We consider a bottom-up AdS/QCD model with a conformal exponential deformation $e^{k\,z^2}$ on a Lorentz invariant AdS background. In this model, we assume the conformal dimension associated with the operator that creates pions at the boundary as $Δ=3$. Regarding the infrared scale related to photon field $k_γ$, we analyze two cases: constant and depending on the transferred momentum $q$. In these two cases, we computed the electromagnetic pion form factor as well as the pion radius. We compare our results with experimental data as well as other theoretical (holographic and non-holographic) models. In particular, for the momentum-dependent infrared scale, we find good agreement with the available experimental data as well as non-holographic models.
We show that in a deformed ${\rm AdS}_5$ model with an explicit infrared cutoff included in the logarithmic correction $-c_0\log[(z_{IR}-z)/z_{IR}]$, the heavy quark Cornell potential can be fitted very well, the corresponding beta-function agrees with the QCD beta-function at 2-loop level reasonably well, and its dual dilaton potential is bounded from below in infrared. The results are compared with those in the Andreev-Zakharov model and the Pirner-Galow model.
We consider non-perturbative effects in the beta-deformed N=4 supersymmetric gauge theory in the context of the AdS/CFT correspondence. We concentrate on the correlators of the Yang-Mills operators which correspond to the lowest Kaluza-Klein modes propagating on the dual supergravity background found by Lunin and Maldacena in hep-th/0502086. In particular, we calculate all multi-instanton contributions to these correlators in the beta-deformed SYM and find a compelling agreement with the results expected in supergravity.
We extend an infrared-deformed soft-wall anti de-Sitter/QCD model at zero temperature to a model at finite temperature and perform hydrodynamics. To have the infalling boundary condition to make the hydrodynamic analysis possible, we treat the infrared energy scale factor in our metric as a temperature-depending parameter. Then, by carrying out the hydrodynamic analysis, we compute the transport coefficients, the diffusion constant, and the shear viscosity, through the linear response theory.
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.
Because of the presence of modified warp factors in metric tensors, we use deformed AdS$_5$ spaces to apply the AdS/CFT correspondence to calculate the spectra for even and odd glueballs, scalar and vector mesons, and baryons with different spins. For the glueball cases, we derive their Regge trajectories and compare them with those related to the pomeron and the odderon. For the scalar and vector mesons as well as baryons the determined masses are compatible with the PDG. In particular for these hadrons we found Regge trajectories compatible with another holographic approach as well as with t…
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.
By solving the Einstein equations of the graviton coupling with a real scalar dilaton field, we establish a general framework to self-consistently solve the geometric background with black-hole for any given phenomenological holographic models. In this framwork, we solve the black-hole background, the corresponding dilaon field and the dilaton potential for the deformed AdS$_5$ model with a positive/negative quadratic correction. We systematically investigate the thermodynamical properties of the deformed AdS$_5$ model with a positive and negative quadratic correction, respectively, and compar…
In this work we calculate the static limit of the energy for a quark-antiquark pair from the Nambu-Goto action using a holographic approach with a deformed AdS space, with warp factor $\exp\{(κz)^n/n\}$. From this energy we derive the Cornell potential for the quark-antiquark interaction. We also find a range of values for our parameters which fits exactly the Cornell potential parameters. In particular, setting the zero energy of the Cornell potential at 0.33 fermi, we find that $κ=0.56$ GeV and $n=1.3$.
Several physical quantities of light hadrons are examined by a new holographic model of QCD, which is the modified version of the one proposed by Erlich et al. defined on AdS${}_5$. In our model, AdS${}_5$ is deformed by a non-trivial bulk scalar, this is corresponding to adding the mass term of the adjoint fermions to the 4d SYM theory dual to the gravity on AdS${}_5$. We find that this deformation should be taken to be rather small, but its important effects are also seen.
