Dynamical Holographic QCD Model Research Articles

Dynamical holographic QCD model for spontaneous chiral symmetry breaking and confinement

Dynamical holographic QCD model for spontaneous chiral symmetry breaking and confinement

Anisotropic and frame dependent chaos of suspended strings from a dynamical holographic QCD model with magnetic field

We investigate both from a qualitative as well as quantitative perspective the emergence of chaos in the QCD confining string in a magnetic field from a holographic view-point. We use an earlier developed bottom-up solution of the Einstein-Maxwell-Dilaton action that mimics QCD and its thermodynamics quite well. Surprisingly, our predictions depend on the used frame: the magnetic field tends to suppress the chaos in both perpendicular and parallel directions relative to the magnetic field in the string frame whilst in the Einstein frame, the chaos suppression only happens in the perpendicular direction, with an enhanced chaos along the magnetic field. The amount of suppression/enhancement in both frames does depend on the relative orientation of the string and magnetic field.

Hadron spectra and pion form factor in dynamical holographic QCD model with anomalous 5D mass of scalar field* *Supported in part by the National Natural Science Foundation of China (NSFC) (12235016, 12221005, 11725523, 11735007, 12275108), the Strategic Priority Research Program of Chinese Academy of Sciences (XDB34030000, XDPB15), the start-up funding from University of Chinese Academy of Sciences (UCAS), and the

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 AdS 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.

Chiral transition in the probe approximation from an Einstein-Maxwell-dilaton gravity model

We refine an earlier introduced 5-dimensional gravity solution capable of holographically capturing several qualitative aspects of (lattice) QCD in a strong magnetic background such as the anisotropic behaviour of the string tension, inverse catalysis at the level of the deconfinement transition or sensitivity of the entanglement entropy to the latter. Here, we consistently modify our solution of the considered Einstein-Maxwell-dilaton system to not only overcome an unphysical flattening at large distances in the quark-antiquark potential plaguing earlier work, but also to encapsulate inverse catalysis for the chiral transition in the probe approximation. This brings our dynamical holographic QCD model yet again closer to a stage at which it can be used to predict magnetic QCD quantities not directly computable via lattice techniques.

Quarkyonic phase from quenched dynamical holographic QCD model

Chiral and deconfinement phase transitions at finite temperature T and quark number chemical potential μ are simultaneously studied in the quenched dynamical holographic QCD model within the Einstein-Dilaton-Maxwell framework. By calculating the corresponding order parameters, i.e., the chiral condensate and Polyakov loop, it is shown that the transition lines of these two phase transitions are separated in the T − μ plane. The deconfinement phase transition is shown to be always of crossover type and the transition line depends weakly on the baryon number density. Differently, the chiral transition is of crossover at small baryon number density and it turns to be of first order at sufficient large baryon number density. A critical endpoint (CEP), at which the transition becomes second order type, appears in the chiral transition line. This is the first time to realize the CEP of chiral phase transition in the (T, μ) plane using the holographic EMD (Einstein-Maxwell-Dilaton) model for two flavour case. It is observed that between these two phase transition lines, there is a region with chiral symmetry restored and color degrees still confined, which could be considered as the quarkyonic phase. Qualitatively, this behavior is in consistent with the result in the Polyakov-loop improved Nambu-Jona-Lasinio (PNJL) model.

Gravitation waves from QCD and electroweak phase transitions

We investigate the gravitation waves produced from QCD and electroweak phase transitions in the early universe by using a 5-dimension holographic QCD model and a holographic technicolor model. The dynamical holographic QCD model is to describe the pure gluon system, where a first order confinement-deconfinement phase transition can happen at the critical temperature around 250 MeV. The minimal holographic technicolor model is introduced to model the strong dynamics of electroweak, it can give a first order electroweak phase transition at the critical temperature around 100-360 GeV. We find that for both GW signals produced from QCD and EW phase transitions, in the peak frequency region, the dominant contribution comes from the sound waves, while away from the peak frequency region the contribution from the bubble collision is dominant. The peak frequency of gravitation wave determined by the QCD phase transition is located around 10−7 Hz which is within the detectability of FAST and SKA, and the peak frequency of gravitational wave predicted by EW phase transition is located at 0.002 – 0.007 Hz, which might be detectable by BBO, DECIGO, LISA and ELISA.

Two-gluon and trigluon glueballs from dynamical holography QCD**Supported by the NSFC (11175251, 11621131001), DFG and NSFC (CRC 110), CAS Key Project KJCX2-EW-N01, K.C.Wong Education Foundation, and Youth Innovation Promotion Association of CAS

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.

