We construct a new solution of five-dimensional gravity coupled to a dilaton which encodes essential features of holographic QCD backgrounds dynamically. In particular, it implements linear confinement, i.e. the area law behavior of the Wilson loop, by means of a dynamically deformed anti-de Sitter metric. The predicted square masses of the light-flavored natural-parity mesons and their excitations lie on linear trajectories of approximately universal slope with respect to both radial and spin quantum numbers and are in satisfactory agreement with experimental data.
We use the holographic hardwall model to calculate the masses of light glueball states with odd spin and P= C= -1 associated with odderons. Considering Dirichlet and Neumann boundary conditions we obtain expressions for the odderon Regge trajectories consistent with those calculated using other approaches.
In this work we propose a modified holographic softwall model, analytically solvable, to calculate the masses of lightest scalar glueball and its radial excitations and of higher spin glueball states for both even and odd spins. From these results we obtain their respective Regge trajectories, associated with the pomeron for even spins and with the odderon for odd spins. These results are in agreement with those calculated using other approaches.
The soft wall model in holographic QCD has Regge trajectories but wrong operator product expansion (OPE) for the two-point vectorial QCD Green function. We modify the dilaton potential to comply OPE. We study also the axial two-point function using the same modified dilaton field and an additional scalar field to address chiral symmetry breaking. OPE is recovered adding a boundary term and low energy chiral parameters, $F_π$ and $L_{10}$, are well described analytically by the model in terms of Regge spacing and QCD condensates. The model nicely supports and extends previous theoretical analys…
We advance in constructing a bottom-up holographic theory of linear meson Regge trajectories that generalizes and unites into one logical framework various bottom-up holographic approaches proposed in the past and scattered in the literature. The starting point of the theory is a quadratic in fields holographic five-dimensional action in which the Poincaré invariance along the holographic coordinate is violated in the most general way compatible with the linear Regge behavior of the discrete spectrum in four dimensions. It is further demonstrated how different Soft Wall (SW) like holographic m…
We initiate the study of Regge theory in a bottom-up holographic model for QCD in the Veneziano limit, where the backreaction of the quarks to the gluon dynamics is included. We determine the parameters of the model by carrying out a precise fit to the meson spectrum in QCD. The spectrum for spin-one and pseudoscalar mesons is well reproduced. We then generalise the model to incluce higher spin fields in the bulk trajectories dual to the Pomeron and meson Regge trajectories at the boundary. With this setting, we fit the masses of the mesons with spins $J=2$, $3$, and $4$,as well as the experim…
We study the possible holographic connection between the Regge limit in QCD and critical gravitational collapse of a perfect fluid in higher dimensions. We begin by analyzing the problem of critical gravitational collapse of a perfect fluid in any number of dimensions and numerically compute the associated Choptuik exponent in d=5, 6 and 7 for a range of values of the speed of sound of the fluid. Using continuous self-similarity as guiding principle, a holographic correspondence between this process and the phenomenon of parton saturation in high-energy scattering in QCD is proposed. This holo…
We reassess a work done by Migdal on the spectrum of low-energy vector mesons in QCD in the light of the AdS-QCD correspondence. Recently, a tantalizing parallelism was suggested between Migdal's work and a family of holographic duals of QCD. Despite the intriguing similarities, both approaches face a major drawback: the spectrum is in conflict with well-tested Regge scaling. However, it has recently been shown that holographic duals can be modified to accomodate Regge behavior. Therefore, it is interesting to understand whether Regge behavior can also be achieved in Migdal's approach. In this…
The problem of obtaining the Regge-like behaviour for meson mass spectrum in the hard-wall AdS/QCD models is addressed. We show that the problem can be solved by a simple incorporation of the effects of local vacuum condensates into such models. The slope of trajectories turns out to be determined by the local condensate of dimension~2 that is absent in the standard Operator Product Expansion. This pitfall, however, can be escaped by means of physically plausible modification of boundary conditions for the holographic fields corresponding to the usual gluon condensate, the latter then determin…
The couplings $g_{ρHH}$ of the $ρ$ meson with any hadron H are calculated in a holographic dual of QCD where the Regge trajectories for mesons are manifest. The resulting couplings grow linearly with the exciting number of H, thus are far from universal. A simple argument has been given for this behavior based on quasi-classical picture of excited hadrons. It seems that in holographic duals with exact Regge trajectories the $g_{ρHH}$ universality should be violated. The $ρ$-dominance for the electromagnetic form factors of H are also strongly violated, except for the lowest state, the pion. Qu…
A simple relativistic quantum field model with the Yukawa-type interaction is considered to demonstrate that the analytic confinement of the constituent ("quarks") and carrier ("gluons") particles explains qualitatively the basic dynamical properties of the spectrum of mesons considered as two-particle stable bound states of quarks and gluons: the quarks and gluons are confined, the glueballs represent bound states of massless gluons, the masses of mesons are larger than the sum of the constituent quark masses and the Regge trajectories of mesonic orbital excitations are almost linear.
