformed AdS_5 is believed to help us better understand the data which is expected to be measured in the RHIC.
Based on gauge-gravity duality, by using holographic entanglement entropy, we have done a phenomenological study to probe confinement-deconfinement phase transition in the QCD-like gauge theory. Our outcomes are in perfect agreement with the expected results, qualitatively and quantitatively. We find out that the (holographic) entanglement entropy is a reliable order parameter for probing the phase transition.
We present results of modeling the temperature dependence of the spatial string tension and thermal phase transition in a five-dimensional framework nowadays known as AdS/QCD. For temperatures close to the critical one we find a behaviour remarkably consistent with the lattice results.
We build on the success of AdS/QCD in predicting diffractive $ρ$ meson production to obtain the transition form factors for B decays to light mesons. Consequently, we predict several observables associated with $B\to ρ\ellν$ semileptonic and $B\to K^*μ^+μ^-$ dileptonic decays. Our predictions are compared to the available experimental data.
We study the confinement/deconfinement phase transition of holographic AdS/QCD models by using Ricci flat $AdS_5$ black holes up to ${\cal O}(α'^3)$, which corresponds to the $λ$ expansion correction in the dual field theory to $λ^{-3/2}$, where $λ$ is the 't Hooft coupling constant. We consider two cases: one is the hard-wall AdS/QCD model where a small radius region of the $AdS_5$ is removed; the other is the case where one of spatial coordinates for the $AdS_5$ space is compactified, resulting in Witten's QCD model in 2+1 dimensions. We find that in the hard-wall AdS/QCD model, the deconfin…
In a theory with linear confinement, such as QCD, the masses squared m^2 of mesons with high spin S or high radial excitation number n are expected, from semiclassical arguments, to grow linearly with S and n. We show that this behavior can be reproduced within a putative 5-dimensional theory holographically dual to QCD (AdS/QCD). With the assumption that such a dual theory exists and describes highly excited mesons as well, we show that asymptotically linear m^2 spectrum translates into a strong constraint on the INFRARED behavior of that theory. In the simplest model which obeys such a const…
The holographic recipe for the calculation of decay constants is revisited. Starting from the holographic 2-point function and using the fact that normalizable bulk modes scale as $z^{Δ-S}$, with $S$ the spin, we can obtain a consistent expression that depends on the value of the mode at the boundary, not the derivative. We apply our decay constant expression to other AdS/QCD (static and dynamic) models proving its consistency. We also demonstrated that our approach is equivalent to the usual holographic prescription.
Recently, deeper understanding of QCD emerges from the study of the AdS/CFT correspondence. New results include the properties of quark-gluon plasma and the confinement/deconfinement phase transition, which are both very important for the scenario of the QCD phase transition in the early universe. In this paper, we study some aspects of how the new results may affect the old calculations of the cosmological QCD phase transition, which are mainly based on the studies of perturbative QCD, lattice QCD and the MIT bag model.
We construct a new holographic description of QCD using domain wall fermions. The construction consists of probe D7 branes in a D5 brane geometry describing quarks on a 4+1d defect in a 5+1d gauge theory. We then compactify one dimension of the D5 to introduce confinement in the gauge degrees of freedom. In addition we allow a spatial dependent mass term for the D7 brane quarks to isolate chiral fermions on 3+1d domain walls. The D7 world volume fields, when restricted to the domain wall position, provide an AdS/QCD description. We compute the spectrum and compare to data. We include higher di…
We discuss some attempts for the construction of gravity duals of QCD-like theories. It is analysed some properties of solutions of 10D Type IIB supergravity theory that attempt to be dual to $\mathcal{N}$=1 gauge theories, in particular the solutions that belong to Papadoulos-Tseytlin ansatz. We argue that one could obtain 5D effective theories from 10d solutions and it motivates the use of phenomenological AdS/QCD models.
We show how to incorporate chiral symmetry breaking in the soft-wall version of the AdS/QCD model by using a modified dilaton profile and a quartic term in the bulk scalar potential. This allows one to separate the dependence on spontaneous and explicit chiral symmetry breaking. Moreover our 5D model automatically incorporates linear trajectories and non chiral-symmetry restoration for highly excited radial states. We compare our resulting mass spectra in the scalar, vector and axial-vector sectors with the respective QCD resonances and find reasonable agreement using the known values for the …
The configurational entropy setup is employed to study dynamical tachyonic holographic AdS/QCD models. The phenomenology of light-flavour mesonic states is then corroborated by the Shannon's information. Tachyonic bulk corrections to the dynamical AdS/QCD show more dominant and abundant dual mesonic states in the 4D boundary QCD, when compared to the dual mesons in the standard dynamical AdS/QCD. Entropic Regge-like trajectories are also emulated.
The two flavour AdS/QCD, with chiral and gluon condensates, sets in the description of the pion family and its mass spectra. Using gravity-dilaton-gluon backgrounds, entropic Regge-like trajectories for the pion family are then derived. They relate the $π$ mesons underlying configurational entropy to both the pions excitation wave mode number and the pions experimental mass spectra, yielding a reliable prediction for the mass spectra of higher excitation pion modes, to be experimentally detected.
