4,878 research outputs found
Scaling Function, Spectral Function and Nucleon Momentum Distribution in Nuclei
The link between the scaling function extracted from the analysis of (e,e')
cross sections and the spectral function/momentum distribution in nuclei is
revisited. Several descriptions of the spectral function based on the
independent particle model are employed, together with the inclusion of nucleon
correlations, and effects of the energy dependence arising from the width of
the hole states are investigated. Although some of these approaches provide
rough overall agreement with data, they are not found to be capable of
reproducing one of the distinctive features of the experimental scaling
function, namely its asymmetry. However, the addition of final-state
interactions, incorporated in the present study using either relativistic mean
field theory or via a complex optical potential, does lead to asymmetric
scaling functions in accordance with data. The present analysis seems to
indicate that final-state interactions constitute an essential ingredient and
are required to provide a proper description of the experimental scaling
function.Comment: 29 pages, 13 figures, accepted for publication in Physical Review
Generator Coordinate Method Calculations for Ground and First Excited Collective States in He, O and Ca Nuclei
The main characteristics of the ground and, in particular, the first excited
monopole state in the He, O and Ca nuclei are studied
within the generator coordinate method using Skyrme-type effective forces and
three construction potentials, namely the harmonic-oscillator, the square-well
and Woods-Saxon potentials. Calculations of density distributions, radii,
nucleon momentum distributions, natural orbitals, occupation numbers and
depletions of the Fermi sea, as well as of pair density and momentum
distributions are carried out. A comparison of these quantities for both ground
and first excited monopole states with the available empirical data and with
the results of other theoretical methods are given and discussed in detail.Comment: 15 pages, LaTeX, 6 Postscript figures, submitted to EPJ
Effects of turbulent mixing on critical behaviour in the presence of compressibility: Renormalization group analysis of two models
Critical behaviour of two systems, subjected to the turbulent mixing, is
studied by means of the field theoretic renormalization group. The first
system, described by the equilibrium model A, corresponds to relaxational
dynamics of a non-conserved order parameter. The second one is the strongly
non-equilibrium reaction-diffusion system, known as Gribov process and
equivalent to the Reggeon field theory. The turbulent mixing is modelled by the
Kazantsev-Kraichnan "rapid-change" ensemble: time-decorrelated Gaussian
velocity field with the power-like spectrum k^{-d-\xi}. Effects of
compressibility of the fluid are studied. It is shown that, depending on the
relation between the exponent \xi and the spatial dimension d, the both systems
exhibit four different types of critical behaviour, associated with four
possible fixed points of the renormalization group equations. The most
interesting point corresponds to a new type of critical behaviour, in which the
nonlinearity and turbulent mixing are both relevant, and the critical exponents
depend on d, \xi and the degree of compressibility. For the both models,
compressibility enhances the role of the nonlinear terms in the dynamical
equations: the region in the d-\xi plane, where the new nontrivial regime is
stable, is getting much wider as the degree of compressibility increases. In
its turn, turbulent transfer becomes more efficient due to combined effects of
the mixing and the nonlinear terms.Comment: 25 pages, 4 figure
Breaking of ergodicity and long relaxation times in systems with long-range interactions
The thermodynamic and dynamical properties of an Ising model with both short
range and long range, mean field like, interactions are studied within the
microcanonical ensemble. It is found that the relaxation time of
thermodynamically unstable states diverges logarithmically with system size.
This is in contrast with the case of short range interactions where this time
is finite. Moreover, at sufficiently low energies, gaps in the magnetization
interval may develop to which no microscopic configuration corresponds. As a
result, in local microcanonical dynamics the system cannot move across the gap,
leading to breaking of ergodicity even in finite systems. These are general
features of systems with long range interactions and are expected to be valid
even when the interaction is slowly decaying with distance.Comment: 4 pages, 5 figure
Two-Body Density Matrix for Closed s-d Shell Nuclei
The two-body density matrix for and within the
Low-order approximation of the Jastrow correlation method is considered. Closed
analytical expressions for the two-body density matrix, the center of mass and
relative local densities and momentum distributions are presented. The effects
of the short-range correlations on the two-body nuclear characteristics are
investigated.Comment: 13 pages(LaTeX), 4 figures (ps
Gravothermal Catastrophe, an Example
This work discusses gravothermal catastrophe in astrophysical systems and
provides an analytic collapse solution which exhibits many of the catastrophe
properties. The system collapses into a trapped surface with outgoing energy
radiated to a future boundary, and provides an example of catastrophic
collapse.Comment: To appear in Phys. Rev.
String Nature of Confinement in (Non-)Abelian Gauge Theories
Recent progress achieved in the solution of the problem of confinement in
various (non-)Abelian gauge theories by virtue of a derivation of their string
representation is reviewed. The theories under study include QCD within the
so-called Method of Field Correlators, QCD-inspired Abelian-projected theories,
and compact QED in three and four space-time dimensions. Various
nonperturbative properties of the vacua of the above mentioned theories are
discussed. The relevance of the Method of Field Correlators to the study of
confinement in Abelian models, allowing for an analytical description of this
phenomenon, is illustrated by an evaluation of field correlators in these
models.Comment: 100 pages, LaTeX2e, no figures, 1 table, based on the Ph.D. thesises
at the Humboldt University of Berlin (1999) (available under
http://dochost.rz.hu-berlin.de) and the Institute of Theoretical and
Experimental Physics, Moscow (2000), new results are included, extended with
respect to the journal versio
Confinement in the Abelian-Higgs-type theories: string picture and field correlators
Field correlators and the string representation are used as two complementary
approaches for the description of confinement in the SU(N)-inspired dual
Abelian-Higgs-type model. In the London limit of the simplest, SU(2)-inspired,
model, bilocal electric field-strength correlators have been derived with
accounting for the contributions to these averages produced by closed dual
strings. The Debye screening in the plasma of such strings yields a novel
long-range interaction between points lying on the contour of the Wilson loop.
This interaction generates a Luescher-type term, even when one restrics oneself
to the minimal surface, as it is usually done in the bilocal approximation to
the stochastic vacuum model. Beyond the London limit, it has been shown that a
modified interaction appears, which becomes reduced to the standard Yukawa one
in the London limit. Finally, a string representation of the SU(N)-inspired
model with the theta-term, in the London limit, can be constructed.Comment: 17 pages, no figures, REVTeX 4; Invited contribution to the
collection of articles devoted to the 70th birthday of Yu.A. Simono
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