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1.
In this paper we study the chiral phase transition of QCD at finite temperature and density by using the rank-2 confining separable gluon propagator model in the framework of Dyson–Schwinger Equations. The critical end point is located at (T CEP , μ CEP ) = (69, 270.3 MeV). It is also found that the first order phase transition might not end at one point, but experiences a two-phase coexisting meta-stable state. A comparison with the results in the previous literature is given. 相似文献
2.
Chengfu Mu Pengfei Zhuang 《The European Physical Journal C - Particles and Fields》2008,58(2):271-279
We investigate the effect of the restoration of chiral symmetry on the quark potential in a quark–meson plasma by considering
meson exchanges in the two flavor Nambu–Jona-Lasinio model at finite temperature and density. There are two possible oscillations
in the chiral restoration phase; one is the Friedel oscillation due to the sharp quark Fermi surface at high density, and
the other is the Yukawa oscillation driven by the complex meson poles at high temperature. The quark–meson plasma is strongly
coupled in the temperature region 1≤T/T
c≤3, with T
c being the critical temperature of the chiral phase transition. The maximum coupling in this region is located at the phase
transition point. 相似文献
3.
We study the O(N) symmetric linear sigma-model at finite temperature as the low-energy effective models of quantum chromodynamics (QCD) using
the Cornwall-Jackiw-Tomboulis (CJT) effective action for composite operators. It has so far been claimed that the Nambu-Goldstone
theorem is not satisfied at finite temperature in this framework unless the large-N limit in the O(N) symmetry is taken. We show that this is not the case. The pion is always massless below the critical temperature, if one
determines the propagator within the form such that the symmetry of the system is conserved, and defines the pion mass as
the curvature of the effective potential. We use a regularization for the CJT effective potential in the Hartree approximation,
which is analogous to the renormalization of auxiliary fields. A numerical study of the Schwinger-Dyson equation and the gap
equation is carried out including the thermal and quantum loops. We point out a problem in the derivation of the sigma meson
mass without quantum correction at finite temperature. A problem about the order of the phase transition in this approach
is also discussed.
Received: 21 June 2000 / Accepted: 13 September 2000 相似文献
4.
Two cellular automata models with directed mass flow and internal time scales are studied by numerical simulations. Relaxation
rules are a combination of probabilistic critical height (probability of toppling p) and deterministic critical slope processes with internal correlation time tc equal to the avalanche lifetime, in model A, and ,in model B. In both cases nonuniversal scaling properties of avalanche distributions are found for , where is related to directed percolation threshold in d=3. Distributions of avalanche durations for are studied in detail, exhibiting multifractal scaling behavior in model A, and finite size scaling behavior in model B,
and scaling exponents are determined as a function of p. At a phase transition to noncritical steady state occurs. Due to difference in the relaxation mechanisms, avalanche statistics
at approaches the parity conserving universality class in model A, and the mean-field universality class in model B. We also
estimate roughness exponent at the transition.
Received: 29 May 1998 / Revised: 8 September 1998 / Accepted: 10 September 1998 相似文献
5.
H.??en?ariková P.?Farka?ovsky 《The European Physical Journal B - Condensed Matter and Complex Systems》2010,77(3):393-399
The canonical Monte-Carlo is used to study the phase transitions from the
low-temperature ordered phase to the high-temperature disordered phase in
the two-dimensional half-filled Falicov-Kimball model with correlated
hopping. As the low-temperature ordered phase we consider the chessboard
phase, the axial striped phase and the segregated phase.
It is shown specifically for weak coupling, which is the most interesting
regime, that all three phases persist also at finite temperatures (up to
the critical temperature τ
c
) and that the phase transition at the
critical point is of the first order for the chessboard and axial striped
phase and of the second order for the segregated phase. In addition, it is
found that the critical temperature is reduced with the increasing amplitude
of correlated hopping t' in the chessboard phase and it is strongly
enhanced by t' in the axial striped and segregated phase. 相似文献
6.
Within the framework of the Dyson-Schwinger equations and by means of Multiple Reflection Expansion,we study the effect of finite volume on the chiral phase transition in a sphere, and discuss in particular its influence on the possible location of the critical end point(CEP). According to our calculations, when we take a sphere instead of a cube, the influence of finite volume on phase transition is not as significant as previously calculated. For instance,as the radius of the spherical volume decreases from infinite to 2 fm, the critical temperature T c, at zero chemical potential and finite temperature, drops only slightly. At finite chemical potential and finite temperature, the location of CEP shifts towards smaller temperature and higher chemical potential, but the amplitude of the variation does not exceed 20%. As a result, we find that not only the size of the volume but also its shape have a considerable impact on the phase transition. 相似文献
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8.