In this paper, we study the destruction of heavy quarkonium due to the entropic force in a deformed $AdS_5$ model. The effects of the deformation parameter on the inter-distance and the entropic force are investigated. The influence of the deformation parameter on the quarkonium dissociation is analyzed. It is shown that the inter-distance increases in the presence of the deformation parameter. In addition, the deformation parameter has the effect of decreasing the entropic force. This results imply that the quarkonium dissociates harder in a deformed AdS background than that in an usual AdS b…
We investigate the mass spectra of scalar and vector glueballs in the so-called bottom-up approach of the AdS/QCD correspondence. The holographic model of QCD includes a static dilaton background field. We study the constraints on the masses coming from perturbing the dilaton field and the geometry of the bulk.
In this paper, we investigate the heavy quark potential in some holographic QCD models. The calculation relies on a modified renormalization scheme mentioned in a previous work of Albacete et al. After studying the heavy quark potential in Pirner-Galow model and Andreev-Zakharov model, we extend the discussion to a general deformed $AdS_5$ case. It is shown that the obtained potential is negative definite for all quark-antiquark separations, differs from that using the usual renormalization scheme.
Finite isospin chemical potential $μ_I$ and temperature $T$ have been introduced in the framework of soft-wall AdS/QCD model. By self-consistently solve the equation of motion, we obtain the phase boundary of pion condensation phase, across which the system undergoes a phase transition between pion condensation phase and normal phase. Comparing the free energy of solutions with and without pion condensation, we find that the phase transition is of first order type both at large $μ_I$ and small $μ_I$. Qualitatively, the behavior at large $μ_I$ is in agreement with the lattice simulation in Phys…
We stude the \textit{holographic} QCD model which contains a quadratic term $ -σz^2$ and a logarithmic term $-c_0\log[(z_{IR}-z)/z_{IR}]$ with an explicit infrared cut-off $z_{IR}$ in the deformed ${\rm AdS}_5$ warp factor. We investigate the heavy quark potential for three cases, i.e, with only quadratic correction, with both quadratic and logarithmic corrections and with only logarithmic correction. We solve the dilaton field and dilation potential from the Einstein equation, and investigate the corresponding beta function in the G{ü}rsoy -Kiritsis-Nitti (GKN) framework. Our studies show tha…
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…
To study drag force on a moving heavy quark through a plasma, we use a deformed AdS space-time, in which deformation parameter $c$ describes non-conformality in AdS/QCD. In this case the quark is mapped to a probe string in the AdS space. Considering probable contribution of deformation parameter in the probe string, we apply a general form of c-dependent string ansatz in the drag force computation. Then we find the acceptable value of this parameter as it satisfies QCD calculations. Using this result, we also discuss diffusion constant which is in agreement with phenomenological result for no…
The AdS/CFT correspondence between string theory in AdS space and conformal field theories in physical space-time leads to an analytic, semi-classical model for strongly-coupled QCD which has scale invariance and dimensional counting at short distances and color confinement at large distances. The AdS/CFT correspondence also provides insights into the inherently non-perturbative aspects of QCD such as the orbital and radial spectra of hadrons and the form of hadronic wavefunctions. In particular, we show that there is an exact correspondence between the fifth-dimensional coordinate of anti-de …
We study the generalized parton distributions (GPDs) of pion for non-zero skewness by considering the leading $| q \bar{q} \rangle$ Fock state component. Inspired from AdS/QCD light-front wave functions, we calculate the pion GPDs. By taking the Fourier transforms we obtain the results for impact-parameter dependent parton distribution functions (ipdpdf) and for GPDs in longitudinal boost-invariant space. We also calculate the charge density and gravitational form factor of the pion. The pion unpolarized transverse momentum distribution (TMD) have also been calculated. The results provide rich…
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.
We study the internal structure of the pion using a model inspired by the AdS/QCD correspondence. The holographic approach provides the light-front wave function (LFWF) for the leading Fock state component of the pion. We adopt two different forms for the LFWF derived from the AdS/QCD soft-wall model, with free parameters fitted to the available experimental information on the pion electromagnetic form factor and the leading-twist parton distribution function. The intrinsic scale of the model is taken as an additional fit parameter. Within this framework, we provide predictions for the unpolar…
Holographic QCD provides a unique framework in which to compute QCD observables. In this talk we summarize recent numerical work on computing the pion electromagnetic form factor using an AdS/QCD action that includes both spontaneous and explicit chiral symmetry breaking. We consider both hard- and soft-wall model results and develop an intermediate background that supports the best features of both. We also begin to see possible evidence in the fit for the presence of 1/N_c corrections.