We investigate the softwall AdS/CFT model. We specifically looked at the Pomeron, leading Regge contribution to a scattering process and used it to fit deep inelastic scattering data from the HERA collaboration. We find that the model fits the data with much more success than the purely conformal case, and find similar success to previous confinement models.
The essence of the chiral magnetic effect is generation of an electric current along an external magnetic field. Recently it has been studied by Rebhan et al. within the Sakai--Sugimoto model, where it was shown to be zero. As an alternative, we calculate the chiral magnetic effect in soft-wall AdS/QCD and find a non-zero result with the natural boundary conditions. The mechanism of the dynamical neutralization of the chiral chemical potential via the string production is discussed in the dual two-form representation.
Estimates of the light hadron masses, decay constants and couplings in AdS/QCD models are generally more accurate than should have been expected. Certain predictions based on the AdS/CFT correspondence, such as the ratio of the equilibrium viscosity to entropy density, are universal and therefore provide firm experimental tests of these models. Other observables, while not completely universal, may be relatively insensitive to model details. We calculate the dependence of a number of low-energy hadronic observables on details of the hard-wall AdS/QCD model. In particular, we vary the infrared …
We consider the Soft-Wall-model of AdS/QCD to calculate photon production in strongly coupled Quark Gluon Plasma (sQGP). The IR cut-off only affects the low-frequency-component of the production rate. The full spectral function is determined numerically and shows remarkable similarity to computations of the photon production rate in AdS-duals of $\mathcal{N}=2$ theories with massive flavor. It is further support that Soft-Wall AdS-QCD correctly captures the IR physics of the chiral perturbation theory regime of QCD. We confirm this by relating the IR-effects of the massive flavor deformations …
We propose an extension of the hard-wall AdS/QCD model by including the Chern-Simons term required to reproduce the chiral anomaly of QCD. In the framework of this holographic model, we study the vertex function F_{πγ^* γ^*}(Q_1^2,Q_2^2) which accumulates information about the coupling of the pion to two (in general virtual) photons. We calculate the slope of the form factor with one real and one slightly virtual photon and show that it is close to experimental findings. We analyze the formal limit of large virtualities and establish that predictions of the holographic model analytically (incl…
Bottomonium and charmonium, representing quarkonia states, are scrutinized under the point of view of the information theory, in the AdS/QCD holographic setup. A logarithmic measure of information, comprised by the configurational entropy, is here employed to quantitatively study quarkonia radially excited S-wave states. The configurational entropy provides data regarding the relative dominance and the abundance of the bottomonium and charmonium states, whose underlying information is more compressed, in the Shannon's theory meaning. The derived configurational entropy, therefore, identifies t…
We study an improved AdS/QCD model at finite temperature and chemical potential. An Ansatz for the beta-function for the boundary theory allows for the derivation of a charged dilatonic black hole in bulk. The solution is asymptotically RN-AdS in the UV and AdS2 * R3 in the IR. We discuss the thermodynamical aspects of the solution. The fermionic susceptibilities are shown to deviate from the free fermionic limits at asymptotic temperatures despite the asymptotically free nature of the gauge coupling at the boundary. The Polyakov line, the temporal and spatial string tensions dependence on bot…
Based on the IR-improved bulk holographic AdS/QCD model which provides a consistent prediction for the mass spectra of resonance scalar, pseudoscalar, vector and axial vector mesons, we investigate its finite temperature behavior. By analyzing the spectral function of mesons and fitting it with a Breit-Wigner form, we perform an analysis for the critical temperature of mesons. The back-reaction effects of bulk vacuum are considered, the thermal mass spectral function of resonance mesons is calculated based on the back-reaction improved action. A reasonable melting temperature is found to be $T…
An extended version of the AdS/QCD Soft-Wall model that incorporates QCD-like anomalous contributions to the dimensions of gauge theory operators is proposed. This exploratory approach leads to a relation between scalar glueball masses and beta functions. Using this relation, properties of the glueball mass spectroscopy that emerge from phenomenological beta functions proposed in the literature are investigated. The reverse problem is also considered: starting from a linear Regge trajectory which fits the lattice glueball masses, beta functions with different asymptotic infrared behaviours are…
In this work we study unpolarized spin $1/2$ baryonic deep inelastic scattering (DIS) in the regime of large Bjorken parameter $x$. We calculate the corresponding structure functions $F_{1,2}(x,q^2)$. Our approach is based on an AdS/QCD model with a deformed background, where we consider an exponential factor in the AdS$_5$ metric. Such a deformation implies the introduction of an anomalous dimension in the model. Our results for the structure functions are consistent with those found in the literature from experimental data.
The recently measured $γγ^*\rightarrow π^0$ anomalous form factor is analyzed using the $D4/D8\bar{D8}$ holographic approach to QCD. The half-on-shell transition form factor is vector meson dominated and is shown to exactly tie to the pion form factor. The holographic result compares well with the data for the lowest vector resonance.
We aim at providing an overview on the applications of the AdS/CFT correspondence to non-perturbative aspects of non-Abelian gauge theories, addressed to particle physicists. The finite temperature case, in connection with the physics of the quark-gluon plasma, is emphasized.
