Hadrons from a hard wall AdS/QCD model

We review a recent work on masses of mesons and nucleons within a hard wall model of holographic QCD in a unified approach.In order to treat meson and nucleon properties on the same footing,we introduced the same infrared(IR)cut for both sectors.In framework of present approach,the best fit to the experimental data is achieved introducing the anomalous dimension for baryons.     

Jet quenching parameter from a soft wall AdS/QCD model

We study the effect of chemical potential and nonconformality on the jet quenching parameter in a holographic QCD model with conformal invariance broken by background dilaton. The presence of chemical potential and nonconformality both increase the jet quenching parameter, thus enhancing the energy loss, consistently with the findings of the drag force.     

Scalar glueball in a soft-wall model of AdS/QCD

The scalar glueball is investigated in a soft-wall model of AdS/QCD.Constraints of the mass of the scalar glueball are given through an analysis of a relation between the bulk mass and the anomalous dimension.The mass of the ground scalar glueball is located at 0.96_(-0.07)~(+0.04)GeVmGl.36_(-0.10)~(+0.05)GeV.In terms of a background dilaton fieldΦ(z)=cz~2,the two-point correlation function for the scalar gluon operator is obtained.The two-point correlation function at△=4 gives a different behavior compared with the one in QCD.     

Trouble finding the optimal AdS/QCD

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.     

Finite temperature effect in infrared-improved AdS/QCD model with back reaction of bulk vacuum

Based on an IR-improved soft-wall AdS/QCD model for mesons,which provides a consistent prediction for the mass spectra of resonance scalar,pseudoscalar,vector and axial-vector mesons,we investigate its finite temperature effect.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 and 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_c≈150 ± 7 MeV.which is consistent with the recent results from lattice QCD simulations.     

Equation of state and chiral transition in soft-wall AdS/QCD with a more realistic gravitational background

We construct an improved soft-wall AdS/QCD model with a cubic coupling term of the dilaton and the bulk scalar field. The background fields in this model are solved by the Einstein-dilaton system with a nontrivial dilaton potential, which has been shown to reproduce the equation of state from the lattice QCD with two flavors. The chiral transition behaviors are investigated in the improved soft-wall AdS/QCD model with the solved gravitational background, and the crossover transition can be realized. Our study provides the possibility to address the deconfining and chiral phase transitions simultaneously in the bottom-up holographic framework.     

[Review] An Introduction to AdS/CFT Correspondence forPhenomenologists

We give a brief introduction to the AdS/CFT correspondence and its application to QCD physics, especially its application in the study of quark-gluon-plasma(QGP) formed in the relativistic heavy ion collision (RHIC). This review is based on the talksgiven in several schools and programs for the phenomenologists working on nuclear physicsand particle physics.     

Hadrons in dense QCD

The theoretical foundation of the in-medium hadron properties is discussed from the point of view of the QCD spectral functions. The dynamical models of in-medium hadrons proposed so far are also summarized.     

Holographic models of the scalar sector of QCD

We investigate the AdS/QCD duality for the two-point correlation functions of the lowest dimension scalar meson and scalar glueball operators,in the case of the Soft Wall holographic model of QCD.Masses and decay constants as well as gluon condensates are compared to their QCD estimates.In particular,the role of the boundary conditions for the bulk-to-boundary propagators is emphasized.     

Holographic models of the scalar sector of QCD

We investigate the AdS/QCD duality for the two-point correlation functions of the lowest dimension scalar meson and scalar glueball operators,in the case of the Soft Wall holographic model of QCD.Masses and decay constants as well as gluon condensates are compared to their QCD estimates.In particular,the role of the boundary conditions for the bulk-to-boundary propagators is emphasized.     

Quark dynamics, thermal QCD, and the gravity dual

We perform a holographic renormalization of the supergravity action and compute the stress tensor of the dual gauge theory incorporating the logarithmic running of the gauge coupling. From the stress tensor we obtain the shear viscosity and the entropy of the medium at temperature T, and investigate the ratio η/s.     

