Complexity growth in a holographic QCD model

In this study,we utilize the complexity-action duality to study the evolution of complexity in a holographic QCD model at finite temperature and chemical potential.By inserting a fundamental string as a probe,we investigated the properties of complexity growth in this Einstein-Maxwell-scalar gravity system,which is affected by the string velocity,chemical potential,and temperature.Our results show that the complexity growth is maximized when the probe string is stationary,and it decreases as the velocity of the string increases.When the string approaches relativistic velocities,the complexity growth always increases monotonically with respect to the chemical potential.Furthermore,we find that the complexity growth can be used to identify phase transitions and crossovers in the model.

Hadron spectra and pion form factor in dynamical holographic QCD model with anomalous 5D mass of scalar field

The simplest version of the dynamical holographic QCD model is described by adding the KKSS model action on a dilaton-graviton coupled background,in which the AdS5 metric is deformed by the gluon condensation and further deformed by the chiral condensation.In this framework,both the chiral symmetry breaking and linear confinement can be realized.The light-flavor hadron spectra and the pion form factor were investigated,but it was difficult to reconcile the light-flavor hadron spectra and pion form factor.By considering the anomalous 5-dimension mass correction of the scalar field from QCD running coupling,it is found that the light flavor hadron spectra and pion form factor can be described well simultaneously.In particular,the ground state and lower excitation states of the scalar,pseudo scalar,and axial vector meson spectra are improved.However,the vector meson spectra are not sensitive to the anomalous 5-dimension mass correction of the scalar field.

Criticality of QCD in a holographic QCD model with critical end point

The thermodynamics of strongly interacting matter near the critical end point are investigated in a holographic QCD model, which can describe the QCD phase diagram in T-μ plane qualitatively. Critical exponents along different axes(α,β,γ,δ) are extracted numerically. It is given that α≈0,β≈0.54,γ≈1.04, and δ≈2.97,which is similar to the three-dimensional Ising mean-field approximation and previous holographic QCD model calculations. We also discuss the possibilities to go beyond the mean field approximation by including the full back-reaction of the chiral dynamics in the holographic framework.

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.

The dynamical holographic QCD method for hadron physics and QCD matter

In this paper we present a short overview on the dynamical holographic QCD(DhQCD)method for hadron physics and QCD matter.The five-dimensional DhQCD model is constructed in the graviton-dilaton-scalar framework with the dilaton background fieldΦand the scalar field X dual to the gluon condensate and the chiral condensate operator thus can represent the gluodynamics(linear confinement)and chiral dynamics(chiral symmetry breaking),respectively.The dilaton background field and the scalar field are a function of the 5th dimension,which plays the role of the energy scale,in this way,the DhQCD model can resemble the renormalization group from ultraviolet(UV)to infrared(IR).By solving the Einstein equation,the metric structure at IR is automatically deformed by the nonperturbative gluon condensation and chiral condensation in the vacuum.We review the results on the hadron spectra including the glueball spectra,the light/heavy meson spectra,as well as on QCD phase transitions,and thermodynamical as well as transport properties in the framework of the DhQCD model.

The entanglement properties of holographic QCD model with a critical end point

We investigated different entanglement properties of a holographic QCD(hQCD)model with a critical end point at the finite baryon density.Firstly,we considered the holographic entanglement entropy(HEE)of this hQCD model in a spherical shaped region and a strip shaped region.It was determined that the HEE of this hQCD model in both regions can reflect QCD phase transition.Moreover,although the area formulas and minimal area equations of the two regions were quite different,the HEE exhibited a similar behavior on the QCD phase diagram.Therefore,we assert that the behavior of the HEE on the QCD phase diagram is independent of the shape of the subregions.However,the HEE is not an ideal parameter for the characterization of the entanglement between different subregions of a thermal system.As such,we investigated the mutual information(MI),conditional mutual information(CMI),and the entanglement of purification(Ep)in different strip shaped regions.We determined that the three entanglement quantities exhibited some universal behavior;their values did not change significantly in the hadronic matter phase but increased rapidly with the increase in T andμin the QGP phase.Near the phase boundary,these three entanglement quantities changed smoothly in the crossover region and continuously but not smoothly at CEP;they exhibited discontinuous behavior in the first phase transition region.These properties can be used to distinguish between the different phases of strongly coupled matter.