We develop a formalism to calculate form factor and charge density distribution of pion in the chiral limit using the holographic dual model of QCD with hard-wall cutoff. We introduce two conjugate pion wave functions and present analytic expressions for these functions and for the pion form factor. They allow to relate such observables as the pion decay constant and the pion charge electric radius to the values of chiral condensate and hard-wall cutoff scale. The evolution of the pion form factor to large values of the momentum transfer is discussed, and results are compared to existing exper…
We study the phase transition between pion condensed phase and normal phase, as well as chiral phase transition in a two flavor($\mathcal{N}_f=2$) IR- improved soft-wall AdS/QCD model at finite isospin chemical potential $μ_I$ and temperature $T$. By self-consistently solving the equations of motion, we obtain the phase diagram in the plane of $μ_I$ and $T$. The pion condensation appears together with a massless Nambu-Goldstone boson $m_{π_1}(T_c, μ_I^c)=0$, which is very likely to be a second-order phase transition with mean-field critical exponents in small $μ_I$ region. When $T=0$, the crit…
In this paper, we revisit a scale-invariant extension of the standard model (SM) with a strongly interacting hidden sector within AdS/QCD approach. Using the AdS/QCD, we reduce the number of input parameters to three, {\it i.e.} hidden pion decay constant, hidden pion mass and $\tanβ$ that is defined as the ratio of the vacuum expectation values (VEV) of the singlet scalar field and the SM Higgs boson. As a result, our model has sharp predictability. We perform the phenomenological analysis of the hidden pions which is one of the dark matter (DM) candidates in this model. With various theoreti…
We calculate the stress tensor, or energy-momentum tensor, form factors of the pion and of axial vector mesons in the chiral limit of a hard wall AdS/CFT model of QCD. One (of the two) pion gravitational form factors is directly related to the second moment of the pion generalized parton distribution, thus providing a sum rule for the latter. As was also the case for vector mesons, both the pion and the axial vector mesons appear strikingly more compact measured by the gravitational form factor than by the electromagnetic form factor.
We study a modification of the five-dimensional description of dynamical electro-weak symmetry breaking inspired by the AdS/CFT correspondence. Conformal symmetry is broken in the low-energy region near the IR brane by a power-law departure from the pure AdS background. Such a modification--while not spoiling the identification of the IR brane with the scale of confinement-- has a dramatic effect on both the coupling of the first composite states to the standard model currents and their self-couplings. Chiral symmetry breaking can take place at a scale larger than the IR cut-off. This study sh…
Pseudo-Goldstone modes appear in many physical systems and display robust universal features. First, their mass $m$ obeys the so-called Gell-Mann-Oakes-Renner (GMOR) relation $f^2\,m^2=H\,\barσ$, with $f$ the Goldstone stiffness, $H$ the explicit breaking scale and $\barσ$ the spontaneous condensate. More recently, it has been shown that their damping $Ω$ is constrained to follow the relation $Ω=m^2 D_φ$, where $D_φ$ is the Goldstone diffusivity in the purely spontaneous phase. Pions are the most paradigmatic example of pseudo-Goldstone modes and they are related to chiral symmetry breaking in…
In a previous paper, we have analyzed high energy QCD from AdS-CFT and proved the saturation of the Froissart bound (a purely QCD proof of which is still lacking). In this paper we describe the calculation in more physical terms and map it to QCD language. We find a remarkable agreement with the 1952 Heisenberg description of the saturation (pre-QCD!) in terms of shockwave collisions of pion field distributions. It provides a direct map between gauge theory physics and the gravitational physics on the IR brane of the Randall-Sundrum model. Saturation occurs through black hole production on the…
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.
