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1.
The lattice QCD studies indicate that the critical temperature T
c ≃ 260-280 MeV of the deconfinement phase transition in quenched QCD is considerably smaller than the lowest-lying glueball
mass m
G ≃ 1500-1700 MeV, i.e., T
c ≪ m
G. As a consequence of this large difference, the thermal excitation of the glueball in the confinement phase is strongly suppressed
by the statistical factor e
-mG/Tc ≃ 0.00207 even near T ≃ T
c. We consider its physical implication, and argue the abnormal feature of the deconfinement phase transition in quenched QCD
from the statistical viewpoint. To appreciate this, we demonstrate a statistical argument of the QCD phase transition using
the recent lattice QCD data. From the phenomenological relation between T
c and the glueball mass, the deconfinement transition is found to take place in quenched QCD before a reasonable amount of
glueballs is thermally excited. In this way, quenched QCD reveals a question “what is the trigger of the deconfinement phase
transition ?”
Received: 18 November 2002 / Accepted: 4 February 2003 / Published online: 29 April 2003 相似文献
2.
We consider a forest-fire model which, somewhat informally, is described as follows: Each site (vertex) of the square lattice is either vacant or occupied by a tree. Vacant sites become occupied at rate 1. Further, each site is hit by lightning at rate λ. This lightning instantaneously destroys (makes vacant) the occupied cluster of the site.This model is closely related to the Drossel-Schwabl forest-fire model, which has received much attention in the physics literature. The most interesting behaviour seems to occur when the lightning rate goes to zero. In the physics literature it is believed that then the system has so-called self-organized critical behaviour.We let the system start with all sites vacant and study, for positive but small λ, the behaviour near the ‘critical time’ t
c
, defined by the relation 1 − exp(− t
c
) = p
c
, the critical probability for site percolation.Intuitively one might expect that if, for fixed t > t
c
, we let simultaneously λ tend to 0 and m to ∞, the probability that some tree at distance smaller than m from O is burnt before time t goes to 1. However, we show that under a percolation-like assumption (which we can not prove but believe to be true) this intuition is false. We compare with the case where the square lattice is replaced by the directed binary tree, and pose some natural open problems.Part of vdB’s research is supported by BRICKS project AFM 2.2. 相似文献
3.
A simple physical model is proposed for dissociating dense fluid hydrogen. We propose that free dissociated atoms interact
via quantum electron-electron exchange analogously to the interaction in the liquid-metal phase of alkali metals. The density
dependence of a hydrogen atom’s binding energy in such a quasi-liquid is calculated. It is shown that the transition from
the molecular fluid to liquid hydrogen is a first-order phase transition. The critical parameters of the transition are determined:
P
c
= 72 GPa, T
c
= 10500 K, and ρ
c
= 0.5 g/cm3. The possibility of the metastable existence of atomic liquid hydrogen in a dissociated molecular fluid under decreased pressure
is established. 相似文献
4.
Muhammad Zakria Butt Mozina Noshi Farooq Bashir 《Central European Journal of Physics》2008,6(4):834-842
The mode of planar distribution of solute atoms in Cu single crystals alloyed with 0.5 to 8.0 at.%Ge has been investigated
via the temperature dependence of the critical resolved shear stress of these alloys. It is found that there exists a critical
solute concentration c
m
≈ 5 at.%Ge below which the distribution of solute atoms in the crystal is random, and above which some local ordering occurs.
This together with such data available in the literature for Cu-Zn, Cu-Al and Cu-Mn alloys, i.e. c
m
≈7 at. %Zn, 7 at.%Al and 1 at.%Mn, when examined as a function of the size-misfit factor δ = (1/b)(db/dc)of a given binary alloy system, shows that the value of c
m
strongly depends on δ; the smaller the magnitude of δ, the greater the value of c
m
and vice versa. Also, the value of c
m
is found to correlate well with the electron-to-atom ratio (e/a)of the Cu-Zn, Cu-Al, Cu-Ge and Cu-Mn alloys with the solute concentration c = c
m
. However, no systematic correlation exists between the critical solute concentration c
m
for the onset of local ordering and the modulus-mismatch parameter η = (1/G)(dG/dc).
