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Subjects: Physics >> Condensed Matter: Structural, Mechanical and Thermal Properties

Chiral Phase Transition in the Soft-Wall Model of AdS/QCD

Kaddour Chelabi; Zhen Fang; Mei Huang; Danning Li; Yue-Liang WuaSubjects: Physics >> Nuclear Physics

We investigate the chiral phase transition in the soft-wall model of AdS/QCD at zero chemical potential for two-flavor and three-flavor cases, respectively. We show that there is no spontaneous chiral symmetry breaking in the original soft-wall model. After detailed analysis, we find that in order to realize chiral symmetry breaking and restoration, both profiles for the scalar potential and the dilaton field are essential. The scalar potential determines the possible solution structure of the chiral condensate, except the mass term, it takes another quartic term for the two-flavor case, and for the three-flavor case, one has to take into account an extra cubic term due to the t'Hooft determinant interaction. The profile of the dilaton field reflects the gluodynamics, which is negative at a certain ultraviolet scale and approaches positive quadratic behavior at far infrared region. With this set-up, the spontaneous chiral symmetry breaking in the vacuum and its restoration at finite temperature can be realized perfectly. In the two-flavor case, it gives a second order chiral phase transition in the chiral limit, while the transition turns to be a crossover for any finite quark mass. In the case of three-flavor, the phase transition becomes a first order one in the chiral limit, while above sufficient large quark mass it turns to be a crossover again. This scenario agrees exactly with the current understanding on chiral phase transition from lattice QCD and other effective model studies. |

Realization of chiral symmetry breaking and restoration in holographic QCD

Kaddour Chelabi; Zhen Fang; Mei Huang; Danning Li; Yue-Liang WuSubjects: Physics >> Nuclear Physics

With proper profiles of the scalar potential and the dilaton field, for the first time, the spontaneous chiral symmetry breaking in the vacuum and its restoration at finite temperature are correctly realized in the holographic QCD framework. In the chiral limit, a nonzero chiral condensate develops in the vacuum and decreases with temperature, and the phase transition is of 2nd order for two-flavor case and of 1st order for three-flavor case. In the case of explicit chiral symmetry breaking, in two-flavor case, the 2nd order phase transition turns to crossover with any nonzero current quark mass, and in three-flavor case, the 1st order phase transition turns to crossover at a finite current quark mass. The correct description of chiral symmetry breaking and restoration makes the holographic QCD models more powerful in dealing with non-perturbative QCD phenomena. This framework can be regarded as a general set up in application of AdS/CFT to describe conventional Ginzburg-Landau-Wilson type phase transitions, e.g. in condensed matter and cosmology systems. |

Topological susceptibility near T$_c$ in SU(3) gauge theory

Guang-Yi Xiong; Jian-Bo Zhang; Ying Chen; Chuan Liu; Yu-Bin Liu; Jian-Ping MaSubjects: Physics >> Nuclear Physics

Topological charge susceptibility?χt?for pure gauge SU(3) theory at finite temperature is studied using anisotropic lattices. The over-improved stout-link smoothing method is utilized to calculate the topological charge. Near the phase transition point we find a rapid declining behavior for?χt?with values decreasing from?(188(1)MeV)4?to?(67(3)MeV)4?as the temperature increased from zero temperature to?1.9Tc?which demonstrates the existence of topological excitations far above?Tc. The 4th order cumulant?c4?of topological charge, as well as the ratio?c4/χt?are also investigated. Results of?c4?show step-like behavior near?Tc?while the ratio at high temperature agrees with the value as predicted by the diluted instanton gas model. |

Efficient numerical evaluation of Feynman integrals

Zhao Li; Jian Wang; Qi-Shu Yan; Xiaoran ZhaoSubjects: Physics >> Nuclear Physics

Feynman loop integrals are a key ingredient for the calculation of higher order radiation effects, and are responsible for reliable and accurate theoretical prediction. We improve the efficiency of numerical integration in sector decomposition by implementing a quasi-Monte Carlo method associated with the CUDA/GPU technique. For demonstration we present the results of several Feynman integrals up to two loops in both Euclidean and physical kinematic regions in comparison with those obtained from FIESTA3. It is shown that both planar and non-planar two-loop master integrals in the physical kinematic region can be evaluated in less than half a minute with?O(10?3)accuracy, which makes the direct numerical approach viable for precise investigation of higher order effects in multi-loop processes, e.g. the next-to-leading order QCD effect in Higgs pair production via gluon fusion with a finite top quark mass. |

Subjects: Physics >> Nuclear Physics

The robust conjugate direction search (RCDS) method has high tolerance to noise in beam experiments. It has been demonstrated that this method can be used to optimize the machine performance of a light source online. In our study, taking BEPCII as an example, the feasibility of online tuning of the luminosity in a circular collider is explored, through numerical simulation and preliminary online experiments. It is shown that the luminosity that is artificially decreased by a deviation of beam orbital offset from optimal trajectory can be recovered with this method. |

Fluid/gravity correspondence: Second order transport coefficients in compactified D4-branes

Chao Wu; Yidian Chen; Mei HuangSubjects: Physics >> Nuclear Physics

We develop the boundary derivative expansion (BDE) formalism of fluid/gravity correspondence to nonconformal version through the compactified, near-extremal black D4-brane. We offer an explicit calculation of 9 second order transport coefficients, i.e., the?τπ,?τ?π,?τΠ,?λ1,2,3?and?ξ1,2,3?for the strongly coupled, uncharged and nonconformal relativistic fluid which is the holographic dual of compactified, near extremal black D4-brane. We also show that the nonconformal fluid considered in this work is free of causal problem and admits the relation?4λ1?λ2=2ητπ. |

Possible formation of high temperature superconductor at early stage of heavy-ion collisions

Hao Liu; Lang Yu; Maxim Chernodu; Mei HuangSubjects: Physics >> Nuclear Physics

We investigate the effect of the inverse magnetic catalysis (IMC) on the charged?ρ?meson condensation at finite temperature in the framework of the Nambu--Jona-Lasinio model, where mesons are calculated to the leading order of?1/Nc?expansion by summing up infinity quark-loops. IMC for chiral condensate has been considered in three different ways, i.e. fitting Lattice data, using the running coupling constant and introducing the chiral chemical potential, respectively. It is observed that, with no IMC effect included, the critical magnetic field?eBc?for charged?ρ?condensation increases monotonically with the temperature. However, including IMC substantially affects the polarized charged?ρ?condensation around the critical temperature?Tc?of chiral phase transition, the critical magnetic field?eBc?for charged?ρ?condensation decreases with the temperature firstly, reaches to a minimum value around?Tc, then increases with the temperature. Our calculation indicates that the charged?ρ?condensation can exist in the temperature region of?1?1.5Tc?with critical magnetic field?eBc?0.15?0.3GeV2, which suggests that high temperature superconductor might be created through non-central heavy ion collisions at LHC energies. We also show that a growing electric conductivity in early stage of non-central heavy-ion collisions substantially delays the decay of strong magnetic field, which is helpful for the formation of the high temperature superconductor. |

[1 Pages/ 8 Totals]