Decay constants of pseudoscalar and vector mesons with improved holographic wavefunction

We calculate the decay constants of light and heavy-light pseudoscalar and vector mesons with improved soft-wall holographic wavefuntions, which take into account the effects of both quark masses and dynamical spins. We find that the predicted decay constants, especially for the ratio fV/fP, based on light-front holographic QCD, can be significantly improved, once the dynamical spin effects are taken into account by introducing the helicity-dependent wavefunctions. We also perform detailed χ2 analyses for the holographic parameters （i.e. the mass-scale parameter κ and the quark masses）, by confronting our predictions with the data for the charged-meson decay constants and the meson spectra. The fitted values for these parameters are generally in agreement with those obtained by fitting to the Regge trajectories. At the same time, most of our results for the decay constants and their ratios agree with the data as well as the predictions based on lattice QCD and QCD sum rule approaches, with only a few exceptions observed.

Two-gluon and trigluon glueballs from dynamical holography QCD

We study the scalar, vector and tensor two-gluon and trigluon glueball spectra in the framework of the 5-dimension dynamical holographic QCD model, where the metric structure is deformed self-consistently by the dilaton field. For comparison, the glueball spectra are also calculated in the hard-wall and soft-wall holographic QCD models. In order to distinguish glueballs with even and odd parities, we introduce a positive and negative coupling between the dilaton field and glueballs, and for higher spin glueballs, we introduce a deformed 5-dimension mass. With this set-up, there is only one free parameter from the quadratic dilaton profile in the dynamical holographic QCD model, which is fixed by the scalar glueball spectra. It is found that the two-gluon glueball spectra produced in the dynamical holographic QCD model are in good agreement with lattice data. Among six trigluon glueballs, the produced masses for 1±- and 2-- are in good agreement with lattice data, and the produced masses for 0--, 0＋- and 2＋- are around 1.5 GeV lighter than lattice results. This result might indicate that the three trigluon glueballs of 0--, 0＋- and 2＋- are dominated by the three-gluon condensate contribution.

A holographic description of theta-dependent Yang-Mills theory at finite temperature

Theta-dependent gauge theories can be studied using holographic duality through string theory in certain spacetimes.By this correspondence we consider a stack of N_0 dynamical DO-branes as D-instantons in the background sourced by N_c coincident non-extreme black D4-branes.According to the gauge-gravity duality,this D0-D4 brane system corresponds to Yang-Mills theory with a theta angle at finite temperature.We solve the IIA supergravity action by taking account into a sufficiently small backreaction of the Dinstantons and obtain an analytical solution for our D0-D4-brane configuration.Subsequently,the dual theory in the large N_c limit can be holographically investigated with the gravity solution.In the dual field theory,we find that the coupling constant exhibits asymptotic freedom,as is expected in QCD.The contribution of the theta-dependence to the free energy gets suppressed at high temperatures,which is basically consistent with the calculation using the Yang-Mills instanton.The topological susceptibility in the large N_c limit vanishes,and this behavior remarkably agrees with the implications from the simulation results at finite temperature.Moreover,we finally find a geometrical interpretation of the theta-dependence in this holographic system.

Studying the potential of QQq at finite temperature in a holographic model

Using gauge/gravity duality,we investigate the string breaking and dissolution of two heavy quarks coupled to a light quark at finite temperature.It is found that three configurations of QQq exist with the increase in separation distance for heavy quarks in the confined phase.Furthermore,string breaking occurs at the distance L_(QQq)=1.27 fm(T=0.1 GeV)for the decay mode QQq→QQq+Qq.In the deconfined phase,QQq melts at a certain distance and then becomes free quarks.Finally,we compare the potential of QQq with that of QQ,and it is found that QQ is more stable than QQq at high temperatures.