相似文献
5.
M. R. Galpin D. E. Logan 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,62(2):129-145
We develop a non-perturbative local moment approach (LMA) for the gapped Anderson impurity model (GAIM), in which a locally
correlated orbital is coupled to a host with a gapped density of states.
Two distinct phases arise, separated by a level-crossing quantum phase transition: a screened singlet phase, adiabatically
connected to the non-interacting limit and as such a generalized Fermi liquid (GFL); and an incompletely screened, doubly
degenerate local moment (LM) phase.
On opening a gap (δ) in the host, the transition occurs at a critical gap δc, the GFL [LM] phase occurring for δ<δc [ δ>δc] . In agreement with numerical renormalization group (NRG) calculations, the critical
δc = 0 at the particle-hole symmetric point of the model, where the LM phase arises immediately on opening the gap. In the generic
case by contrast δc > 0, and the resultant LMA phase boundary is in good quantitative agreement with NRG results. Local single-particle dynamics
are considered in some detail.
The major difference between the two phases resides in bound states within the gap: the GFL phase is found to be characterised
by one bound state only, while the LM phase contains two such states straddling the chemical potential. Particular emphasis
is naturally given to the
strongly correlated, Kondo regime of the model. Here,
single-particle dynamics for both phases are found to exhibit universal scaling as a function of scaled frequency ω/ωm
0 for fixed gaps
δ/ωm
0, where ωm
0 is the characteristic Kondo scale for the gapless (metallic) AIM; at particle-hole symmetry in particular, the
scaling spectra are obtained in closed form. For frequencies
|ω|/ωm
0 ≫δ/ωm
0, the
scaling spectra are found generally to reduce to those of the gapless, metallic Anderson model;
such that for small gaps δ/ωm
0≪ 1 in particular, the Kondo resonance that is the spectral hallmark of the usual metallic Anderson model persists more or
less in its entirety in the GAIM. 相似文献
6.
Yu. N. Zakharov A. G. Lutokhin N. A. Korchagina V. G. Kuznetsov 《Bulletin of the Russian Academy of Sciences: Physics》2008,72(4):556-558
The temperature dependences of the pyroelectric and dielectric properties of ferroelectric ceramics of the PbZr1 − x
Ti
x
O3 binary system with x = 0.06, 0.07, 0.08, 0.1, 0.15, 0.2, 0.25, 0.3, and 0.35 have been obtained synchronously for each sample in the range of
the structural phase transition between the states with the symmetry space groups R3c ↔ R3m. It is established that the temperatures of this phase transition for unpolarized and polarized samples coincide in the range
0.06 ≤ x ≤ 0.15. In this case, the x−T phase diagram, constructed on the basis of the pyroelectric and dielectric data, is in excellent agreement with the X-ray
diffraction data on single crystals in this concentration range. The effect of dc electric fields from 5 × 105 V m−1 did not lead to any temperature shifts of the R3c ↔ R3m phase transition for the compositions with 0.06 ≤ x ≤ 0.25.
Original Russian Text ? Yu.N. Zakharov, A.G. Lutokhin, N.A. Korchagina, V.G. Kuznetsov, 2008, published in Izvestiya Rossiiskoi
Akademii Nauk. Seriya Fizicheskaya, 2008, Vol. 72, No. 4, pp. 589–591. 相似文献
7.
Xing-Bin Pan 《Communications in Mathematical Physics》2008,280(1):77-121
P. G. de Gennes predicted the analogies between the effect of the elastic coefficients to liquid crystals and the effect of
applied magnetic fields to superconductors, and predicted that all elastic coefficients diverge to infinity at smectic-C to
nematic transition. One would expect quantitative comparison in the analogies. In the case of equal elastic coefficients (K
1 = K
2 = K
3 = K), we define the critical value K
c
of the elastic coefficients and make comparison of it with the upper critical magnetic field H
C
3 for type II superconductors. We classify the smectic liquid crystals into subcritical, critical and supercritical cases according
to the Ginzburg-Landau parameter κ, the wave number q and the boundary value of the director at the surface. We show that in the subcritical case the liquid crystal does not undergo
phase transition; and in the supercritical case both phase transition and hysteresis occur. The prediction of de Gennes is
true in the critical case where μ
π
(u
0, q) = κ
2 and K
c
= + ∞. 相似文献
8.
