pinecone/core-2020-05-10-deduplication huggingface dataset:
Spin-Isospin Modes in Heavy-Ion Collisions I: Nuclear Matter at Finite
  Temperatures

With a view towards implementation in microscopic transport simulations of
heavy-ion collisions, the properties of spin-isospin modes are studied in
nuclear matter consisting of nucleons and Delta isobars that interact by the
exchange of pi and rho mesons. For a standard p-wave interaction and an
effective g' short-range interaction, the dispersion relations for the spin-
isospin modes, and the associated amplitudes, are calculated at various nuclear
densities and temperatures, within the random-phase approximation. Quantities
of physical interest are then extracted, including the total and partial Delta
decay widths and the Delta cross sections in the nuclear medium. The
self-consistent inclusion of the Delta width has a strong effect on the Delta
cross sections at twice normal nuclear density, as compared with the result of
ignoring the width. Generally, the obtained quantities exhibit a strong density
dependence, but are fairly insensitive to the temperature, at least up to T=25
MeV. Finally, it is described how these in-medium effects may be consistently
included into microscopic transport simulations of nuclear collisions, and the
improvements over previous approaches are discussed.Comment: LaTeX 47 pages, 17 postscript figures in accompanying uuencoded fil
Particle Mechanics Models with W-symmetries

We introduce a particle mechanics model with Sp($2M$) gauge invariance.
Different partial gauge-fixings by means of sl(2) embeddings on the gauge
algebra lead to reduced models which are invariant under diffeomorphisms and
classical non-linear \W-transformations as the residual gauge symmetries thus
providing a set of models of gauge and matter fields coupled in a \W-invariant
way. The equations of motion for the matter variables give Lax operators in a
matrix form. We examine several examples in detail and discuss the issue of
integration of infinitesimal \W-transformations.Comment: 34 pages, LaTeX, no figures. Several changes (including Title) and
  new material added. Version to appear in Ann. Phy
A general formulation of discrete-time quantum mechanics, restrictions
  on the action and the relation of unitarity to the existence theorem for
  initial-value problems

A general formlulation for discrete-time quantum mechanics, based on
Feynman's method in ordinary quantum mechanics, is presented. It is shown that
the ambiguities present in ordinary quantum mechanics (due to noncommutativity
of the operators), are no longer present here. Then the criteria for the
unitarity of the evolution operator is examined. It is shown that the unitarity
of the evolution operator puts restrictions on the form of the action, and also
implies the existence of a solution for the classical initial-value problem.Comment: 13 pages, Te
Weyl Expansion for Symmetric Potentials

We present a semiclassical expansion of the smooth part of the density of
states in potentials with some form of symmetry. The density of states of each
irreducible representation is separately evaluated using the Wigner transforms
of the projection operators. For discrete symmetries the expansion yields a
formally exact but asymptotic series in $\hbar$, while for the rotational
$SO(n)$ symmetries the expansion requires averaging over angular momentum as
well as energy. A numerical example is given in two dimensions, in which we
calculate the leading terms of the Weyl expansion as well as the leading
periodic orbit contributions to the symmetry reduced level density.Comment: Four of the five figures are appended as a postscript file. The fifth
  figure is available by snail mail
Complete Semiclassical Treatment of the Quantum Black Hole Problem

Two types of semiclassical calculations have been used to study quantum
effects in black hole backgrounds, the WKB and the mean field approaches. In
this work we systematically reconstruct the logical implications of both
methods on quantum black hole physics and provide the link between these two
approaches. Our conclusions completely support our previous findings based
solely on the WKB method: quantum black holes are effectively p-brane
excitations and, consequently, no information loss paradox exists in this
problem.Comment: 14 pages, REVTE
Proper Field Quantization in Black Hole Spacetimes