9.
I. Bombaci D. Logoteta P.K. Panda C. Providência I. Vidaa 《Physics letters. [Part B]》2009,680(5):448-452
We study the quark deconfinement phase transition in hot β-stable hadronic matter. Assuming a first order phase transition, we calculate the enthalpy per baryon of the hadron–quark phase transition. We calculate and compare the nucleation rate and the nucleation time due to thermal and quantum nucleation mechanisms. We compute the crossover temperature above which thermal nucleation dominates the finite temperature quantum nucleation mechanism. We next discuss the consequences for the physics of proto-neutron stars. We introduce the concept of limiting conversion temperature and critical mass Mcr for proto-hadronic stars, and we show that proto-hadronic stars with a mass M<Mcr could survive the early stages of their evolution without decaying to a quark star. 相似文献
10.
Alfred Hüller 《Zeitschrift für Physik B Condensed Matter》1994,93(3):401-405
In the canonical ensemble any singularity of a thermodynamic function at a temperatureT
c
is smeared over a temperature range of orderT
T
/N. Therefore it is rather difficult to distinguish between a discontinuous and a continuous phase transition on the basis of numerical data obtained for finite systems in the canonical ensemble. It is demonstrated for four model systems that this problem cannot be circumvented by considering higher cumulants of the energy distribution or cumulant ratios. On the other hand, the distinction between first and a second order phase transition is rather direct if based on the microcanonical density of states which is readily obtainable in the dynamical ensemble. 相似文献
11.
We study the dynamics of geometric spin system on the torus with long-range interaction. As the number of particles goes to infinity, the process converges to a deterministic, dynamical magnetization field that satisfies an Euler equation (law of large numbers). Its stable steady states are related to the limits of the equilibrium measures (Gibbs states) of the finite particle system. A related equation holds for the magnetization densities, for which the property of propagation of chaos also is established. We prove a dynamical central limit theorem with an infinite-dimensional Ornstein-Uhlenbeck process as a limiting fluctuation process. At the critical temperature of a ferromagnetic phase transition, both a tighter quantity scaling and a time scaling is required to obtain convergence to a one-dimensional critical fluctuation process with constant magnetization fields, which has a non-Gaussian invariant distribution. Similarly, at the phase transition to an antiferromagnetic state with frequencyp
0, the fluctuation process with critical scaling converges to a two-dimensional critical fluctuation process, which consists of fields with frequencyp
0 and has a non-Gaussian invariant distribution on these fields. Finally, we compute the critical fluctuation process in the infinite particle limit at a triple point, where a ferromagnetic and an antiferromagnetic phase transition coincide.Work supported by Deutsche Forschungsgemeinschaft 相似文献
12.
J. Cao S.-J. Gu Y. Wang H.-Q. Lin 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,63(1):147-151
The critical behaviors of the entropy correlation
effects in the one dimensional J1-J2 Heisenberg model are
studied. It is shown that the mutual information or the
correlation entropy captures the key features of information about
critical fluctuations and can be used to quantify the quantum and
finite-temperature phase transitions. At the critical point, the
mutual information is power-law decay and the entanglement
correlation length is infinite. While far away from the critical
point, the mutual information is exponential decay and the
entanglement correlation length is finite. A universal property of
the mutual information is also found. Based on the critical
behaviors of the mutual information, a new method to quantify the
infinite order phase transition in the system is proposed. 相似文献
13.
M. Motamedifar S. Mahdavifar S. Farjami Shayesteh 《The European Physical Journal B - Condensed Matter and Complex Systems》2011,83(2):181-189
We study the magnetic behaviors of a spin-1/2 quantum compass chain (QCC) in a transverse magnetic field, by means of the
analytical spinless fermion approach and numerical Lanczos method. In the absence of the magnetic field, the phase diagram
is divided into four gapped regions. To determine what happens by applying a transverse magnetic field, using the spinless
fermion approach, critical fields are obtained as a function of exchanges. Our analytical results show, the field-induced
effects depend on in
which one of the four regions the system is. In two regions of the phase diagram, the Ising-type phase transition happens
in a finite field. In another region, we have identified two quantum phase transitions (QPT)s in the ground state magnetic
phase diagram. These quantum phase transitions belong to the universality class of the commensurate-incommensurate phase transition.
We also present a detailed numerical analysis of the low energy spectrum and the ground state magnetic phase diagram. In particular,
we show that the intermediate state (h
c1 < h < h
c2) is gapful, describing the spin-flop phase. 相似文献
14.