Deep-inelastic diffractive scaling violations have provided fundamental insight into the QCD pomeron, suggesting a single gluon inner structure rather than that of a perturbative two-gluon bound state. This paper derives a high-energy, transverse momentum cut-off, confining solution of QCD. The pomeron, in first approximation, is a single reggeized gluon plus a ``wee parton'' component that compensates for the color and particle properties of the gluon. This solution corresponds to a supercritical phase of Reggeon Field Theory. Beginning with the multi-regge behavior of massive quark and gluon…
In this work we use gauge/string dualities and a dynamical model that takes into account dynamical corrections to the metric of the anti de Sitter space due to a quadratic dilaton field and calculate the masses of even and odd spin glueball states with $P=C=+1$, and $P=C=-1$, respectively. Then we construct the corresponding Regge trajectories which are associated with the pomeron for even states with $P=C=+1$, and with the odderon for odd states with $P=C=-1$. We compare our results with those coming from experimental data as well as other models.
We derive the general 5-dimension metric structure of the $Dp-Dq$ system in type II superstring theory, and demonstrate the physical meaning of the parameters characterizing the 5-dimension metric structure of the \textit{holographic} QCD model by relating them to the parameters describing Regge trajectories. By matching the spectra of vector mesons $ρ_1$ with deformed $Dp-Dq$ soft-wall model, we find that the spectra of vector mesons $ρ_1$ can be described very well in the soft-wall $D3-Dq$ model, i.e, $AdS_5$ soft-wall model. We then investigate how well the $AdS_5$ soft-wall model can descr…
We use holographic QCD to study Pomeron- and Reggeon-mediated central production in Regge regime hadronic scattering. We focus specifically on $η$ production in proton-proton collisions. While previous work studied the Pomeron-mediated process, the mesonic Regge trajectories ("Reggeons") we now incorporate contribute significantly at experimentally probed energies. We use the five-point open string amplitude (in flat space) to construct approximate propagators for the Reggeon states, and the five-point closed string amplitude for the Pomeron. Using these "holographic" Reggeons and Pomerons, an…
We study the gravity dual of four dimensional pure Yang-Mills theory through D4 branes, as proposed by Witten (holographic QCD). In this holographic QCD, it has been widely believed that the confinement phase in the pure Yang-Mills theory corresponds to the AdS D4 soliton in gravity and the deconfinement phase corresponds to the black D4 brane. We inspect this conjecture carefully and show that the correspondence between the black D4 brane and the deconfinement phase is not correct. Instead, by using a slightly different set up, we find an alternative gravity solution called "localized soliton…
We consider the holographic abelian Higgs model and show that, in the absence of the scale symmetry breaking effect, chiral symmetry breaking gives linear confinement where the slope is given by the value of the chiral condensation. The model can be considered either as the theory of superconductivity or as the axial sector of QCD depending on the interpretation of the charge. We also provided a few models with linear confinement.
