arXiv subjects

Pengfei Zhuang

Publications and source records attributed to Pengfei Zhuang.

At least 127 records · Page 7Linked to original sources

arXiv2007

Asymmetric Fermion Superfluid with Inter- and Intra-Species Pairings

We investigate the phase structure of an asymmetric fermion superfluid with inter- and intra-species pairings. The introduction of the intra-species pairing mechanism in canonical ensemble changes significantly the phase diagram and brings in a new state with coexisting inter- and intra-species pairings. Different from the case with only inter-species pairing, all the fermion excitations are fully gapped in the region with intra-species pairing.

cond-mat.supr-con↗

arXiv2007

Chiral Phase Transition beyond Mean Field Approximation

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.

hep-ph↗

arXiv2007

Relativistic BCS-BEC Crossover at Finite Temperature and Its Application to Color Superconductivity

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.

hep-ph↗

arXiv2007

Meson Mixing in Pion Superfluid

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.

hep-ph↗

arXiv2007

Hadronization Approach for a Quark-Gluon Plasma Formed in Relativistic Heavy Ion Collisions

A transport model is developed to describe hadron emission from a strongly coupled quark-gluon plasma formed in relativistic heavy ion collisions. The quark-gluon plasma is controlled by ideal hydrodynamics, and the hadron motion is characterized by a transport equation with loss and gain terms. The two sets of equations are coupled to each other, and the hadronization hypersurface is determined by both the hydrodynamic evolution and the hadron emission. The model is applied to calculate the transverse momentum distributions of mesons and baryons, and most of the results agree well with the experimental data at RHIC.

nucl-th↗

arXiv2007

Relativistic BCS-BEC Crossover at Zero Temperature

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.

hep-ph↗

arXiv2007

Nucleon Mass Splitting at Finite Isospin Chemical Potential

We investigate nucleon mass splitting at finite isospin chemical potential in the frame of two flavor Nambu--Jona-Lasinio model. It is analytically proved that, in the phase with explicit isospin symmetry breaking the proton mass decreases and the neutron mass increases linearly in the isospin chemical potential.

nucl-th↗

arXiv2007

Phase Diagram of Neutron-Proton Condensate in Asymmetric Nuclear Matter

We investigate the phase structure of homogeneous and inhomogeneous neutron-proton condensate in isospin asymmetric nuclear matter. At extremely low nuclear density the condensed matter is in homogeneous phase at any temperature, while in general case it is in Larkin-Ovchinnikov-Fulde -Ferrell phase at low temperature. In comparison with the homogeneous superfluid, the inhomogeneous superfluid can survive at higher nuclear density and higher isospin asymmetry.

nucl-th↗

arXiv2006

Finite Temperature Phase Diagram of a Two-Component Fermi Gas with Density Imbalance

We investigated possible superfluid phases at finite temperature in a two-component Fermi gas with density imbalance. In the frame of a general four-fermion interaction theory, we solved in the BCS region the gap equations for the pairing gap and pairing momentum under the restriction of fixed number densities, and analyzed the stability of different phases by calculating the superfluid density and number susceptibilities. The homogeneous superfluid is stable only at high temperature and low number asymmetry, the inhomogeneous LOFF survives at low temperature and high number asymmetry, and in between them there exists another possible inhomogeneous phase, that of phase separation. The critical temperatures and the orders of the phase transitions among the superfluid phases and normal phase are calculated analytically and numerically. The phase diagram we obtained in the temperature and number asymmetry plane is quite different from the one in temperature and chemical potential difference plane for a system with fixed chemical potentials.

cond-mat.supr-con↗

arXiv2006

J/psi Production in Quark-Gluon Plasma

We study J/psi production at RHIC and LHC energies with both initial production and regeneration. We solve the coupled set of transport equation for the J/psi distribution in phase space and the hydrodynamic equation for evolution of quark-gluon plasma. At RHIC, continuous regeneration is crucial for the J/psi momentum distribution while the elliptic flow is still dominated by initial production. At LHC energy, almost all the initially created J\psis are dissociated in the medium and regeneration dominates the J/psi properties.

nucl-th↗

arXiv2006

Neutrino Oscillations Induced by Chiral Phase Transition in a Compact Star

Electric charge neutrality in a compact star provides an important relation- ship between the chiral dynamics and neutrino propagation in the star. Since the sudden drop of the electron density at the critical point of the first-order chiral phase transition, the oscillation for low energy neutrinos is significant and can be regarded as a signature of chiral symmetry restoration in the core of the star.

astro-ph↗

arXiv2006

Volume Effect of Bound States in Quark Gluon Plasma

Bound states, such as $qq$ and $q\bar{q}$, may exist in the Quark Gluon Plasma. As the system is at high density, the volume of the bound states may evoke a reduction to the phase space. We introduce an extended bag model to investigate qualitatively the volume effect on the properties of the system. We find a limit temperature where the bound states start to be completely melted.