I. Bâldea H. Köppel L.S. Cederbaum 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,3(4):507-515
We investigate the Peierls transition in finite chains by exact (Lanczos) diagonalization and within a seminumerical method
based on the factorization of the electron-phonon wave function (Adiabatic Ansatz, AA). AA can be applied for mesoscopic chains
up to micrometer sizes and its reliability can be checked self-consistently. Our study demonstrates the important role played
for finite systems by the tunneling in the double well potential. The chains are dimerized only if their size N exceeds a critical value Nc which increases with increasing phonon frequency. Quantum phonon fluctuations yield a broad transition region. This smooth Peierls transition contrasts not only to the sharp mean field transition, but also with the sharp RPA soft mode instability,
although RPA partially accounts for quantum phonon fluctuations. For weak coupling the dimerization disappears below micrometer
sizes; therefore, this effect could be detected experimentally in mesoscopic systems.
Received: 3 January 1998 / Revised: 13 March 1998 / Accepted: 3 April 1998 相似文献
15.
Low-temperature specific-heat measurements on YbRh2Si2 at the second order antiferromagnetic (AF) phase transition reveal a sharp peak at TN=72 mK. The corresponding critical exponent α turns out to be α=0.38, which differs significantly from that obtained within the framework of the fluctuation theory of second order phase transitions based on the scale invariance, where α?0.1. We show that under the application of magnetic field the curve of the second order AF phase transitions passes into a curve of the first order ones at the tricritical point leading to a violation of the critical universality of the fluctuation theory. This change of the phase transition is generated by the fermion condensation quantum phase transition. Near the tricritical point the Landau theory of second order phase transitions is applicable and gives α?1/2. We demonstrate that this value of α is in good agreement with the specific-heat measurements. 相似文献
16.
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18.
S. Sarkar C. V. Tomy A. D. Thakur G. Balakrishnan D. McK Paul S. Ramakrishnan A. K. Grover 《Pramana》2006,66(1):179-192
We have studied metastability effects pertaining to the peak effect (PE) in critical current density (J
c) via isofield scans in AC susceptibility measurements in a weakly pinned single crystal of Yb3Rh4Sn13 (T
c(0) ≈ 7.6 K). The order-disorder transition in this specimen proceeds in a multi-step manner. The phase coexistence regime
between the onset temperature of the PE and the spinodal temperature (where metastability effects cease) seems to comprise
two parts, where ordered and disordered regions dominate the bulk behavior, respectively. The PE line in the vortex phase
diagram is argued to terminate at the low field end at a critical point in the elastic (Bragg) glass phase. 相似文献
19.
E. Arrigoni G.C. Strinati 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,19(3):433-448
We study the zero-temperature spin fluctuations of a two-dimensional itinerant-electron system with an incommensurate magnetic
ground state described by a single-band Hubbard Hamiltonian. We introduce the (broken-symmetry) magnetic phase at the mean-field
(Hartree-Fock) level through a spiral spin configuration with characteristic wave vector Q different in general from the antiferromagnetic wave vector Q
AF, and consider spin fluctuations over and above it within the electronic random-phase (RPA) approximation. We obtain a closed system of equations for the generalized wave vector and frequency dependent susceptibilities, which are equivalent to the
ones reported recently by Brenig. We obtain, in addition, analytic results for the spin-wave dispersion relation in the strong-coupling
limit of the Hubbard Hamiltonian and find that at finite doping the spin-wave dispersion relation has a hybrid form between that associated with the (localized) Heisenberg model and that associated with the (long-range) RKKY exchange interaction.
We also find an instability of the spin-wave spectrum in a finite region about the center of the Brillouin zone, which signals
a physical instability toward a different spin- or, possibly, charge-ordered phase, as, for example, the stripe structures
observed in the high-T
c materials. We expect, however, on physical grounds that for wave vectors external to this region the spin-wave spectrum that
we have determined should survive consideration of more sophisticated mean-field solutions.
Received 15 September 2000 相似文献
20.
The critical endpoint (CEP) and the phase structure are studied in the Polyakov-loop extended Nambu–Jona-Lasinio model in which the scalar type eight-quark (σ4) interaction and the vector type four-quark interaction are newly added. The σ4 interaction largely shifts the CEP toward higher temperature and lower chemical potential, while the vector type interaction does oppositely. At zero chemical potential, the σ4 interaction moves the pseudo-critical temperature of the chiral phase transition to the vicinity of that of the deconfinement phase transition. 相似文献