AdS/QCD and light front holography: A new approximation to QCD

The combination of Anti-de Sitter space （AdS） methods with light-front holography leads to a semi-classical first approximation to the spectrum and wavefunctions of meson and baryon light-quark bound states.Starting from the bound-state Hamiltonian equation of motion in QCD,we derive relativistic lightfront wave equations in terms of an invariant impact variable ζ which measures the separation of the quark and gluonic constituents within the hadron at equal light-front time.These equations of motion in physical space-time are equivalent to the equations of motion which describe the propagation of spin-J modes in anti–de Sitter （AdS） space.Its eigenvalues give the hadronic spectrum,and its eigenmodes represent the probability distributions of the hadronic constituents at a given scale.Applications to the light meson and baryon spectra are presented.The predicted meson spectrum has a string-theory Regge form M^ 2 = 4κ ^2 （n＋L＋S/2）;i.e.,the square of the eigenmass is linear in both L and n,where n counts the number of nodes of the wavefunction in the radial variable ζ.The space-like pion and nucleon form factors are also well reproduced.One thus obtains a remarkable connection between the description of hadronic modes in AdS space and the Hamiltonian formulation of QCD in physical space-time quantized on the light-front at fixed light-front time τ.The model can be systematically improved by using its complete orthonormal solutions to diagonalize the full QCD lightfront Hamiltonian or by applying the Lippmann-Schwinger method in order to systematically include the QCD interaction terms.

Running coupling constant at finite chemical potential and magnetic field from holography

According to gauge/gravity duality,we use an Einstein-Maxwell-dilaton(EMD)model to study the running coupling constant at finite chemical potential and magnetic field.First,we calculate the effect of temperature on the running coupling constant and find the results are qualitatively consistent with lattice guage theory.Subsequently,we calculate the effect of chemical potential and magnetic field on running coupling.It is found that the chemical potential and magnetic field both suppress the running coupling constant.However,the effect of the magnetic field is slightly larger than that of chemical potential for a fixed temperature.Compared with the confinement phase,the magnetic field has a large influence on the running coupling in the deconfinement phase.

A comparison of condensate mass of QCD vacuum between Wilson line approach and Schwinger effect

We studied the condensate mass of QCD vacuum through the duality approach via dilaton wall back-ground in the presence of the parameter c,which represents the condensation in a holographic set up.First,fromWilson line calculation,we found m_(0)^(2)(i.e.,the condensate parameter in mixed non-local condensation),whose beha-vior mimics that of QCD.The value of m_(0)^(2)that we found by this approach is in agreement with QCD data.Second we considered the produced mass m via the Schwinger effect mechanism in the presence of the parameter c.We show that vacuum condensation generally contributes the mass dominantly and that the produced mass via Schwing.er effect is suppressed by m_(0).

Three-quark potential at finite temperature and chemical potential

Using gauge/gravity duality,we study the potential energy and the melting of triply heavy baryon at finite temperature and chemical potential in this paper.First,we calculate the three-quark potential and compare the results with quark-antiquark potential.With the increase of temperature and chemical potential,the potential energy will decrease at large distances.It is found that the three-quark potential will have an endpoint at high temperature and/or large chemical potential,which means triply heavy baryons will melt at enough high temperature and/or large chemical potential.We also discuss screening distance which can be extracted from the three-quark potential.At last,we draw the melting diagram of triply heavy baryons in the T-μplane.

Moving doubly heavy baryon in a strongly coupled plasma via holography

Gauge/gravity duality is used to study the properties of the doubly heavy baryon(QQq)at finite rapidity and temperature in heavy-ion collisions.We investigate the impact of rapidity on string breaking and screening of QQq and compare these effects with the results for QQ¯in detail.Computations reveal that the string-breaking distances of QQq and QQ¯are close in the confined state,and the effects of rapidity and temperature on the string breaking are not significant.An interesting result shows that QQq cannot be determined at sufficiently high temperatures and rapidities.However,QQ¯can exist under any conditions as long as the separation distance is sufficiently small.Furthermore,the screening distances of QQq and QQ¯are compared at finite rapidity and temperature.Based on the above analysis,we infer that QQ¯is more stable than QQq at finite rapidity and temperature.

On the Next-leading order Heavy-Quark Potential from AdS/CFT

Applying the AdS/CFT correspondence,the expansion of the heavy-quark potential of N = 4 supersymmetric Yang-Mills theory at large N c is carried out to the next-leading term in the large ’t Hooft coupling at zero temperature.The strong coupling corresponds to the semi-classical expansion of the stringsigma model,the gravity dual of the Wilson loop operator,with the next-leading term expressed in terms of functional determinants of fluctuations.The singularities of these determinants are examined and their contributions are evaluated numerically.We find the next-leading order correction is negative and suppressed by minus square root of the ’t Hooft coupling relative to the leading order.