Strongly interacting matter from holographic QCD model

We introduce the 5-dimension dynamical holographic QCD model, which is constructed in the graviton-dilaton-scalar framework with the dilaton background field $\Phi$ and the scalar field $X$ responsible for the gluodynamics and chiral dynamics, respectively. We review our results on the hadron spectra including the glueball and light meson spectra, QCD phase transitions and transport properties in the framework of the dynamical holographic QCD model.

Temperature dependent transport coefficients in a dynamical holographic QCD model

We investigate temperature dependent behavior of various transport coefficients in a dynamical holographical QCD model. We show the nontrivial temperature dependent behavior of the transport coefficients, like bulk viscosity, electric conductivity as well as jet quenching parameter, and it is found that all these quantities reveal information of the phase transition. Furthermore, with introducing higher derivative corrections in 5D gravity, the shear viscosity over entropy density ratio also shows a valley around phase transition, and it is found that the shear viscosity over entropy density ratio times the jet quenching over temperature cubic ratio almost remains as a constant above phase transition, and the value is two times larger than the perturbative result in Phys.Rev.Lett.99.192301(2007).

Enhancement of jet quenching around phase transition: Result from the dynamical holographic model

The phase transition and jet quenching parameter $\stackrel{^}{q}$ are investigated in the framework of the dynamical holographic QCD model. We find that both the trace anomaly and the ratio of the jet quenching parameter over cubic temperature $\stackrel{^}{q}/{T}^{3}$ show a peak around the critical temperature ${T}_{c}$, and the ratio of the jet quenching parameter over entropy density $\stackrel{^}{q}/s$ sharply rises at ${T}_{c}$. This indicates that the jet quenching parameter can characterize the phase transition. The effect of the jet quenching parameter enhancement around the phase transition on the nuclear modification factor ${R}_{AA}$ and elliptic flow ${v}_{2}$ are also analyzed, and we find that the temperature-dependent jet quenching parameter from the dynamical holographic QCD model can considerably improve the description of jet quenching azimuthal anisotropy as compared with the conformal case.

Dynamical holographic QCD model

We develop a dynamical holographic QCD model, which resembles the renormalization group from ultraviolet (UV) to infrared (IR). The dynamical holographic model is constructed in the graviton-dilaton-scalar framework with the dilaton background field $\Phi$ and scalar field $X$ responsible for the gluodynamics and chiral dynamics, respectively. We summarize our results on hadron spectra, QCD phase transition and transport properties including the jet quenching parameter and the shear/bulk viscosity in the framework of the dynamical holographic QCD model.

Dynamical holographic QCD model for glueball and light meson spectra

In this work, we offer a dynamical soft-wall model to describe the gluodynamics and chiral dynamics in one systematical framework. We firstly construct a quenched dynamical holographic QCD (hQCD) model in the graviton-dilaton framework for the pure gluon system, then develop a dynamical hQCD model for the two flavor system in the graviton-dilaton-scalar framework by adding light flavors on the gluodynamical background. For two forms of dilaton background field $\Phi=\mu_G^2z^2$ and $\Phi=\mu_G^2z^2\tanh(\mu_{G^2}^4z^2/\mu_G^2)$, the quadratic correction to dilaton background field at infrared encodes important non-perturbative gluodynamics and naturally induces a deformed warp factor of the metric. By self-consistently solving the deformed metric induced by the dilaton background field, we find that the scalar glueball spectra in the quenched dynamical model is in very well agreement with lattice data. For two flavor system in the graviton-dilaton-scalar framework, the deformed metric is self-consistently solved by considering both the chiral condensate and nonperturbative gluodynamics in the vacuum, which are responsible for the chiral symmetry breaking and linear confinement, respectively. It is found that the mixing between the chiral condensate and gluon condensate is important to produce the correct light flavor meson spectra. The pion form factor and the vector couplings are also investigated in the dynamical hQCD model. Besides, we give the criteria for the existence of linear quark potential from the metric structure, and show a negative quadratic dilaton background field is not favored in the graviton-dilaton framework.

Scalar mesons within a dynamical holographic QCD model

We show that the infrared dynamics of string modes dual to q q ¯ states within a Dynamical AdS/QCD model of coupled dilaton-gravity background gives the Regge-like spectrum of f 0 's scalars and higher spin mesons consistent with experimental data. The pion mass and its trajectory were also described with a scale deformation of the metric and a rescaled string mass. The available experimental decay widths of the S → P P decays provided a complementary check of the proposed classification scheme for f 0 ( 980 ) , f 0 ( 1370 ) , f 0 ( 1500 ) and f 0 ( 1710 ) as radial excitations of f 0 ( 600 ) . For f 0 ( 980 ) we estimated a mixing angle of ± 20 o with other structures.