We study confinement-deconfinement phase transition in a holographic soft-wall QCD model. By solving the Einstein-Maxwell-scalar system analytically, we obtain the phase structure of the black hole backgrounds. We then impose probe open strings in such background to investigate the confinement-deconfinement phase transition from different open string configurations under various temperatures and chemical potentials. Furthermore, we study the Wilson loop by calculating the minimal surface of the probing open string world-sheet and obtain the Cornell potential in confinement phase analytically.
We compute the holographic quark potential in the realm of brane cosmology. We show that under certain conditions the very geometry due to an inflationary 3-brane induces a D3-D7-brane system. The cosmological constant that appears involved in the original geometry is attributed to the D7-brane position itself in its embedding process. We address the issues of confinement at low distances, screening effects at sufficiently large distances, and quark condensate.
A self-consistent holographic QCD model is proposed which can realize both chiral symmetry breaking and confinement, two most important phenomena of QCD. It is pointed out that the model can accommodate both Regge spectra of hadrons and the linear potential between quarks. The model is formulated in the framework of graviton-dilaton-scalar system, where the dilaton field is dual to the dimension-2 gluon condensate and can lead to the linear confinement, while the scalar field corresponds to the quark anti-quark condensate and can explain the property of chiral dynamics.
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.
In this work we use the holographic softwall AdS/QCD model with anomalous dimension contributions coming from two different QCD beta functions to calculate the masses of higher spin glueball states for both even and odd spins and its respective Regge trajectories, related to the pomeron and the odderon, respectively. We further investigate this model taking into account dynamical corrections due to a dilaton potential consistent with Einstein equations in 5 dimensions. The results found in this work for the Regge trajectories within the anomalous softwall model with dynamical corrections are c…
We present a five-dimensional anisotropic holographic model for light quarks supported by Einstein-dilaton-two-Maxwell action. This model generalizing isotropic holographic model with light quarks is characterized by a Van der Waals-like phase transition between small and large black holes. We compare the location of the phase transition for Wilson loops with the positions of the phase transition related to the background instability and describe the QCD phase diagram in the thermodynamic plane -- temperature $T$ and chemical potential $μ$. The Cornell potential behavior in this anisotropic mo…
A high-energy, transverse momentum cut-off, solution of QCD is outlined. Regge pole and ``single gluon'' properties of the pomeron are directly related to the confinement and chiral symmetry breaking properties of the hadron spectrum. This solution, which corresponds to a supercritical phase of Reggeon Field Theory, may only be applicable to QCD with a very special quark content.
We establish a holographic QCD model for four flavors, where a light scalar field $X$ and a heavy scalar field $H$ are introduced, separately. The $H$ field is responsible for the breaking of $SU(N_f=4)$ to $SU(N_f=3)$. The ground state and its Regge excitation of meson spectra in the light flavor sector and heavy flavor sector as well as the ligh-heavy mesons are well in agreement with the Particle data group (PDG). Due to the additional introduction of the $H$ field in the model, different Regge slopes for light and heavy mesons can be achieved.
