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Search Results: 1 - 10 of 3164 matches for " Pengfei Zhuang "
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Multiplicity Moments and Hard Processes in Relativistic Heavy Ion Collisions
Pengfei Zhuang
Physics , 2001, DOI: 10.1103/PhysRevC.66.064901
Abstract: The normalized multiplicity moments and their relation with soft and hard processes in relativistic heavy ion collisions are analyzed in a general two-component model. It is found that, the strong fluctuations in binary collision number N_c in minimum-bias events can enhance the hard component, especially for the higher order moments. This enhancement can not be effectively described by modifying the participant number in the one-component model.
Low-momentum Pion Enhancement Induced by Chiral Symmetry Restoration
Pengfei Zhuang
Physics , 2003, DOI: 10.1142/S0217751X04016490
Abstract: The thermal and nonthermal pion production by sigma decay and its relation with chiral symmetry restoration in a hot and dense matter are investigated. The nonthermal decay into pions of sigma mesons which are popularly produced in chiral symmetric phase leads to a low-momentum pion enhancement as a possible signature of chiral phase transition at finite temperature and density.
Relativistic BCS-BEC Crossover at Zero Temperature
He, Lianyi;Zhuang, Pengfei
High Energy Physics - Phenomenology , 2007, DOI: 10.1103/PhysRevD.75.096003
Abstract: We investigate the BCS-BEC crossover at zero temperature in the frame of a relativistic model. The universality of the BCS-BEC crossover for non-relativistic systems breaks down in relativistic case and the crossover can be induced by changing the density. When the effective scattering length is much less than the fermion Compton wavelength, we recover the non-relativistic result if the gas is initially in non-relativistic state. At ultra-strong coupling where the scattering length is of the order of the Compton wavelength, a new BEC state appears. In this state the condensed bosons become nearly massless and anti-fermions are excited. The behavior of the Goldstone mode and the mixing between the amplitude and phase modes are significantly different in different condensed regions.
Relativistic BCS-BEC Crossover at Finite Temperature and Its Application to Color Superconductivity
He, Lianyi;Zhuang, Pengfei
High Energy Physics - Phenomenology , 2007, DOI: 10.1103/PhysRevD.76.056003
Abstract: The non-relativistic $G_0 G$ formalism of BCS-BEC crossover at finite temperature is extended to relativistic fermion systems. The uncondensed pairs contribute a pseudogap to the fermion excitations. The theory recovers the BCS mean field approximation at zero temperature and the non-relativistic results in a proper limit. For massive fermions, when the coupling strength increases, there exist two crossovers from the weak coupling BCS superfluid to the non-relativistic BEC state and then to the relativistic BEC state. For color superconductivity at moderate baryon density, the matter is in the BCS-BEC crossover region, and the behavior of the pseudogap is quite similar to that found in high temperature superconductors.
Chiral Phase Transition beyond Mean Field Approximation
He, Lianyi;Zhuang, Pengfei
High Energy Physics - Phenomenology , 2007,
Abstract: Based on the analogy between the Nambu--Jona-Lasinio model of chiral symmetry breaking and the BCS theory of superconductivity, we investigate the effect of $\bar q q$ pair fluctuations on the chiral phase transition. We include uncondensed $\bar q q$ pairs at finite temperature and chemical potential in a self-consistent T-matrix formalism, the so-called $G_0 G$ scheme. The pair fluctuations reduce significantly the critical temperature and make quarks massive above the critical temperature.
Stable Sarma State in Two-band Fermi Systems
Lianyi He,Pengfei Zhuang
Physics , 2008, DOI: 10.1103/PhysRevB.79.024511
Abstract: We investigate fermionic superconductivity with mismatched Fermi surfaces in a general two-band system. The exchange interaction between the two bands changes significantly the stability structure of the pairing states. The Sarma state with two gapless Fermi surfaces which is always unstable in single-band systems, can be the stable ground state in two-band systems. To realize a visible mismatch window for the stable Sarma state, two conditions should be satisfied: a nonzero inter-band exchange interaction and a large asymmetry between the two bands.
Equal-Time Hierarchies for Quantum Transport Theory
Pengfei Zhuang,Ulrich Heinz
Physics , 1996, DOI: 10.1103/PhysRevD.57.6525
Abstract: We investigate in the equal-time formalism the derivation and truncation of infinite hierarchies of equations of motion for the energy moments of the covariant Wigner function. From these hierarchies we then extract kinetic equations for the physical distribution functions which are related to low-order energy moments, and show how to determine the higher order moments in terms of these lowest order ones. We apply the general formalism to scalar and spinor QED with classical background fields and compare with the results derived from the three-dimensional Wigner transformation method.
Leakage Effect on J/psi Pt Distributions in Different Centrality Bins for Pb-Pb Collisions at E/A=160 GeV
Pengfei Zhuang,Xianglei Zhu
Physics , 2003, DOI: 10.1103/PhysRevC.67.067901
Abstract: A transport approach including a leakage effect for J/psi's in the transverse phase space is used to calculate the ratios between the J/psi transverse momentum distributions in several centrality bins for Pb-Pb collisions at E/A = 160 GeV. From the comparison with the CERN-SPS data, where the centrality is characterized by the transverse energy Et, the leakage effect is extremely important in the region of high transverse momentum and high transverse energy, and both the threshold and the comover models can describe the ratio well for all centrality bins except the most central one (Et < 100 GeV), for which the comover model calculation is considerably better than the threshold one.
Relativistic BCS-BEC Crossover at Finite Temperature and Its Application to Color Superconductivity
Lianyi He,Pengfei Zhuang
Physics , 2007, DOI: 10.1103/PhysRevD.76.056003
Abstract: The non-relativistic $G_0 G$ formalism of BCS-BEC crossover at finite temperature is extended to relativistic fermion systems. The uncondensed pairs contribute a pseudogap to the fermion excitations. The theory recovers the BCS mean field approximation at zero temperature and the non-relativistic results in a proper limit. For massive fermions, when the coupling strength increases, there exist two crossovers from the weak coupling BCS superfluid to the non-relativistic BEC state and then to the relativistic BEC state. For color superconductivity at moderate baryon density, the matter is in the BCS-BEC crossover region, and the behavior of the pseudogap is quite similar to that found in high temperature superconductors.
Meson Mixing in Pion Superfluid
Xuewen Hao,Pengfei Zhuang
Physics , 2006, DOI: 10.1016/j.physletb.2007.07.011
Abstract: We investigate meson mixing and meson coupling constants in pion superfluid in the framework of two flavor NJL model at finite isospin density. The mixing strength develops fast with increasing isospin chemical potential, and the coupling constants in normal phase and in the pion superfluid phase behave very differently.
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