Canonical quantization of local field theories is classical black hole
spacetimes with a single horizon leads to a particle number density with a
thermal distribution in equilibrium at the Hawking temperature. A complete
treatment including non-local quantum gravity effects has shown however that
the full "thermal vacuum" of the theory is the false vacuum. In this work we
find the true vacuum consistent with the complete semiclassical analysis of
quantum black holes. The theory is described by a "microcanonical" quantum
field theory with fixed energy E = M, the mass of the black hole.
Considerations making use of the microcanonical density matrix as well as the
idempotency condition show that particles in black hole backgrounds are
described by pure states, unlike the canonical formulation.Comment: 16 pages, REVTE
Nonabelian Gauge Theories: The Causal Approach

We present the causal construction of perturbative Yang-Mills theories in
four(3+1)-dimensional space-time. We work with free quantum fields throughout.
The inductive causal method by Epstein and Glaser leads directly to a finite
perturbation series and does not rely on an intermediary regularization of the
theory. The causal method naturally separates the physical infrared problem of
massless theories from ultraviolet-sensitive features like normalizability by
regarding the distributional character of the S-matrix. We prove the
normalizability of the Yang-Mills theory with fermionic matter fields and study
the discrete symmetry transformations in the causal formalism. We introduce a
definition of nonabelian gauge invariance which only involves the free
asymptotic field operators and give mathematically rigorous and conceptually
simple proofs of nonabelian gauge invariance and of the physical unitarity of
the S-matrix in all orders of perturbation theory.Comment: 77 pages, latex, no figures, final versio
Quantum KAM technique and Yang-Mills quantum mechanics

We study a quantum analogue of the iterative perturbation theory by Kolmogorov used in the proof of the Kolmogorov-Arnold-Moser (KAM) theorem. The method is based on sequent canonical transformations with a "running" coupling constant \lm,\lm^{2},\lm^{4} etc. The proposed scheme, as its classical predecessor, is "superconvergent" in the sense that after the n-th step, a theory is solved to the accuracy of order \lm^{2^{n-1}} . It is shown that the Kolmogorov technique corresponds to an infinite resummation of the usual perturbative series. The corresponding expansion is convergent for the quantum anharmonic oscillator due to the fact that it turns out to be identical to the Padé series. The method is easily generalizable to many-dimensional cases. The Kolmogorov technique is further applied to a non-perturbative treatment of Yang-Mills quantum mechanics. A controllable expansion for the wave function near the origin is constructed. For large fields, we build an asymptotic adiabatic expansion in inverse powers of the field. This asymptotic solution contains arbitrary constants which are not fixed by the boundary conditions at infinity. To find them, we approximately match the two expansions in an intermediate region. We also discuss some analogies between this problem and the method of QCD sum rules
Canonical Chern-Simons Theory and the Braid Group on a Riemann Surface

We examine the problem of determining which representations of the braid
group on a Riemann surface are carried by the wave function of a quantized
Abelian Chern-Simons theory interacting with non-dynamical matter. We
generalize the quantization of Chern-Simons theory to the case where the
coefficient of the Chern-Simons term, $k$, is rational, the Riemann surface has
arbitrary genus and the total matter charge is non-vanishing. We find an
explicit solution of the Schr\"odinger equation. We find that the wave
functions carry a representation of the braid group as well as a projective
representation of the discrete group of large gauge transformations. We find a
fundamental constraint which relates the charges of the particles, $q_i$, the
coefficient $k$ and the genus of the manifold, $g$.Comment: 19 page
Black holes in generalized dilaton gravity in two dimensions

We consider two-dimensional dilaton-gravity theories with a generic
exponential potential for the dilaton, and obtain the most general black hole
solutions in the Schwarzshild form. We discuss their geometrical and
thermodynamical properties. We also study these models from the point of view
of gauge theories of the extended Poincar\'e group and show that they can be
considered as gauge theories with broken symmetry. Finally, we examine the
theory in a hamiltonian formalism and discuss its quantization and its
symmetries.Comment: 12 pages, plain Tex, 4 figures available on reques
Classical and Quantum Dynamics of a Periodically Driven Particle in a
  Triangular Well