S. V. Grigor’ev S. A. Klimko S. V. Maleev A. I. Okorokov V. V. Runov D. Yu. Chernyshov 《Journal of Experimental and Theoretical Physics》1997,85(6):1168-1179
A magnetic phase transition in carbon-doped (0.1 and 0.7 at. %) Fe70Ni30 Invar alloys was investigated by the method of depolarization of a transmitted neutron beam and by small-angle scattering
of polarized neutrons. It is shown that for both alloys, two characteristic length scales of magnetic correlations coexist
above T
c. Small-angle scattering by critical correlations with radius R
c is described well by the Ornstein-Zernike (OZ) expression. The longer-scale (second) correlations, whose size can be estimated
from depolarization data, are not described by the OZ expression, and hypothetically can be modeled by a squared OZ expression,
which in coordinate space corresponds to the relation 〈M(r)M(0)〉∝exp(−r/R
d), where R
d is the correlation length of the second scale. The temperature dependence of the correlation radius R
c was obtained: R
c ∝ ((T−T
c)/Tc)−ν
, where ν≈2/3 is the critical exponent for ferromagnets, over a wide temperature range up to T
c
exp
, at which the correlation radius becomes constant and equals its maximum value R
c(T
c)=R
c
max
. The maximum correlation radius established (R
c
max
=140 Å and 230 Å for the first and second alloys, respectively) characterizes the length-scale of the fluctuation for which
the appearance of critical correlations first results in the formation of a ferromagnetic phase, and the phenomenon itself
exhibits a “disruption” of the second-order phase transition at T=T
c
exp
, as a result of which a first-order transition arises. Temperature hysteresis was also detected in the measured polarization
of the transmitted beam and intensity of small-angle neutron scattering in the alloy above T
c, confirming the character of this magnetic transition as a first-order transition close to a second-order transition.
Zh. éksp. Teor. Fiz. 112, 2134–2155 (December 1997) 相似文献
9.
Tomohiko Sakaguchi Kouji Kashiwa Masayuki Matsuzaki Hiroaki Kouno Masanobu Yahiro 《Central European Journal of Physics》2008,6(1):116-121
We test the stability of the mean field solution in the Nambu-Jona-Lasinio model in a semi-quantitative manner. For stable
solutions with respect to both the σ and π directions, we investigate effects of the mesonic loop corrections of 1/N
c
, which correspond to the next-to-leading order in the 1/N
c
expansion, on the high density chiral phase transition. The corrections weaken the first order phase transition and shift
the critical chemical potential to a lower value. At N
c
= 3, however, instability of the mean field effective potential prevents us from determining the minimum of the corrected
one.
相似文献
10.
We revisit the problem of a two-dimensional polymer ring subject to an inflating pressure differential. The ring is modeled
as a freely jointed closed chain of N monomers. Using a Flory argument, mean-field calculation and Monte Carlo simulations, we show that at a critical pressure,
pc ∼ N-1, the ring undergoes a second-order phase transition from a crumpled, random-walk state, where its mean area scales as 〈A〉 ∼ N, to a smooth state with 〈A〉 ∼ N2. The transition belongs to the mean-field universality class. At the critical point a new state of polymer statistics is
found, in which 〈A〉 ∼ N3/2. For p ≫ pc we use a transfer-matrix calculation to derive exact expressions for the properties of the smooth state. 相似文献
11.
We study the chiral phase transition in the linear sigma model with 2 quark flavors and N
c
colors. One-loop calculations predict a first-order phase transition at both μ = 0 and μ ≠ 0. We also discuss the phase diagram and make a comparison with a thermal parametrization of existing heavy-ion experimental
data. 相似文献
12.
