Mei Huang

Inverse magnetic catalysis induced by sphalerons

The recently discovered inverse magnetic catalysis around the critical temperature indicates that some important information is missing in our current understanding of conventional chiral dynamics of QCD, which is enhanced by the magnetic field. In this work, we provide a mechanism to explain that the inverse magnetic catalysis around T-c is induced by sphalerons. At high temperatures, sphaleron transitions between distinct classical vacua cause an asymmetry in the chiral number density due to the axial anomaly of QCD. In the presence of a strong magnetic field, the chiral imbalance is enhanced and destroys the pairings between the different chiralities, which naturally lowers the critical temperature of the chiral phase transition for increasing magnetic field. The inverse magnetic catalysis at finite baryon density and the critical end point in the presence of a strong magnetic field is also explored in this work.

Thermodynamics of deformed AdS 5 model with a positive/negative quadratic correction in graviton-dilaton system

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 framework, we solve the black-hole background, the corresponding dilaon field and the dilaton potential for the deformed AdS5 model with a positive/negative quadratic correction. We systematically investigate the thermodynamical properties of the deformed AdS5 model with a positive and negative quadratic correction, respectively, and compare with lattice QCD on the results of the equation of state, the heavy quark potential, the Polyakov loop and the spatial Wilson loop. We find that the bulk thermodynamical properties are not sensitive to the sign of the quadratic correction, and the results of both deformed holographic QCD models agree well with lattice QCD result for pure SU(3) gauge theory. However, the results from loop operators favor a positive quadratic correction, which agree well with lattice QCD result. Especially, the result from the Polyakov loop excludes the model with a negative quadratic correction in the warp factor of AdS5.

Confront holographic QCD with Regge trajectories of vectors and axial-vectors

By matching the predictions of the Dp–Dq soft-wall model in type II superstring theory with the spectra of vector and axial-vector mesons, we show the dependence of the Regge trajectories parameters on the metric parameters of the model. From the experimental results of Regge parameters for vector mesons, it is found that the D3 background brane with both q=5 and q=7 probe brane and D4 background brane with q=4 probe brane are close to the realistic holographic QCD. We also discuss how to realize chiral symmetry breaking in the vacuum and asymptotic chiral symmetry restoration in high excitation states. We find that the constant component of the 5-dimension mass square of axial-vector mesons plays an efficient role to realize the chiral symmetry breaking, and a small negative z4 correction in the 5-dimension mass square is helpful to realize the chiral symmetry restoration in high excitation states.

Spontaneous generation of local CP violation and inverse magnetic catalysis

In the chiral symmetric phase, the polarized instanton--anti-instanton molecule pairing induces a nontrivial repulsive interaction in the iso-scalar axial-vector channel. As a consequence, one unusual property is observed that in the chiral restoration phase, there is a first order phase transition for the spontaneous generation of local CP violation and chiral imbalance. Furthermore, it is found that external magnetic fields will lower the critical temperature for the local CP-odd phase transition and catalyze the chiral imbalance, which destroys the chiral condensate with pairing quarks between different chiralities. A reasonable strength of the repulsive interaction in the iso-scalar axial-vector channel can naturally explain the inverse magnetic catalysis around the critical temperature under external magnetic fields.

A dynamical soft-wall holographic QCD model for chiral symmetry breaking and linear confinement

A self-consistent dynamical soft-wall holographic QCD model is formulated in the framework of graviton–dilaton–scalar system, which can realize both chiral symmetry breaking and confinement, two of the most important phenomena of QCD. The scalar field corresponds to the quark–antiquark condensate and can explain the property of chiral dynamics. The quadratic dilaton background field ϕ=μ2z2 as in the original soft-wall model can accommodate two aspects in the manifestation of color confinement, i.e. the Regge spectra of hadrons and the linear potential between quarks. It is observed that both the slope of the Regge spectra and the string tension of the quark potential are proportional to μ2. More interesting observation is that the best fitted value of μ is around the dynamical gluon mass extracted from lattice data. It is also shown that the negative dilaton background ϕ=−μ2z2 can be safely excluded in this framework.

Dynamical holographic QCD model for glueball and light meson spectra

A bstractIn 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

Phase diagram and thermodynamics of the Polyakov linear sigma model with three quark flavors

\Phi =\mu_G^2{z^2}

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

and

Chiral phase transition in the soft-wall model of AdS/QCD

\Phi =\mu_G^2{z^2} \tanh \left( {{{{\mu {{{_{{{G^2}}}^4}}^z}^2}} \left/ {{\mu_G^2}} \right.}} \right)

Realization of chiral symmetry breaking and restoration in holographic QCD

, 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.