46,696 research outputs found
Quark deconfinement in high-mass neutron stars
In this paper, we explore whether or not quark deconfinement may occur in
high-mass neutron stars such as J1614-2230 (1.97 \pm 0.04 M_Sun) and J0348+0432
(2.01 \pm 0.04 M_Sun). Our study is based on a non-local extension of the SU(3)
Nambu Jona-Lasinio (n3NJL) model with repulsive vector interactions among the
quarks. This model goes beyond the frequently used local version of the Nambu
Jona-Lasinio (NJL) model by accounting for several key features of QCD which
are not part of the local model. Confined hadronic matter is treated in the
framework of non-linear relativistic mean field theory. We find that both the
local as well as the non-local NJL model predict the existence of extended
regions of mixed quark-hadron (quark-hybrid) matter in high-mass neutron stars
with masses of 2.1 to 2.4 M_Sun. Pure quark matter in the cores of neutron
stars is obtained for certain parametrizations of the hadronic lagrangian and
choices of the vector repulsion among quarks. The radii of high-mass neutron
stars with quark-hybrid matter and/or pure quark matter cores in their centers
are found to lie in the canonical range of 12 to 13 km.Comment: 31 pages, 17 figures, PRC accepted versio
Quark-hybrid matter in the cores of massive neutron stars
Using a nonlocal extension of the SU(3) Nambu-Jona Lasinio model, which
reproduces several of the key features of Quantum Chromodynamics, we show that
mixed phases of deconfined quarks and confined hadrons (quark-hybrid matter)
may exist in the cores of neutron stars as massive as around 2.1 M_Sun. The
radii of these objects are found to be in the canonical range of
km. According to our study, the transition to pure quark matter does not occur
in stable neutron stars, but is shifted to neutron stars which are unstable
against radial oscillations. The implications of our study for the recently
discovered, massive neutron star PSR J1614-2230, whose gravitational mass is
, are that this neutron star may contain an extended
region of quark-hybrid matter at it center, but no pure quark matter.Comment: 13 pages, 3 figure
Association of ultracold double-species bosonic molecules
We report on the creation of heterospecies bosonic molecules, associated from
an ultracold Bose-Bose mixture of 41K and 87Rb, by using a resonantly modulated
magnetic field close to two Feshbach resonances. We measure the binding energy
of the weakly bound molecular states versus the Feshbach field and compare our
results to theoretical predictions. We observe the broadening and asymmetry of
the association spectrum due to thermal distribution of the atoms, and a
frequency shift occurring when the binding energy depends nonlinearly on the
Feshbach field. A simple model is developed to quantitatively describe the
association process. Our work marks an important step forward in the
experimental route towards Bose-Einstein condensates of dipolar molecules.Comment: 5 pages, 4 figure
Exact and Quasi-exact Models of Strange Stars
We construct and compare a variety of simple models for strange stars,
namely, hypothetical self-bound objects made of a cold stable version of the
quark-gluon plasma. Exact, quasi-exact and numerical models are examined to
find the most economical description for these objects. A simple and successful
parametrization of them is given in terms of the central density, and many
differences among the models are explicitly shown and discussed.Comment: 20 pp. 15 figures, to appear in IJMP
LOX/hydrocarbon auxiliary propulsion system study
Liquid oxygen (LOX)/hydrocarbon propulsion concepts for a "second generation' orbiter auxiliary propulsion system was evaluated. The most attractive fuel and system design approach identified, and the technology advancements that are needed to provide high confidence for a subsequent system development were determined. The fuel candidates were ethanol, methane, propane, and ammonia. Even though ammonia is not a hydrocarbon, it was included for evaluation because it is clean burning and has a good technology base. The major system design options were pump versus pressure feed, cryogenic versus ambient temperature RCS propellant feed, and the degree of OMS-RCS integration. Ethanol was determined to be the best fuel candidate. It is an earth-storable fuel with a vapor pressure slightly higher than monomethyl hydrazine. A pump-fed OMS was recommended because of its high specific impulse, enabling greater velocity change and greater payload capability than a pressure fed system
Collisional and molecular spectroscopy in an ultracold Bose-Bose mixture
The route toward a Bose-Einstein condensate of dipolar molecules requires the
ability to efficiently associate dimers of different chemical species and
transfer them to the stable rovibrational ground state. Here, we report on
recent spectroscopic measurements of two weakly bound molecular levels and
newly observed narrow d-wave Feshbach resonances. The data are used to improve
the collisional model for the Bose-Bose mixture 41K87Rb, among the most
promising candidates to create a molecular dipolar BEC.Comment: 13 pages, 3 figure
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