S. Rabinovich 《Journal of Experimental and Theoretical Physics》2011,112(4):637-641
A simple assumption of the emergence in gas of small atomic clusters consisting of c particles each leads to a phase separation (first-order transition). It reveals itself by the emergence of a “forbidden”
density range starting at a certain temperature. Defining this latter value as the critical temperature predicts the existence
of an interval with the anomalous heat capacity behavior c
p
∝ ΔT
−1/c
. The value c = 13 suggested in the literature yields the heat capacity exponent α = 0.077. 相似文献
13.
S. S. Murzin 《JETP Letters》2010,91(3):155-157
It has been shown that the observation of the transitions between the dielectric phase and the integer-quantum-Hall-effect
phases with the quantized Hall conductivity σ
xy
q ≥ 3e
2/h announced in a number of works is unjustified. In these works, the crossing points of the magnetic-field dependence of the
diagonal resistivity ρ
xx
at different temperatures T and ωcτ = 1 have been misidentified as the critical points of the phase transitions. In fact, these crossing points are due to the
sign change of the derivative dρ
xx
/dT owing to the quantum corrections to the conductivity. Here, ωc = eB/m is the cyclotron frequency, τ is the transport relaxation time, and m is the effective electron mass. 相似文献
14.
A new relation for the density parameter Ω is derived as a function of expansion velocity υ based on Carmeli's cosmology.
This density function is used in the luminosity distance relation D
L. A heretofore neglected source luminosity correction factor (1 − (υ/c)2)−1/2 is now included in D
L. These relations are used to fit type Ia supernovae (SNe Ia) data, giving consistent, well-behaved fits over a broad range
of redshift 0.1 < z < 2. The best fit to the data for the local density parameter is Ωm = 0.0401 ± 0.0199. Because Ωm is within the baryonic budget there is no need for any dark matter to account for the SNe Ia redshift luminosity data. From
this local density it is determined that the redshift where the universe expansion transitions from deceleration to acceleration
is z
t = 1.095+0.264
−0.155. Because the fitted data covers the range of the predicted transition redshift z
t, there is no need for any dark energy to account for the expansion rate transition. We conclude that the expansion is now
accelerating and that the transition from a closed to an open universe occurred about 8.54 Gyr ago. 相似文献
15.
R. F. Bishop P. H. Y. Li 《The European Physical Journal B - Condensed Matter and Complex Systems》2011,81(1):37-48
The zero-temperature phase diagrams of a two-dimensional (2D) frustrated quantum antiferromagnetic system, namely the Union
Jack model, are studied using the coupled cluster method (CCM) for the two cases when the lattice spins have spin quantum
number s = 1 and s =
\frac32\frac{3}{2}. The system is defined on a square lattice and the spins interact via isotropic Heisenberg interactions such that
all nearest-neighbour (NN) exchange bonds are present with identical
strength J
1 > 0, and only half of the next-nearest-neighbour (NNN) exchange bonds are present with identical strength J
2
≡
κ
J
1 > 0. The bonds are arranged such that on the 2×2 unit cell they form the pattern of the Union Jack
flag. Clearly, the NN bonds by themselves (viz., with J
2 = 0)
produce an antiferromagnetic Néel-ordered phase, but as the
relative strength κ of the frustrating NNN bonds is increased
a phase transition occurs in the classical case (s→ ∞) at κ
c
cl = 0.5 to a canted ferrimagnetic
phase. In the quantum cases considered here we also find strong
evidence for a corresponding phase transition between a
Néel-ordered phase and a quantum canted ferrimagnetic phase at a
critical coupling κ
c1 = 0.580 ± 0.015 for s = 1 and
κ
c1 = 0.545 ± 0.015 for s =
\frac32\frac{3}{2}. In both cases
the ground-state energy E and its first derivative dE/dκ
seem continuous, thus providing a typical scenario of a second-order
phase transition at κ = κ
c1. However, the order
parameter for the transition (viz., the average ground-state on-site
magnetization) does not go to zero there on either side of the
transition. Thus, the phase transition at κ = κ
c1 between the Néel antiferromagnetic phase and the canted ferrimagnetic phase for both the s = 1 and s =
\frac32\frac{3}{2} Union Jack models is similar in nature to that found previously for the s =
\frac12\frac{1}{2} Union Jack model. It is thus also completely
comparable to the transition in the s =
\frac12\frac{1}{2}
XXZ model on the
2D square lattice between two Néel antiferromagnetic phases, one aligned along the z-axis and the other along some perpendicular direction in the xy-plane. 相似文献
16.
