785 research outputs found
The continuum threshold and the Polyakov loop: A comparison between two deconfinement order parameters
We compare two order parameters for the deconfinement transition, induced by
thermal and density effects, commonly used in the literature, namely the
thermal and density evolution of the continuum threshold , within the
frame of the QCD sum rules, and the trace of the Polyakov loop in the
framework of a nonlocal chiral quark model. We include in our
discussion the evolution of the chiral quark condensate, the parameter that
characterizes the chiral symmetry restoration. We found that essentially both
order parameters, and , provide the same information for the
deconfinement transition, both for the zero and finite chemical potential
cases. At zero density, the critical temperatures in both cases coincide
exactly and, in the case of finite baryonic chemical potential , we find
evidence for the appearance of a quarkyonic phase.Comment: 6 pages, 1 table, 2 figures. Contribution to the proceedings of the
20th International Conference in Quantum Chromodynamics (QCD 17), 3 July - 7
July 2017, Montpellier, Franc
Chiral symmetry restoration and deconfinement in QCD at finite temperature
The light-quark correlator in the axial-vector channel is used, in
conjunction with finite energy QCD sum rules at finite temperature, in order to
(a) establish a relation between chiral-symmetry restoration and deconfinement,
and (b) determine the temperature behavior of the width and
coupling. Results indicate that deconfinement takes place at a slightly lower
temperature than chiral-symmetry restoration, although this difference is not
significant given the accuracy of the method. The behaviour of the
parameters is consistent with quark-gluon deconfinement, as the width grows and
the coupling decreases with increasing temperature
(Pseudo)Scalar Charmonium in Finite Temperature QCD
The hadronic parameters of pseudoscalar () and scalar ()
charmonium are determined at finite temperature from Hilbert moment QCD sum
rules. These parameters are the hadron mass, leptonic decay constant, total
width, and continuum threshold (). Results for in both channels
indicate that starts approximately constant, and then it decreases
monotonically with increasing until it reaches the QCD threshold, , at a critical temperature T = T_c \simeq 180 \; \mbox{MeV}
interpreted as the deconfinement temperature. The other hadronic parameters
behave qualitatively similarly to those of the , as determined in this
same framework. The hadron mass is essentially constant, the total width is
initially independent of T, and after it begins to increase
with increasing up to for
(), and subsequently it decreases sharply up to , for (), beyond which the sum rules are no
longer valid. The decay constant of at first remains basically flat up
to , then it starts to decrease up to , and finally it increases sharply with increasing . In the case of
the decay constant does not change up to where
it begins a gentle increase up to beyond which it
increases dramatically with increasing . This behaviour contrasts with that
of light-light and heavy-light quark systems, and it suggests the survival of
the and the states beyond the critical temperature, as
already found for the from similar QCD sum rules. These conclusions
are very stable against changes in the critical temperature in the wide range
T_c = 180 - 260 \; \mbox{MeV}.Comment: 12 pages, 5 figures. A wide range of critical temperatures has been
considered. No qualitative changes to the conclusion
On the algebraic structure of rotationally invariant two-dimensional Hamiltonians on the noncommutative phase space
We study two-dimensional Hamiltonians in phase space with noncommutativity
both in coordinates and momenta. We consider the generator of rotations on the
noncommutative plane and the Lie algebra generated by Hermitian rotationally
invariant quadratic forms of noncommutative dynamical variables. We show that
two quantum phases are possible, characterized by the Lie algebras
or according to the relation between the
noncommutativity parameters, with the rotation generator related with the
Casimir operator. From this algebraic perspective, we analyze the spectrum of
some simple models with nonrelativistic rotationally invariant Hamiltonians in
this noncommutative phase space, as the isotropic harmonic oscillator, the
Landau problem and the cylindrical well potential.
PACS: 03.65.-w; 03.65.Fd
MSC: 81R05; 20C35; 22E70Comment: 49 pages. No figures. Version to appear in JP
Chiral Condensates in Quark and nuclear Matter
We present a novel treatment for calculating the in-medium quark condensates.