Holographic Schwinger effect in a soft wall AdS/QCD model

We perform a potential analysis for the holographic Schwinger effect in a deformed AdS5 model with conformal invariance broken by a background dilaton.We evaluated the static potential by analyzing the classical action of a string attached to a rectangular Wilson loop on a probe D3 brane located at an intermediate position in the bulk AdS space.We observed that the inclusion of the chemical potential tends to enhance the production rate,which is opposite to the effect of the confining scale.In addition,we calculated the critical electric field based on the Dirac-Born-Infeld(DBI)action.     

AdS/QCD and Applications of Light-Front Holography

Light-front holography leads to a rigorous connection between hadronic amplitudes in a higher dimensional anti-de Sitter(AdS) space and frame-independent light-front wavefunctions of hadrons in(3 + 1)-dimensional physical space-time,thus providing a compelling physical interpretation of the AdS/CFT correspondence principle and AdS/QCD,a useful framework which describes the correspondence between theories in a modified AdS 5 background and confining field theories in physical space-time.To a first semiclassical approximation,where quantum loops and quark masses are not included,this approach leads to a single-variable light-front Schro¨dinger equation which determines the eigenspectrum and the light-front wavefunctions of hadrons for general spin and orbital angular momentum.The coordinate z in AdS space is uniquely identified with a Lorentz-invariant coordinate ζ which measures the separation of the constituents within a hadron at equal light-front time.The internal structure of hadrons is explicitly introduced and the angular momentum of the constituents plays a key role.We give an overview of the light-front holographic approach to strongly coupled QCD.In particular,we study the photon-to-meson transition form factors(TFFs) FMγ(Q 2) for γ→ M using light-front holographic methods.The results for the TFFs for the η and η ' mesons are also presented.Some novel features of QCD are discussed,including the consequences of confinement for quark and gluon condensates.A method for computing the hadronization of quark and gluon jets at the amplitude level is outlined.     

Exotic and excited-state meson spectroscopy and radiative transitions from lattice QCD

We discuss recent progress in extracting the excited meson spectrum and radiative transition form factors from lattice QCD.We mention results in the charmonium sector,including the first lattice QCD calculation of radiative transition rates involving excited charmonium states,highlighting results for high spin and exotic states.We present recent results on a highly excited isovector meson spectrum from dynamical anisotropic lattices.Using carefully constructed operators we show how the continuum spin of extracted states can be reliably identified and confidently extract excited states,states with exotic quantum numbers and states of high spin.This spectrum includes the first spin-four state extracted from lattice QCD.We conclude with some comments on future prospects.     

Exotic and excited-state meson spectroscopy and radiative transitions from lattice QCD

We discuss recent progress in extracting the excited meson spectrum and radiative transition form factors from lattice QCD.We mention results in the charmonium sector,including the first lattice QCD calculation of radiative transition rates involving excited charmonium states,highlighting results for high spin and exotic states.We present recent results on a highly excited isovector meson spectrum from dynamical anisotropic lattices.Using carefully constructed operators we show how the continuum spin of extracted states can be reliably identified and confidently extract excited states,states with exotic quantum numbers and states of high spin.This spectrum includes the first spin-four state extracted from lattice QCD.We conclude with some comments on future prospects.     

Logarithmic corrections to entropy and AdS/CFT

We calculate the correction to the Bekenstein-Hawking entropy formula for five-dimensional AdS-Schwarzschild black holes due to thermodynamic fluctuations. The result is then compared with the boundary gauge theory entropy corrections via AdS/CFT correspondence.     

Comparing AdS/CFT dipole model to HERA F2 data

We apply an AdS/CFT-inspired color-dipole model which contains only three free parameters to describe the HERA data for the inclusive structure function F 2 at small Bjorken-x and virtuality.We found that the saturation scale in our AdS/CFT-based parameterization varies in the range of 1 ÷ 3 GeV becoming independent of energy/Bjorken-x at very small x.This leads to the prediction of x-independence of the structure functions at very small x.With the fitted parameters in our model,the predictions for F 2,longitudinal structure function,charm structure function and total photo-production cross-sections in the kinematic regions of future experiments can be given.