We investigate the correspondence between classical and quantum mechanics for
periodically time dependent Hamiltonian systems, using the example of a
periodically forced particle in a one-dimensional triangular well potential. In
particular, we consider quantum mechanical Floquet states associated with
resonances in the classical phase space. When the classical motion exhibits
{\it sub}harmonic resonances, the corresponding Floquet states maintain the
driving field's periodicity through dynamical tunneling. This principle applies
both to Floquet states associated with classical invariant vortex tubes
surrounding stable, elliptic periodic orbits and to Floquet states that are
associated with unstable, hyperbolic periodic orbits. The triangular well model
also poses a yet unsolved mathematical problem, related to perturbation theory
for systems with a dense pure point spectrum. The present approximate
analytical and numerical results indicate that quantum tunneling between
different resonance zones is of crucial importance for the question whether the
driven triangular well has a dense point or an absolutely continuous
quasienergy spectrum, or whether there is a transition from the one to the
other.Comment: revtex, 36 pages, 18 figures (available upon request), to appear in
  Annals of Physic
Deformed Heisenberg algebra, fractional spin fields and supersymmetry
  without fermions

Within a group-theoretical approach to the description of (2+1)-dimensional
anyons, the minimal covariant set of linear differential equations is
constructed for the fractional spin fields with the help of the deformed
Heisenberg algebra (DHA), $[a^{-},a^{+}]=1+\nu K$, involving the Klein operator
$K$, $\{K,a^{\pm}\}=0$, $K^{2}=1$. The connection of the minimal set of
equations with the earlier proposed `universal' vector set of anyon equations
is established. On the basis of this algebra, a bosonization of supersymmetric
quantum mechanics is carried out. The construction comprises the cases of exact
and spontaneously broken $N=2$ supersymmetry allowing us to realize a
Bose-Fermi transformation and spin-1/2 representation of SU(2) group in terms
of one bosonic oscillator. The construction admits an extension to the case of
OSp(2$\vert$2) supersymmetry, and, as a consequence, both applications of the
DHA turn out to be related. A possibility of `superimposing' the two
applications of the DHA for constructing a supersymmetric (2+1)-dimensional
anyon system is discussed. As a consequential result we point out that
$osp(2|2)$ superalgebra is realizable as an operator algebra for a quantum
mechanical 2-body (nonsupersymmetric) Calogero model.Comment: 21 pages, LaTe
Physical States in Matter-Coupled Dilaton Gravity

We revisit the quantization of matter-coupled, two-dimensional dilaton
gravity. At the classical level and with a cosmological term, a series of field
transformations leads to a set of free fields of indefinite signature. Without
matter the system is represented by two scalar fields of opposite signature.
With a particular quantization for the scalar with negative kinetic energy, the
system has zero central charge and we find some physical states satisfying {\it
all} the Virasoro conditions. With matter, the constraints cannot be solved
because of the Virasoro anomaly. We discuss two avenues for consistent
quantization: modification of the constraints, and BRST quantization. The first
avenue appears to lead to very few physical states. The second, which roughly
corresponds to satisfying half of the Virasoro conditions, results in a rich
spectrum of physical states. This spectrum, however, differs significantly from
that of free matter fields propagating on flat two-dimensional space-time.Comment: 43 pages in REVTe
Cosmic microwave background polarization

Polarization of the cosmic microwave background, though not yet detected, provides a source of information about cosmological parameters complementary to temperature fluctuations. This paper provides a complete theoretical treatment of polarization fluctuations. After a discussion of the physics of polarization, the Boltzmann equation governing the evolution of the photon density matrix is derived from quantum theory and applied to microwave background fluctuations, resulting in a complete set of transport equations for the Stokes parameters from both scalar and tensor metric perturbations. This approach is equivalent at lowest order in scattering kinematics to classical radiative transfer, and provides a general framework for treating the cosmological evolution of density matrices. The metric perturbations are treated in the physically appealing longitudinal gauge. Expressions for various temperature and polarization correlation functions are derived. Detection prospects and theoretical utility of microwave background polarization are briefly discussed
Qualitative Analysis of Brans-Dicke Universes with a Cosmological
  Constant