An approach to QCD vacuum as a medium describable in terms of statistical ensemble of almost everywhere homogeneous Abelian (anti-)self-dual gluon fields is briefly reviewed. These fields play the role of the confining medium for color charged fields as well as underline the mechanism of realization of chiral $SU_{\rm L}(N_f)\times SU_{\rm R}(N_f)$ and $U_A(1)$ symmetries. Hadronization formalism based on this ensemble leads to manifestly defined quantum effective meson action. Strong, electromagnetic and weak interactions of mesons are represented in the action in terms of nonlocal $n$-point …
We discuss the phase structure of N D4 branes wrapped on a temporal (Euclidean) and a spatial circle, in terms of the near-horizon AdS geometries. This system has been studied previously to understand four dimensional pure SU(N) Yang-Mills theory (YM4) through holography. In the usual treatment of the subject, the phase transition between the AdS soliton and the black D4 brane is interpreted as the strong coupling continuation of the confinement/deconfinement transition in YM4. We show that this interpretation is not valid, since the black D4 brane and the deconfinement phase of YM4 have diffe…
The structure of generalized parton distributions is determined from light-front holographic QCD up to a universal reparametrization function $w(x)$ which incorporates Regge behavior at small $x$ and inclusive counting rules at $x \to 1$. A simple ansatz for $w(x)$ which fulfills these physics constraints with a single-parameter results in precise descriptions of both the nucleon and the pion quark distribution functions in comparison with global fits. The analytic structure of the amplitudes leads to a connection with the Veneziano model and hence to a nontrivial connection with Regge theory …
We consider the effect of including a non-minimal coupling between a $U(1)$ vector gauge field and the graviton Regge trajectory in holographic QCD models. This coupling describes the QCD interaction between the quark bilinear electromagnetic current and the Pomeron. We test this new coupling against DIS data at low Bjorken $x$ and obtain an excellent fit with a chi squared of 1.1 over a very large kinematical range in the photon virtuality $Q^2<400 \ {\rm GeV}^2$ and for $x<10^{-2}$. The scale of the new dimension full coupling, which arises from integrating higher spin fields, is of order $6…
Single quarks moving in the vacuum of confining gauge theories are stopped by a drag force. The holographic description relates the confining scale in the bulk geometry with a range of physical values for the drag force in the vacuum. The vacuum drag force acting on the isolated quark directly manifests quark confinement since it prevents the quark from walking freely in the vacuum. However, analytical expressions for the drag force as a function of the quark velocity were lacking. In the present work, we propose that the vacuum drag force is given by the regularized zero-temperature limit of …
We derive and analyze the confinement potential of the Cornell type within the framework of the generalized Soft Wall holographic model that includes a parameter controlling the intercept of the linear Regge spectrum. In the phenomenology of Regge trajectories, this parameter is very important for the quantitative description of experimental data. Our analysis shows that the ''linear plus Coulomb'' confinement potential obtained in the scalar channel is quantitatively consistent with the phenomenology and lattice simulations while the agreement in the vector channel is qualitative only. This r…
A comprehensive phenomenological analysis of experimental data and some theoretical models is presented here (for mesons) to critically discuss how Regge trajectory parameters depend on flavor. Through analytic continuation of physical trajectories (obtained from resonance data) into the space like region, we derive the suppression factor for heavy flavor production. The case of our D Regge exchange, both for D and $Λ_c$ production, is considered in some detail. Good agreement with data is reached confirming that indeed the slopes of heavier flavors decrease. This result suggests that the conf…
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.
The breaking of chiral symmetry in holographic light-front QCD is encoded in its longitudinal dynamics with its chiral limit protected by the superconformal algebraic structure which governs its transverse dynamics. The scale in the longitudinal light-front Hamiltonian determines the confinement strength in this direction: It is also responsible for most of the light meson ground state mass consistent with the Gell-Mann-Oakes-Renner constraint. Longitudinal confinement and the breaking of chiral symmetry are found to be different manifestations of the same underlying dynamics as found in 't Ho…
The typical AdS/QCD models deal with the large-N_c limit of QCD, as a consequence the meson spectrum consists of the infinite number of states that is far from the real situation. Basing on introduction of anharmonic corrections to the holographic potential, the corrections whose existence has been recently advocated, we construct a class of bottom-up holographic models describing arbitrary finite number of states in the sector of light mesons. Within the proposed approach, the spectrum of masses square has the following properties: It is linear, $m_n^2\sim n$, at not very large n, nonlinear a…
By matching the $Dp-Dq$ system in type II superstring theory with the Regge trajectories of vector and axial-vector meson spectra, a possible 5-dimension metric of a $Dp-Dq$ soft-wall model has been determined. The dependence of the metric parameters on Regge trajectory parameters has been demonstrated. It is shown that the models defined in $Dp$ brane background for $p=3$ or 4 can be consistent with experimental data.
