1,557 research outputs found
Responses of quark condensates to the chemical potential
The responses of quark condensates to the chemical potential, as a function
of temperature T and chemical potential \mu, are calculated within the
Nambu--Jona-Lasinio (NJL) model. We compare our results with those from the
recent lattice QCD simulations [QCD-TARO Collaboration, Nucl. Phys. B (Proc.
Suppl.) 106, 462 (2002)]. The NJL model and lattice calculations show
qualitatively similar behavior, and they will be complimentary ways to study
hadrons at finite density. The behavior above T_c requires more elaborated
analyses.Comment: 3 pages, 2 figs, based on a contribution to the Prof. Osamu Miyamura
memorial symposium, Hiroshima University, Nov. 16-17, 2001; slightly revised,
accepted for publication in Physical Review
Theory of semiconductor quantum-wire based single- and two-qubit gates
A GaAs/AlGaAs based two-qubit quantum device that allows the controlled
generation and straightforward detection of entanglement by measuring a
stationary current-voltage characteristic is proposed. We have developed a
two-particle Green's function method of open systems and calculate the
properties of three-dimensional interacting entangled systems
non-perturbatively. We present concrete device designs and detailed, charge
self-consistent predictions. One of the qubits is an all-electric Mach-Zehnder
interferometer that consists of two electrostatically defined quantum wires
with coupling windows, whereas the second qubit is an electrostatically defined
double quantum dot located in a second two-dimensional electron gas beneath the
quantum wires. We find that the entanglement of the device can be controlled
externally by tuning the tunneling coupling between the two quantum dots.Comment: 16 pages, 13 figures, RevTex4 two-column format, to appear in Phys.
Rev.
Gate control of low-temperature spin dynamics in two-dimensional hole systems
We have investigated spin and carrier dynamics of resident holes in
high-mobility two-dimensional hole systems in GaAs/AlGaAs
single quantum wells at temperatures down to 400 mK. Time-resolved Faraday and
Kerr rotation, as well as time-resolved photoluminescence spectroscopy are
utilized in our study. We observe long-lived hole spin dynamics that are
strongly temperature dependent, indicating that in-plane localization is
crucial for hole spin coherence. By applying a gate voltage, we are able to
tune the observed hole g factor by more than 50 percent. Calculations of the
hole g tensor as a function of the applied bias show excellent agreement with
our experimental findings.Comment: 8 pages, 7 figure
Consistency in Regularizations of the Gauged NJL Model at One Loop Level
In this work we revisit questions recently raised in the literature
associated to relevant but divergent amplitudes in the gauged NJL model. The
questions raised involve ambiguities and symmetry violations which concern the
model's predictive power at one loop level. Our study shows by means of an
alternative prescription to handle divergent amplitudes, that it is possible to
obtain unambiguous and symmetry preserving amplitudes. The procedure adopted
makes use solely of {\it general} properties of an eventual regulator, thus
avoiding an explicit form. We find, after a thorough analysis of the problem
that there are well established conditions to be fulfiled by any consistent
regularization prescription in order to avoid the problems of concern at one
loop level.Comment: 22 pages, no figures, LaTeX, to appear in Phys.Rev.
Dynamical Chiral Symmetry Breaking on the Light Front I. DLCQ Approach
Dynamical chiral symmetry breaking in the DLCQ method is investigated in
detail using a chiral Yukawa model closely related to the Nambu-Jona-Lasinio
model. By classically solving three constraints characteristic of the
light-front formalism, we show that the chiral transformation defined on the
light front is equivalent to the usual one when bare mass is absent. A quantum
analysis demonstrates that a nonperturbative mean-field solution to the
``zero-mode constraint'' for a scalar boson (sigma) can develop a nonzero
condensate while a perturbative solution cannot. This description is due to our
identification of the ``zero-mode constraint'' with the gap equation. The
mean-field calculation clarifies unusual chiral transformation properties of
fermionic field, which resolves a seemingly inconsistency between triviality of
the null-plane chiral charge Q_5|0>=0 and nonzero condensate. We also calculate
masses of scalar and pseudoscalar bosons for both symmetric and broken phases,
and eventually derive the PCAC relation and nonconservation of Q_5 in the
broken phase.Comment: Revised version to appear in Phys. Rev. D. 19 pages, 4 figures,
REVTEX. Derivation of the PCAC relation is given. Its relation to the
nonconservation of chiral charge is clarified. 1 figure and some references
adde
Topological susceptibility at zero and finite temperature in the Nambu-Jona-Lasinio model
We consider the three flavor Nambu-Jona-Lasinio model with the 't Hooft
interaction incorporating the U(1)_A anomaly. In order to set the coupling
strength of the 't Hooft term, we employ the topological susceptibility
instead of the eta' meson mass. The value for is taken from lattice
simulations. We also calculate at finite temperature within the model.
Comparing it with the lattice data, we extract information about the behavior
of the U(1)_A anomaly at finite temperature. We conclude that within the
present framework, the effective restoration of the U(1)_A symmetry does not
necessarily take place even at high temperature where the chiral symmetry is
restored.Comment: 9 pages, 14 figures, to be published in Phys.Rev.
Comparison of Temperature-Dependent Hadronic Current Correlation Functions Calculated in Lattice Simulations of QCD and with a Chiral Lagrangian Model
The Euclidean-time hadronic current correlation functions, and
, of pseudoscalar and vector currents have recently been
calculated in lattice simulations of QCD and have been used to obtain the
corresponding spectral functions. We have used the Nambu-Jona-Lasinio (NJL)
model to calculate such spectral functions, as well as the Euclidean-time
correlators, and have made a comparison to the lattice results for the
correlators. We find evidence for the type of temperature dependence of the NJL
coupling parameters that we have used in previous studies of the mesonic
confinement-deconfinement transition. We also see that the spectral functions
obtained when using the maximum-entropy-method (MEM) and the lattice data
differ from the spectral functions that we calculate in our chiral model.
However, our results for the Euclidean-time correlators are in general
agreement with the lattice results, with better agreement when our
temperature-dependent coupling parameters are used than when
temperature-independent parameters are used for the NJL model. We also discuss
some additional evidence for the utility of temperature-dependent coupling
parameters for the NJL model. For example, if the constituent quark mass at T=0
is in the chiral limit, the transition temperature is for the NJL model with a standard momentum cutoff parameter. (If a
Gaussian momentum cutoff is used, we find in the chiral limit,
with at T=0.) The introduction of a weak temperature dependence
for the coupling constant will move the value of into the range 150-170
MeV, which is more in accord with what is found in lattice simulations of QCD
with dynamical quarks
The phase diagram and bulk thermodynamical quantities in the NJL model at finite temperature and density
We reexamine the recent instanton motivated studies of Alford, Rajagopal and
Wilczek, and Berges and Rajagopal in the framework of the standard SU(2)
Nambu-Jona-Lasinio model. The chiral phase diagram is calculated in the
temperature--density plane, and the pressure is evaluated as the function of
the density. Obtaining simple approximate relations describing the -
and - phase transition lines we find that the results of the instanton
based model and that of the NJL model are identical. The diquark transition
line is also given.Comment: 11 pages LaTeX plus 7 PS figures. One figure has been added and there
are some changes in the text describing thi
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