1,978 research outputs found
A Model for QCD at High Density and Large Quark Mass
We study the high density region of QCD within an effective model obtained in
the frame of the hopping parameter expansion and choosing Polyakov type of
loops as the main dynamical variables representing the fermionic matter. To get
a first idea of the phase structure, the model is analyzed in strong coupling
expansion and using a mean field approximation. In numerical simulations, the
model still shows the so-called sign problem, a difficulty peculiar to non-zero
chemical potential, but it permits the development of algorithms which ensure a
good overlap of the Monte Carlo ensemble with the true one. We review the main
features of the model and present calculations concerning the dependence of
various observables on the chemical potential and on the temperature, in
particular of the charge density and the diquark susceptibility, which may be
used to characterize the various phases expected at high baryonic density. We
obtain in this way information about the phase structure of the model and the
corresponding phase transitions and cross over regions, which can be considered
as hints for the behaviour of non-zero density QCD.Comment: 21 pages, 29 figure
A Gaussian Weave for Kinematical Loop Quantum Gravity
Remarkable efforts in the study of the semi-classical regime of kinematical
loop quantum gravity are currently underway. In this note, we construct a
``quasi-coherent'' weave state using Gaussian factors. In a similar fashion to
some other proposals, this state is peaked in both the connection and the spin
network basis. However, the state constructed here has the novel feature that,
in the spin network basis, the main contribution for this state is given by the
fundamental representation, independently of the value of the parameter that
regulates the Gaussian width.Comment: 15 pages, 3 figures, Revtex file. Comments added and references
updated. Final version to appear in IJMP-
Gauging kinematical and internal symmetry groups for extended systems: the Galilean one-time and two-times harmonic oscillators
The possible external couplings of an extended non-relativistic classical
system are characterized by gauging its maximal dynamical symmetry group at the
center-of-mass. The Galilean one-time and two-times harmonic oscillators are
exploited as models. The following remarkable results are then obtained: 1) a
peculiar form of interaction of the system as a whole with the external gauge
fields; 2) a modification of the dynamical part of the symmetry
transformations, which is needed to take into account the alteration of the
dynamics itself, induced by the {\it gauge} fields. In particular, the
Yang-Mills fields associated to the internal rotations have the effect of
modifying the time derivative of the internal variables in a scheme of minimal
coupling (introduction of an internal covariant derivative); 3) given their
dynamical effect, the Yang-Mills fields associated to the internal rotations
apparently define a sort of Galilean spin connection, while the Yang-Mills
fields associated to the quadrupole momentum and to the internal energy have
the effect of introducing a sort of dynamically induced internal metric in the
relative space.Comment: 32 pages, LaTex using the IOP preprint macro package (ioplppt.sty
available at: http://www.iop.org/). The file is available at:
http://www.fis.unipr.it/papers/1995.html The file is a uuencoded tar gzip
file with the IOP preprint style include
The Phase Structure of the Polyakov--Quark-Meson Model
The relation between the deconfinement and chiral phase transition is
explored in the framework of an Polyakov-loop-extended two-flavor quark-meson
(PQM) model. In this model the Polyakov loop dynamics is represented by a
background temporal gauge field which also couples to the quarks. As a novelty
an explicit quark chemical potential and N_f-dependence in the Polyakov loop
potential is proposed by using renormalization group arguments. The behavior of
the Polyakov loop as well as the chiral condensate as function of temperature
and quark chemical potential is obtained by minimizing the grand canonical
thermodynamic potential of the system. The effect of the Polyakov loop dynamics
on the chiral phase diagram and on several thermodynamic bulk quantities is
presented.Comment: 13 pages, 12 figures, RevTex4; discussion of mu-dependence extended,
references added, version to be published in PR
Continuum spin foam model for 3d gravity
An example illustrating a continuum spin foam framework is presented. This
covariant framework induces the kinematics of canonical loop quantization, and
its dynamics is generated by a {\em renormalized} sum over colored polyhedra.
Physically the example corresponds to 3d gravity with cosmological constant.
Starting from a kinematical structure that accommodates local degrees of
freedom and does not involve the choice of any background structure (e. g.
triangulation), the dynamics reduces the field theory to have only global
degrees of freedom. The result is {\em projectively} equivalent to the
Turaev-Viro model.Comment: 12 pages, 3 figure
Group Field Theory: An overview
We give a brief overview of the properties of a higher dimensional
generalization of matrix model which arises naturally in the context of a
background independent approach to quantum gravity, the so called group field
theory. We show that this theory leads to a natural proposal for the physical
scalar product of quantum gravity. We also show in which sense this theory
provides a third quantization point of view on quantum gravity.Comment: 10 page
Combined battery SOC/SOH estimation using a nonlinear adaptive observer
International audience— This work presents a modeling and estimation techniques for State of Charge and State of Health estimation for Li-ion batteries. The analysis is done using an adaptive estimation approach for joint state and parameter estimation and by simplifying an existing nonlinear model previously obtained from experiments tests. A switching mechanism between two observers, one for the charging phase and one for the discharging phase, is done to avoid transients due to the discontinuity of model's parameters. Simulations on experimental data show that the approach is feasible and enhance the interest of the proposed estimation technique
A generalized Hamiltonian Constraint Operator in Loop Quantum Gravity and its simplest Euclidean Matrix Elements
We study a generalized version of the Hamiltonian constraint operator in
nonperturbative loop quantum gravity. The generalization is based on admitting
arbitrary irreducible SU(2) representations in the regularization of the
operator, in contrast to the original definition where only the fundamental
representation is taken. This leads to a quantization ambiguity and to a family
of operators with the same classical limit. We calculate the action of the
Euclidean part of the generalized Hamiltonian constraint on trivalent states,
using the graphical notation of Temperley-Lieb recoupling theory. We discuss
the relation between this generalization of the Hamiltonian constraint and
crossing symmetry.Comment: 35 pp, 20 eps figures; minor corrections, references added; version
to appear in Class. Quant. Gra
Photons from quantized electric flux representations
The quantum theory of U(1) connections admits a diffeomorphism invariant
representation in which the electric flux through any surface is quantized.
This representation is the analog of the representation of quantum SU(2) theory
used in loop quantum gravity. We investigate the relation between this
representation, in which the basic excitations are `polymer-like', and the Fock
representation, in which the basic excitations are wave-like photons. We show
that normalizable states in the Fock space are associated with `distributional'
states in the quantized electric flux representation. This work is motivated by
the question of how wave-like gravitons in linearised gravity arise from
polymer-like states in non-perturbative loop quantum gravity.Comment: 22 pages, no figure
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