hep-ph↗

arXiv2006

Fermion Cooper Pairing with Unequal Masses: Standard Field Theory Approach

The fermion Cooper pairing with unequal masses is investigated in a standard field theory approach. We derived the superfluid density and Meissner mass squared of the U(1) gauge field in a general two species model and found that the often used proportional relation between the two quantities is broken down when the fermion masses are unequal. In weak coupling region, the superfluid density is always negative but the Meissner mass squared becomes mostly positive when the mass ratio between the pairing fermions is large enough. We established a proper momentum configuration of the LOFF pairing with unequal masses and showed that the LOFF state is energetically favored due to the negative superfluid density. The single plane wave LOFF state is physically equivalent to an anisotropic state with a spontaneously generated superflow. The extension to finite range interaction is briefly discussed.

cond-mat.supr-con↗

arXiv2006

Magnetic Stability Analysis for Abelian and Non-Abelian Superconductors

We investigate the origin of Abelian and non-Abelian type magnetic instabilities induced by Fermi surface mismatch between the two pairing fermions in a non-relativistic model. The Abelian type instability occurs only in gapless state and the Meissner mass squared becomes divergent at the gapless-gapped transition point, while the non-Abelian type instability happens in both gapless and gapped states and the divergence vanishes. The non-Abelian type instability can be cured in strong coupling region.

hep-ph↗

arXiv2006

Superfluidity in a Three-flavor Fermi Gas with SU(3) Symmetry

We investigate the superfluidity and the associated Nambu-Goldstone modes in a three-flavor atomic Fermi gas with SU(3) global symmetry. The s-wave pairing occurs in flavor anti-triplet channel due to the Pauli principle, and the superfluid state contains both gapped and gapless fermionic excitations. Corresponding to the spontaneous breaking of the SU(3) symmetry to a SU(2) symmetry with five broken generators, there are only three Nambu-Goldstone modes, one is with linear dispersion law and two are with quadratic dispersion law. The other two expected Nambu-Goldstone modes become massive with a mass gap of the order of the fermion energy gap in a wide coupling range. The abnormal number of Nambu-Goldstone modes, the quadratic dispersion law and the mass gap have significant effect on the low temperature thermodynamics of the matter.

cond-mat.other↗

arXiv2006

Pion Condensation in Baryonic Matter: from Sarma Phase to Larkin-Ovchinnikov-Fudde-Ferrell Phase

We investigated two pion condensed phases in the frame of the two flavor Nambu--Jona-Lasinio model at finite baryon density: the homogeneous and isotropic Sarma phase and inhomogeneous and anisotropic Larkin-Ovchinnikov-Fudde-Ferrell(LOFF) phase. At small isospin chemical potential $μ_I$, the Sarma state is free from the Sarma instability and magnetic instability due to the strong coupling and large enough effective quark mass. At large $μ_I$, while the Sarma instability can be cured via fixing baryon density $n_B$ to be nonzero, its magnetic instability implies that the LOFF state is more favored than the Sarma state. In the intermediate $μ_I$ region, the stable ground state is the Sarma state at higher $n_B$ and LOFF state at lower $n_B$.

hep-ph↗

arXiv2006

LOFF Pairing vs. Breached Pairing in Asymmetric Fermion Superfluids

A general analysis for the competition between breached pairing (BP) and LOFF pairing mechanisms in asymmetric fermion superfluids is presented in the frame of a four fermion interaction model. Two physical conditions which can induce mismatched Fermi surfaces are considered: (1) fixed chemical potential asymmetry $δμ$ and (2) fixed fermion number asymmetry $α$. In case (1), the BP state is ruled out because of Sarma instability and LOFF state is thermodynamically stable in a narrow window of $δμ$. In case (2), while the Sarma instability can be avoided and both the BP and LOFF states can survive provided $α$ is less than the corresponding critical value, the BP state suffers magnetic instability and the LOFF state is always thermodynamically stable. While the LOFF window in case (2) is much larger than the one in the conventional case (1), for small $α$ the longitudinal superfluid density of the LOFF state is negative and it suffers also magnetic instability.

cond-mat.supr-con↗

arXiv2006

Sound Velocity and Meissner Effect in Light-heavy Fermion Pairing Systems

In the frame of a four fermion interaction theory, we investigated the collective excitation in light-heavy fermion pairing systems. When the two species of fermions posses different masses and chemical potentials but keep the same Fermi surface, we found that the sound velocity in superfluids and the Meissner mass or inverse penetration depth in superconductors have the same mass ratio dependence as the ratio of the transition temperature to the zero temperature gap.

cond-mat.supr-con↗