We consider the Einstein-Maxwell-dilaton system with an arbitrary kinetic gauge function and a dilaton potential. A family of analytic solutions is obtained by the potential reconstruction method. We then study its holographic dual QCD model. The kinetic gauge function can be fixed by requesting the linear Regge spectrum of mesons. We calculate the free energy to obtain the phase diagram of the holographic QCD model.
It is well known that the Soft-Wall holographic model for QCD successfully reproduces not only the linear Regge spectrum, but also, via the holographic Wilson confinement criterion, the ''linear plus Coulomb'' confinement potential similar to the Cornell potential. This property could be interpreted as a holographic counterpart of the hadron string picture, where the linearly rising potential and Regge-like spectrum are directly related. However, such a relation does not take place in the bottom-up holographic approach. Namely, the Cornell-like potentials arise in a broad class of bottom-up ho…
We consider the soft wall model for a heuristic holographical modelling of a confining gauge theory and discuss how the introduction of a (constant) magnetic field influences the (de)confinement phase structure. We use the entanglement entropy as a diagnostic tool in terms of the length of an entangling strip geometry. Due to the anisotropy introduced by the magnetic field, we find that the results depend on the orientation of the strip relative to the field. This allows to identify a richer, anisotropic, interplay between confinement and a magnetic field than possibly can be extracted from a …
Traditional idea of Pomeron/Reggeon description for hadron scattering is now being given theoretical foundation in gravity dual descriptions, where Pomeron corresponds to exchange of spin-$j \in 2\mathbb{Z}$ states in the graviton trajectory. Deeply virtual Compton scattering (DVCS) is essentially a 2 to 2 scattering process of a hadron and a photon, and hence one should be able to study non-perturbative aspects (GPD) of this process by the Pomeron/Reggeon process in gravity dual. We find, however, that even one of the most developed formulations of gravity dual Pomeron (Brower--Polchinski--St…
The AdS/QCD models are believed to interpolate between low and high energy sectors of QCD. This belief is usually based on observations that many phenomenologically reasonable predictions follow from bounds imposed at high energies although the hypothetical range of applicability of semiclassical bottom-up holographic models is restricted by the gauge/gravity duality to low energies where QCD is strongly coupled. For testing the feasibility of high energy constraints it is interesting to calculate holographically some observable constants at low and high momenta independently and compare. We c…
One of the most fundamental problems in Quantum Chromodynamics is to understand the origin of the mass scale which controls the range of color confinement and the hadronic spectrum. We show that a mass gap and a fundamental color confinement scale arise when one extends the formalism of de Alfaro, Fubini and Furlan to frame-independent light-front Hamiltonian theory. Remarkably, the resulting light-front potential has a unique form of a harmonic oscillator in the light-front invariant impact variable if one requires that the action remains conformally invariant. The result is a single-variable…
We study the graviton Regge trajectory in Holographic QCD as a model for high energy scattering processes dominated by soft pomeron exchange. This is done by considering spin J fields from the closed string sector that are dual to glueball states of even spin and parity. In particular, we construct a model that governs the analytic continuation of the spin J field equation to the region of real J < 2, which includes the scattering domain of negative Maldelstam variable t. The model leads to approximately linear Regge trajectories and is compatible with the measured values of 1.08 for the inter…
The holographic methods inspired by the gauge/gravity correspondence from string theory have been actively applied to the hadron spectroscopy in the last eleven years. Within the phenomenological bottom-up approach, the linear Regge-like trajectories for light mesons are naturally reproduced in the so-called "Soft-wall" holographic models. I will give a very short review of the underlying ideas and technical aspects related to the meson spectroscopy. A generalization of soft-wall description of Regge trajectories to arbitrary intercept is proposed. The problem of incorporation of the chiral sy…
