539 research outputs found
Effects of the liquid-gas phase transition and cluster formation on the symmetry energy
Various definitions of the symmetry energy are introduced for nuclei, dilute
nuclear matter below saturation density and stellar matter, which is found in
compact stars or core-collapse supernovae. The resulting differences are
exemplified by calculations in a theoretical approach based on a generalized
relativistic density functional for dense matter. It contains nucleonic
clusters as explicit degrees of freedom with medium dependent properties that
are derived for light clusters from a quantum statistical approach. With such a
model the dissolution of clusters at high densities can be described. The
effects of the liquid-gas phase transition in nuclear matter and of cluster
formation in stellar matter on the density dependence of the symmetry energy
are studied for different temperatures. It is observed that correlations and
the formation of inhomogeneous matter at low densities and temperatures causes
an increase of the symmetry energy as compared to calculations assuming a
uniform uncorrelated spatial distribution of constituent baryons and leptons.Comment: 20 pages, 19 figures, version accepted for publication in EPJA
special volume on Nuclear Symmetry Energ
Composition and thermodynamics of nuclear matter with light clusters
We investigate nuclear matter at finite temperature and density, including
the formation of light clusters up to the alpha particle The novel feature of
this work is to include the formation of clusters as well as their dissolution
due to medium effects in a systematic way using two many-body theories: a
microscopic quantum statistical (QS) approach and a generalized relativistic
mean field (RMF) model. Nucleons and clusters are modified by medium effects.
Both approaches reproduce the limiting cases of nuclear statistical equilibrium
(NSE) at low densities and cluster-free nuclear matter at high densities. The
treatment of the cluster dissociation is based on the Mott effect due to Pauli
blocking, implemented in slightly different ways in the QS and the generalized
RMF approaches. We compare the numerical results of these models for cluster
abundances and thermodynamics in the region of medium excitation energies with
temperatures T <= 20 MeV and baryon number densities from zero to a few times
saturation density. The effect of cluster formation on the liquid-gas phase
transition and on the density dependence of the symmetry energy is studied.
Comparison is made with other theoretical approaches, in particular those,
which are commonly used in astrophysical calculations. The results are relevant
for heavy-ion collisions and astrophysical applications.Comment: 32 pages, 15 figures, minor corrections, accepted for publication in
Physical Review
On Unconstrained SU(2) Gluodynamics with Theta Angle
The Hamiltonian reduction of classical SU(2) Yang-Mills field theory to the
equivalent unconstrained theory of gauge invariant local dynamical variables is
generalized to the case of nonvanishing theta angle. It is shown that for any
theta angle the elimination of the pure gauge degrees of freedom leads to a
corresponding unconstrained nonlocal theory of self-interacting second rank
symmetric tensor fields, and that the obtained classical unconstrained
gluodynamics with different theta angles are canonically equivalent as on the
original constrained level.Comment: 13 pages Revtex, no figures; several misprints corrected; version to
appear in Eur. Phys. J.
Alpha-particle condensation in nuclei
A round up of the present status of the conjecture that n alpha nuclei form
an alpha-particle condensate in excited states close to the n alpha threshold
is given. Experiments which could demonstrate the condensate character are
proposed. Possible lines of further theoretical developments are discussed.Comment: 6 page
Analysis of previous microscopic calculations for second state in C in terms of 3-alpha particle Bose-condensed state
The wave function of the second state of C which was obtained
long time ago by solving the microscopic 3 problem is shown to be
almost completely equivalent to the wave function of the 3 condensed
state which has been proposed recently by the present authors. This equivalence
of the wave functions is shown to hold in two cases where different effective
two-nucleon forces are adopted. This finding gives strong support for
interpreting the second state of C which is the key state for the
synthesis of C in stars ('Hoyle' state), and which is one of the typical
mysterious states in light nuclei, as a gas-like structure of three
particles, Bose-condensed into an identical s-wave function.Comment: revtex, 5 pages, 2 figures, submitted to Phys. Rev.
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