183 research outputs found
Color symmetrical superconductivity in a schematic nuclear quark model
In this note, a novel BCS-type formalism is constructed in the framework of a
schematic QCD inspired quark model, having in mind the description of color
symmetrical superconducting states. The physical properties of the BCS vacuum
(average numbers of quarks of different colors) remain unchanged under an
arbitrary color rotation. In the usual approach to color superconductivity, the
pairing correlations affect only the quasi-particle states of two colors, the
single particle states of the third color remaining unaffected by the pairing
correlations. In the theory of color symmetrical superconductivity here
proposed, the pairing correlations affect symmetrically the quasi-particle
states of the three colors and vanishing net color-charge is automatically
insured. It is found that the groundstate energy of the color symmetrical
sector of the Bonn model is well approximated by the average energy of the
color symmetrical superconducting state proposed here
Hyperons in neutron star matter within relativistic mean-field models
Since the discovery of neutron stars with masses around 2 solar masses the
composition of matter in the central part of these massive stars has been
intensively discussed. Within this paper we will (re)investigate the question
of the appearance of hyperons. To that end we will perform an extensive
parameter study within relativistic mean field models. We will show that it is
possible to obtain high mass neutron stars (i) with a substantial amount of
hyperons, (ii) radii of 12-13 km for the canonical mass of 1.4 solar masses,
and (iii) a spinodal instability at the onset of hyperons. The results depend
strongly on the interaction in the hyperon-hyperon channels, on which only very
little information is available from terrestrial experiments up to now.Comment: 15 pages, 10 figure
Aspects of short range correlations in a relativistic model
In the present work short range correlations are introduced for the first
time in a relativistic approach to the equation of state of the infinite
nuclear matter in the framework of the Hartree-Fock approximation using an
effective Hamiltonian derived from the Walecka model. The
unitary correlation method is used to introduce short range correlations. The
effect of the correlations in the ground state properties of the nuclear matter
is discussed.Comment: 7 pages, 3 figure
Short range correlations in relativistic nuclear matter models
Short range correlations are introduced using unitary correlation method in a
relativistic approach to the equation of state of the infinite nuclear matter
in the framework of the Hartree-Fock approximation. It is shown that the
correlations give rise to an extra node in the ground-state wave-function in
the nucleons, contrary to what happens in non-relativistic calculations with a
hard core. The effect of the correlations in the ground state properties of the
nuclear matter and neutron matter is studied. The nucleon effective mass and
equation of state (EOS) are very sensitive to short range correlations. In
particular, if the pion contact term is neglected a softening of the EOS is
predicted. Correlations have also an important effect on the neutron matter EOS
which presents no binding but only a very shallow minimum contrary to the
Walecka model.Comment: 8pages, 4 figure
BCS theory of hadronic matter at high densities
The equilibrium between the so-called 2SC and CFL phases of strange quark
matter at high densities is investigated in the framework of a simple schematic
model of the NJL type. Equal densities are assumed for quarks and .
The 2SC phase is here described by a color-flavor symmetric state, in which the
quark numbers are independent of the color-flavor combination. In the CFL phase
the quark numbers depend on the color-flavor combination, that is, the number
of quarks associated with the color-flavor combinations is different
from the number of quarks associated with the color flavor combinations
. We find that the 2SC phase is stable for a chemical
potential below GeV, while the CFL phase is stable above,
the equilibrium pressure being GeV. We have used a 3-momentum
regularizing cutoff GeV, which is somewhat larger than is usual
in NJL type models. This should be adequate if the relevant chemical potential
does not exceed 0.6 GeV.Comment: 6 figures, 13 page
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