We develop a formalism where the hard and soft pomeron contributions to high energy scattering arise as leading Regge poles of a single kernel in holographic QCD. The kernel is obtained using effective field theory inspired by Regge theory of a 5-d string theory. It describes the exchange of higher spin fields in the graviton Regge trajectory that are dual to glueball states of twist two. For a specific holographic QCD model we describe Deep Inelastic Scattering in the Regge limit of low Bjorken x, finding good agreement with experimental data from HERA. The observed rise of the effective pome…
We present the mass spectra of radial and orbital excited states of singly heavy bottom baryons; $Σ_{b}^{+}, Σ_{b}^-, Ξ_b^-, Ξ_b^0, Λ_b^0$ and $Ω_b^-$. The QCD motivated hypercentral quark model is employed for the three body description of baryons and the form of confinement potential is hyper coulomb plus linear. The first order correction to the confinement potential is also incorporated in this work. The semi-electronic decay of $Ω_b$ and $Ξ_b$ are calculated using the spectroscopic parameters of the baryons. The computed results are compared with other theoretical predictions as well as w…
We construct a self-consistent holographic QCD model which can realize two most important phenomena of QCD, i.e. chiral symmetry breaking and confinement. The model is formulated in the framework of graviton-dilaton-scalar system, where the dilaton field is of dimension-2 which might be dual to the dimension-2 gluon condensate and can lead to the linear confinement, while the scalar field corresponds to the quark anti-quark condensate and can explain the property of chiral dynamics. Within this framework, both Regge spectra of hadrons and the linear potential between quarks can be accommodated…
In this report we explore the remarkable connections between light-front dynamics, its holographic mapping to gravity in a higher-dimensional anti-de Sitter (AdS) space, and conformal quantum mechanics. This approach provides new insights into the origin of a fundamental mass scale and the physics underlying confinement dynamics in QCD in the limit of massless quarks. The result is a relativistic light-front wave equation for arbitrary spin with an effective confinement potential derived from a conformal action and its embedding in AdS space. This equation allows for the computation of essenti…
In the holographic model of QCD, theta dependence sharply changes at the point of confinement deconfinement phase transition. In large N QCD such a change in theta behavior can be related to the breakdown of the instanton expansion at some critical temperature T_c. Associating this temperature with confinement-deconfinement phase transition leads to the description of the latter in terms of dissociation of instantons into the fractionally charged instanton quarks. To elucidate this picture, we introduce the nonvanishing chiral condensate in the deconfining phase and assume a specific lagrangia…
Bulk mesons propagating in chiral and gluon condensates, in a gravity background, are scrutinized in holographic soft wall AdS/QCD models, involving deformed dilatonic backgrounds. The configurational entropy of the $a_1$ axial vector, the $ρ$ vector, and the $f_0$ scalar meson families is then computed. Two types of informational entropic Regge trajectories are then obtained, where the logarithm of the mesons configurational entropy is expressed in terms of both the experimental meson mass spectra and their excitation number as well. Therefore the mass spectra of the next generation of elemen…
We consider the Einstein-Maxwell-dilaton system with an arbitrary kinetic gauge function and a dilaton potential. A family of analytic solutions is obtained by the potential reconstruction method. We then study its holographic dual QCD model. The kinetic gauge function can be fixed by requesting the linear Regge spectrum of mesons. We calculate the free energy to obtain the phase diagram of the holographic QCD model and interpret our result as the heavy quarks system by comparing the recent lattice QCD simulation. We finally obtain the equations of state in our model.
The spectrum of light baryons and mesons has been reproduced recently by Brodsky and Teramond from a holographic dual to QCD inspired in the AdS/CFT correspondence. They associate fluctuations about the AdS geometry with four dimensional angular momenta of the dual QCD states. We use a similar approach to estimate masses of glueball states with different spins and their excitations. We consider Dirichlet and Neumann boundary conditions and find approximate linear Regge trajectories for these glueballs. In particular the Neumann case is consistent with the Pomeron trajectory.