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
17.
Electrical resistivity (ρ) of the amorphous (a-)Fe100−c
Zr
c
(c=8.5, 9.5 and 10) alloys has been measured in the temperature range 77 to 300 K, which embraces the second-order magnetic
phase transition at the Curie temperature point T
c. Analysis of the resistivity data particularly in the critical region reveals that these systems have a much wider range
of critical region compared to other crystalline ferromagnetic materials. The value of T
c and specific heat critical exponent, α has the same values as those determined from our earlier magnetic measurements. The value of α for all the present investigated alloys are in close agreement with the values predicted for three-dimensional (3D) Heisenberg
ferromagnet systems, which gives contradiction to the earlier results on similar alloys. It is observed from the analysis
that the presence of quenched disorder does not have any influence on critical behavior. 相似文献
18.
M. V. Tokarev I. Zborovský A. Kechechyan A. Alakhverdyants 《Physics of Particles and Nuclei Letters》2011,8(6):533-541
The general concepts in the critical phenomena related with the notions of “scaling” and “universality” are considered. Behavior
of various systems near a phase transition is displayed. Search for clear signatures of the phase transition of the nuclear
matter and location of the critical point in heavy-ion collisions (HIC) is discussed. The experimental data on inclusive spectra measured in HIC at RHIC and SPS over a wide range of energies s
N N
1/2 = 9–200 GeV are analyzed in the framework of z-scaling. A microscopic scenario of the constituent interactions is presented. Dependence of the energy loss on the momentum
of the produced hadron, energy and centrality of the collision is studied. Self-similarity of the constituent interactions
described in terms of momentum fractions is used to characterize the nuclear medium by “specific heat” and colliding nuclei
by fractal dimensions. Preferable kinematical regions to search for signatures of the phase transition of the nuclear matter
produced in HIC are discussed. Discontinuity of the “specific heat” is assumed to be a signature of the phase transition and the critical
point. 相似文献
19.
We report on study of the vortex liquid in Pb-doped Bi-2223 single crystal using the in-plane resistivity measurements as
a function of temperature and magnetic field up to 6 T applied perpendicular to CuO planes. Below T
c
at the upper part of superconducting transition we found Arrhenius-like resistivity behavior. With further temperature decrease
close to onset of dissipation resistivity shows power law dependence on temperature signaling approaching vortex-glass transition.
The critical exponents ν(z − 1) = 4.6 ± 0.5 are found to be field independent within experimental errors. We also present magnetic phase diagram defining
region of nonzero critical current for Pb-doped Bi-2223 single crystal. 相似文献
20.
L. Álvarez-Gaumé P. Basu M. Mariño S.R. Wadia 《The European Physical Journal C - Particles and Fields》2006,48(2):647-665
In this paper we discuss the black hole–string transition of the small Schwarzschild black hole of AdS
5×S5 using the AdS/CFT correspondence at finite temperature. The finite temperature gauge theory effective action, at weak and strong coupling, can be expressed entirely in terms of constant Polyakov lines which are SU(N) matrices. In showing this we have taken into account that there are no Nambu–Goldstone modes associated with the fact that the 10-dimensional black hole solution sits at a point in S5. We show that the phase of the gauge theory in which the eigenvalue spectrum has a gap corresponds to supergravity saddle points in the bulk theory. We identify the third order N=∞ phase transition with the black hole–string transition. This singularity can be resolved using a double scaling limit in the transition region where the large N expansion is organized in terms of powers of N-2/3. The N=∞ transition now becomes a smooth crossover in terms of a renormalized string coupling constant, reflecting the physics of large but finite N. Multiply wound Polyakov lines condense in the crossover region. We also discuss the implications of our results for the resolution of the singularity of the lorenztian section of the small Schwarzschild black hole. 相似文献