Solutions to flat space Friedmann-Robertson-Walker cosmologies in Brans-Dicke
theory with a cosmological constant are investigated. The matter is modelled as
a $\gamma$-law perfect fluid. The field equations are reduced from fourth order
to second order through a change of variables, and the resulting
two-dimensional system is analyzed using dynamical system theory. When the
Brans-Dicke coupling constant is positive $(\omega > 0)$, all initially
expanding models approach exponential expansion at late times, regardless of
the type of matter present. If $\omega < 0$, then a wide variety of
qualitatively distinct models are present, including nonsingular ``bounce''
universes, ``vacillating'' universes and, in the special case of $\omega = -1$,
models which approach stable Minkowski spacetime with an exponentially
increasing scalar field at late times. Since power-law solutions do not exist,
none of the models appear to offer any advantage over the standard deSitter
solution of general relativity in achieving a graceful exit from inflation.Comment: Paper has been shortened and discussion clarified. The stability
  analysis is now presented in tabular form. Some references adde
Monopole Gauge Fields and Quantum Potentials Induced by the Geometry in
  Simple Dynamical Systems

A realistic analysis shows that constraining a quantomechanical system
produces the effective dynamics to be coupled with {\sl abelian/non-abelian
gauge fields} and {\sl quantum potentials} induced by the {\sl intrinsic} and
{\sl extrinsic geometrical properties} of the constraint's surface.
  This phenomenon is observable in the effective rotational motion of some
simple polyatomic molecules. By considering specific examples it is shown that
the effective Hamiltonians for the nuclear rotation of linear and symmetric top
molecules are equivalent to that of a charged system moving in a background
magnetic-monopole field. For spherical top molecules an explicit analytical
expression of a non-abelian monopole-like field is found. Quantum potentials
are also relevant for the description of rotovibrational interactions.Comment: 24, LaTex, UPRF-94-40
The Relaxation Effect in Dissipative Relativistic Fluid Theories

The dynamics of the fluid fields in a large class of causal dissipative fluid
theories is studied. It is shown that the physical fluid states in these
theories must relax (on a time scale that is characteristic of the microscopic
particle interactions) to ones that are essentially indistinguishable from the
simple relativistic Navier-Stokes descriptions of these states. Thus, for
example, in the relaxed form of a physical fluid state the stress energy tensor
is in effect indistinguishable from a perfect fluid stress tensor plus small
dissipative corrections proportional to the shear of the fluid velocity, the
gradient of the temperature, etc.Comment: Plain TeX -- 16 Page
Covariant four-dimensional scattering equations for the $NN-\pi NN$
  system

We derive a set of coupled four-dimensional integral equations for the
$NN-\pi NN$ system using our modified version of the Taylor method of
classification-of-diagrams. These equations are covariant, obey two and
three-body unitarity and contain subtraction terms which eliminate the
double-counting present in some previous four-dimensional $NN-\pi NN$
equations. The equations are then recast into a from convenient for computation
by grouping the subtraction terms together and obtaining a set of two-fragment
scattering equations for the amplitudes of interest.Comment: Version accepted for publication in ``Annals of Physics''. New
  section containing two new figures added. 58 pages, 20 figures. Uses RevTeX.
  For copies of figures email Daniel.Phillips@flinders.edu.a
Generalized uncertainty relations: Theory, examples, and Lorentz
  invariance

The quantum-mechanical framework in which observables are associated with
Hermitian operators is too narrow to discuss measurements of such important
physical quantities as elapsed time or harmonic-oscillator phase. We introduce
a broader framework that allows us to derive quantum-mechanical limits on the
precision to which a parameter---e.g., elapsed time---may be determined via
arbitrary data analysis of arbitrary measurements on $N$ identically prepared
quantum systems. The limits are expressed as generalized Mandelstam-Tamm
uncertainty relations, which involve the operator that generates displacements
of the parameter---e.g., the Hamiltonian operator in the case of elapsed time.
This approach avoids entirely the problem of associating a Hermitian operator
with the parameter. We illustrate the general formalism, first, with
nonrelativistic uncertainty relations for spatial displacement and momentum,
harmonic-oscillator phase and number of quanta, and time and energy and,
second, with Lorentz-invariant uncertainty relations involving the displacement
and Lorentz-rotation parameters of the Poincar\'e group.Comment: 39 pages of text plus one figure; text formatted in LaTe
Gravitational Wave Interaction with Normal and Superconducting Circuits

