2,750 research outputs found
Correlations in Nuclear Matter
We analyze the nuclear matter correlation properties in terms of the pair
correlation function. To this aim we systematically compare the results for the
variational method in the Lowest Order Constrained Variational (LOCV)
approximation and for the Bruekner-Hartree-Fock (BHF) scheme. A formal link
between the Jastrow correlation factor of LOCV and the Defect Function (DF) of
BHF is established and it is shown under which conditions and approximations
the two approaches are equivalent. From the numerical comparison it turns out
that the two correlation functions are quite close, which indicates in
particular that the DF is approximately local and momentum independent. The
Equations of State (EOS) of Nuclear Matter in the two approaches are also
compared. It is found that once the three-body forces (TBF) are introduced the
two EOS are fairly close, while the agreement between the correlation functions
holds with or without TBF.Comment: 11 figure
Non-locality in the nucleon-nucleon interaction and nuclear matter saturation
We study the possible relationship between the saturation properties of
nuclear matter and the inclusion of non-locality in the nucleon-nucleon
interaction. To this purpose we compute the saturation curve of nuclear matter
within the Bethe-Brueckner-Goldstone theory using a recently proposed realistic
non-local potential, and compare it with the corresponding curves obtained with
a purely local realistic interaction (Argonne v) and the most recent
version of the one-boson exchange potential (CD Bonn). We find that the
inclusion of non-locality in the two-nucleon bare interaction strongly affects
saturation, but it is unable to provide a consistent description of few-body
nuclear systems and nuclear matter.Comment: 9 pages, 8 figures; v2: introduction extended, references added,
discussion of fig.8 reformulated; to be published in Phys. Rev.
Low-temperature ion beam mixing of Pt and Si markers in Ge
The mixing of Pt and Si marker atoms in Ge during 750-keV Xe irradiation was measured at temperatures between 6 and 500 K. The low-temperature measurements show that the mixing parameter for Pt is nearly twice that for Si. This result is in strong contradiction to the collisional theory of ion beam mixing. A weak temperature dependence in the mixing is found for both markers
Temperature dependence of single-particle properties in nuclear matter
The single-nucleon potential in hot nuclear matter is investigated in the
framework of the Brueckner theory by adopting the realistic Argonne V18 or
Nijmegen 93 two-body nucleon-nucleon interaction supplemented by a microscopic
three-body force. The rearrangement contribution to the single-particle
potential induced by the ground state correlations is calculated in terms of
the hole-line expansion of the mass operator and provides a significant
repulsive contribution in the low-momentum region around and below the Fermi
surface. Increasing temperature leads to a reduction of the effect, while
increasing density makes it become stronger. The three-body force suppresses
somewhat the ground state correlations due to its strong short-range repulsion,
increasing with density. Inclusion of the three-body force contribution results
in a quite different temperature dependence of the single-particle potential at
high enough densities as compared to that adopting the pure two-body force. The
effects of three-body force and ground state correlations on the nucleon
effective mass are also discussed.Comment: 14 pages, 5 figure
The Equation of State of Dense Matter : from Nuclear Collisions to Neutron Stars
The Equation of State (EoS) of dense matter represents a central issue in the
study of compact astrophysical objects and heavy ion reactions at intermediate
and relativistic energies. We have derived a nuclear EoS with nucleons and
hyperons within the Brueckner-Hartree-Fock approach, and joined it with quark
matter EoS. For that, we have employed the MIT bag model, as well as the
Nambu--Jona-Lasinio (NJL) and the Color Dielectric (CD) models, and found that
the NS maximum masses are not larger than 1.7 solar masses. A comparison with
available data supports the idea that dense matter EoS should be soft at low
density and quite stiff at high density.Comment: 8 pages, 5 figures, invited talk given at NPA3, Dresden, March 200
Highly efficient, dual state emission from an organic semiconductor
We report highly efficient, simultaneous fluorescence and phosphorescence
(74% yield) at room temperature from a single molecule ensemble of (BzP)PB
dispersed into a polymer host. The slow phosphorescence (208 ms lifetime) is
very efficient (50%) at room temperature and only possible because the
non-radiative rate for the triplet state is extremely low. The ability of an
organic molecule to function as an efficient dual state emitter at room
temperature is unusual and opens new fields of applications including the use
as broadband down-conversion emitters, optical sensors and attenuators, exciton
probes, and spin-independent intermediates for F\"orster resonant energy
transfer
Convergence of Ginzburg-Landau functionals in 3-d superconductivity
In this paper we consider the asymptotic behavior of the Ginzburg- Landau
model for superconductivity in 3-d, in various energy regimes. We rigorously
derive, through an analysis via {\Gamma}-convergence, a reduced model for the
vortex density, and we deduce a curvature equation for the vortex lines. In a
companion paper, we describe further applications to superconductivity and
superfluidity, such as general expressions for the first critical magnetic
field H_{c1}, and the critical angular velocity of rotating Bose-Einstein
condensates.Comment: 45 page
Computation of Neutron Star Structure Using Modern Equation of State
Using the modern equations of state derived from microscopic calculations, we
have calculated the neutron star structure. For the neutron star, we have
obtained a minimum mass about which is nearly independent
of the equation of state, and a maximum mass between and
which is strongly dependent on the equation of state. It
is shown that among the equations of state of neutron star matter which we have
used, the stiffest one leads to higher maximum mass and radius and lower
central density. It is seen that the given maximum mass for the Reid-93
equation of state shows a good consistency with the accurate observations of
radio pulsars. We have indicated that the thickness of neutron star crust is
very small compared to the predicted neutron star radius.Comment: 16 pages, 6 figure
Hybrid stars with the Dyson-Schwinger quark model
We study the hadron-quark phase transition in the interior of neutron stars.
For the hadronic sector, we use a microscopic equation of state involving
nucleons and hyperons derived within the Brueckner-Hartree-Fock many-body
theory with realistic two-body and three-body forces. For the description of
quark matter, we employ the Dyson-Schwinger approach and compare with the MIT
bag model. We calculate the structure of neutron star interiors comprising both
phases and find that with the Dyson-Schwinger model, the hadron-quark phase
transition takes place only when hyperons are excluded, and that a
two-solar-mass hybrid star is possible only if the nucleonic equation of state
is stiff enough.Comment: 10 pages, 8 figure
Elementary excitations in homogeneous superfluid neutron star matter: Role of the proton component
The thermal evolution of neuron stars depends on the elementary excitations
affecting the stellar matter. In particular, the low-energy excitations, whose
energy is proportional to the transfered momentum, can play a major role in the
emission and propagation of neutrinos. In this paper, we focus on the density
modes associated with the proton component in the homogeneous matter of the
outer core of neutron stars (at density between one and three times the nuclear
saturation density, where the baryonic constituants are expected to be neutrons
and protons). In this region, it is predicted that the protons are
superconductor. We study the respective roles of the proton pairing and Coulomb
interaction in determining the properties of the modes associated with the
proton component. This study is performed in the framework of the Random Phase
Approximation, generalized in order to describe the response of a superfluid
system.The formalism we use ensures that the Generalized Ward's Identities are
satisfied. An important conclusion of this work is the presence of a
pseudo-Goldstone mode associated with the proton superconductor in neutron-star
matter. Indeed, the Goldstone mode, which characterizes a pure superfluid, is
suppressed in usual superconductors due to the long-range Coulomb interaction,
which only allows a plasmon mode. However, for the proton component of stellar
matter, the Coulomb field is screened by the electrons and a pseudo-Goldstone
mode occurs, with a velocity increased by the Coulomb interaction.Comment: Submitted for publicatio
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