The advantage of this approach is that one does not need to make further
assumptions on the derivatives of model parameters with respect to the quark
current mass. The normally accepted model-independent result in nuclear matter
is naturally reproduced. The change of the quark condensate induced by
interactions depends on the incompressibility of nuclear matter. When it is
greater than 260 MeV, the density at which the condensate vanishes is higher
than that from the linear extrapolation. For the chiral condensate in quark
matter, a similar model-independent linear behavior is found at lower
densities, which means that the decreasing speed of the condensate in quark
matter is merely half of that in nuclear matter if the pion-nucleon sigma
commutator is six times the average current mass of u and d quarks. The
modification due to QCD-like interactions is found to slow the decreasing speed
of the condensate, compared with the linear extrapolation.Comment: 12 pages, 7 figures, revtex4 styl
Gamow-Jordan Vectors and Non-Reducible Density Operators from Higher Order S-Matrix Poles
In analogy to Gamow vectors that are obtained from first order resonance
poles of the S-matrix, one can also define higher order Gamow vectors which are
derived from higher order poles of the S-matrix. An S-matrix pole of r-th order
at z_R=E_R-i\Gamma/2 leads to r generalized eigenvectors of order k= 0, 1, ...
, r-1, which are also Jordan vectors of degree (k+1) with generalized
eigenvalue (E_R-i\Gamma/2). The Gamow-Jordan vectors are elements of a
generalized complex eigenvector expansion, whose form suggests the definition
of a state operator (density matrix) for the microphysical decaying state of
this higher order pole. This microphysical state is a mixture of non-reducible
components. In spite of the fact that the k-th order Gamow-Jordan vectors has
the polynomial time-dependence which one always associates with higher order
poles, the microphysical state obeys a purely exponential decay law.Comment: 39 pages, 3 PostScript figures; sub2.eps may stall some printers and
should then be printed out separately; ghostview is o.
Thermal nonlocal Nambu--Jona-Lasinio model in the real time formalism
The real-time formalism at finite temperature and chemical potential for the
nonlocal Nambu--Jona-Lasinio model is developed in the presence of a Gaussian
covariant regulator. We construct the most general thermal propagator, by means
of the spectral function. As a result, the model involves the propagation of
massive quasiparticles. The appearance of complex poles is interpreted as a
confinement signal, and in this case we have unstable quasiparticles with a
finite decay width. An expression for the propagator along the critical line,
where complex poles start to appear, is also obtained. A generalization to
other covariant regulators is proposed.Comment: 9 pages, 5 figures, minor changes, to appear in Phys. Rev.
Pion condensation in quark matter with finite baryon density
The phase structure of the Nambu -- Jona-Lasinio model at zero temperature
and in the presence of baryon- and isospin chemical potentials is investigated.
It is shown that in the chiral limit and for a wide range of model parameters
there exist two different phases with pion condensation. In the first, ordinary
phase, quarks are gapped particles. In the second, gapless pion condensation
phase, there is no energy cost for creating only - or both and
quarks, and the density of baryons is nonzero.Comment: 7 pages, 6 figures; two references adde
Space storm measurements of the July 2005 solar extreme events from the low corona to the Earth
The Athens Neutron Monitor Data Processing (ANMODAP) Center recorded an
unusual Forbush decrease with a sharp enhancement of cosmic ray intensity right
after the main phase of the Forbush decrease on 16 July 2005, followed by a
second decrease within less than 12 h. This exceptional event is neither a
ground level enhancement nor a geomagnetic effect in cosmic rays. It rather
appears as the effect of a special structure of interplanetary disturbances
originating from a group of coronal mass ejections (CMEs) in the 13-14 July
2005 period. The initiation of the CMEs was accompanied by type IV radio bursts
and intense solar flares (SFs) on the west solar limb (AR 786); this group of
energetic phenomena appears under the label of Solar Extreme Events of July
2005. We study the characteristics of these events using combined data from
Earth (the ARTEMIS IV radioheliograph, the Athens Neutron Monitor (ANMODAP)),
space (WIND/WAVES) and data archives. We propose an interpretation of the
unusual Forbush profile in terms of a magnetic structure and a succession of
interplanetary shocks interacting with the magnetosphere.Comment: Advances in Space Research, Volume 43, Issue 4, p. 600-60
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