The interaction, in the long--wavelength approximation, of normal and
superconducting electromagnetic circuits with gravitational waves is
investigated. We show that such interaction takes place by modifying the
physical parameters R, L, C of the electromagnetic devices. Exploiting this
peculiarity of the gravitational field we find that a circuit with two plane
and statically charged condensers set at right angles can be of interest as a
detector of periodic gravitational waves.Comment: 33 pages plus 1 postscript figure, TeX, macro newsym.tex include
Measurement quantum mechanics and experiments on quantum Zeno effect

Measurement quantum mechanics, the theory of a quantum system which undergoes
a measurement process, is introduced by a loop of mathematical equivalencies
connecting previously proposed approaches. The unique phenomenological
parameter of the theory is linked to the physical properties of an
informational environment acting as a measurement apparatus which allows for an
objective role of the observer. Comparison with a recently reported experiment
suggests how to investigate novel interesting regimes for the quantum Zeno
effect.Comment: 18 pages RevTeX, 2 postscript figures included with PSFIG, uuencoded
  gz-compressed .tar file; to be published in Annals of Physic
Quantized chaotic dynamics and non-commutative KS entropy

We study the quantization of two examples of classically chaotic dynamics,
the Anosov dynamics of "cat maps" on a two dimensional torus, and the dynamics
of baker's maps. Each of these dynamics is implemented as a discrete group of
automorphisms of a von Neumann algebra of functions on a quantized torus. We
compute the non- commutative generalization of the Kolmogorov-Sinai entropy,
namely the Connes-Stormer entropy, of the generator of this group, and find
that its value is equal to the classical value. This can be interpreted as a
sign of persistence of chaotic behavior in a dynamical system under
quantization.Comment: a number of misprints corrected, new references and a new section
  added. 21 pages, plain Te
Oscillating Friedman Cosmology

The non-singular, oscillating Friedman cosmology within the framework of
General Relativity is considered. The general oscillatory solution given in
terms of elliptic functions and the conditions for its existence are discussed.
It is shown that the wall-like-matter and the small, but negative cosmological
constant are required for oscillations. The oscillations can , in principle, be
deep enough to allow standard hot universe processes like recombination and
nucleosynthesis. It is shown that the wall-like-matter and string-like-matter
can be interpreted as scalar fields with some potentials. This may give another
candidate for the dark matter which may be compatible with observational data.
For an exact elementary oscillatory solution it is shown that the associated
scalar field potential is oscillating as well.Comment: Latex file, 27 pages, figures available on reques
Improved Convergence Proof of the Delta Expansion and Order Dependent
  Mappings

We improve and generalize in several accounts the recent rigorous proof of
convergence of delta expansion - order dependent mappings (variational
perturbation expansion) for the energy eigenvalues of anharmonic oscillator.
For the single-well anharmonic oscillator the uniformity of convergence in
$g\in[0,\infty]$ is proven. The convergence proof is extended also to complex
values of $g$ lying on a wide domain of the Riemann surface of $E(g)$. Via the
scaling relation \`a la Symanzik, this proves the convergence of delta
expansion for the double well in the strong coupling regime (where the standard
perturbation series is non Borel summable), as well as for the complex ``energy
eigenvalues'' in certain metastable potentials. Sufficient conditions for the
convergence of delta expansion are summarized in the form of three theorems,
which should apply to a wide class of quantum mechanical and higher dimensional
field theoretic systems.Comment: some bugs of uuencoded postscript figures are fixe